2.9. Essentials of air conditioning system

The following are the essentials of an air conditioning system;

1. Filtration.

2. Heating (in winter season).

3. Cooling (in summer season).

4. Humidification.

5. Dehumidification.

1. Air circulation or distribution.

1. Filtration

The aim of the filters is to exclude from incoming air dust particles, ash, chemical soot, bacteria and other micro-organisms, so that clean air is obtained. The filters should possess the following qualities :

(i) They should be capable of removing dust, ash, chemical soot, bacteria etc., from the incoming air.

(ii) They should be capable of holding a moderate amount of dust, cleaned from incoming air, on their surface without affecting their working efficiency. Filtering media should be of some fibrous material such as spun glass, steel wool, porous paper, wood fibre, etc., so that dust can adhere to it.

(iii) They should offer low frictional resistance to the flow of air.

(iv) They should be workable under a sufficient range of air velocities.

(v) They should afford easy cleaning, either manually or automatically.

Types : Filters may be of the following types :

(i) Viscous type filters. These are made of mats or .screens of split wire or glass wool or of similar material, and coated with non-drying viscous oil so that dust in the incoming air can be caught and removed. They may be either of unit type or automatic type. In the unit type, the mats are replaced for cleaning and recoiling. In the automatic type an endless moving chain is provided over the mat so that it is mechanically rotated in a continuous cycle of air cleaning, removal of air-pollution particles and replacement of viscous filter media.

(ii) Dry filter. They are made of cloth such as flannel, cellulose, felt, etc., which is discarded when it becomes dirty.

(iii) Spray washers. The incoming air is allowed to pass through water sprays, where the dust and fumes arc removed by drops of water.

(iv) Electric precipitators. These remove the dust by subjecting it to a strong electric field and then getting it attached to negative electrode. The particles collected on negative electrode are removed at intervals. The initial installation cost of this is high but operational cost is low.

2. Heating

Heating of air is necessary in winter, so as to compensate the heat loss from the room. Pre-heating of incoming air may be done by passing .it over warm air furnaces, or by coils around which hot water or steam is circulating.

3. Cooling

Cooling of incoming air is necessary in summer. As stated previously, there are two methods of cooling the air (i) direct expansion system, and (ii) chilled water system. In the direct expansion (DX) system, the principle of mechanical refrigeration is used, where in a volatile frigerant is compressed, cooled, allowed to expand and then it is passed through coils. These coils absorb the heat from incoming air. In the chilled water system, a secondary medium such as water is utilised to cool the air. The incoming air is circulated around the coils containing chilled water. Thus, the refrigerant first cools the water and then the water cools ihe air. Chilled water is produced in the refrigeration plant housed in the main plant room.