National Building Code : Building Services
- 1. PART 8 BUILDING SERVICES Section 3 Air Conditioning 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. TERMINOLOGY • 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. • 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. • Dew point Temperature — The temperature at which condensation of moisture begins when the air is cooled at same pressure. • Dry-Bulb Temperature — The temperature of the air, read on a thermometer, taken in such a way as to avoid errors due to radiation. • Evaporative Air Cooling — The evaporative air cooling application is the simultaneous removal of sensible heat and the addition of moisture to the air. • 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. • Fire Separation Wall — The wall providing complete separation of one building from another or part of a building from another 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.
- 3. • Evaporative Air Cooling — The evaporative air cooling application is the simultaneous removal of sensible heat and the addition of moisture to the air. • 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. • Fire Separation Wall — The wall providing complete separation of one building from another or part of a building from another 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. • 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 odours 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 surrogate ventilation index. • Infiltration/Exfiltration — The phenomenon of outside air leaking into/out of an air conditioned space. • Recirculated Air — The return air that has been passed through the conditioning apparatus before being re-supplied to the space.
- 4. • Sick Building Syndrome (SBS) — A term, which is used to describe the presence of acute nonspecific symptoms in the majority of people caused by working in buildings with an adverse indoor environment. • 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. • Supply Air — The air that has been passed through the conditioning apparatus and taken through the duct system and distributed in the conditioned space. • Water Conditioning — The treatment of water circulating in a hydronic system, to make it suitable for air conditioning system due to its effect on the economics of air conditioning plant.
- 5. 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: a) Air purity and filtration, b) Air movement, c) Dry-bulb temperature, d) Relative humidity, e) Noise and vibration, f) Energy efficiency, and g) Fire safety. • 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’.
- 6. • 3.1.4 The plans for air conditioning, heating and mechanical ventilation systems shall include all details and data necessary for review of installation such as: a) building: name, type and location; b) owner: name; c) orientation: north direction on plans; d) general plans: dimensions and height of all rooms; e) intended use of all rooms; f) detail or description of wall construction,including insulation and finish; g) detail or description of roof, ceiling and floor construction, including insulation and finish; h) detail or description of windows and outside doors, including sizes, weather stripping, storm sash sills, storm doors, etc; j) internal equipment load, such as number of people, motor, heaters and lighting load; layout showing the location, size and construction of the cooling tower (apparatus),ducts, distribution system; m) information regarding location, sizes and capacity of air distribution system, refrigeration and heating plant, air handling equipment; n) information on air and water flow rates;
- 7. k) information regarding location and accessibility of shafts; q) information regarding type and location of dampers used in air conditioning system; r) chimney or gas vent size, shape and height; s) location and grade of the required fire separations; t) water softening arrangement; and u) information on presence of any chemical fumes or gases.
- 8. 3.2.2 Planning of Equipment Room for Central Air Conditioning Plant • 3.2.2.1 Plant room shall be located as centrally as possible with respect to the area to be air conditioned and shall be fre from obstructing columns. • 3.2.2.2 The floors of the equipment rooms should be light coloured and finished smooth. • 3.2.2.4 Equipment rooms, wherever necessary, shall have provision for mechanical ventilation. In hot climate, evaporative air-cooling may also be considered. • 3.2.2.6 Equipment room should preferably be 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.
- 9. 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.
- 10. 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 recirculating 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 and leaving water. • 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 convection 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 air side (forced draft) or exit air side (induced draft).
- 11. • 3.2.6.4 Factors to be considered for cooling tower selection are: a) Design wet-bulb temperature and approachof cooling tower. b) Height limitation and aesthetic requirement. c) Location of cooling tower considering possibility of easy drain back from the system. d) Placement with regard to adjacent walls and windows, other buildings and effects of any water carried over by the air stream. e) Noise levels, particularly during silent hours and vibration control. f) Material of construction for the tower. g) Direction and flow of wind. h) Quality of water used for make-up. j) Maintenance and service space. k) Ambient air quality. • 3.2.6.5 The recommended floor area requirement for various types of cooling tower is as given below: • a) Natural draft cooling Tower 0.15 to 0.20 m2/t of refrigeration • b) Induced draft cooling Tower 0.10 to 0.13 m2/t of refrigeration • c) Fibre-reinforced Plastic 0.07 to 0.08 m2/t of refrigeration
- 12. 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 1 Lighting 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 12° also helps curtail transmission of direct solar radiation through the glazing. • 3.2.7.3 Where sun breakers are used, the following aspects shall be kept in view: a) The sun breakers shall shade the maximum glazed area possible, specially from the altitude and azimuth angle of the sun, which is likely to govern the heat load. b) The sun breakers shall preferably be light and bright in colour so as to reflect back as much of the sunlight as possible. c) The sun breakers shall preferably be 1 m away from the wall face, with free ventilation, particularly from top to bottom and are meant for carrying away the heat which is likely to get boxed between the sun breakers and the main building face.
- 13. d) The sun breakers shall be installed as to have minimum conduction of heat from sun breakers to the main building. • 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 surfaces.
- 14. • 3.2.7.5 Day light transmittance for various type of glass is given in Table 1.
- 15. 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.
- 16. 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,etc (for example, from smoking). • Local extract systems may be necessary to remove polluted air from kitchens, toilets, etc. Special air filters may be required to remove contaminants or smells when air is recirculated. • 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.
- 17. • Inlets should not be positioned near any flue outlets, dry cleaning or washing machine extraction outlets, kitchen, water-closets, etc. 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.
- 18. 4.4.1 Temperature o 4.4.1.1 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. • When large windows/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. 4.4.2 Humidity o 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. • For normal comfort conditions, relative humidity (RH) values between 40 percent and 70 percent are acceptable.
- 19. 4.4.3 Inside Design Conditions
- 20. 4.4.4 Outside Design Conditions
- 22. 4.4.5 Minimum Outside 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. • 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.
- 25. 4.4.6 Air Movement a) In air conditioned spaces • Air movement is desirable, as it contributes a feeling of freshness, although excessive movement should be avoided as this leads to complaints of draughts. • The quantity of fresh air should not be increased solely to create air movement; this should be effected by air re-circulation within the space or by inducing air movement with the ventilation air system. b) In buildings • Air flow within a building should be controlled to minimize transfer of fumes and smells, for example from kitchens to restaurants. • This is achieved by creating air pressure gradients within the building, by varying the balance between the fans introducing fresh air and those extracting the stale air. • For example, the pressure should be reduced in a kitchen below that of the adjacent restaurant. 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.
- 26. 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.
- 27. 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. o 4.5.2.2 Ductwork and enclosures • All ductwork including connectors fittings and plenums should be constructed of steel, aluminium 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. • 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
- 28. • 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 devices 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. • 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 systems 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
- 29. 4.6 Application Factors o 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.
- 30. • 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. • 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 vary widely
- 31. • 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 a 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.
- 32. 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 in 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 difference 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 microorganisms; c) Close tolerances in temperatures and humidities may be required for various areas;and d) The design should allow for accurate control of environmental conditions.
- 33. • 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 • 4.6.1.8 Residential buildings • Very few residences are air conditioned. Some individual houses have unitary systems comprising of window/split air conditioners.