Classification of Air Conditioning Systems
The air conditioning systems may be broadly classified as follows:
(1) According to purpose:
a) Comfort air conditioning system:
The purpose of such a system is to create atmospheric conditions conductive to human health, comfort and efficiency. This system is used for homes, office, shop, restaurants, hospitals, school, etc.
b) Industrial air conditioning system:
The purpose of these air conditioning system is to control the atmospheric conditions primarily for the proper conduct of research and manufacturing process. This type of air conditioning used in textile mills, paper mills, machine parts manufacturing plant, tool rooms, printing, photo processing plant, etc.
◆ Comparison of comfort air conditioning and Industrial air conditioning
Comfort Air conditioning → Industrial air conditioning
1. The main purpose to provide comfort to human beings. → The main purpose is to improve the quality and efficiency of product.
2. Temperature and R.H. maintain which are suitable for human comfort which vary from person to person. → The temperature and RH are maintain which is suitable for Industrial process.
3. In general, the conditions are 22 to 25°C DBT, 30 to 60 % RH. and 5 to 8 m/min air motion. →The condition very from process to process.
4. eg Office restaurant, building etc. → e.g. Textile industries chemical plant, photographic industry etc.
(2) According to season of the year :
a) Winter air conditioning system:
● Such system, when properly designed and installed, maintain indoor atmospheric conditions for winter comfort. The major problems of winter air conditioning are to heat the air and to bring moisture content up to an acceptable level.
● Heating is accomplished by electric heaters or furnaces and boilers fired by gas oil or coal. Humidifiers may be of the simple pan type or spray type.
b) Summer air conditioning system:
● These systems controls all the four atmospheric conditions for summer comfort. The major problem is to cool the air and remove excess moisture from air. Cooling of air is done by mechanical refrigeration.
● Removal of moisture (dehumidification) is accomplished by condensation of water vapour in the air occurs on the cold coil surfaces.
c) Year round air conditioning system: (All Weather Air conditioning) :
● These system are composed of heating and cooling equipment with automatic controls according to the season requirement.
● This system must be capable of maintaining a specified temperature and humidity within the conditioned space regardless of outside conditions:
(1) Heating and humidification in winter.
(2) Cooling and dehumidification in summer.
(3) Classification according to equipment arrangement :
a) Central air conditioning :
● When more than one room in the same building are to be air-conditioned which required approximately same temperature and R.H.
● This can be achieved by central air conditioning system than from a number of self-conditioned unit.
b) Unitary air conditioning :
● These system make use of air-conditioners which are completely factory assembled A single air-conditioner may serve if the building is a small one or the area may be divided into several small zone, cach being served by a conditioner of small to medium capacity.
● This has advantage of more flexibility of operation and low initial cost.
(4) According to working substance used in the system :
a) All air system.
b) Chilled water system
c) Air water system.
(6) According to volume of air handle by the system :
a) Constant volume system.
b) Variable air volume system (VAV).
Seasonal Air Conditioning :
According to season of the year air conditioning system can be classified as:
a) Winter air conditioning system :
● Such system, when properly designed and installed, maintain indoor atmospheric conditions for winter comfort.
● The major problems of winter air conditioning are to be heat the air and to bring moisture content up to an acceptable level.
● Heating is accomplished by electric heater or furnace or boilers fired by gas, oil or coal. Humidifier may be of the simple pan type or spray type.
b) Summer air conditioning system :
● These systems control all the four atmospheric condition for summer comfort.
● The major problems are to be cooled the air and to remove excess moisture from it. Cooling is accomplished by mechanical refrigeration.
● Removal of moisture (dehumidification) is accomplished by condensation of water in the occurs on cold coil surfaces.
(c) Year round air conditioning system:
● These systems are composed of heating and cooling equipment with automatic control and associated components to produce four atmospheric conditions for human comfort at all times.
Summer Air Conditioning System for Hot and Dry Weather:
The comfort condition required for an air-conditioned space is 26°C DBT and 60% RH.
● When the atmospheric air temperature is high at low relative humidity, it is always necessary to cool and humidity the ir for comfort conditions.
● The outside air flows through damper and mixes up with recirculated air.which is obtained from air conditioned space.
● It is first passed through air filter for removal of dust, and bacterial and clean the air, then it is passed over the cooling coil.
● The temperature of air is considerably reduced with the help of cooling coil.
● The temperature of air is controlled with the help of coolant quantity and its temperature circulated through the cooling coil.
● The condition of air leaving the cooling coil is represented by point 2. Then the air is passed through spray type humidifier where air humidity is increased upto required condition. This produce effective cooling by combining natural process of evaporation of water with air. This help to reduce soluble impurities and particles.
● The relative humidity of air is controlled by controlling the quantity of water spray in the humidifier.
● The air is then the cooled air passes through a perforated membrane (eliminator) where water droplets are removed before supplying air to air-conditioned space.
● Now conditioned air passes to conditioned space a fan. From the conditioned space the part of air is exhausted to atmosphere by exhaust fans or ventilators. The remaining part of the used air or recirculated air is again conditioned
● The quantity of air passed through the air conditioning system depend upon the load. The quantity of air supply is controlled with the help of damper.
● The outside air is sucked and made to mix with recirculated air in order to make up for the loss of conditioned or used air through exhaust fans or ventilators from conditioned.
Summer Air Conditioning System for Hot and Wet Weather:
● When the air is hot and wet (high R.H.), the treatment of the air in air conditioning system differs from the system Hot and Dry weather. This is because air contains more quantity of water vapour than required, therefore, it is necessary to remove the water vapour from the air by dehumidification.
● The average summer conditions in some places are 32°C DBT and 75% relative humidity. The required comfort condition is 26°C DBT and 60% R.H. The arrangement of the required equipments and the representation of psychrometric process.
● The air is first passed through air filter to remove the dust and then it is passed over the cooling coil.
● The water vapour is removed from the air in the form of water droplets as air is cooled below its dew point temperature.
● The surface temperature of the cooling coil is always maintained below DPT of the outdoor air for dehumidification
● The quantity of water removal from air is controlled by controlling the cooling coil surface temperature and the cooling coil surface temperature is controlled by controlling the quantity of coolant (brine or refrigerant) passed through the coil.
● The temperature of air leaving the cooling coil (point 3) is lower than the required temperature for comfort. Therefore it is necessary to heat the air.
● The air coming out from the cooling coil is passed over heating coil and heated upto required temperature. The temperature of air is controlled by controlling the resistance of the heating coil as per the type of heating used.
● The air coming out from the heating coil at required condition is directly supplied to conditioned space. The function of damper is to controlled the quantity of air entering in conditioned space according to load.
Winter Air Conditioning System :
● In winter season, it is necessary to heat the air for comfort condition, but the R.H. of the air decreases as it is heated. therefore, it became necessary to increase the R.H. by humidifying the air.
● The air conditioning for winter requires heating and humidifying. The heating of air is generally done in two stages for the control.
● The winter conditions at some places are 15°C and 80% relative humidity. The required comfort conditions are same as 26°C DBT and 60% RH. The arrangement of required equipments and representation of psychrometric processes.
The air is first passed through air filter to remove dust and bacteria then it passed over primary (first) heating coil.
● The temperature of the air coming out of the heating coil is controlled by the energy input to the coil. This air is passed through adiabatic humidifier where it is humidified with water spray and remove soluble impurities and particle.
● The air coming out from humidifier is passed through eliminator to remove water particles. Then the temperature of air increased to required condition by passing this air over second heating coil and then supply to conditioned space.
● The air damper control the flow rate of air according to load on air-conditioned space.
Year-round Air Conditioning System :
The principal parts of a modem summer and winter air conditioning.
● The mixture of recirculated air and fresh air from atmosphere is passed first through a filter so as to remove any dust particles and harmful bacteria from it.
● In winter, the cooling coil is made inoperative and heating coil operates to heat the air. The spray type humidifier is also made use in the dry season to humidify the air.
Difference between Summer and Winter Air Conditioning System :
Summer air conditioning → Winter air conditioning
1. Psychrometric process
 |
| Sammer |
 |
| Winter |
2. Water eliminator is not required. → Required water eliminator.
3. For dehumidification, cooling coil is used whose temperature is below dew point temperature. → For humidification, adiabatic humidifier is used to humid the air upto required (60%) relative humidity.
4. One heating coil is used to control the temperature of air to comfort condition i.e. 26°C DBT. → Two heating coils are used of which secondary heating coil is used to control the temperature of comfort condition and primary coil is used to increase the temperature of atmospheric air as per energy input.
5. In this system, secondary refrigerant is used for dehumidification of air which circulate through cooling coil. → For humidification water is used.
6. Operating cost is less. → Operating cost is more.
