AIR CONDITIONING, HEATING AND MECHANICAL VENTILATION
1. SCOPE
This Section covers the design, construction and installation of air conditioning and heating systems and equipment installed in buildings for the purpose of providing and maintaining conditions of air temperature, humidity, purity and distribution suitable for the use and occupancy of the space.
2. TERMINOLOGIES
2.0. For the purpose of this Section the following definitions shall apply.
2.1. Air Conditioning – The process of treating air so as to control simultaneously its temperature, humidity, purity, distribution and air movement and pressure to meet the requirements of the conditioned space.
2.2. Atmospheric Pressure – The weight of air column on unit surface area of earth by atmospheric column. At sea level, the standard atmospheric or barometric pressure is 76 mm of mercury (1 033mm of water column/101.325 kpa).
Generally atmospheric pressure is used as a datum for indicating the system pressures in air conditioning and accordingly, pursuers are mentioned above the atmospheric pressures or below the atmospheric pressure considering the atmospheric pressure to be zero. A’U’ tube manometer will indicate zero pressure when pressure measured is equal to atmospheric pressure.
2.3. Buildings Related Illnesses (BRI) – The illness attributed directly to the specific air-borne building contaminants like the outbreak of the Legionnaire’s disease after a convention and sensitivity nomination of the building.
Some of the other symptoms relating to BRI are sensory irritation of eyes, ears and throat, shin irritation, headache, nausea, drowsiness, asthma like symptoms in non-asthmatics persons. The economic consequence of BRI is decreased productivity, absenteeism and the legal implications if occupants IAQ complaints are left unresolved.
2.4. Dew point Temperature— The temperature at which condensation of moisture begins when the air is cooled at same pressure.
2.5. Dry-Bulb Temperature – The temperature of the air, read on a thermometer, taken in such a way as to avoid errors due to radiation.
2.6. Duct system – A continuous passageway for the transmission of air which, in addition to the ducts, may include duct fittings, dampers, plenums, and grilles and diffusers.
2.7. Enthalpy – A thermal property indicating the quantity of heat in the air above an arbitrary datum, in kilo Joules per Kg of dry air (or in Btu per pound of dry air).
2.8. Evaporative Air Cooling – The evaporative air cooling application is the simultaneous removal of sensible heat and the addition of moisture to the air. The water temperature remains essentially constant at the wer-bulb temperature of the air.
2.9. Fire Damper – A closure which consists of a normally held open damper installed in an air distribution system or in a wall or floor assembly and designed to close automatically in the event of a fire in order to maintain the integrity of the fire separation.
2.10. Fire Separation wall – The wall providing complete separation of one building from another or part of the same building to prevent any communication of fire or heat transmission to wall itself which may cause or assist in the combustion of materials of the side opposite to that portion which may be on fire.
2.11. Global Warning potential GWP – The potential of a refrigerant to contribute to global warming.
Global warming can make our planet and its climate less hospitable and more hostile to human life, thus necessitating reduction in emission of green house gases such as CO2, SOx, NOx, and refrigerants. Long atmospheric life time of refrigerants results in global warming unless the emissions are controlled.
GWP values of some of the refrigerants are given below:
|
Sl No. |
Refrigerant |
GWP values |
|
(1) |
(2) |
(3) |
|
i) |
R-12 |
10 600 |
|
ii) |
R-22 |
1 900 |
|
iii) |
R-134a |
1 600 |
|
iv) |
R-123 |
120 |
|
v) |
R-407c |
1 980 |
|
vi) |
R-407a |
2 340 |
|
vii) |
R-410a |
2 340 |
The values indicated above are for an integration period of 100 years.
2.12. Hydronic System – The water systems that convey heat to or from a conditioned space or process with hot or chilled water. The water flows through piping that connects a chiller or the water heater to suitable terminal heat transfer units located at the space or process.
2.13. Indoor Air Quality (IAQ)—Air quality that refers to the nature of conditioned air that circulates throughout the space/area where one works or lives, that is, the air one breathes when indoors.
It not only refers to comfort which is affected by temperature, humidity, air movement and odors but also to harmful biological contaminants and chemicals present in the conditioned space. Poor IAQ may be serious health hazard. Carbon dioxide has been recognized as the surrogated ventilation index.
2.14. Infiltration/Exfiltration—the phenomenon of outside air leaking into/out of an air conditioned space.
2.15. Ozone Depletion Potential (ODP) —μ the potential of refrigerant or gases to deplete the ozone in the atmosphere.
The ODP values for various refrigerants are as given below.
|
R-11 |
1.000 |
|
R-12 |
0.820 |
|
R-22 |
0.050 |
|
R-123 |
0.012 |
|
R-134a |
0.000 |
|
R-407a |
0.000 |
|
R-407c |
0.000 |
|
R-410a |
0.000 |
Due to high ODP of R-11, R-12 and R-22 their use in the air conditioning and refrigeration is being phased-out. R-123 is also in the phase-out category of refrigerants.
2.16. plenum –- An air compartment or chamber to which one or more ducts are connected and which forms part of an air distribution system.
The pressure drop and air velocities in the plenum should be low. Generally, the velocity in plenum should not exceed 1.5 m/s to 2.5 m/s.
2.17. Positive ventilation – The supply of outside air by means of a mechanical device, such as a fan.
2.18. Psychometric – The science involving thermodynamic properties of moist air and the effect of atmospheric moisture on materials and human comfort, It also includes methods of controlling thermal properties of moist air.
2.19. Psychometric chart – A chart graphically representing the thermodynamic properties of moist air.
2.20. Reticulated Air – The return air that has been passed through the conditioning apparatus before being re-supplied to the space.
2.21. Refrigerant – The fluid used for heat transfer in a refrigerating system, which absorbs heat at a low temperature and low pressure of the fluid and rejects heat at a higher temperature and higher pressure of the fluid, usually involving changes of state of the fluid
2.22. Relative Humidity – Ratio of the partial pressure of actual water vapour in the air compared to the partial pressure of maximum amount of water that may be contained at its dry bulb temperature.
2.23. Return Air - The air that is collected from the conditioned space and returned to the conditioning equipment.
2.24. Shade Factor – The ratio of instantaneous heat gain through the fenestration with shading device to that through the fenestration.
2.25. Sick Building Syndrome (SBS) – A term, which is used to describe the presence of acute non-specific symptoms in the majority of people caused by working in buildings with an adverse indoor environment. It could be cluster of complex irrigative symptoms like irritation of the eyes, block ended nose and throat, headaches, dizziness, lethargy, fatigue irritation, wheezing, sinusitis, congestion, skin rash, sensory discomfort from odours, nausea, etc. These symptoms are usually short-lived and experienced immediately after exposure; and may disappear when one leaves the building.
SBS is suspected when significant number of people spending extended time in a building report or experience acute an-site discomfort. The economic consequences of SBS, like BRI, are decreased productivity absenteeism and the legal implications if occupants IQO complaints are left unresolved.
2.26. Smoke Damper – A damper similar to fire damper, however, having provisions to close automatically on sensing presence of smoke in air distribution system or in conditioned space.
2.27. Static Pressure – The pressure that is required to be created by the fan over the atmospheric pressure to overcome the system resistances such as resistances in ducts, elbows, filters, dampers, heating/cooling coils, etc.
Static pressure is measured by a U tube manometer relative to the atmospheric pressure, which is considered as zero pressure. In exhaust systems, fan produces negative static pressure, which is again used to overcome the system resistances.
2.28. Supply Air – The air that has been passed through the conditioning apparatus and taken through the duct system and distributed in the conditioned space.
2.29. Supply and Return Air Grilles and Diffusers – Grilles and diffusers are the devices fixed in the air conditioned space for distribution of conditioned supply air and return of air collected from the conditioned space for re-circulation.
2.30. Thermal Transmittance – Thermal transmission per unit time through unit area of the given building unit divided by temperature difference between the air or some other fluid on either side of the building unit in ‘steady state’ conditions.
2.31. Thermal Energy Storage – Storage of thermal energy, sensible, latent or combination there of for use in central system for air conditioning or refrigeration. It uses a primary source of refrigeration for cooling and storing thermal energy for reuse at peak demand or for backup as planned.
2.32. Water Conditioning – The treatment of water circulating in a hydraulic system, to make it suitable for air conditioning system due to its effect on the economics of air conditioning plant.
Untreated water used in air conditioning system may create problems such as scale formation, corrosion and organic growth. Appraisal of the water supply source including chemical analysis and determination of composition of dissolved solids is necessary to devise a proper water-conditioning programmer.
2.33. Water Hardness – Hardness in water represented by the sum of calcium and magnesium salts in water, which may also include aluminium, iron, manganese, zinc, etc. A chemical analysis of water sample should provide number of total dissolved solids (TDS) in a water sample in parts per million (ppm) as also composition of each of the salts in parts per million.
Temporary hardness is attributed to carbonates and bicarbonates of calcium and/or magnesium expressed in parts per million (ppm) as CaCO3. The remainder of the hardness is known as permanent hardness, which is due to subparts, chloride, nitrites of calcium and/or magnesium expressed in ppm as CaCO3.
Temporary hardness is primarily responsible for scale formation, which results in poor heat transfer resulting in increased cost of energy for refrigeration and air conditioning. Permanent hardness (non-carbonate) is not as serious a factor in water conditioning because it has a solubility which is approximately 70 times greater than the carbonate hardness. In many cases, water may contain as much as 1 200 ppm of non-carbonate hardness and not deposit a calcium sulfate scale.
The treated water where hardness as ppm of CaCO3 is reduced to 50 ppm or below is recommenced for air conditioning applications.
pH is a measure of acidity, pH is a negative logarithm base10, of the concentration of hydrogen ion in grams per liter. Water having a pH of 7.0 is neutral, a pH value less than 7 is acidic and pH value greater than 7 is alkaline. Water with pH less than 5 is quite acidic and corrosive to ordinary metals and needs to be treated.
2.34. Wet - Bulb Temperature – The temperature registered by a thermometer whose bulb is covered by a wetted wick and exposed to a current of rapidly moving air of velocity not less than 4.5 m/s.
Wet-bulb temperature is indicated by a wet bulb psychomotor constructed and used according to specifications.
3. PLANNING DESIGN CRITERIA
3.1. Fundamental Requirements
3.1.1. The object of installing ventilation and air conditioning facilities in buildings shall be to provide conditions under which people can live in comfort, work safely and efficiently.
3.1.2. Ventilation and air conditioning installation shall aim at controlling and optimizing following factors in the building.
3.1.3. All plans, specifications and data for air conditioning, heating and mechanical ventilation systems of all buildings and serving all occupancies within the scope of the Code shall be supplied to the Authority, where called for see Part 2 ‘Administration’.
3.1.4. The plans for air conditioning, heating and mechanical ventilation system shall include all details and data necessary for review installation such as:
3.2. Pre-planning
3.2.1. Design considerations
3.2.1.1. Cooling load estimate shall be carried out prior to installing air conditioning equipment. Calculation of cooling load shall take into account the following factors:
3.2.1.2. The design of system and its associated controls shall also take into account the following:
3.2.1.3. The operation of system in the following condition should be considered when assessing the complete design:
3.2.1.4. Consideration should be given to changes in building load and the system designed so that maximum operational efficiency is maintained.
3.2.1.5. Special applications like hospitals/operating theatres, computer rooms, clean rooms, laboratories, libraries, museums/art galleries, sound recording studios, shopping malls, etc shall be handled differently.
3.2.2.1. Planning of Equipment Room for Central Air Conditioning Plant.
3.2.2.1. In selecting the location for plant room, the aspects of efficiency, economy and good practice should be considered and wherever possible it shall be made contiguous with the building. This room shall be located as centrally as possible with respect to the area to be air conditioned and shall be free from obstructing columns.
In the case of large installations (500 TR and above), it is advisable to have a separate isolated equipment room where possible. The clear headroom below sophist of beam should be minimum 4.5m for centrifugal plants, and minimum 3.6m for reciprocating and screw type plants.
3.2.2.2. The floors of the equipment rooms should be light coloured and finished smooth. For floor loading the air conditioning engineer should be consulted (see the part 6 ‘Structural Design, Section 1 Loads, Forces and Effects’).
3.2.2.3. Supporting of pipe within plant room spaces should be normally from the floor. However, outside plant room areas, structural provisions shall be made for supporting the water pipes from the floor/ceiling slabs. All floor and ceiling supports shall be isolated from the structure to prevent transmission of vibrations.
3.2.2.4. Equipment rooms, wherever necessary, shall have provision for mechanical ventilation. In hot climate, evaporative air – cooling may also be considered
3.2.2.5. Plant machinery in the plant room shall be placed on plain/reinforced cement concrete foundation and provided with anti- vibratory supports. All foundations should be protected from damage by providing epoxy coated angle nosing. Seismic restraints requirement may also be considered.
3.2.2.6. Equipment room should preferably by located adjacent to external wall to facilitate equipment movement and ventilation.
3.2.2.7. Wherever necessary, acoustic treatment should be provided in plant room space to prevent noise transmission to adjacent occupied areas.
3.2.2.8. Air conditioning plant room should preferably be located close to main electrical panel of the building in order to avoid large cable lengths.
3.2.2.9. In case air conditioning plant room is located in basement, equipment movement route shall be planned to facilitate future replacement and maintenance. Service ramps or hatch in ground floor slab should be provided in such cases.
3.2.2.10. Floor drain channels or dedicated drain pipes in slope shall be provided within plant room space for effective disposal of waste water. Fresh water connection may also be provided in the air conditioning plant room.
3.2.2.11. Thermal energy storage
In case of central plants, designed with thermal energy storage its location shall be decided in consultation with the air conditioning engineer. The system may be located in plant room, on rooftop, in open space near plant room or buried in open space near plant room.
For roof top Installations, structural provision shall take into account load coming due to the same.
For open area surface installation horizontal or vertical system options shall be considered and approach ladders for manholes provided.
Buried installation shall take into account loads due to movement above, of vehicles, ect.
Provision for adequate expansion tank and its connection to thermal storage tanks shall be made.
3.2.3. Planning Equipment Room for Air Handling Units and Package Units.
3.2.3.1. This shall be located as centrally as possible to the conditioned area and contiguous it the corridors or other spaces for carrying air ducts. For floor loading, air conditioning
engineer shall be consulted (see also part 6’ Structural Design, Section Loads, Forces and Effects’).
3.2.3.2. In the case of large and multistoried buildings, independent air handling unit should be provided for each floor. The area to be served by the air- handling unit should be decided depending upon the provision of fire protection measures adopted. Air handling unit rooms should preferably be located vertically one above the other.
3.2.3.3. Provision should be made for the entry of fresh air. The fresh air intake shall have louvers having rain protection profile, with volume control damper and bird screen.
3.2.3.4. In all cases air intakes shall be so located as to avoid contamination from exhaust outlets or to the sources in concentrations greater than normal in the bird screen.
3.2.3.5. Exterior openings for outdoor air intakes and exhaust outlets shall preferably be shielded from weather and insects.
3.2.3.6. No air from any dwelling unit shall be circulated directly or indirectly to any other dwelling unit, public corridor or public stairway.
3.2.3.7. All air handling rooms should preferably have floor drains and water supply. The trap in floor drain shall provide a water seal between the airs conditioned space and the drain line.
3.2.3.8. Supply/return air duct shall not be taken through emergency fire staircase. However, exception can be considered if fire isolation of ducts at wall crossings is carried out.
3.2.3.9. Waterproofing of air handling unit rooms shall be carried out to prevent damage to floor below.
3.2.3.10. The floor should be light colored, smooth finished with terrazzo tiles or the equivalent. Suitable floor loading should also be provided after consulting with the air conditioning engineer.
3.2.3.11. Where necessary, structural design should avoid beam obstruction to the passage of supply and return air ducts. Adequate ceiling space should be made available outside the air handling unit room to permit installation of supply and return air ducts and fire dampers at air handling unit room wall crossing.
3.2.3.12. The air handling unit rooms may be acoustically treated, if located in close proximity to occupied areas.
3.2.3.13. Access door to air handling unit room shall be single/double leaf type, air tight, opening outwards and should have a sill to prevent flooding of adjacent occupied areas. It is desired that access doors in air conditioned spaces should be provided with tight sealing, gasket and self closing devices for air conditioning to be effective.
3.2.3.14. It should be possible to isolate the air handling unit room in case of fire. The door shall be fire resistant and fire/smoke dampers shall be provided in supply/return air duct at air handling unit room wall crossings and the annular space between the duct and the wall should be fire-sealed using appropriate fire resistance rated material.
3.2.3.15. For buildings with large structural glazing areas, care should be taken for providing fresh air intakes in air handling unit rooms. Fire isolation shall be provided for vertical fresh air duct, connecting several air handling units.
3.2.4. Planning of Pipe Shafts
3.2.4.1. The shafts carrying chilled water pipes should be located adjacent to air handling unit room or within the room.
3.2.4.2. Shaft carrying condensing water pipes to cooling towers located on terrace should be vertically aligned.
3.2.4.3. All shafts shall be provided with fire barrier at floor crossings (see Part 4 ‘Fire and Life Safety’).
3.2.4.4. Access to shaft shall be provided at every floor.
3.2.4.5. Planning for Supply Air Ducts and Return Air
3.2.5.1. Duct supports, preferably in the from of angles of mild steel supported using stud anchors shall be provided on the ceiling slab from the drilled hole. Alternately, duct supports may be fixed with internally threaded anchor fasters and threaded roads without damaging the slabs or structural members.
3.2.5.2. If false ceiling is provided, the supports for the duct and the false ceiling shall be independent. Collars for grilles and diffusers shall be taken out only after false ceiling/boxing framework is done and frames for fixing grilles and diffusers have been installed.
3.2.5.3. Where a duct penetrates the masonry wall it shall either be suitably covered on the outside to isolate it from masonry or an air gap shall be left around it to prevent vibration transmission. Further, where a duct passes through a fire resisting compartment/barrier, the annular space shall be sealed with fire sealant to prevent smoke transmission (see also Part 4. ‘Fire and Life Safety’).
3.2.6. Cooling Tower
3.2.6.1. Cooling towers are used to dissipate heat from water cooled refrigeration, air conditioning and industrial process systems. Cooling is achieved by evaporating a small proportion of recirculation water into outdoor air stream. Cooling towers are installed at a place where free flow of atmospheric air is available.
3.2.6.2. Range of a cooling tower is defined as temperature difference between the entering an leaving water. Approach of the cooling tower is the difference between leaving water temperature and the entering air wet bulb temperature.
3.2.6.3. Types of cooling tower
3.2.6.3.1. Natural draft
This type of tower is larger than mechanical draft tower as it relies on natural convention to obtain the air circulation. A natural draft tower needs to be tall to obtain the maximum chimney effect or rely on the natural wind currents.
3.2.6.3.2. Mechanical draft
The fans on mechanical draft towers may be on the inlet sir side (induced draft). Typically, these have centrifugal or propeller type fans, depending on pressure drop in tower, permissible sound levels and energy usage requirement, On the basis of direction of air and water flow, mechanical draft cooling towers can be counter flow or cross flow type.
3.2.6.4. Factors to be considered for cooling tower selection are:
3.2.6.5. The recommended floor area requirement for various types of cooling tower is as given below:
3.2.6.6. Any obstruction to free flow of air to the cooling tower shall be avoided.
3.2.6.7. Structural provision for the cooling tower shall be taken into account while designing the building. Vibration isolation shall be an important consideration in structural design.
3.2.6.8. Special design requirements are necessary where noise to the adjoining building is to be avoided.
3.2.6.9. As given below, certain amount of water is lost from circulating water in the cooling tower.
If simple blow-down is inadequate to control scale formation, chemicals may be added to inhibit corrosion and limit microbiological growth.
Provision shall be made to make-up for the loss of circulation water.
3.2.6.10. Provision for make-up water tank to the cooling tower shall be made. Make-up water tank to the cooling tower shall be separate from the tank serving drinking water.
3.2.6.11. Make-up water having contaminants or hardness, which can adversely affect the refrigeration plant life, shall be treated.
3.2.6.12. Cooling tower should be so located as to eliminate nuisance form drift to adjoining structures.
3.2.7. Glazing
3.2.7.1. Glazing contributes significantly to heat addition in air conditioned space; measures shall therefore, be adopted to minimize the gain.
3.2.7.2. While considering orientation of the building, (See part 8 ‘Building Services, Section 1Lighting and Ventilation’) glazing in walls subjected to heavy sun exposure shall be avoided. In case it is not possible to do so, double glazing or heat resistant glass should be used. Glazing tilted inward at about 120 also helps curtail transmission of direct solar radiation through the glazing.
3.2.7.3. Where sun breakers are sued, the following aspects shall be kept in view:
3.2.7.4. Where resort is taken to provide reflecting surfaces for keeping out the heat load, care should be taken regarding the hazards to the traffic and people on the road from the reflected light from the surface.
3.2.7.5. Day light transmittance for various type of glass is given in Table1.
Table 1 Day Light Transmittance for Various Types of Glass
|
Sl No.
|
Type of Glass
|
Visible Transmittance w/ (m2 oc) |
|
i |
3 mm regular sheet or plate glass |
0.86 to 0.91 |
|
ii |
3 mm grey sheet glass |
0.31 to 0.71 |
|
iii |
5 mm grey sheet glass |
0.61 |
|
iv |
5.5 mm grey sheet glass |
0.14 to 0.56 |
|
|
6 mm grey sheet glass |
0.52 |
|
v |
6 mm grey/float glass |
0.75 |
|
vi |
6 mm grey plate glass |
0.44 |
|
vii |
6 mm bronze plate glass |
0.49 |
|
viii |
13 mm grey plate glass |
0.21 |
|
ix |
13 mm bronze plate glass |
0.25 |
|
x |
Coated glasses (single, laminated, insulating) |
0.07 to 0.50 |
3.2.8. Roof insulation
3.2.8.1. Under-deck or over-deck insulation shall be provided for exposed roof surface using suitable insulating materials. Over-deck insulation should be properly waterproofed to prevent loss of insulating properties.
3.2.8.2. The overall thermal transmittance from the exposed roof should be kept as minimum as possible and under normal conditions, the desirable value should be not exceed 0.58 W/ (m2 oc).
3.2.8.3. The ceiling surface of floors which are not to be air conditioned may be suitably insulated to give an overall thermal transmittance not exceeding 1.16 W/ (m2 oc).
4. DESIGN OF AIR CONDITIONING
4.1. General
A ventilation and air conditioning system installed in a building should clean, freshen and condition the air within the space to be air conditioned. This can be achieved by providing the required amount of fresh air either to remove totally or to dilute odours, fumes, ect (for example, from smoking). Local extract systems may be necessary to remove polluted air from kitchens, toilets, ect. Special air filters may be required to remove contaminants or small when air is recalculated.
It is desirable that access doors to air conditioned space are provided with tight sealing gaskets and self closing devices for air conditioning to be effective.
Positions of air inlets and extracts to the system are most important and care should be taken in their location. Consideration should be given to relatively nearby buildings and any contaminated discharges from those buildings. Inlets should not be positioned near any flue outlets, dry cleaning or washing machine extraction outlets, kitchen, water-closets, ect. When possible, air inlets should be at high level so as to induce air from as clean an area as possible. If low level intakes are used, care should be taken to position them well away from roadways and car parks.
4.2. Design Considerations
4.2.1. Type of system
Systems for air conditioning need to control temperature and humidity within predetermined limits throughout the year. Various types of refrigerating systems are available to accomplish the tasks of cooling and dehumidifying, which are an essential feature of air conditioning. Systems for air conditioning may be grouped as all-air type, air and type, all water type or unitary type.
4.2.1.1. All-air system
This type of air conditioning system provides complete sensible and latent cooling, preheating and humidification in the air supplied by the system. Most plants operate on the recirculation principle, where a percentage of the air is extracted and the remainder mixed with incoming fresh air.
Low velocity system may be used, High velocity systems although require smaller ducts, are high on fan energy, require careful acoustic treatment and higher standards of duct construction.
4.2.1.1.1. Constant volume system
Accurate temperature control is possible, according to the system adopted. Low velocity system variations include dehumidification with return air by pass, and multi-zone (hot deck/cold deck mixing). High velocity system may be single or dual duct type.
4.2.1.1.2. Variable volume system
Most Indian air conditioning system operate at partial load for most of the year and the variable air volume (VAV) system is able to reduce energy consumption by reducing the supply air volume to the space under low load conditions. The VAV system can be applied to interior or perimeter zones, with common or separate fans, with common or separate air temperature control. The greatest energy saving associated with VAV occurs at the perimeter zones, where variation in solar and outside temperature allow the supply air quantity to be reduced. Good temperature control is possible but care should be taken at partial load to ensure adequate fresh air supply and satisfactory control of air distribution and space humidity.
4.2.1.2. Air and water system
Control of conditions within the space is achieved by initial control of the supply air from a central l plant but with main and final control at a terminal unit within the conditioned space. The supply air provides the necessary ventilation air and the small part of the total conditioning. The major part of room load is balanced by water through a coil in the terminal unit, which can be either a fan coil or an induction unit.
Depending on the degree of control required, the water circulating system can be either of two, three or four pipe arrangement. With two pipe circulation a single flow and a single return circulate chilled or hot water as required. Such a system can only provide heating or cooling to the system on a changeover basis, so it is ineffective where wide modulations of conditions over short periods are required. The installed cost however is naturally the lowest of all the circulation systems. The three pipe system is a way of overcoming the disadvantages of the two pipe system without raising the installed cost too high. In this system a separate hot water flow is taken to the terminal units but a common return is taken from these units to the plant room. The best system from a control point of view is the four pipe system, where separate hot water and chilled water supply and returns are taken the most expensive method of circulating the water it is the only satisfactory one, if reasonable control is required throughout the year.
4.2.1.3. All water system.
In the simple layout, the fan coil units may be located against an outside wall with a direct, fresh air connection. A superior arrangement utilizes a ducted, conditioned, fresh air supply combined with mechanical extract ventilation.
Control of unit out put may be achieved by fan speed and water flow/temperature control. Electric power is required at each terminal unit.
Provision of variable volume water flow system for chilled water circulation is recommended for varying load conditions. This may be incorporated with the help of constant volume primary chilled water circuit and variable flow secondary chilled water circuit having pumps with variable speed drives and pressure sensor on control the speed. This system allows better control on energy consumption under partial load conditions due to diversity or seasonal load variations.
4.2.1.4. Unitary systems
Such systems are usually those incorporating one or more units or packaged air conditioners having direct expansion vapour compression refrigeration system. Similar units using chilled water from a central plant would be designated fan coil systems. Most units are only suitable for comfort applications but specially designed units are also available for process and industrial applications.
4.2.2. Vapour compression Water chiller
These normally contain the complete refrigerating system, comprising the compressor, condenser, expansion device and evaporator together with the automatic control panel. The unite can be set down on to a solid foundation on resilient mountings. Pipe connections require flexible couplings; these should be considered in conjunction with the design of the pump mountings and the pipe supports.
Capacity control is normally arranged to maintain an approximately constant temperature of the chilled water leaving the evaporator. This may be adequate for one or two package, but a more elaborate central control system may be necessary for a large number. The design of the refrigeration control system should be integrated, or be compatible, with the control system for the heat transfer medium circulated to the air cooler.
It is normal for installation to have several water chilling packages, both to provide for stand-by and enable the cooling load to be matched with the minimum consumption of power. Although most packages can reduce capacity to match the cooling demand, the consumption of the power per unit of cooling increases; the resulting drop in efficiency is most serious below on-third capacity.
Power consumption can be reduced by taking advantage of a fall in the ambient temperature, which permits a corresponding fall in the condensing temperature and consequent reduction in the operation, that the optimum equipment selection and design of the control system is achieved.
The classification of the water chilling packages is by the type of compressor.
4.2.2.1. Centrifugal compressor
These compressors have an impeller that imparts to the refrigerant vapour a high kinetic energy, which is then transformed into pressure energy. For water chilling applications, compressors with one or two stage of compression are used. Two stage units often incorporate an interstate economizer for improving efficiency.
The compressor can be modulated down to approaching 10 percent of full load capacity, with some control of the condensing pressure. Because of the nature of compression process, the flow through the compressor can become unstable if the compressor is called upon to produce a pressure rise in excess of its design limits. This phenomenon, known as surging, is a serious problem but occurs only under a fault condition. Typical faults are excessive fouling of the condenser, a partial failure of the condenser coolant flow or an accumulation of a non-condensable gas (air) in the condenser. Unchecked surging can lead to damage to the compressor or its drive and does increase the noise level.
The use of low pressure refrigeration to suit the characteristics of the compressor in the smaller size range, means that the evaporator o0perates at below atmospheric pressure, that a leak can draw in air and atmospheric moisture. These should be prevented from accumulating, since these interfere with the operation of the plant and cause corrosion.
The compressors may be driven either directly by electric motor or via a speed-increasing gear train. Units are available in ‘open’ from, that is, compressor and motor are separate items, or in semi-hermetic form where the motor and compressor are contained in a common pressure-tight casing that is bolted together. The latter type eliminates the drive shaft gland seal (a potential point of leakage), which is necessary on the former.
Certain types of open centrifugal compressors could conveniently be directly be a steam or gas turbine. This arrangement could be advantageous when the refrigeration plant part of total energy system.
The centrifugal compressor type water chilling packages normally include a shell-and-tube water cooled condenser and a flooded shell-and-tube evaporator, but unit are also available incorporating an air cooled condenser the expansion device is commonly an electronic expansion valve or high pressure float regulating value.
4.2.2.2. Screw compressors
Two types of screw compressors are available, that is, single and twin screw, and both are positive displacement machines. Compression of the refrigerant vapour is achieved by the progressive reduction of the volume contained with in helical flutes of the cylindrical rotor(s) as they rotate.
Oil is injected into the rotor chamber for sealing and lubrication purposes and is removed from the refrigerant discharge gas in an oil separator before the refrigerant passes on to the condenser. No oil separator is 100 percent efficient and so a small quantity of oil always passes through with the refrigerant. On systems using a direct expansion evaporator the oil is trapped in the evaporator and an oil recovery system is necessary.
With some systems oil cooler is required in the oil circulation system, to remove the heat gathered by the oil during compression cycle. On other systems liquid refrigerants is injected into the compressor to remove the heat of compressions instead of using the conventional oil cooler. Such an arrangement can impose a small penalty on the plant capacity.
The condenser most commonly used on packaged unit is the water cooled shell-and tube type, but equipment with air cooled condensers is also available. The expansion device used will depend on the evaporator type but it is often a electronic expansion valve (single or in multiple) of conventional or modified from.
Screw compressors are available in open and semi hermetic from (see 4.2.2.1) and are generally coupled direct to two-pole motors. The capacity of the compressor can be modulated down to 10 percent of full load capacity.
4.2.2.3. Reciprocating compressor
These are available in a wide range of size and designs. They are almost invariably used in packages up to 120 TR cooling capacity.
Because the cylinders have automatic valves, a single compressor may be used over wide range of operating conditions with near optimum efficiency, whereas, other types of compressor require detailed modification to give optimum efficiency at different conditions. These conditioning duties.
Capacity control is achieved by making cylinders in operative, usually by propping open the suction valves, thus, capacity reduction is in a series of steps rather than by modulation. Typically, a four-cylinder compressor would be unloaded in four steps. It is therefore necessary to allow for this stepwise operation in designing the chilled water temperature control system.
The evaporator is normally of the dry expansion type, to permit oil form the compressor to circulate round the system with the refrigerant. Shell-and-tube water cooled condensers are common, but any type of condenser can be used. With air cooled condenser it is normal practice to build the machine package so that it may be located on the roof in a package including the condenser.
It is common for the electric drive motors to be built into the compressor assembly; this is known as a ‘semi-hermetic’ drive to distinguish it from the ‘hermetic’, in which the compressor and motor are enclosed within a pressure vessel and cannot therefore be serviced.
The semi-hermetic compressor is more compact and is quieter in operation than the ‘open’ drive compressor, but involves a more difficult service operation in the event of a motor failure. It gains in reliability, however, by avoiding the shaft seal of the ‘open’ compressor.
It is recommended that multiple hermetic or semi-hermetic compressor unit should not be connected to a common refrigerant system, as failure of one motor can precipitate failure of the others. Separate refrigerant circuits of each compressor should be used.
4.2.3. Absorption system
The absorption cycle uses a solution that by absorbing the refrigerant replaces the function of the compressor. The absorbent/refrigerant mixture is then pumped to a higher pressure where the refrigerant is boiled off by the application of heat, to be condensed in the condenser.
Absorption machines are mostly used in liquid-chilling applications. These are most suitable for hotels and hospitals where steam is readily available from the boilers.
4.2.3.1. Indirect firing
The lithium bromide/water absorption system can be powered by medium or high temperature hot water and low or medium pressure steam. Water is the refrigerant and the lithium bromide the absorbent. The four compartments enclosing the heat exchanger tube bundles for the condenser, evaporator, generator and absorber can be in a single or multiple pressure vessel arrangement. The whole assembly has to be maintained under a high vacuum, which is essential for the correct functioning of the unit. Water and absorbent solutions are circulated within the unit by electrically driven pumps.
Capacity control down to 10 percent of full load capacity is achieved by modulating the flow of the heating medium in relation to the cooling demand. There is some loss in performance at part load, which can be compensated by refinements in the system design and control.
4.2.3.2. Direct firing
Direct fired lithium bromide/water absorption plants have become common, by incorporating precise control of generator temperature necessary to avoid crystallization.
Ammonia/water systems can be and are direct fired, but are rarely used for water chilling duties except for small sized units, which are installed outside the building. There are two reasons or this, firstly capital costs are higher and secondly the danger to personnel in the event of leakage of the refrigerant.
Direct firing has the advantage that the losses in an indirect heating system are avoided, but in an air conditioning installation where a boiler system is installed to provide heating, the advantage is minimal.
4.3. System Design
4.3.1. Ductwork and Air distribution
4.3.1.1. Materials
Ductwork is normally fabricated, erected and finished to the requirements in accordance with accepted standard [8-3(1)]. Designers should specify and requirement as appropriate for the velocity and pressure, and materials to be employed. Ductwork is generally manufactured from galvanized steel sheet. Ductwork may also be manufactured from aluminum sheet for applications like operation theatres and intensive care units where stringent cleanliness standards are a functional requirement. Galvanized steel sheets shall be accordance with the accepted standard [8-3(2)] whereas aluminium sheet shall be in accordance with the accepted standard [8-3(3)]. Where building materials, such as concrete or brick, are used in the formation of airways, the interior surface should be fire resistant, smooth, airtight and not liable to erosion.
4.3.1.2. Ductwork design
Design calculation made to determine the size and configuration of ductwork in respect of pressure drop and noise generation should conform to standard methods.
Ductwork design should also take into account the recommendations for fire protection (see part 4 ‘Fire and Life Safety’) relating to the design of air handling system to fire and smoke control in buildings.
4.3.1.3. Layout consideration
When designing ductwork, consideration should be given to:
4.3.2. Piping and Water Distribution System
4.3.2.1. Materials
Steel piping with welded or flanged joints is commonly used. Flanges for flanged joint are welded to pipes. The choice of materials or any installation will be governed by economic considerations, but care should be taken to minimize the possibility of corrosion when choosing material combinations.
4.3.2.2. Design principles
The system design should achieve the following two main objectives:
Excessive water velocities should be avoided, as they may lead to noise at pipe junctions and bends.
When multiple water-chilling package have to be used in a large system, the control of the machines and the arrangement of the water circulation should be considered as an integrated whole. It is not possible to obtain satisfactory result by considering control and system design separately.
Temperature changes in the system lead to changes in the volume of water, which has to be allowed to expand into a suitable expansion tank. It is essential that the point at which the expansion tank is connected into the system be such that it is never shutoff. It is normal practice to locate the expansion tank above the highest point in the system, so that a positive pressure is maintained when all the pumps are stopped; if this is not possible, a closed tank can be installed at a lower level and pressurized by an inert gas. Closed expansion tank with air separator in the chilled water system helps in improving the life and efficiency of chilled water piping and heat exchange equipment.
For central chilled water air conditioning systems, water is the usual heat transfer medium use to convey the heat from the air-handling units to the primary refrigerant in the evaporator. In certain special cases, when temperatures lower than 50C are required, an anti-freeze such as ethylene glycol may be added to depress the freezing point.
4.3.2.3. Piping design
The arrangement of the water piping will depend upon the cooling or heating systems chosen as being the most suitable for the building.
The water velocities normally used are dependent on pipe size but are usually in the range 1m/s to 3m/s.
Main headers in the plant room are designed for very low velocity around 1m/s. Noise can be caused by velocities in excess of 4 m/s but this is more likely to be caused by air left in the pipes by inadequate venting. Where materials other than steel are used, erosion can occur at the higher velocities particularly if the water is allowed to become acidic.
Friction factor in piping should not exceed 5 m of water for 100 m of pipe length. The power consumed in circulating the water around the system is proportional to the pressure loss (due to friction) and the flow. It is therefore an advantage to design system with a water temperature rise say 50C-70C which results in minimizing the flow rate.
Air-conditioning system operate for a large part of the time at less than the design load, and this means that operating costs can be minimized if the water quantity circulated can be reduced at partial load. This should be done with variable speed pumping systems.
4.3.2.4. Layout consideration
The layout of the main pipe runs should be considered in relation to the building structure, which will have to support their weight and carry the imposed axial loads. The positioning of expansion joints should be considered in relation to the branches, which may only accommodate small movements. The pumps should not be subjected to excessive loads from the piping.
Provision should be made for venting air and any gas formed by corrosion processes from the high points in the system: failure to do this can lead to restricted water flows and poor performance.
New system invariably contain debris of one sort or another left during construction, and this can cause trouble by blocking pipes, control valves and pumps if it is not removed during testing and commissioning piping system should be designed to permit proper cleaning and flushing and should include suitable strainers at appropriate locations.
4.3.3. Thermal insulation
4.3.3.1. Air conditioning and water distribution system carry chilled or heated fluids. Thermal insulation is required to prevent undue heat gain or loss and also to prevent undue heat gain or loss and also to prevent internal and external condensation; a vapour seal is essential if there is a possibility of condensation within the insulating materials.
4.3.3.2. The selection of suitable thermal insulating materials requires that consideration be given to physical characteristics as follows:
4.4. Design conditions
4.3.1.1. General consideration
Certain minimum temperatures may be required depending on type of application and by local regulations. Maximum permitted cooling temperatures may be stipulated by relating to energy conservation.
From the comfort aspect, it is important to take into account the effect of radiant temperature in fixing the desired air temperatures to maintain comfortable conditions.
When large window/curtain walls are used, it may be necessary to provide shading/north orientation to protect the occupants from solar radiation and to reduce the cooling load on the system. It is not practical to fully compensate for solar heating, owing to its intermittent nature, simply by lowering air temperature.
A person’s loss, and hence his feeling of comfort, depends not only on the air temperature but also on the radiant heat gain, the air movement and the humidity of the air. Many attempts have been made to devise a single index that combines the effect of two or more of these separate variables. In practice the difference between these indices is small provided the various parameters do not vary beyond certain limits.
4.3.1.2. Design temperatures
I should be noted that, although comfort conditions are established in terms of resultant temperature, the design air temperature for air conditioning should be as specified in this Section in terms of dry-bulb temperature and relative humidity or wet-bulb temperature
4.4.2. Humidity
4.4.2.1. Comfort considerations
The controlled temperature levels should also be considered in relation to the humidity of the air. A high humidity reduces evaporative cooling from the body and hence creates the sensation of a higher temperature. Beyond certain limits, however, humidity produces disagreeable sensations.
For normal comfort conditions, relative humidity (RH) values between 40 percent and 70 percent are acceptable.
4.4.3. Inside Design Conditions
The inside design conditions for some of the applications are indicated in Table 2.
4.4.4. Outside Design Conditions
The outside design condition (dry-bulb and mean coincidental wet-bulb) taken shall be in accordance with the summary of the conditions given in the Table 3.
Values of ambient dry-bulb and wet-bulb temperatures against the various annual percentiles represent the value that is exceeded on average by the indicated percentage of the total number of hours. The 0.4 percent, 1.0 percent, 2.0 percent values are exceeded on average 35,88 and 175 h in a year. The 99.0 percent and 99.6 percent values are defined in the same way but are usually reckoned as the values for which the corresponding weather elements are less than the design conditions for 88 h and 35h, respectively.
Mean coincidental values are the average of the indicated weather element occurring concurrently with the corresponding design value.
After the calculation of design dry-bulb temperatures, the programmer located the values of corresponding wet-bulb temperatures from the database for that particular station, the average of these values were computed, which were then called mean of coincidental wet-bulb temperature.
In the same way design wet-bulb temperatures and coincidental dry-bulb temperatures were evaluated.
Selection: The design values of 0.4 percent, 1.0 percent and 2.0 percent annual cumulative frequency of occurrence may be selected depending upon application of air conditioning system.
For normal comfort jobs values under 1percent column could be used for cooling loads and 99 percent column
Table 2 inside Design Conditions for Some Applications (Clause 4.4.3)
|
Sl No. |
Category |
Inside Design Conditions |
||
|
Summer |
|
Winter |
||
|
i) |
Restaurants |
DB 23 to 260C RH 55 to 60% DB 23 to 260C RH 50 to 60% DB 23 to 260C RH 45 to 60% DB 23 to 260C RH 50 to 60% DB 23 to 260C RH 50 to 60% DB 23 to 260C RH 50 to 60% |
DB 21 to 230C RH not less than40% DB 21 to 230C RH not less than40% DB 21 to 230C RH 40 to 50% DB 21 to 230C RH not less than40% DB 23 to 240C RH not less than40% DB 23 to 240C RH not less than40% |
|
|
ii) |
Office buildings |
|||
|
iii) |
Radio and television studios |
|||
|
iv) |
Departmental stores |
|||
|
v) |
Hotel guest rooms |
|||
|
vi) |
Class rooms |
|||
|
vii) |
Auditoriums |
|||
|
viii) |
Recovery rooms |
|
DB 24 to 260C RH 45 to 55% DB 24 to 260C RH 45 to 55% DB 17 to 270C RH 45 to 55% DB 20 to 220C RH 40 to 55% DB 22 to 260C RH 40 to 50% |
|
|
ix) |
Patient rooms |
|||
|
x) |
Operation theatres |
|||
|
xi) |
Museums and libraries |
|||
|
xii) |
Telephone terminal rooms |
|||
Table 3—Concluded
|
(1) |
(2) |
(3) |
(4) |
(5) |
(6) |
(7) |
(8) |
(9) |
(10) |
(11) |
(12) |
(13) |
(14) |
(15) |
(16) |
(17) |
|
Gwalior |
43.9 |
23.0 |
42.5 |
22.9 |
41.3 |
23.5 |
27.9 |
32.9 |
27.6 |
32.4 |
27.3 |
32.7 |
4.9 |
3.8 |
6.4 |
5.3 |
|
Hissar |
44.7 |
26.5 |
43.3 |
25.8 |
41.7 |
27.9 |
30.1 |
40.2 |
29.9 |
39.0 |
29.4 |
36.8 |
5.0 |
4.2 |
6.1 |
5.2 |
|
Hyderabad |
40.4 |
22.5 |
39.2 |
22.5 |
38.2 |
22.4 |
25.6 |
33.7 |
25.2 |
32.4 |
24.8 |
32.0 |
14.4 |
12.4 |
15.5 |
12.9 |
|
Imphal |
31.1 |
23.3 |
30.2 |
23.5 |
29.6 |
22.9 |
25.0 |
29.5 |
24.6 |
28.6 |
24.3 |
28.3 |
3.9 |
3.6 |
0.5 |
4.6 |
|
Indore |
41.1 |
20.7 |
40.4 |
20.6 |
38.9 |
21.0 |
25.7 |
31.0 |
25.2 |
30.0 |
24.8 |
29.8 |
8.2 |
5.0 |
9.7 |
6.5 |
|
Jabalpur |
42.6 |
22.7 |
41.2 |
23.2 |
39.8 |
22.5 |
26.8 |
31.8 |
26.4 |
32.0 |
26.0 |
31.2 |
7.8 |
6.7 |
9.3 |
7.6 |
|
Jagdelpur |
39.4 |
22.3 |
38.6 |
22.5 |
37.4 |
22.4 |
26.4 |
32.4 |
25.9 |
31.8 |
25.4 |
30.7 |
8.9 |
7.9 |
10.1 |
8.7 |
|
Jaipur |
42.8 |
22.5 |
41.4 |
22.6 |
39.4 |
22.6 |
27.4 |
33.1 |
27.0 |
32.1 |
26.6 |
31.7 |
6.4 |
4.5 |
8.0 |
5.8 |
|
Jaisalmer |
43.7 |
23.7 |
42.5 |
23.1 |
41.4 |
23.5 |
27.7 |
34.8 |
27.3 |
34.5 |
26.9 |
34.4 |
5.0 |
2.5 |
6.5 |
3.7 |
|
Jamnagar |
37.1 |
24.4 |
36.1 |
25.6 |
35.3 |
25.1 |
29.2 |
33.0 |
28.4 |
32.5 |
27.9 |
32.0 |
10.0 |
8.6 |
11.7 |
10.5 |
|
Jodhpur |
42.0 |
23.2 |
40.8 |
23.0 |
39.6 |
22.7 |
28.0 |
35.4 |
27.4 |
33.7 |
26.9 |
33.8 |
7.5 |
4.3 |
8.7 |
5.4 |
|
Jorhat |
34.4 |
28.2 |
33.6 |
27.7 |
32.9 |
27.3 |
28.7 |
32.7 |
28.3 |
32.1 |
28.0 |
31.8 |
9.6 |
9.0 |
10.6 |
10.1 |
|
Kolkata |
37.2 |
25.4 |
36.2 |
26.1 |
35.2 |
26.5 |
29.5 |
34.3 |
29.0 |
33.4 |
28.6 |
32.7 |
12.0 |
10.9 |
13.1 |
12.9 |
|
Kota |
43.5 |
23.0 |
42.4 |
22.6 |
41.2 |
22.6 |
27.3 |
35.2 |
26.8 |
33.0 |
26.5 |
31.8 |
9.9 |
6.7 |
10.8 |
7.6 |
|
Kurnool |
41.6 |
23.2 |
40.3 |
24.6 |
38.9 |
24.4 |
29.3 |
34.8 |
28.8 |
34.8 |
28.4 |
33.4 |
2.7 |
2.3 |
4.0 |
3.5 |
|
Lucknow |
42.0 |
24.2 |
40.8 |
24.8 |
39.3 |
24.5 |
28.8 |
33.3 |
28.4 |
32.4 |
28.0 |
32.2 |
7.5 |
6.8 |
8.4 |
7.7 |
|
Manglore |
33.9 |
24.4 |
33.9 |
24.0 |
33.4 |
24.2 |
27.1 |
31.0 |
26.7 |
31.0 |
26.4 |
30.7 |
19.7 |
17.0 |
20.5 |
18.1 |
|
Mumbai |
35.3 |
22.8 |
34.3 |
23.3 |
33.5 |
24.0 |
27.9 |
31.8 |
27.5 |
31.3 |
27.2 |
31.1 |
16.5 |
13.9 |
17.8 |
14.8 |
|
Nagpur |
43.8 |
23.6 |
42.6 |
23.9 |
41.4 |
23.6 |
27.3 |
31.2 |
26.6 |
33.2 |
26.2 |
31.9 |
11.5 |
9.4 |
12.8 |
10.2 |
|
Nellore |
40.4 |
27.8 |
39.0 |
28.1 |
37.8 |
27.2 |
30.0 |
37.1 |
29.4 |
35.4 |
28.8 |
34.0 |
19.4 |
18.3 |
20.2 |
19.3 |
|
New Delhi |
41.8 |
23.6 |
40.6 |
23.8 |
39.4 |
23.5 |
28.4 |
33.3 |
28.0 |
33.3 |
27.6 |
32.7 |
6.0 |
5.2 |
7.1 |
6.3 |
|
Panjim |
34.0 |
24.8 |
33.5 |
25.2 |
33.0 |
25.2 |
27.7 |
32.3 |
27.4 |
31.5 |
27.0 |
30.9 |
19.6 |
17.8 |
20.3 |
18.7 |
|
Patna |
40.7 |
23.4 |
39.5 |
23.7 |
38.0 |
24.7 |
29.0 |
33.9 |
28.6 |
33.1 |
28.3 |
32.6 |
8.0 |
7.6 |
9.2 |
8.6 |
|
Pune |
38.4 |
20.5 |
37.4 |
20.4 |
36.3 |
20.6 |
24.8 |
30.9 |
24.4 |
30.6 |
24.0 |
29.6 |
9.2 |
8.0 |
10.3 |
9.2 |
|
Raipur |
43.6 |
23.3 |
42.2 |
23.3 |
40.8 |
23.0 |
27.1 |
31.8 |
26.8 |
32.0 |
26.5 |
31.2 |
11.3 |
9.9 |
12.6 |
10.4 |
|
Rajkot |
40.8 |
23.1 |
39.9 |
23.8 |
38.9 |
23.4 |
28.1 |
33.9 |
27.6 |
33.3 |
27.1 |
32.3 |
10.9 |
6.5 |
12.2 |
7.7 |
|
Ramagundam |
43.4 |
25.6 |
42.2 |
25.1 |
40.7 |
25.8 |
28.3 |
37.3 |
27.9 |
35.6 |
27.4 |
34.4 |
12.5 |
11.2 |
13.7 |
12.5 |
|
Ranchi |
38.9 |
22.1 |
37.7 |
21.8 |
36.4 |
21.5 |
26.2 |
31.7 |
25.6 |
30.4 |
25.2 |
29.2 |
9.1 |
7.2 |
10.4 |
8.3 |
|
Ratnagiri |
34.1 |
22.4 |
33.4 |
23.2 |
32.8 |
23.6 |
27.6 |
31.1 |
27.3 |
30.8 |
27.0 |
30.2 |
18.3 |
14.9 |
19.2 |
16.5 |
|
Raxaul |
38.6 |
23.1 |
36.9 |
24.5 |
35.5 |
24.6 |
28.9 |
33.0 |
28.4 |
32.0 |
28.1 |
31.8 |
7.5 |
7.3 |
8.5 |
8.2 |
|
Sahranpur |
41.3 |
23.8 |
39.6 |
24.6 |
38.1 |
24.0 |
28.5 |
33.6 |
28.1 |
32.9 |
27.8 |
32.5 |
1.7 |
1.5 |
3.0 |
2.7 |
|
Shillong |
24.2 |
19.7 |
23.5 |
19.4 |
22.8 |
18.9 |
20.7 |
23.3 |
20.3 |
22.7 |
19.9 |
22.2 |
-1.0 |
-1.1 |
0.1 |
-0.5 |
|
Sholapur |
41.1 |
21.6 |
40.1 |
21.6 |
39.1 |
21.2 |
26.6 |
32.6 |
25.8 |
32.1 |
25.1 |
31.5 |
16.3 |
12.4 |
17.2 |
12.5 |
|
Sundernagar |
36.1 |
19.1 |
34.6 |
19.9 |
33.1 |
19.4 |
25.2 |
30.1 |
24.8 |
29.2 |
24.4 |
28 |
1.8 |
1.3 |
2.8 |
2.2 |
|
Surat |
38.4 |
22.7 |
36.9 |
23.9 |
35.7 |
23.4 |
28.3 |
32.4 |
27.9 |
31.7 |
27.6 |
31.4 |
14.8 |
12.6 |
16.2 |
12.5 |
|
Tezpur |
34.2 |
27.4 |
33.3 |
26.5 |
32.5 |
27.1 |
28.9 |
32.8 |
28.4 |
31.8 |
28.0 |
31.4 |
10.5 |
10.0 |
12.4 |
10.9 |
|
Tiruchirapalli |
39.6 |
24.6 |
38.7 |
25.1 |
37.8 |
24.9 |
27.7 |
34.5 |
27.2 |
33.7 |
26.9 |
33.3 |
19.3 |
18.2 |
20.1 |
18.7 |
|
Thiruvanantha- Puram |
33.9 |
26.0 |
33.4 |
26.1 |
32.9 |
25.9 |
27.7 |
32.4 |
27.4 |
31.9 |
27.0 |
31.0 |
21.6 |
20.1 |
22.2 |
20.8 |
|
Verval |
35.2 |
23.9 |
33.8 |
23.5 |
32.8 |
26.6 |
29.1 |
32.3 |
28.7 |
31.6 |
28.4 |
31.1 |
14.3 |
10.1 |
15.6 |
12.3 |
|
Visakapatnam |
36.4 |
26.5 |
35.6 |
27.3 |
35.0 |
27.1 |
29.2 |
33.8 |
28.8 |
33.0 |
28.4 |
32.5 |
15.4 |
14.9 |
16.8 |
16.2 |
NOTE- Abbreviations used
DBT -- Dry-bulb temperature
WBT -- Wet-bulb temperature
MCDB -- Mean coincidental dry-bulb temperature
MCWB-- Mean coincidental wet-bulb temperature
For heating loads. For critical applications values under 0.4 percent column could be used for cooling loads and 99.6 percent column for heating loads.
For critical jobs and high energy consumption application, hourly load analysis should be evaluated using computer programmers.
For industrial and others specific applications, the design conditions shall be as per user’s requirement.
Adequate movement of air shall always be provided in an air conditioned enclosure, but velocities in excess of 0.5 m/s in the zone between floor level and 1.5 m level shall generally be avoided; in the case of comfort air conditioning, recommended air velocity is 0.13 m/s to 0.23 m/s in this zone, except in the vicinity of a supply or return air grille.
4.4.5. Minimum Out side Fresh Air
The fresh air supply is required to maintain an acceptably non-odorous atmosphere (by diluting body odorous and tobacco smoke and to dilute the carbon dioxide exhaled. This quantity may be quoted per person and is related to the occupant density and activity within the space. Table 4 gives minimum fresh air supply rates for mechanically ventilated or air conditioned space. The quantity and distribution of introduced fresh air should take into account the natural infiltration of the building.
Table 4 specifies requirements for ventilation air quantities for 100 percent outdoor air when the outdoor air quality meets the specifications for acceptable outdoor air quality. While these Quantities are for 100 percent outdoor air, they also set the amount of air required to dilute contaminants to acceptable levels. Therefore, it is necessary that at least this amount of air be delivered to the conditioned space at all times the building is in use.
The proportion of fresh air introduced into a building may be varied to achieve economical operation. When the fresh air can provide a useful cooling effect the quantity shall be controlled to balance the cooling demand. However, when the air is too warm or humid the quantity may be reduced to a minimum to reduce the cooling load.
For transfer of heat/moisture, air circulation is required to transfer the heat and humidity generated within the building. In simple systems the heat generated by the occupants, lighting, solar heat and heat from electrical and mechanical equipment may be removed by the introduction and extraction of large quantities of fresh air. In more elaborate systems air may be re-circulated through conditioning equipment to maintain the desired temperature and humidity. The air circulation rates are decided in relation to the thermal of moisture loads and the practical cooling and hearing range of the air.
4.4.6. Air Movement
Care should be taken, however, to avoid excessive pressure differences that may cause difficulty in opening door or cause them to slam. In other cases, such as computer room, the area may be pressurized to minimize the introduction of dust from adjacent areas.
4.4.6.1. Fire and smoke control
Air circulation system may be designed to extract smoke in event of a fire, to assist in the fire fighting operation and to introduce fresh air to pressurize escape routes.
4.4.6.2. Removal of particulate matter from air
Efficient air filtration prevents fouling of the system and is of special importance in urban areas, where damage is likely to be caused to decorations and fittings by discoloration owing to airborne dust particles. In order to obtain maximum filtration efficiently within the minimum capital and maintenance expenditure, the utmost care should be given to the location of the air intake in relation to the prevailing wind, the position of chimneys and the relative atmospheric dust concentration in the environs of the building; the recommendation for sitting of air inlets given in 4.1
Table 4 Outdoor Air requirement for Ventilation 1) of Air Conditioned Areas and Commercial Facilities
(Clause 4.4.5)
|
Sl No. |
Application |
Estimated Maximum2) Occupancy |
Outdoor Air Requirement |
Remarks |
|
|
|
|
Persons/100m2 |
1/sPerson(1/s)m2 |
|
|
|
i) |
Commercial dry cleaner |
30 |
15 |
|
|
|
ii) |
Food and Beverage Service |
|
|
|
|
|
|
Dining rooms |
70 |
10 |
|
|
|
|
Cafeteria, fast food |
100 |
10 |
|
|
|
|
Bars, cocktail lounges |
100 |
15 |
|
Supplementary smoke removal equipment may be required. |
|
|
Kitchen (cooking) |
20 |
8 |
|
Make up air for food exhaust may require more ventilating air. The sum of the outdoor air and transfer air of acceptable quality from adjacent spaces shall be sufficient to provide an exhaust rate of not less than 27.5 m3/h.m2(7.51/s.m2). |
|
iii) |
Hotels, Motels, Resorts, Dormitories |
|
|
|
Independent of room size. |
|
|
Bedrooms |
|
15 |
|
|
|
|
Living rooms |
|
|
15 |
Installed capacity for intermittent use. |
|
|
Baths |
|
|
18 |
|
|
|
Lobbies |
30 |
8 |
|
|
|
|
Conference rooms |
50 |
10 |
|
|
|
|
Assemble rooms |
120 |
8 |
|
|
|
|
Dormitory sleeping areas |
20 |
8 |
|
See also food and beverage services, merchandising, barber and beauty shops, garages, offices. |
|
|
Office space |
7 |
10 |
|
Some office equipment may require local exhaust. |
|
|
Reception areas |
60 |
8 |
|
|
|
|
Telecommunication center and data entry areas |
60 |
10 |
|
|
|
|
Conference room |
50 |
10 |
|
|
|
iv) |
Public Spaces |
|
|
|
|
|
|
Corridors and utilities |
|
|
0.25 |
|
|
|
Public restrooms,1/s/wc or urinal |
|
25 |
|
Normally supplied transfer air. |
|
|
Locker and dressing rooms |
|
|
2.5 |
Local mechanical exhaust with no re-circulation Recommended. |
|
|
Elevators |
|
|
5.0 |
Normally supplied by transfer air. |
|
|
Retail stores, sales floors and show room floors. |
|
|
|
|
|
|
Basement and street |
30 |
|
1.50 |
|
|
|
Upper floors |
20 |
|
1.00 |
|
|
|
Storage rooms |
15 |
|
0.75 |
|
|
|
Dressing rooms |
|
|
1.00 |
|
|
|
Malls and arcades |
20 |
|
1.00 |
|
|
|
Shipping and receiving |
10 |
|
0.75 |
|
|
|
Warehouses |
5 |
|
0.25 |
|
|
|
Smoking lounge |
70 |
30 |
|
Normally supplied by transfer air, local mechanical exhaust with no re-circulation recommended. |
|
v) |
Specialty Shop |
|
|
|
|
|
|
Barber shop |
25 |
8 |
|
|
|
|
Beauty parlor |
25 |
13 |
|
|
|
|
Florists |
8 |
8 |
|
Ventilation to optimize growth may dictate requirements. |
|
|
Clothiers, furniture |
|
|
1.50 |
|
|
|
Hardware, drugs, fabric |
8 |
8 |
|
|
|
|
Supermarkets |
8 |
8 |
|
|
|
|
Pet shop |
|
|
5.00 |
|
|
vi) |
Sports and Amusement |
|
|
|
|
|
|
Spectator areas |
150 |
8 |
|
When internal combustion engines are operated for maintenance of playing surfaces, increased ventilation rates may be required. |
|
|
Game rooms |
70 |
13 |
2.50 |
|
|
|
Ice arenas (playing areas |
|
|
|
|
Table 4-- Concluded
|
|
Swimming pools(pool and deck area) |
|
|
2.50 |
Higher values may be required for humidity control. |
|
|
Playing floors (gymnasium) |
30 |
10 |
|
|
|
|
Ballrooms and discos |
100 |
13 |
|
|
|
|
Bowling alleys (Seating area) |
70 |
13 |
|
|
|
vii) |
Theatre |
|
|
|
|
|
|
Ticket booths |
60 |
10 |
|
Special ventilation will be needed to eliminate special stage effects (for example, dry ice vapours mists, etc). |
|
|
Lobbies |
150 |
10 |
|
|
|
|
Auditorium |
150 |
8 |
|
|
|
|
Stages, studios |
70 |
8 |
|
|
|
vii) |
Transportation |
|
|
|
|
|
|
Waiting rooms |
100 |
8 |
|
Ventilation within vehicles may require special consideration. |
|
|
Platforms |
100 |
8 |
|
|
|
|
Vehicles |
150 |
8 |
|
|
|
ix) |
Workrooms |
|
|
|
|
|
|
Meat processing |
10 |
8 |
|
Spaces maintained at low temperature at (-100 F to +500 or-230C to +100C) are not covered by these requirement unless the occupancy is continuous. Ventilation from adjoining spaces is permissible. When the occupancy is intermittent, infiltration will normally exceed the ventilation requirement |
|
|
Photo studios |
10 |
8 |
|
|
|
|
Darkrooms |
10 |
|
2.50 |
|
|
|
Pharmacy |
20 |
8 |
|
|
|
|
Bank vaults |
5 |
8 |
|
|
|
|
Duplicating, Printing |
|
|
2.50 |
Installed equipment shall incorporate positive exhaust and control (as required) of undesirable contaminants (toxic and otherwise) |
|
x) |
Education |
|
|
|
|
|
|
Classrooms |
50 |
8 |
|
Special contaminant control systems may be required for processes or functions including laboratory animal occupancy. |
|
|
Laboratories |
30 |
10 |
|
|
|
|
Training shop |
30 |
10 |
|
|
|
|
|
|
|
|
|
|
|
Music rooms |
50 |
8 |
|
|
|
|
Libraries |
20 |
8 |
|
|
|
|
Locker rooms |
|
|
2.50 |
|
|
|
Corridors |
|
|
0.50 |
|
|
|
Auditoriums |
150 |
8 |
|
|
|
xi) |
Hospital, Nurses and Convalescent Homes |
|
|
|
|
|
|
Patient rooms |
10 |
13 |
|
Special requirements or codes provisions and pressure relationships may determine minimum ventilation rates and filter efficiency. |
|
|
Medical procedure |
20 |
8 |
|
|
|
|
Operating rooms |
20 |
15 |
|
|
|
|
Procedure Recovery and ICU |
|
20 |
8 |
Generating contaminants may require higher rates. |
|
|
|
|
|
2.50 |
Air shall not be re-circulated into other spaces. |
|
|
Autopsy |
|
|
|
|
|
|
Physical therapy |
20 |
8 |
|
|
|
|
Correctional Cells |
20 |
10 |
|
|
|
|
Dining halls |
100 |
8 |
|
|
|
|
Guard stations |
40 |
8 |
|
|
This table prescribes supply rates of acceptable outdoor air required for acceptable indoor air quality. These values have been chosen to dilute human bioeffluent and other contaminants with an adequate margin of safety and to account for heath variations among people and varied activity levels.
Net occipital space.
Should also be taken into account. Air filtration equipment should be regularly serviced.
Air borne dust and dirt may be generated within the building, from the interior finishes such as partitions, laminations, carpets, upholstery, etc, personnel and their movements as well as by machines such as, printers and fax machines.
The degree of filtration necessary will depend on the use of the building or the conditioned space. Certain specialized equipment, normally associated with computers, will require higher than normal air filter efficiencies for satisfactory operation. It is important to ascertain the necessary standard of air cleanliness required for equipment of this type.
The choice of filtration systems will depend on the degree of contamination of the air and the cleanliness required. A combination of filter types may well give the best service and the minimum operating costs.
The normal standard for intake filters in ventilating and air conditioning applications is an efficiency of 95 percent for a particle size up to 15 μm although there may be a requirement for a higher efficiency to give increased protection against atmospheric staining.
Special applications, such as computer server rooms, clean room, healthcare, pharmaceutical or food processing, and air systems having induction units, require a higher standard that is achieved by two stage filtration. The exact requirements will depend on the equipment or process involved.
4.4.6.3. Removal of fumes and smells from air
Fumes and smells may be removed from air by physical or chemical processes. These may be essential when ambient air is heavily polluted.
The decision to use odour-removing equipment will normally be made on economic grounds, this may become necessary by the currently rising cost of fuel. Once such equipment is installed, it has to be regularly serviced to ensure satisfactory performance. Failure to do this may result in unacceptable conditions within the building.
4.5. Statutory Regulation and Safety Considerations
4.5.1. Authorities and Approval of Schemes
A ventilation or air conditioning system should comply with the requirements laid down in the current statutory legislation or any revisions currently in force and consideration should also be given to any relevant insurance company requirements.
4.5.2. Fire and Safety Considerations
Fire protection requirement of air conditioning system shall be in accordance with part 4 ‘Fire and Life Safety’.
4.5.2.1. Design principles
The design of air conditioning system and mechanical ventilation shall take into account the fire risk within the building, both as regards structural protection and means of escape in case of fire.
The extent and detail of statutory control and other specialist interest may very considerable according to the design, use occupation and location of the building, and the type of system of mechanical ventilation and air conditioning proposed. It is therefore particularly important that the appropriate safeguards are fully considered at the concept design stage of the building.
The degree of control and the requirements vary according to the application.
Full details may have to be approved by the Authority in following cases:
a. From the point of view of the means of escape (except dwelling houses) where recirculation of air is involved and/or where pressurized staircases are contemplated as part of the smoke control arrangement.
b. Place of public entertainment; and
c. Large car parks, hotels, parts of building used for trades or processes involving a special risk, and departmental stores and similar shop risks in large buildings.
4.5.2.2. Ductwork and enclosures
All ductwork including connectors’ fittings and plenums should be constructed of steel, aluminum or other approved metal or from non-combustible material. All exhaust ducts, the interior of which is liable in normal use to accumulate dust, grease or other flammable matter, should be provided with adequate means of access to facilitate cleaning and inspection. Also, the concerned provisions of Part 4 ‘Fire and Life Safety’ shall be complied with.
4.5.2.3. Thermal and acoustic insulation
To reduce the spread of fire or smoke by an air conditioning system, care should be taken for the choice of materials used for such items as air filters, silencers and insulation both internal and external (see part 4 ‘Fire and Life Safety’ and part 5 ‘Building Materials’).
4.5.2.4. Fire and smoke detection
When the system involves the recirculation of air, consideration should be given to the installation of detection device that would either shut off the plant and close dampers or discharge the smoke-laden air to atmosphere. Detectors may be advisable in certain applications even when the system is not a recirculatory one. Exhausts should not be positioned near the fire escapes, main staircases or where these could be a hindrance to the work of fire authorities. The local fire authorities should be consulted.
A careful study of operating characteristics of each type of sensing device should be made before selection. Smoke detectors are normally withered of the optical or ionization chamber type. These can be used to either sound an alarm system or operate fire dampers. Care should be taken with their location as various factors affect the satisfactory operation.
Ionization type detectors are sensitive to high velocity air streams and if used in ductwork the manufacturer should be consulted. Activation of smoke detector should stop the air handling unit supply air fan, close the fire damper in supply and return air duct and operate a suitable alarm system.
In all the above instances the appropriate controls would require manual re-setting.
4.5.2.5. Smoke control
While it is essential that the spread of smoke through a building to be considered in the design of air conditioning system for all types of applications, it assumes special significance in high rise buildings, because the time necessary for evacuation may be greater than the time for the development of untenable smoke conditions on staircases, in lift shafts and in other parts of the building far away from the fire. Lifts may be filled with smoke or unavailable, and if mass evacuation is attempted, staircase may be filled with people.
One or more escape staircase connecting to outdoors at ground level, should be pressurized, to enable mass evacuation of high rise buildings (see also part 4 ‘Fire and Life Safety’).
Therefore all air handling systems of a building should be designed with fire protection and smoke control aspects incorporating, where appropriate, facilities to permit their operation for the control of smoke within the building in event of fire.
The pressurization systems for staircases use large volumes of outside air. The system may be designed to operate continuously at low speed, being increased to high speed in the event of fire, or to operate only in emergency. Noise and droughts are not considered a problem in an emergency situation. Fan motor and starter should be protected from fire and connected to the emergency electrical supply through cables with special fire resistant coating (see also part 4 ‘Fire and Life Safety’).
4.6. Application Factors
4.6.1. General
This clause gives general guidance, for various applications, for the factors that usually influence the selection of the type, design and layout of the air conditioning or ventilating system to be used.
4.6.1.1. Commercial applications
The primary objective of the application described under this heading is provision of comfort conditions for occupants.
4.6.1.2. Offices
Office building may include both external and internal zones.
The external zone may be considered as extending from approximately 4m to 6 m inwards from the external wall, and is generally subjected to wide load variation owing to daily and annual changes in outside temperature and solar radiation. Ideally, the system(s) selected to serve an external zone should be able to provide summer cooling and winter heating. During intermediate seasons the external zone of one side of the building may require cooling and at some time the external zone on another side of the building may require heating. The main factors affecting load are usually window area and choice of shading devices. The other important factors are the internal gain owing to people, light and office equipment. Choice of system may be affected by requirements to counteract down draughts and chilling effect due to radiation associated with single glazing during winter.
Internal zone loads are entirely due to heat gain from people, lights and office equipment, which represent a fairly uniform cooling load throughout the year.
Other important considerations in office block applications may include requirements for individual controls, partitioning flexibility serving multiple tenants, and requirement of operating selected areas outside of normal office hours. Areas such as conference rooms, board room, canteens, etc, will often require independent system.
For external building zone with large glass areas, for example, greater than 60 percent of the external façade, the air-water type of system, such as induction or fan coil is generally economical than all air systems and has lower space requirements. For external zones with small glass areas, an all air system, such as variable average glass areas, other factors may determine the choice of system.
For internal zone, a separate all-air system with volume control may be the best choice. Systems employing reheat or air mixing, while technically satisfactory, are generally poor as regards energy conservation.
4.6.1.3. Hotel guest rooms
In ideal circumstances, each guest room in a hotel or motel should have an air conditioning system that enables the occupant to select heating or cooling as required to maintain the room at the desired temperature. The range of temperature adjustment should be reasonable but, from the energy conservation view point, should not permit wasteful overcooling or overheating.
Guest room systems are required to be available for operation on a continuous basis. The room may be unoccupied for most of the day and therefore provision for operating at reduced capacity, or switching off, is essential. Low operating noise level, reliability and ease of maintenance are essential. Treated fresh air introduced through the system is generally balanced with the bathroom extract ventilation to promote air circulation into the bathroom. In tropical climates, where the humidity is high an all-air system with individual room reheat (and/or recolor) may be necessary to avoid condensation problems. Fan coil units are generally found to be most suitable for this kind of application with speed control for fan and motorized/modulating valve for chilled water control for cooling.
4.6.1.4. Restaurants, cafeteria, bars and night-clubs
Such applications have several factors in common; highly variable loads, with high latent gains (low sensible heat factor) from occupants and meals, and high odour concentrations (body, food and tobacco smoke odours) requiring adequate control of fresh air extract volumes and direction of air movement for avoidance of draughts and make up air requirements for associated kitchens to ensure an uncontaminated supply.
This type of application is generally best served by the all-air type of system preferably with some reheat or return air bypass control to limit relative humidity. Either self-contained packaged units or split systems, or air-handling unit served from a central chilled system may be used. Sufficient control flexibility to handle adequately the complete range of anticipated loads is essential.
4.6.1.5. Department stores/shops
For small shops and stores unitary split type air conditioning systems offer many advantages, including low initial cost, minimum space requirement and ease of installation.
For large department stores a very careful analysis of the location and requirement of individual department is essential as these may very widely, for example, for lighting departments, food halls, restaurants, etc. some system flexibility to accommodate future changes may be required.
Generally, internal loads from lighting and people predominate. Important considerations include initial and operating costs, system space requirements, ease of maintenance and type of operating personnel who will operate the system.
The all-air type of system, with variable volume distribution from local air handling units, may be the most economical option. Facilities to take all outside air for ‘free-cooling’ under favorable conditions should be provided.
4.6.1.6. Theatres/Auditoria
Characteristics of this type of application are buildings generally large in size, with high ceiling, low external loads, and high occupancy producing high latent gain and having low sensible heat factor. These give rise to the requirements of large fresh air quantities and low operating noise levels. Theatres and auditoria may be in use only a few hours a day.
4.6.1.7. Special applications
4.6.1.7.1. Hospitals/Operating theatres
In many cases proper air conditioning can be a factor in the therapy of the patient and is some instances part of the major treatment. For special application areas of hospitals such as operation theatres, reference may be made to specialist literature.
The main differences in application compared with other applications are:
a. Restriction of air movement between various departments and control of air movement within certain departments, to reduce the risk of airborne cross infection;
b. Specific need for the ventilation and filtration equipment to dilute and/or remove particulate or gaseous contamination and airborne micro-organisms;
c. Close tolerances in temperatures and humid it’s may be required for various areas; and
d. The design should allow for accurate control of environmental conditions.
For (a) and (b) the air movement patterns should minimize the spread of contaminants as for instance, in operating departments where the air flow should be such as to reduce the risk of periphery or floor-level air returning to the patient owing to secondary air currents whilst the general pressurization pattern should cause air to flow through the department from sterile to less sterile rooms in progression. In operating theatres 100 percent fresh air system is normally provided and air pressures in various rooms are set by use of pressure stabilizers. Many types of air distribution pattern within operation theatres are in use but generally they conform to high-level supply and low-level pressure relief or exhaust. There is also need for a separates scavenging system for exhaled and waste anesthetic gases with in theatre suites where general anesthetic may be administered.
When zoning air distribution system to compensate for building orientation and shape, consideration should be given to ensure that the mixing of air from different departments is reduced to a minimum.
This can be accomplished by the use of 100 percent conditioned fresh air with no re-circulation or, where re-circulation is employed, by providing separate air handling systems for different departments based on the relative sensitivity of each to contamination. A degree of stand-by is provided by this system so that breakdown will affect only a limited section of the hospital.
Lavatories and other areas dealing with infectious diseases or viruses, and sanitary accommodation adjacent to wards, should be at a negative air pressure compared to any other area to prevent exfiltration of any exhaust to atmosphere form these areas has to pass through high efficiency sub-micron particulate air (HEPA) filters.
4.6.1.7.2. Computer rooms
The equipment in computer rooms generates heat and contains components that are sensitive to sudden variations of temperature and humidity. These are sensitive to the deposition of dust. Exposure beyond the prescribed limits may result in improper operation or need for shut-down of the equipment. The temperature and humidity in computer rooms need to be controlled within reasonably close limits, although this depends on the equipment involved. The relative humidity??? may be controlled within ±5 percent in the range 40 percent to 60 percent. Manufacturers normally prescribe specific conditions to be maintained. Typical conditions are air dry-bulb: 21±1.60C; relative humidity 50±5 percent; and filtration 90 percent down to 10 microns.
A low velocity re-circulation system may be used with 5 percent to 10 percent fresh air make-up which is allowed to exfiltrate from the room and ensure a positive pressure to prevent entry of dust and untreated air. The air distribution should be zoned to minimize temperature variations owing to fluctuation in heat load. Overhead air supply through ceiling plenums utilizing linear diffuser or ventilated ceilings is eminently suited to computer room application, permitting high air change rates to be achieved without undue discomfort to personnel.
The air conditioning system should be reliable because failures to maintain conditions for even a short duration can cases substantial monetary loss and possible more serious consequence. As such standby equipment is recommended.
4.6.1.8. Residential buildings
Very few residences are air conditioned. Some individual houses have unitary systems comprising of window/split air conditioners. Some large houses have VRV based splits and some luxury applications with chilled water applications. In the latter case, most of the considerations of 4.6.1.3 apply.
5. NOISE AND VIBRATION CONTROL
5.1. General
Noise is unwanted sound. All ventilating and air conditioning systems will produce noise, and this may cause annoyance or disturbance in:
In the case of external environment particular care should be taken to avoid a nuisance in the ‘silent’ hours, and local authorities have statutory powers to ensure that noise from plant is limited.
It is important that expert advice be sought in dealing with noise and vibration problems, as for obvious reasons the most economical solutions should be used, without impairing the performance.
5.2. Types of Noise in Building
5.2.1. Externally Created Noise
Reduction of externally created noise is mainly dealt with by choice of building profile and window construction. The air conditioning designer should, however, ensure that noise does not enter via air inlets or exhausts: it may be reduced by suitable attenuators.
5.2.2. Generated Noise
Noise produced by the components of air conditioning and ventilation plant installed within the building can escape via ventilation grilles or door openings and can cause nuisance to neighbor. Equipment mounted outside the building may well need to be selected or installed with the noise problem in mind.
Another type of generated noise is created by the air-circulating system itself and its associated equipment. Fans are an obvious source, but noise can be produced by turbulence, which may cause vibration of the ducts and noise transmission by air diffusers. This problem can be avoided by careful selection of and installation equipment or by the noise absorbing devices.
5.2.3. Transmitted Noise
Noise transmitted through the building structure is particularly acute in modern frame and reinforced concrete buildings. Such noise can be controlled by isolating the machines form the structures, and from pipe work connected to the building, by suitable mountings and pipe couplings.
Another problem is the transmission of sound form one room to another via air ducting, ventilated ceilings to other continuous air space. Such sound includes the noise form machines and equipment and also of conversation as well as annoying. Again, this problem can be tackled by careful design and the inclusion of sound absorbing devices in ducts.
5.2.4. Intermittent Noise
Such noise arises from the sto0pping and starting of equipment, and the opening and closing of valves and dampers. This may or may not cause problems in the air conditioned spaces, but it is often objectionable to plant operators and maintenance engineers. This should be considered by air conditioning designer.
5.3. The source of noise in the air conditioning system could be from the following:
5.4. The approach must always be to reduce the source noise rather than controlling them in the path
5.5. Noise Control
5.5.1. From Room Air Conditioners (RAC)
The following measures should be adopted:
5.5.2. From Split Air Conditioner/Furred Inn
The following measures should be adopted:
5.5.3. Air Handing Units (Floor Mounted and Ceiling Suspended)
The following measures should be adopted:
5.5.4. From Plenum Chamber
The following measures should be adopted/considered:
5.5.5. From Fans
5.5.5.1. Centrifugal fans
There are three basic types of centrifugal fans, backward curved, forward curved, and radial. Noise form centrifugal fans are dominantly a superimposition of discrete tones at the varying frequencies and broadband aerodynamic noise.
5.5.5.2. Axial fans
Axial fans derive their name from the fact that the airflow is along the axis of the fan. To avoid a circular flow pattern and to increase performance, guide vanes are usually installed downstream of the rotor. Axial fans with exit guide vanes are called vane axial and those without guide vanes are called vane axial and those without guide vanes are called tub axial.
Axial fans generally operate at higher pressures than centrifugal fans and are usually considered noisier. Common applications include heating and ventilation systems. Because of
the large number of blades and high rotational speeds, noise form axial fans is generally characterized by strong discrete lade passing tones.
Variable inlet vane system may generate significantly low frequency noise as the vanes shut down. Additional attenuation with a corresponding additional pressure drop is required to attenuate the noise generated by the inlet vanes.
Variable speed motors and drives and variable pitch fan blade systems are actually quieter at reduced air output than at full output. The designer has the option of designing for maximum output as if the system were constant volume, or selecting the sound attenuation for a more normal operating point and allowing fan noise to exceed the design criteria on the rare occasions when the fan operates at full output.
5.5.5.3. To reduce fan noise, the following should be adopted:
5.5.6. From Chillers, Pumps and pipes
Sizing and selecting a chiller is an important aspect in noise control. The following guidelines may be considered for noise control:
5.5.7. From Ducting Work
The following measures should be adopted:
5.6. Structure Borne Noise
Most obvious paths for solid-borne noise are the attached piping and pump support systems. Oscillatory energy generated near the pump can be conducted as solid-borne noise for substantial distances before it is radiated as acoustic noise. It can be controlled using flexible couplings and mechanical isolation.
5.7. Measurement
Measurement should be taken with a sound level meter either using the ‘A’ weighting scale or to draw up a noise criteria curve (see Part 8 ‘Building Services, Section 4 Acoustics, Sound Insulation and Noise Control’). Measurements should be taken in the following locations.
6. MECHANICAL VENTILATION (FOR NON AIR CONDITIONED AREAS) AND EVAPORATIVE COOLING
6.1. Ventilation
Ventilation is the process of changing air in an enclosed space. A proportion of the air in the space should be continuously withdrawn and replaced by fresh air drawn from outside to maintain the required level of air purity. Ventilation is required to control the following:
Mechanical ventilation is one of several forms of ventilation options available. It usually consists of fans, filters, ducts, air diffusers and outlets for air distribution within the building. It may include either mechanical exhaust system or exhaust can occur through natural means.
Natural ventilation and natural exhaust are also options (see Part 8 ‘Building Services, Section 1 Lighting and ventilation’). The scope of this section is therefore restricted to mechanical ventilation.
Ventilation controls heat, odours and hazardous chemical contaminants (in a building) that could affect the health and safety of the occupants. For better control, heat and contaminants, air may need to be exhausted at their sources by local exhaust systems. Usually such systems require lower air flows than general (dilution) ventilation.
Following considerations provide details regarding the various parameters that affect the type of ventilations system selected for a particular application, and the sizing of the ventilation plant:
Typical warm—moist operations are found in textile mills, laundries, dye houses, and deep mines where water is used extensively for dust control.
Warm-moist conditions are more hazardous than the hot-dry conditions.
It will be thus seen that there are many considerations involved in the selection and sizing of suitable ventilation and evaporative cooling plants of meet the requirements of any particular building and/or process. It is the interplay of these various factors listed above like climatic conditions, internal load, exposure to heat and hazardous substances and level of working conditions aimed at, that determines the option, which best meets the requirement and also, the capacity and other attributes of the option selected.
Ventilation control measures alone are frequently inadequate for meeting heat stress standards. Optimum solutions may involve additional controls, such as local exhausts, spot cooling, changes in work-rest patterns, and radiation shielding.
As a rule, it is the mechanical system that provides the best results and controls, for the more complex situations and more stringent requirements arising out of harsher environment and need for better working conditions.
6.2. Beneficial Effects of Ventilation
6.2.1. Fresh air supply
Ventilation system provides the fresh air flow that is required to maintain an acceptable non-odorous atmosphere (by diluting body odours and tobacco smoke) and to dilute the carbon dioxide exhaled.
The quantity and distribution of introduced outside air takes into account infiltration, exhaust and dilution requirements of the building. Proportion of fresh air introduced into a building may be varied to achieve economical operation. When fresh air can provide useful cooling effect, the quantity should be controlled to match the cooling demand.
6.2.2. Transfer of Heat/Moisture
Ventilation system helps air circulation that is required to transfer the heat and humidity generated within the building. Heat generated by the occupants, electrical and mechanical equipment, and solar heat gains may be removed by the introduction of adequate quantities of fresh air and by expelling or extracting of stale air.
6.2.3. Air Movement
Ventilation system provides air movement that is necessary to create a feeling of freshness and avoid discomfort, although excessive movement should be avoided as this may lead to complaints of draughts. The quantity of fresh air should not be increased solely to create air movement; this should be effected by air recirculation within the space or by inducing air movement with the ventilation air system.
Air flow should be controlled to minimize transfer of fumes and smells. In addition, air pressure gradients may be created within the building, by varying the balance between the fresh air and extracting the stale air.
Care should be taken, to avoid excessive pressure differences that can cause difficulty in opening doors or cause them to slam.
6.2.4. Air Purity and Filtration
Ventilation system installed in a building should deliver clean, fresh air to the space served. This may be achieved by providing the required amount of fresh air either to remove totally or to dilute odors, fumes, etc. local extract systems may be necessary to remove polluted air from kitchens, toilets, slaughter houses, crematoria, etc. special air filters may be provided to remove contaminants or smells when air is recalculated.
6.2.5. Removal of Particulate Matter from Air
Efficient air filtration to prevent fouling of the system should be considered, where damage is likely to be caused by discoloration owing to airborne dust particles. In order to obtain the best
performance form the filters provided, care should be taken to locate the air intake appropriately in relation to the prevailing wind, position of chimneys and relative atmospheric dust concentration in the environs of the building.
6.2.6. Fire and Smoke Control
Ventilation system can be designed to extract smoke in the event of a fire, to assist in the fire fighting operation and to introduce fresh air to pressurize escape routes.
6.2.7. Removal of Fumes and Smells from Air
Fumes and smell may be removed from air by physical or chemical processes. Their removal may be essential when the ambient air is heavily polluted, although consideration must be given to limit the thermal loads caused by the introduction of large quantities of fresh air.
6.2.8. Industrial Ventilation
Industrial buildings form a major application of mechanical ventilation.
In industrial buildings, ventilation is needed to provide the fresh air normally required for health and hygiene and also, to mitigate thermal working conditions by assisting in removal of surplus heat due to equipment people and building heat gains.
Following are some of the factors that should be considered in the system design.
Many industrial ventilation systems shall handle simultaneous exposures to heat, toxic and hazardous substances. The number of contaminant sources, their generation rate and effectiveness of exhaust hoods are rarely known; there is no option but to depend on common ventilation/ industrial hygiene practice in such situations.
Reference may also be made to good practice [8-3(4)].
6.4. Types of Ventilation Systems
In the interest of efficient use of energy comfort to the occupants, it is imperative that all modes of ventilation should be considered in relation to the thermal characteristics of the building.
6.4.1. Mechanical Extract/Natural Supply
This is simplest form of extract system comprising one or more fans, usually of the propeller, axial flow or mixed flow type, installed in outside walls or on the roofs. The discharge should terminate in louvers or cowls or a combination of both.
Alternatively, the system may comprise of ductwork arranged for general extraction of the vitiated air or for extraction form localized sources of heat, moisture, odors, fumes and dust. Such duct work may be connected to centrifugal or axial flow fans that discharge through the wall or roof, terminating in louvers or cowls or a combination of both.
It is essential that provision for make-up air is made and that consideration is given to the location and size of inlet. Inlet should not be located in the vicinity of exhaust fan.
6.4.2. Mechanical Supply/Natural Extract
This system is similar in form to the extract system but arranged to deliver fresh air positively into the enclosed space. Such a system necessitates provision for the discharge of vitiated air by natural means. Where there is a requirement for the enclosed space to be at a slightly higher pressure than is surroundings (to exclude dust or smoke, for example), the discharge may be through natural leakage paths or balanced pressure relief dampers, as may be required
6.4.3. Combined Mechanical Supply and Extract
This system is a combination of those described above and may comprise supply and exhaust ductwork systems or may employ a common fan with a fresh air inlet on the low pressure side.
6.5. Ventilation Rate and Design Considerations for Non Air Conditioned Areas
6.5.1. General Ventilation
The care of air circulation recommended for different general areas is as given in Table 5.
Table 5 Recommended Rate of Air Circulation for Different Areas
(Clause 6.5.1)
|
Sl No. |
Application |
Air Change per Hour |
|
1 |
Assembly rooms |
4-8 |
|
2 |
Bakeries |
20-30 |
|
3 |
Banks/building societies |
4.8 |
|
4 |
Bathrooms |
6-10 |
|
5 |
bedrooms |
2-4 |
|
6 |
Billiard rooms |
6-8 |
|
7 |
Boiler rooms |
15-30 |
|
8 |
Cafes and coffee bars |
10-12 |
|
9 |
Canteens |
8-12 |
|
10 |
Cellars |
3-10 |
|
|
Churches |
1-3 |
|
11 |
Cinemas and theatres |
10-15 |
|
12 |
Club rooms |
12, Min |
|
13 |
Compressor rooms |
10-12 |
|
14 |
Conference rooms |
8-12 |
|
15 |
Dairies |
8-12 |
|
16 |
Dance halls |
12, Min |
|
17 |
Dye works |
20-30 |
|
18 |
Electroplating shops |
10-12 |
|
19 |
Engine rooms |
15-30 |
|
20 |
Entrance halls |
3-5 |
|
21 |
Factories and work shops |
8-10 |
|
22 |
Foundries |
15-30 |
|
23 |
Garages |
6-8 |
|
24 |
Glass houses |
25-60 |
|
25 |
Gymnasium |
6,Min |
|
26 |
Hair dressing saloon |
10-15 |
|
27 |
Hospitals-sterilizing |
15-25 |
|
28 |
Hospital-wards |
6-8 |
|
29 |
Hospital domestic |
15-20 |
|
30 |
Laboratories |
6-15 |
|
31 |
Launderettes |
10-15 |
|
32 |
Laundries |
10-30 |
|
33 |
Lavatories |
6-15 |
|
34 |
Lecture theatres |
5-8 |
|
35 |
Libraries |
3-5 |
|
36 |
Living rooms |
3-6 |
|
37 |
Mushroom houses |
6-10 |
|
38 |
Offices |
6-10 |
|
39 |
Paint shops(not cellulose) |
10-20 |
|
40 |
Photo and x-ray darkroom |
10-15 |
|
41 |
Public house bars |
12,Min |
|
42 |
Recording control rooms |
15-25 |
|
43 |
Recording studios |
10-12 |
|
44 |
Restaurants |
8-12 |
|
45 |
School rooms |
5-7 |
|
46 |
Shops and supermarkets |
8-15 |
|
47 |
Shower baths |
15-20 |
|
48 |
Stores and warehouses |
3-6 |
|
49 |
Squash court |
4,Min |
|
50 |
Swimming bath |
10-15 |
|
51 |
Toilets |
6-10 |
|
52 |
Utility rooms |
15-20 |
|
53 |
Welding shops |
15-30 |
Note-- The ventilation rates may be increased by 50 percent where heavy smoking occurs or if the room is below ground.
6.5.2. Kitchen (Industrial and Commercial) Ventilation
Desired ventilation rates in the kitchens depend upon the type of equipment in use and the released impurity loads (including surplus heat). Ventilation Standards set up the guide lines for ventilation volumes, whereas surplus heat and impurity loads determine the actual airflows based on thermal consideration. The design for kitchen airflow must allow for sufficient ventilation.
Suggested design standards for exhaust air flows from different kitchen equipment based on their input power are as given in Table 6.
Table 6 design Exhaust Air Flow in1/s per kW of the Kitchen Equipment
(Clause 6.5.2)
|
Sl No. |
Kitchen Equipment |
Electricity based Equipment |
Gas based Equipment |
|
i) |
Cooking pot |
8 |
12 |
|
ii) |
Pressure cooker cabinet |
5 |
- |
|
iii) |
Convection oven |
10 |
- |
|
iv) |
Roasting oven(salamander) |
33 |
33 |
|
v) |
Griddle |
32 |
35 |
|
vi) |
Frying pan |
32 |
35 |
|
vii) |
Deep fat fryer |
28 |
- |
|
viii) |
Cooker/stove |
32 |
35 |
|
ix) |
Grill |
50 |
61 |
|
x) |
Heated table/bath |
30 |
- |
|
xi) |
Coffee maker |
3 |
- |
|
xii) |
Dish washer |
17 |
- |
|
xiii) |
Refrigeration equipment |
60 |
- |
|
xiv) |
Ceramic cooker/stove |
25 |
- |
|
xv) |
Microwave oven |
3 |
- |
|
xvi) |
Pizza oven |
15 |
- |
|
xvii) |
Induction cooker/stove |
20 |
- |
It is desirable to use compensating exhaust hoods for kitchen equipment installed within air conditioned space. The ventilation rates may be confirmed from the kitchen equipment supplier.
6.5.3. Car Parking Ventilation
Ventilation is essential, in car parking areas to take care of pollution due to emission of carbon monoxide, oxides of nitrogen, presence, of oil and petrol fumes and diesel engine smoke. The contaminants cause undesirable effect like. Nausea, headache, fire hazards, if applicable permissible limits for each of the contaminate noted are exceeded. Although four contaminant are listed above, the capacity of a system designed to tackle concentration of carbon monoxide, will be adequate to keep the other three contaminants also within their respective permissible limits.
The recommended ventilation rate will ensure that the CO level will be maintained within 29 mg/m3 with peak level not to exceed 137 mg/m3.
For partially open garages, the requirement is stated in terms of area of wall/slab openings required to provide adequate ventilation. The value applicable is 2.5 percent to 5 percent of the floor area for free opening.
6.5.4. Sizing the Plant
Sizing the ventilation plant is essentially arriving at the air flow rate required. Based on various considerations already reviewed the sizing of the plant will be influenced by the following requirements:
The air flow rate calculated for the above requirements.
6.5.4.1. Ventilation plant size is often expressed in terms of number of air changes per hour or cmh/m2 of floor area. These expressions fail to evaluate the actual heat release provided by the plant. The unit, cmh/m2 gives a relationship which is independent of the building height. This is a more rational approach than speaking in terms of air changes per hour. This is because, with the same internal load, the same amount of ventilation air, properly applied to the work zone with adequate velocity, will provide the desired heat relief quite independently of the ceiling height of the space, with few exceptions. Ventilation rates of 30 to 60m3/h perm2 have been found to give good trusts in many plants. Notwithstanding these general observations, detailed design should be based on detailed thorough calculations after all necessary data has been evaluated and relevant considerations have been reviewed.
6.6. Evaporative Cooling
6.6.1. Evaporative cooling is defined as the reduction of air dry-bulb temperature by the evaporation of water.
6.6.2. When water evaporates into the air to be cooled, simultaneously humidifying it, the process is called direct evaporation process, and therefore is not humidified as it is cooled, then the process is called indirect evaporative cooling.
It is good practice to use 100 percent fresh air in the evaporative cooling. Re-circulation is not recommended, as it will lead to continuous increase in wet-bulb temperature of the air. When evaporative cooling is provided for comfort application, it may be supplemented by devices like ceiling fans and fan coolers to enhance air movement for circulation of air in internal areas in order to maximize evaporation of moisture from the skin.
6.6.3. The geographic range for the evaporative cooling is based on cooler’s ability to create or approximate human comfort and is limited by relative humidity in the atmosphere. It is more effective in dry climates (hot-dry climate zone) where wet-bulb depression is comparatively large. Factors to be considered—include those listed in 6.5.4; addition the following also apply:
6.6.4. The cooling load control, especially for industrial application shall be carried out in the following manner for effective evaporative cooling.
6.6.5. Two types of water distribution systems may be provided:
The first type is simpler and cheaper but consumes more water, needs constant drainage and has lower efficiency depending upon the temperature of water. The second type has higher cooling efficiency due to recalculate water approaching wet-bulb temperature conserves water and can operate with intermittent drainage. It is recommended to provide periodic bleed-off or blow down to remove accumulated mineral additions. This helps in reducing scaling of pads also.
6.6.6. The air velocity across wetting pad is recommended between 1.0 and 1.5 m/s. the lower face velocity reduces evaporation as damp air film isolates the dry air from the wet surface. Higher face velocity may provide insufficient air-water contact time.
6.6.7. Pad material should be such which provides maximum clean wet surface area with minimum airflow resistance. Materials, which have either good ‘wick’ characteristics or surface that spread water rapidly by capillary action, should be selected.
6.6.8. In the ducted systems, all supply air diffusers, grilles and registers should be preferably adjustable.
6.6.9. General room cooling should be supplemented with spot cooking in the hot workplaces.
6.6.10. Reference may also be made to good practice [8-3(5)].
6.7. Planning
6.7.1. Planning of Equipment Room for Ventilation
6.7.1.1. In selecting the location of equipment room, aspects of efficiency, economy and good practice should be considered and wherever possible, it shall be made contiguous with the building. This room shall be located as centrally as possible with respect to the area served and shall be free from obstructing columns.Proper location helps achieve satisfactory air distribution and also results in a less expensive installation.
6.7.1.2. Equipments room should preferably be located adjacent to external wall to facilitate equipment movement and ventilation. It is should also close to main electrical panel of the building, if possible, in order to avoid large cable lengths.
6.7.1.3. Location and dimensions of shafts, for ducting, cables, pipes, ect (if envisaged), should be planned at the virtual stages itself if planning. They should be located adjacent to the equipment or within the room itself.
Evaporative cooling units (air washers) should be located preferably on summer-windward side. They should be painted white or with reflective coating or thermally insulated, so as to minimize solar heat absorption.
In locating the units, care should be taken to ensure that their noise level will not be objectionable to the neighbors. Appropriate acoustic treatment should be considered, if the noise levels cannot be kept down to permissible limits.
Exhaust air devices, preferably to leeward and overhead side may provided for effective movement of air
In the case of large installations it is advisable to have a separate isolated equipment room if possible.
The equipment room should be adequately dimensioned keeping in view the need to provide required movement space for personnel, space forestry and exit of ducts, the need to accommodate an intakes and discharge, operation, maintenance and service requirements.
6.7.1.4. The floors of the equipment rooms should be light colored and finished smooth. For floor loading, the air conditioning, heating and ventilation engineer should be consulted (see also Part 6 ‘Structural Design, Section 1 Loads Forces and Effects’).
Arrangements for draining the floors shall be provided. The trap in floor drain shall provide a water seal between the equipment room and the drain line. Water proofing shall be provided for floor slabs of equipment rooms housing, evaporative cooling units.
6.7.1.5. Supporting of pipe within equipment rooms spaces should be normally from the floor. However, outside Equipment room areas, structural provisions shall be made for supporting the water pips form the floor/ceiling slabs. All floor and ceiling supports make-up and drain connections pipes, ducting cables/cable trays etc, shall be isolated form the structure to prevent transmission of vibrations.
6.7.1.6. Plant machinery in the plant room shall be places on plain/reinforced cement concrete foundation and provided with anti-vibratory supports. All foundations should be protected from damage by providing epoxy coated angle nosing. Seismic restraints requirement may also be considered.
6.7.1.7. Wherever necessary, acoustic treatment should be provided in plant room space to prevent noise transmission to adjacent occupied areas.
6.7.1.8 In case the equipment is located in basement, equipment movement route shall be planned to facilitate future replacement and maintenance. Service ramps or hatch in ground floor slab should be provided in such cases. Also arrangements for floor draining should be provided.
The trap in floor drain shall provide a water seal between the equipment room and the drain line.
6.7.1.9. In the case of large and multi-storied buildings, independent Ventilation/Air Washer Units should be providing for each floor. The area to be served by the air-handling unit should be decided depending upon the provision of fire protection measures adopted. The Units should preferably be located vertically one above the other to simplify location of pipe shafts, cable shafts, drainers.
6.7.1.10. Opening of adequate size should be provided for intake of fresh air. Fresh air intake shall have louvers having rain protection profile, with volume control damper and bird screen.
6.7.1.11. Outdoor air intakes and exhaust outlets shall be effectively be shielded from weather and insects.
6.7.1.12. In all cases air intakes shall be so located as to avoid contamination from exhaust outlets or to from sources whose contamination concentration levels are greater than normal in the locality in which the building is located.
6.7.1.13. Supply/Return air duct shall not be taken through emergency fire staircase. However, exception can be considered if fire isolation of ducts at wall crossings is carried out.
6.7.1.14. where necessary, structural design should avoid beam obstruction to the passage of supply and return air ducts. Adequate ceiling space should be made available outside the equipment room air ducts and fire dampers at equipment room wall crossings.
6.7.1.15. Access doors to Equipment rooms should be through single/double leaf type, air tight. Opening outwards and should have a sill to prevent flooding of adjacent occupied areas.
6.7.1.16. It should be possible to isolate the equipment room in case of fire. The door shall be fire resistant. Fire/smoke dampers shall be provided in supply/return air duct at air handling
unit room wall crossings and the annular space between the duct and the wall should be fire sealed using appropriate fire resistance rated material.
In the planning stages itself, provision should be made for the following (if they are envisaged):
6.7.3. Bleed-off and chemical water treatment depending on quality of water available for make-up should be planned.
7. UNITARY AIR CONDITIONER
7.1. These are self-contained air conditioning units comprising a compressor and evaporator with fans for evaporator and air-cooled condenser. Unitary air conditioners are generally installed in windows and, therefore, they are also known as window air conditioners. It is designed to provide free delivery of conditioned air to an enclosed space, room or zone. It includes a prime source of refrigeration for cooling and dehumidification and means for circulation and filtration of air. It may also include provision to exhaust room air as also induce fresh air for ventilation in the room. In addition to basic cooling unit, there are several other optional features available, such as:
7.2. Capacity
Most of the manufacturers supply unitary air conditions in capacities of 3 500 W (1 TR), 5,250 W (1.5 TR) and 7 000 W (2 TR). However, some of them may be able to supply window air conditioners of 1 750 W (0.5 TR) and up to 10 500 W (3TR) along with intermediate range. The capacity of windows air conditioners is rated at outside dry bulb temperature of 350C and wet bulb temperature of 300C and they are suitable for 230 V, single phase 50 Hz power supply. Nominal capacity of all the window air conditioners has to be de-rated due to high ambient temperatures in summer months in most of Indian cities. Also, generally a voltage stabilizer has to be installed to ensure that window air conditioner gets stabilized rated voltage.
7.3. Suitability
Unitary air conditioners are suitable for bedrooms, office cabins, general office area, hotel rooms and similar applications where normal comfort conditions are required up to a distance of 6m from unitary air conditioner.
7.4. Power Consumption
Power consumption of window air conditioners of 1 TR (3 500W) rated capacity should not exceed 1.55 kW/TR. However, in smaller sizes, the power consumption may exceed. Rotary compressors normally consume 7 percent to 8 percent less power compared to the above value for reciprocating compressors.
7.5. Noise level
Noise level of window air conditioner inside the conditioned room should be as low as possible. However it should not exceed 65 dBA for 5 250 W (1.5 TR) or smaller capacity window air conditioners. Air conditioners with rotary compressors will have lower noise level as compared to those provided with reciprocating compressors.
7.6. Location
Unitary air conditioners should be mounted preferably at the window sill level on an external wall where not air from air-cooled condenser may be discharged without causing nuisance. There should not be any obstruction to the inlet and discharge air of the condenser. Also while deciding location of the window air conditioners, care should be taken to ensure that the condensates water dripping does not cause nuisance. The opening for the air conditioner is generally made a part of windows or wall construction at the planning stage.
7.7. Limitations
Room air conditioners are not generally recommended in the following situations:
7.8. For detailed information regarding constructional and performance requirements and methods for establishing ratings of room air conditioners, reference may be made to accepted standard [8-3(6)].
8. SPLIT AIR CONDITIONER
8.1. Spilt air conditioner has an indoor unit and an outdoor unit interconnected with refrigerant piping and power and control wiring. Indoor unit comprises of a filter, evaporator an evaporator fan for circulation of air in the conditioned space. Outdoor unit has a compressor, air-cooled condenser with condenser fan housed in a suitable cabinet for outdoor installation. Spilt air conditioner includes primary source of refrigeration for cooling and dehumidification and means for circulation and cleaning of air, with or without external air distribution ducting.
Spilt air conditioners may be provided with either reciprocating compressor or scroll compressor. Scroll compressor generally consumes about 10 to 12 percent less power compared to reciprocating compressor.
Various split air conditioners available may be categorized as under:
8.2. Suitability
Spilt air conditioners are suitable for wide range of applications including residences, small offices, clubs, restaurants, showrooms, departmental stores etc.
8.3. Capacity
Split air conditioners are available in following capacities:
8.4. Location
Spilt air conditioner indoor unit is mounted within the air conditioned space or above the false ceiling from where the air distribution duct is taken to the conditioned space to distribute the air. When the indoor unit is mounted in the false ceiling to attend to the indoor unit including periodic cleaning of air filter. Outdoor unit is mounted at the nearest open area where unobstructed flow of outside air is available for air cooled condenser.
8.5. Installation
Ceiling suspended indoor units are provided with rubber grommet to reduce vibration. Outdoor units are mounted on steel frame in an open area so that the fan of the air cooled condenser can discharge hot air to the atmosphere without any obstruction. Care should be taken to ensure the free intake of air is available to the outdoor air cooled condenser. Also precaution should be taken that hot air from any other outdoor unit does not mix with the intake of the other outdoor air cooled condenser.
8.6. Limitations
Split air conditioners are generally not recommended for:
8. 7. Reference may be made t accepted standard [8-3(7)].
9. PACKAGED AIR CONDITIONER
9.1. Packaged air conditioner is a self-contained unit primarily for floor mounting, designed to provide conditioned air to the space to be conditioned. It includes prime source of refrigeration for cooling and dehumidification and means for circulation and cleaning of air, with or without external air distribution ducting. It may also include means for heating humidifying and ventilating air.
The unit comprises a compressor, condenser and evaporator, which are interconnected with copper refrigerant piping and refrigerant controls. It also includes fan for circulation of air and filter. The unit is provided with compressor and fan motor starter and factory-wired safety controls.
Compressor is a device, which compresses low-pressure low temperature refrigerant gas to high-pressure high temperature super heated refrigerant gas. Compressors may be reciprocating type or scroll type for packaging unit applications.
Condenser condenses high pressure high temperature refrigerant gas to liquid refrigerant at approximately the same temperature and pressure by removal of sensible heat of refrigerant by external means of water cooling or air cooling.
The packaged units are also available with microprocessor-based controller installed in the unit for digital display of faults as also several other functions. The packaged unit can also be provided with winter heating package or humidification package. The packaged unit may be provided with either water-cooled condenser or remote air cooled condenser with interconnected copper refrigerant piping. The units are available with reciprocating compressor as also scroll compressor, which consume about 10 to 12 percent lesser power. In a water-cooled condenser unit, condenser-cooling water is circulated through the cooling tower with necessary piping and pump sets.
The water cooled condenser package unit gives higher capacity at lower power consumption as compared to an air cooled condenser packaged unit which gets considerably de-rated in capacity and also consumes more power in peak summer months in most of the cities of our country due t high ambient temperature.
Package units are generally available with vertical air discharge or horizontal air discharge.
9.2. Suitability
Packaged units are suitable for wide range of application including offices, clubs and restaurants, showrooms and departmental stores, and computer rooms, etc.
9.3. Capacity
Normally the packaged air conditioners are manufactured in size of 17 500 W (5 TR), 26 250 W (7.5 TR), and 35 000 W (10 TR) and 52 500 W (15 TR). Package units with scroll compressors are also available in capacity up to 58 100 W (16.6 TR).
9.4. Location
The packaged unit can be mounted within the air conditioned space with discharge air plenum or in a separate room from where the air distribution duct is taken to the conditioned space. While deciding location for the packaged unit, provision must be kept for proper servicing of the unit.
9.5. Installation
The packaged units are normally mounted on a resilient pad which prevents vibration of the unit from being transmitted to the building.
9.6. Limitations
Packaged air conditioners are not generally recommended for:
9.7. For detailed information regarding constructional and performance requirements and methods for establishing ratings of packaged air conditioners, reference may be made to accepted standard [8-3(8)].
10. HEATING
10.1. The installations for air conditioning system may be used advantageously for the central heating system with additions such as hot water or boiler and hot water coils or strip heater banks.
10.2. The heating equipments as described in 10.2.1 and 10.2.2 are generally used.
10.2.1. Hot Water Heated Coils
Central heating systems using hot water usually required not more than one or two rows of tubes in the direction of air flow, in order to produce the desired heating capacity. To achieve high efficiency without excessive water pressure drop through the coil, various circuit arrangements are used.
Generally, the resistance to the hot water flow through the heater should not exceed 4 k Pa in low pressure hot water heating installations. In high pressure hot water installations, the resistance to the water flow will probably be determined by other factors, for example, the need to balance circuits.
The heaters should be served from hot water flow and return mains with sufficient connections to each row or bank of tubes or sections to give uniform distribution of the heating medium.
The flow connections to the heater should generally be arranged at the lowest point of the heater, and the return connections at the highest, to aid venting. The expansion of the tubes when the heater is in operation should be considered and the necessary arrangements made to accommodate expansion and contraction.
Thermometer wells should be fitted in the pipes near the inlets and outlets of all-heating coils so that the temperature drop through the heater can be readily observed.
10.2.2. Electric Air Heater
The air velocity through the heaters should be sufficient to permit the absorption of the rated output of the finned tube heaters within its range of safe temperatures and the exact velocity determined in conjunction with the manufacturers of the heater. Electrical load should be balanced across the three-phase of the electrical supply.
Where automatic temperature control is required the heater should be divided into a number of sections dependent upon the degree of control to be effected.
Each section of heater elements, which may be two rows of elements should have its own bus bars and connection and be capable of withdrawal from the casing, thus enabling the elements to be cleaned or repaired whilst the remainder is in operation. Each section should be capable of being isolated electrically before being withdrawn from the casing.
All heaters should be electrically interlocked with the fan motors, so that the electrical heater will be switched off when the fan is stopped or when the air velocity is reduced to a level below that for which the heater has been designed.
The air velocity over the face of the heater is of particular importance in the design of electric air heaters, and the manufacturers should be given details of the maximum and minimum air velocities likely to occur.
With all electric air heaters, care should be taken to preclude the risk of fire under abnormal conditions of operation, by the use of a suitably positioned temperature sensitive trip of the manual reset type to cut off the electric supply.
11. SYMBOLS, UNIT, COLOUR CODE AND IDENTIFICTION OF SERVICES
11.1. Units and symbols to be used in air conditioning, ventilation and refrigeration system shall be in accordance with good practice [8-3(9)].
11.2. Colour code for identification for various items in air conditioning installations for easy interpretation and identification is advisable. This shall promote greater safety and shall lessen chances of error, confusion or inaction in times of emergency. Co lour shade shall be generally in accordance with good practice [8-3(10)].
11.3. colour bands shall be 150 mm wide, superimposed on ground colors to distinguish type and condition of fluid. The spacing of band shall not exceed 4.0 m.
11.4. Further identification may also be carried out using lettering and marking direction of flow.
11.5. Service Identification
11.5.1. Pipe work services
11.5.1.1. The scheme of colors code for painting of pipe work services for air conditioning installation shall be as indicated in Table 7.
11.5.1.2. In addition to the closure bands specified above, all pipe work shall be legibly marked with black or white letters to indicate the type of service and the direction of flow, identified as follows:
|
High Temperature Hot Water |
HTHW |
|
Medium Temperature Hot Water |
MTHW |
|
Low Temperature Hot Water |
LTHW |
|
Chilled Water |
CHW |
|
Condenser Water |
CDW |
|
Steam |
ST |
|
Condensate |
CN |
11.5.2. Duck work services
11.5.2.1. For duct work services and its insulation, colors triangle may be provided. The size of the triangle will depend on the size of the duct and viewing distance but the minimum size should not be less than 150 mm length per side.
The colure for various duct work services shall be as given below:
|
Services |
Colour |
|
Conditioned Air |
Red and Blue |
|
Ward Air |
Yellow |
|
Fresh Air |
Green |
|
Exhaust/Extract/Recalculated |
Grey |
|
Foul Air |
Brown |
|
Dual Duct System Hot Supply Air |
Red |
|
Cold Supply Air |
Blue |
Table 7Scheme of Colour Code of Pipe Work Services for Air Conditioning Installation
(Clause 11.5.1.1)
|
Sl No. |
Description |
Ground Colour |
Lettering Colorings |
First Colour Band |
|
i) |
Cooling water |
Sea green |
Black |
French blue |
|
ii) |
Chilled water |
Sea green |
Black |
Black |
|
iii) |
Central heating below 600C |
Sea green |
Black |
Chary yellow |
|
iv) |
Central heating to 1000C |
Sea green |
Black |
Dark violet |
|
v) |
Drain pipe |
Black |
White |
|
|
vi) |
Vents |
White |
Black |
|
|
vii) |
Valves and pipe line fittings |
White with Black handles |
Black |
|
|
viii) |
Belt guard |
Black yellow diagonal strips |
Black |
|
|
ix) |
Machine bases, inertia bases and plinth |
Charcoal grey |
|
|
11.5.3. Valve Labels and Charts
Each valve shall be provided with a label indicating the service being controlled, together with a reference number corresponding with that shown on the Valve Charts and ‘as fitted’ drawings. The labels shall be made from 3 ply (black/white/black) trifoliate material showing
white letters and figures on a black background. Labels shall be tied to each valve with chromium plated linked chain.
12. ENERGY CONSERVATION, ENERGY MANAGEMENT, AUTOMATIC CONTROLS AND BUILDING MANAGEMENT SYSTEM
12.1. In the context of this code, energy conservation signifies the optimum use of energy to operate the air conditioning, hating and ventilation system of a building.
12.2. It is axiomatic that general standards of comfort or specific environmental requirements within the building should not be compromised in an endeavor to achieve lower consumption of energy. Similarly nothing in this Code overrides regulations related to health and safety.
12.3. Considerations for Energy Conservation and Management
12.3.1. Energy Targets
For the purpose of assessing energy conservation efficiency of one system design against another, or in an existing building comparing one period of energy use against, target consumptions may be established.
12.3.2. Demand Targets
Energy demand is mainly determined by location of the building, its structure and the equipment installed within it. Demand targets are readily applied to designs for new buildings and are quoted as an ‘average rate’ of energy use W/m2).
12.3.3. Consumption Targets
The energy actually consumed in a building is determined by the manner in which the building and its services are used and is measured in units of energy (Wh/m2). Targets may be established according to varying climatic conditions and varying pattern of building use.
12.3.4. Air Conditioning/Ventilation
Some of the more important aspects of establishing energy conservation requirements for air conditioning and ventilation system are given below.
12.3.5. The design of the system and its associated controls should take into account the following.
12.3.6. The operation of the system for the following conditions has to be considered when assessing the complete design:
12.3.7. Consideration should be given to changes in building load in the system design so that maximum operational efficiency is maintained under part load conditions. Similarly, the total system should be separated into smaller increments having similar load requirements so that each area can be separately controlled to maintain optimum operating conditions.
12.3.8. The temperature of heating or cooling media circulated with in the system should be maintained at the level necessary to achieve the required output to match the prevailing load conditions with the minimum consumption of energy.
12.3.9. Energy recovery has to be maximized
12.3.10. Operation and maintenance procedures have to be properly planned.
12.3.11. Equipment Consideration
12.3.11.1. All equipment and components should be tested in accordance with the relevant Indian Standards; where no application standard exists, greed international or other standard and test procedure may be adopted.
12.3.11.2. The equipment suppliers should furnish upon request the energy input and output of the equipment, which should cover full and partial loads and standby conditions as required in order that the energy consumption can be assessed over the whole range of operating conditions.
12.3.11.3. Where components from more than one supplier are used in combination, for which published performance data do not exist then the system designer should take the responsibility for ensuring that their combination leads to optimum energy use.
12.3.11.4. Equipment preventive maintenance schedule should be furnished along with all other required information.
12.4. Control System
The designer should aim to select the simplest system of control capable of producing the space conditions required. It is uneconomical to provide controls with a degree of accuracy greater than the required by the application. Consideration should be given to the provision of centralized monitoring and control, thus achieving optimum operation.
12.5. Automatic Controls and Building Management System
12.5.1. Types of Equipment
The basic components that are designed, selected to work together to form a complete control system, together with their function, are shown as follows:
The basic components of a control system are:
|
Element or Component |
Function |
|
Sensing and measuring element of the controller (for example, sensor, transmitters, transducers, meters, detector) |
Measuring changes in one or more controlled conditions or variables. |
|
Controller mechanism |
Translating the changes into forces or energy of a kind that can be used by the final control element. |
|
Connecting members of the control circuit; wiring for electric linkage for mechanical devices |
Transmitting the energy or forces from the point of translation to the point of corrective action. |
|
Controlled devices or actuator such as motor or valve |
Using the force or energy to motivate the final control element and effect a corrective change in the controlled condition. |
|
Controller mechanism, connecting means, and actuator or control device. |
Terminating the call for corrective change, to prevent over-correction. |
12.5.2. Sensing and Measuring Elements
12.5.2.1. Temperature elements;
a) A bimetal element comprises two thin strips of dissimilar metals fused together and arranged as a straight, U-shaped or spiral element. The two metals have different coefficients of thermal expansion, so a change in temperature causes the element to bend and produce a change in position.
b) A rod and tube element is composed of a high expansion metal tube inside which is located a low expansion rod with one end fixed to the rear of the tube so that temperature changes cause the free end of the rod to move.
c) Sealed bellows element is evacuated of air and charged with a liquid, gas or vapour, which changes in pressure or volume as surrounding temperature changes to result in change of force or movement.
d) Remote bulb element consists of a sealed bellows or diaphragm to which a bulb or capsule
is attached by means of capillary tubing, the entire system being filled with liquid, gas or vapour. Temperature changes at the bulb are communicated a s pressure or volume changes through the capillary tube to the bellows or diaphragm.
e) Resistance temperature detectors (RTDs) are temperature sensors containing either a fence wire or a thin metallic element whose resistance increases with temperature and varies in a known manner. RTDs are characterized by their high degree of linearity, good sensitivity and excellent stability. RTDs are used with electronic controllers.
f) Thermocouple element comprises a junction between two dissimilar metals that generates a small voltage related to the temperature.
12.5.2.2. Humidity devices
a) These devices have a hygroscopic organic polymer deposited on a water permeable substrate. The polymer film absorbs moisture until it is in balance with the ambient air. This causes a change in resistance or capacitance.
b) Resistance elements, as employed in electronic systems, consist usually of two interleaved grids of gold foil, each connected to a terminal and mounted on a thin slab of insulating plastic material with a Coating of hygroscopic salt (lithium chloride) on the lock. A conductive path between adjacent strips of foil is formed, and the high electric resistance of this circuit changes a s the chemical film absorbs and releases moisture with changes in the relative humidity of surrounding air.
12.5.2.3. Pressure elements
a) Low-pressure measuring elements for low positive pressure or for vacuum conditions, for example, static pressure in an air duct, usually comprise a large slack diaphragm, or large flexible bellows. In one type of static pressure regulator two bells are suspended from a lever into a tank of oil, so that positive pressure under one of the bells moves the bell and lever up (or down) to complete an electric circuit. The majority of these elements sense differential pressure, and when combined with pint tubes, orifice plates, and venture meters may be used to measure velocity, flow rate or liquid level.
b) High-pressure measuring elements, for pressure or vacuum measurements in the kPa range, are usually of bellows, diaphragm or Bourdon tube type. If one side of the element is left open to atmosphere the element will respond to pressure above or below atmospheric.
12.5.2.4. Special elements
a) Special elements for various measuring or detecting purposes are often necessary for complete control in air conditioning or ventilating systems, for example a ‘paddle blade’ type of air flow switch may be interlocked with an electric heater battery to prevent battery from operating and overheating in the event of an air flow failure.
b) Other elements employed from time to time are measuring smoke density, carbon monoxide (for example in road traffic tunnels or underground car parks) and carbon dioxide, and for flame detection.
12.5.2.5. Controller
Controlling elements normally regulate the application of either electrical or pneumatic energy. Controllers are mainly of three types: thermostat, humidistat and pressure controllers.
12.5.2.6. Thermostats
a) The room type responds to room air temperature and is designed for mounting on a wall.
b) The insertion thermostats respond to the temperature of air in a duct and are designed for mounting on the outside of a duct with its measuring element extending into the air stream.
c) The immersion type responds to the temperature of a fluid in a pipe or tank is designed for mounting on the outside of a pipe or tank with a fluid-tight connection to allow the measuring element to extend into a fluid.
d) The remote bulb thermostat is used where the point of temperature measurement is some distance from the desired thermostat location, which may often be in central panel. A differential type employing two remote bulbs may be used to maintain a given temperature difference between two points.
e) The surface type is designed for mounting on a pipe or similar surface and measuring its temperature, or to give an approximate measurement of temperature of the fluid with in the pipe.
f) The day / night room thermostat is arranged to control at a reduce temperature at night, and may be changed from day to night operation at a remote point by hand or time clock, or from a time switch built into the thermostat itself.
g) The heating / cooling (or summer / winter) thermostat can have its action reversed and, where required, its set points raised or lowered by remote control. This type of thermostat is used to actuate controlled devices, such as valves or dampers, that may regulate a heating medium at one time and cooling medium at another.
h) The multi-step thermostat is arranged to operate in two or more successive steps.
i) A master thermostat measures conditions at one point of another (sub-master) thermostat or controller.
12.5.2.7. Humidistat
Humidistat may be of the room or insertion type. For example, a sub master room humidistat may be used with an outdoor master thermostat to reduce humidity in cold weather and prevent condensation on windows. A wet-bulb thermostat is often used for accurate humidity control, working in conjunctions with a dry bulb controller.
12.5.2.8. Pressure controllers
Pressure or static pressure controller4s are made for mounting directly one pipe or duct. The controller may also be mounted remotely on a panel.
12.5.2.9. Controlled devices
12.5.2.9.1. Automatic control valves
An automatic control valve consists of a valve body to control the flow of fluid passing through it by use of a variable orifice that is positioned by an operator in response to signals from the controller. The fluid handled is generally steam or water, and the operator is usually of the electric motor or pneumatic actuator type. As 75 percent or more of all air conditioning and mechanical ventilation systems utilize a valve of some sort as the final control element, proper control valve selection is one of the most important factors in attaining goof systems performance.
Following are the details of various valve types and valve operators:
a) Valve types – The main type and their characteristics are summarized below;
(1) Single seated valves are designed for tight shut-off.
(2) Double seated valves are designed so that the fluid pressure on the two discs is essential balanced, reducing the power required operating; this type of valve does not provide a tight shut-off.
(3) Pilot operated valves utilize the pressure difference between upstream and downstream sides to act upon a diaphragm or piston to move the valve, and are usually single seated, for two piston applications only, and used where large forces are required for valve operation.
(4) Low flow valves may be a small as 3mm port size and are used for accurate control of low flow rates.
(5) Three way mixing valves have two inlets and one outlet, and operate to vary the proportion of fluid entering each of the two inlets.
(6) Three way diverting valves have one inlet and two outlets and operate to diver or
proportion the inlet flow to either of the two outlets.
(7) Two way modulating valves have one inlet and one outlet and operate to modulate or proportion the flow through the heat exchange equipment.
(8) Butterfly valves comprise a heavy ring enclosing a disc that rotates on an axis at or near its centre and may be used for shut-off where low differential pressures exist.
(9) Special multi-port valves for various type or modulating / sequences operation are available for control of both hot and chilled water to three and four pipe fan coil and induction unit systems.
b) Valve Operators - Valve operators usually comprise an electric solenoid, electric motor, or pneumatic actuator, brief details of which are given below:
1) A solenoid is a magnetic coil that operates a movable plunger to provide two-piston operation
2) An electric motor is arranged to operate the valve stem through a gear train and linkage. Various types are available for different applications, such as;
i) A unidirectional motor is used for two position operation, the valve opening during one half revolution of the output shaft and closing during the next half revolution
ii) A spring return motor for two position control operation is energized electrically, driven to one position, and held there until the circuit is broken, when the spring returns the valves to its normal position.
iii) A reversible motor is used for floating or proportional operation and can run in either direction and stop in any position.
3) A pneumatic actuator usually comprises a spring opposed flexible diaphragm or bellows connected to the valve stem, so that an increase in air pressure acts on the diaphragm or bellows to move the valve stem compress the spring. When the air pressure is removed the spring will return the operator to its normal position.
12.5.2.9.2. Automatic control dampers
Control dampers are designed to control the flow of air in a ductwork system in much the same as an automatic valve operates in a fluid circuit, that it by varying the resistance to flow. Following are the details of various damper valves and damper operators:
a) Damper valves: (1) The single blade damper is generally restricted to small sizes since it does not provide accurate control. When fitted in circular ductwork it may be referred to a butterfly damper.
(2) A multi-leaf damper is two or more blades linked together, which may be: (i) A parallel action multi-leaf damper, having its blades linked so that when operated they all rotate in the same direction. (ii) An opposed action multi-leaf damper, having adjacent blades linked to rotate in opposite directions when operated.
b) Damper operators- These may be electric motors of the unidirectional, spring return or reversible type fitted with suitable linkage mechanisms, or may be pneumatic actuators of a type designed for damper operation.
12.5.2.9.3. Centralized control/monitoring equipment
The centralized control system, which is shown diagrammatically in Fig.1, comprises three main parts: the remote location equipment, the transmission links, and the central equipment.
12.5.2.9.4. Remote location equipment
This includes:
12.5.2.9.5. Transmission links
The transmission links provides the means for communication between the central equipments and the remote data collection panel and may be classified according to a number of variables, which includes:
Other considerations include the physical arrangement of the transmission system, security and supervisory aspect.
12.5.2.9.6. Central equipment
This may comprise:
12.5.3 Selection Factors
12.5.3.1 Common factors
There are a number of factors to be considered in the selections of almost all control system components these common factors include:
Note—these common factors, should only be used as a general guide, and control manufactures should be consulted in establishing exact requirements.
12.5.4. Sensing / Measuring Elements
Sensing and measuring elements frequently form an integral part of a controller and the selection factors to be considered for this arrangement may be a s given in 12.5.3.1. However, a sensor may be designed and arranged for operation with a remote controller and other components, in that case some of the more important selection factors for temperature elements, for example may be as follows:
(a) Control operations, for example reverse or direct-acting
(b) Sensing range, adjustable or non-adjustable
(c) Provision for air filter
(d) Pressure output
(e) Provision for branch pressure indication
(f) Application, for example room, duct immersion in pipeline
(g) Application, for example room, duct immersion in pipeline
(h) Electronic
(j) Function, for example for primary or secondary control
(k) Temperature range
(m) Authority range of throttling range adjustment
(n) Nominal resistance and sensitivity and
(p) Provision for temperature indication
13. INSPECTION, COMMISSIONING AND TESTING
13.1. Inspection, commissioning and testing should be carried out meticulously if a satisfactory installation is to be handed over to the client. It should be ensured that these are carried out thoroughly and all results are properly documented. It is recommended that the whole commissioning procedure should be under the guidance and control of a single authority, to be identified by the client.
13.2. Inspection and Testing
All equipment and components supplied may be subjected to inspection and tests during manufacture, erection / installation and after completion. No tolerances at the time of inspection shall be allowed other than those specified or permitted in the relevant approved standards, unless otherwise stated. Approval at the time of inspection shall not be constructed as acceptance unless the equipment proves satisfactory in service after erection.
High pressure air duct system should also be tested in accordance with the procedures.
13.2.1. Inspection and Testing at Works
The air conditioning system will consist of various items of equipment produced by various manufacturers. Each manufacturer should give facilities for the inspection of his equipment during manufacturing and on completion, as specified.
13.2.2. Inspection and Testing on site
Prior to commissioning, testing adjusting and balancing, preliminary checks and charging of the complete system should be carried out. It is important that all water systems should have been thoroughly flushed through and hydraulically pressure tested to 1.5 times the working pressure for a period of not less than 8 h.
13.3. Commissioning, Testing, Adjusting and Balancing
13.3.1. Basic considerations
13.3.1.1. The basic considerations are:
(a) to test to determine quantitative performance of equipment
(b) to adjust to regulate for specified fluid flow rates and air patterns at terminal; equipment (for example reduce fan speed throttling etc);
(c) to balance to proportion within distribution system (sub mains, branches and terminals) in accordance with design quantities.
13.3.1.2. The objective of testing, adjusting and balancing of air conditioning, hating and mechanical ventilation system shall be to:
(a) Verify design conformity
(b) Establish fluid flow rates, volume and operating pressures
(c) Test all associated electrical panels and electrical installation for earthling continuity and earth resistance
(d) Take electrical power readings for each motor
(e) Establish operating sound and vibration levels
(f) Adjust and balance to design parameters and
(g) Record and report results as per the specified formats
13.3.2. System Testing. Adjusting and Balancing
13.3.2.1. Refrigeration plant.
The refrigeration plant may be tested for the following:
(a) Adjusting water flow rate through chiller and condenser by use of balancing valves
(b) Ascertaining the capacity by measurement of water flow rate and temperature of water at inlet and outlet of chilling machine
(c) Computation of power consumption
(d) Verifying operating noise level as per manufacturer instructions.
13.3.2.2. Air system
13.2.2.2.1. Air handler’s performance
The testing, adjusting and balancing procedure shall establish the right selection and performance of the air handling units with the following results:
(a) Air-in dry-bulb and wet-bulb temperature
(b) Air-out dry-bulb and wet –bulb temperature
(c) Leaving air dew point temperature
(d) Fan air volume
(e) Fan air outlet velocity
(f) Fan static pressure
(g) Fan power consumption
(h) Fan speed and
(i) Check for zero water retention in the condensate drain pan.
13.3.2.2.2. Air distribution
Both supply and return air distribution for each air handling unit and for areas served by the air handling unit shall be determined and adjusted as necessary to provide design air quantities. It shall cover balancing of air through main and branch ducts
13.3.2.2.3. Hydronic system
The hydronic system shall involve the checking and balancing of all water pumps, piping network (main and branches), heat exchange equipment like cooling and heating coils, condensers, chillers and cooling towers in order to provide design water flows.
The essential preparation work shall be done by the air conditioning contractor prior to actual testing, adjusting and balancing and shall ensure the following:
(a) Hydronic system is free of leaks, hydrostatically tested and is thoroughly cleaned, flushed and refilled
(b) Hydronic system is vented
(c) Check pumps operation for proper rotation and motor current drawn etc;
(d) Confirm that provisions for tabulation of measurements (temperature, pressure and flow measurements) have been made; and
(e) Open all shut-off valves and automatic control valves to provide full flow through coils. Set all balancing valves in the preset position, if these valves are known. If not, shut all riser balancing valves except the one intended to be balances first.
Balancing work for both chilled water system and condenser water system shall be carried out in a professional manner and test reports in the specified format shall be prepared.
13.4. Controls
Since most of the control equipment used for air conditioning system is factory calibrated, hence physical verification before installation shall be carried out. In addition, manufacturers’ instructions should be followed for site calibration, if any.
13.5. Notes and Sound Control
Measurements should be taken with a sound level meter either using the ‘A’ weighting scale or to draw up a noise criteria curve. Measurements should be taken in the following locations:
(a) Plant rooms
(b) Occupied rooms adjacent to plant rooms
(c) Outside plant rooms facing air intakes and exhausts and condenser discharge, to assess possible nuisance to adjacent occupied areas
(d) In the space served by the first grille or diffuser after a fan outlet
(e) In at-least two of the spaces served by fan coil units or high velocity system terminal units (where applicable);
(f) In any space and
(g) Air handling unit (AHU) rooms and adjoining areas
13.6. Handover procedure
Handover documentation should contain all information that the user needs to enable the Installation and equipment to be efficiently and economically operated and maintained. It should also provide a record of the outcome of any site testing, balancing and regulation carried out prior to handover.
Handover documentation should include the following;
(a) Description of the installation, including simplified line flow and balance diagrams for the complete installation;
(b) As-built installation drawings;
(c) Operation and maintenance instructions for equipment, manufacturer’s service maintenance manuals, and manufacturer’s spare parts list and spare ordering instructions
(d) Schedules of electrical equipment
(e) Schedules of mechanical equipments
(f) Test results and test certificates as called for under the contract the including any insurance or statutory inspection authority certificate
(g) Copies of guarantee certificates for plant and equipment and
(h) List of keys, tools and spare that is handed over.
LIST OF STANDARDS
The following list records those standards which are ‘accepted standard’ in the fulfillment of the requirements of the Code. The latest version of the standard at the time of enforcement of the Code may be followed. The standards listed may be used by the Authority as a guide in conformance with the requirements of the referred clauses in the Code.
| Sl No. | Title |
| (1) 655-1963 | Specification for metal air ducts (revised) |
| (2) 277-2003 | Specification for galvanized steel sheet (Plain and corrugated) (sixth revision) |
| (3) 737-1986 | Specification for wrought aluminum alloy sheet and strip for general engineering purpose(third revision) |
| (4) 3103-1975 | Code of practice for industrial ventilation (first revision) |
| (5) 3315-1994 | Specification for evaporative air coolers (desert coolers) (second revised) |
| (6) 1391 (Part1) -1992 | Specification for room air conditioners: Unitary air conditioners (second revised) |
| (7) (Part2) -1992 | Spilt air conditioners (second revised) |
| (8) 8148-2003 | Specification for packaged air conditioners (first revised) |
| (9) 4831-1968 | Recommendation on units and symbols for refrigeration |
| (10) 5-1994 | Specification for colures for ready mixed paints and enamels (fourth revision) |
* * * *