AIR CONDITIONING SYSTEM
The air conditioning is that branch of engineering science which deals with the study of conditioning of air for ‘human comfort’. In broad sense this field also deals with the conditioning of air for industrial purposes,food processing, storage of food and other materials.
What is actually human comfort?
Strictly speaking,the human comfort depends upon psychological and physiological conditions.Thus it is difficult to define the term ‘human comfort’.There are many definitions given to this term by different departments.But the most acceptable definition,from the subject point of view is given by the American Society of Heating, Refrigeration and Air conditioning Engineers (ASHRAE).It states that ” human comfort is that condition of mind,which expresses satisfaction with the thermal environment”.
Factors affecting comfort Air conditioning
The four important factors for comfort air conditioning are discussed below:
1.) Temperature of air
In air conditioning,the control of temperature means the maintenance of any desired temperature within an enclosed space even though the temperature of the outside air is above or below the desired room temperature.This is accomplished either by the addition or removal of heat from the enclosed space as and when demanded.
It is quite notable that a human being feels comfortable when the air is at 22°C with 55% relative humidity.
2.) Humidity of air
The control of humidity of air means the increasing or decreasing of moisture contents of air during summer or winter respectively in order to produce comfortable and healthy conditions.The control of humidity is not only necessary for human comfort but it also increases the efficiency of the workers.In general,for summer air conditioning the relative humidity should not be less than 60% whereas for winter air conditioning it should not be more than 40%.
3.) Purity of air
It is an important factor for the comfort of a human body.It has been noticed that people don’t feel comfortable when breathing contaminated air,even it is within acceptable temperature and humidity ranges.It is thus obvious that proper filtration, cleaning and purification of air is essential to keep it free from dust and other impurities.
4.) Motion of air
The motion or circulation of air is another important factor which should be controlled,in order to keep constant temperature throughout the conditioned space.It is therefore necessary that there should be equi- distribution of air throughout the space to be air conditioned.
Now we can clearly say that the systems which which effectively controls above conditions to produce the desired effects upon the occupants of the space,is known as Air conditioning systems.
Equipments used in Air conditioning system
Following are the main equipments or parts used in air conditioning system:
1.) Circulation fan
The main function of this fan is to move air to and from the room.
2.) Air conditioning units
It is a unit which consists of cooling and dehumidifying processes for summer air conditioning or heating and humidification processes for winter air conditioning.
3.) Supply duct
It directs the conditioned air from the circulating fan to the space to be air conditioned at proper point.
4.) Supply outlets
These are grills which distribute the conditioned air evenly in the room.
5.) Return outlets
These are opening in a room surface which allow the room air to enter the return duct.
The main function of the filters is to remove dust,dirt and other harmful bacteria from the air.
Classification of Air conditioning system
The air conditioning system may be broadly classified as below:
1.) According to purpose
A.} COMFORT AIR CONDITIONING SYSTEM-
In comfort air conditioning,the air is brought to the required dry bulb temperature and relative humidity.If sufficient data of the required condition is not given,then it is assumed to be 21°C dry bulb temperature and 50% relative humidity.The sensible heat factor is generally kept as following:
For residence or private office= 0.9
For restaurant or busy office = 0.8
For auditorium or cinema hall= 0.7
Ball room dance hall = 0.6
The comfort air conditioning may be adopted for small cabins, office halls,big halls like cinema houses.
B.} INDUSTRIAL AIR CONDITIONING SYSTEM-
It is an important system of air conditioning now a days in which dry bulb temperature and relative humidity of the air is kept constant for proper working of the machines.Some of the sophisticated electronic and other machines need a particular dry bulb temperature and relative humidity.Sometimes,these machines also require a particular method of psychrometric processes.
2.) According to season of the year (most important)
A.} SUMMER AIR CONDITIONING SYSTEM-
It is the most important type of air conditioning,in which air is generally cooled and dehumidified.
Here the outside air flows through the damper and mixes up with recirculated air (which is obtained from conditioned space). The mixed air passes through a filter to remove dirt, dust and other impurities. The air now passes through a cooling coil. The coil has a temperature much below the required dry bulb temperature of the air in the conditioned space. The cooled air passes through a perforated membrane and looses its moisture in the condensed form which is collected in a sump. After that the air is made to pass through a heating coil which heats up the air slightly. This is done to bring the air to the designed dry bulb temperature and relative humidity.
Now the conditioned air is supplied to the conditioned space by a fan. From the conditioned space a part of the used air is exhausted to the atmosphere by the exhaust fan or ventilator. The remaining part of the used air also known as recirculated air, is again conditioned. The outside air is sucked and made to mix with the recirculated air in order to make up for the loss of conditioned (used) air through exhaust fan or ventilation from the conditioned space.
B.} WINTER AIR CONDITIONING SYSTEM-
In winter air conditioning, the air is generally heated and humidified.
The outside air flows through a damper and mixes up with recirculated air. The mixed air passes through a filter to remove dirt, dust and other impurities. The air now passes through a preheat coil in order to prevent the possible freezing of water and to control the evaporation of water in humidifier. After that the air is made to pass through a reheat coil to bring the air to bring the air to the designed dry bulb temperature. Now the conditioned air is supplied to the conditioned space by a fan. From the conditioned space, a part of the used air is exhausted to the atmosphere by the exhaust fan or ventilator. The remaining part of the used air is again conditioned. The outside air is sucked and made to mix with the recirculated air, in order to make up for the loss of conditioned air through exhaust fan or ventilation from the conditioned space.
Thus we can clearly see that the summer air conditioning and winter air conditioning are same in every prospect but the only difference is that there are two heating coils in winter air conditioning system and there is one heating coil and one cooling coil in summer air conditioning system.
C.} YEAR – ROUND AIR CONDITIONING SYSTEM-
An year round air conditioning system should have equipment for both winter and summer air conditioning. There can be so many combinations for providing year – round air conditioning. The arrangement of the combination should be such that one part is working in winter and part working in summer. For example, heating and humidification should be done in winter, whereas cooling and dehumidification should be done in summer.
This air conditioning system is widely used in compartment of passanger locomotive simply trains which are air conditioned.
3.) According to the arrangement of equipment
A } UNITARY AIR CONDITIONING SYSTEM-
In this system, factory assembled air conditioners are installed in or adjacent to the space to be conditioned. These are of two following types:
* WINDOW UNITS:
These are self contained units of small capacity of 1 ton to 3 ton and are mounted in a window or through the wall. They are employed to condition the air of one room only. If the room is bigger in size then the two or more units are installed.
* VERTICAL PACKED UNITS:
These are also self contained units having capacity of 5 to 10 tonnes and are installed adjacent to the space to be conditioned. This is very useful for conditioning the air of a restaurant, bank or small office.
The unitary air conditioning system may be adopted for winter, summer or year – round air conditioning.
B.} CENTRAL AIR CONDITIONING SYSTEM-
This is the most important type of air conditioning system, which is adopted when the cooling capacity required is 25 tonnes or more. The central air conditioning system is also adopted when the air flow is more than 300 m^3/ min. or different zones in a building are to be conditioned.
That was the detailed analysis about Air conditioning system, factors affecting the comfort of air conditioning, different types air conditioning systems and there uses. Hope you all like this article.
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