Design For Natural Ventilation, Air-conditioning

DESIGN FOR NATURAL VENTILATION

1. By wind action

(a) Inlet openings in the building should be well distributed and should be located on the windward side at a low hotel level. The outlet openings should be located on the leeward (direction of downwind) side near the top. Hence, incoming air stream is passed over the occupants. go the i (Fig. 2.6)

Inlet and outlet openings at high levels may only clear the top air without producing air movement at the level of occupancy. When outlets serve also as inlets, they shall be located at the same level.

(b) Inlet opening should not be obstructed by adjoining buildings, trees, sign boards or by partitions inside the path of air flow.

(c) Maximum flow per unit area of openings is obtained by using inlet and outlet openings of nearly equal areas.

(d) When the stream of wind is quite constant and dependable, the openings may be readily arranged to take full advantage of the wind.

When the wind direction is quite variable, the openings shall be approximately equal areas on all sides and the openings shall be located at the same levels.

Thus, no matter what the wind direction is, there are always some openings directly exposed to wind pressure.

2. By stack effect

Natural ventilation by stack effect occurs when air inside  a building is at a different temperature than air outside. The outside air will tend to enter through openings at low level. The warm air will tend to leave through openings at high level.

Thus, ventilators should be provided as close to ceilings as possible.

Ventilators can also be provided in roofs.

For example, cowl, vent pipe, covered roof and ridge vent. (Fig. 2.7)

Air-conditioning

Air –conditioning  means not only the control of temperature but also of humidity, oxygen content, purity and air movement.

In addition, filtering and cleaning of air is also carried out by the air-conditioning systems.

• Air-conditioning is required for human comfort.

Definition

It is defined as the process of controlling and maintaining the properties of air like temperature, humidity, purity, direction of flow etc., in a closed space.

Principle of Air-conditioning

The air-conditioner continuously draws an air from indoor space and cools it by the refrigeration principle and discharges it back into the same indoor space.

Classification of Air-conditioning systems

The air-conditioning systems are classified into two main categories as,

 (i) Comfort air-conditioning

(ii) Industrial air-conditioning

Comfort air-conditioning system

• It is to provide the environment with the required temperature and humidity for human comfort, health and efficiency.

• Comfort air-conditioning system is used in offices, houses, shops, hospitals, libraries, hotels, theatres etc.

• The comfort air-conditioning is further classified into:

(a) Summer air-conditioning,

(b) Winter air-conditioning,

(c) Year-around air-conditioning.

 (a) Summer air-conditioning system

• During summer, the temperature is high and hence the air conditioning  system involves cooling and dehumidification (removing excess moisture from air).

(b) Winter air-conditioning system

• During winter, atmospheric temperature is quite low ow and hence air conditioning involves heating and humidification to elove (adding moisture of air) to provide comfort.

(c) Year-around air-conditioning system

• Year-around air conditioning system has both summer staiwand winter air-conditioning systems.

• There are so many combinations of arrangement used. One part of the system works in summer and other in winter.

Industrial air-conditioning system

The aim of this system is to provide the environment with the required temperature and humidity, according to the applications.

Classification of air-conditioning based on the equipment arrangement

Based on the equipment arrangement, the air-conditioning can also be classified as unitary and central type.

(i) Unitary air-conditioning: The unitary or window type air-conditioner is of small capacity (of 1/2 to 2 tonnes), used for air-conditioning of rooms, small offices.

(ii) Cental air-conditioning: The central air--conditioning is of large capacity (around 50 to 100 tonnes), used for air-conditioning of large commercial buildings.

General principle of Air-conditioning

All the above systems invariably adopt the same cycle of operations as given below.

• Sucking the air through the filter media.

• Cooling the air in summer and heating it in winter.

• Dehumidifying if it is to be cooled or humidifying if it is to be heated.

• For using the processed air into the rooms space for proper circulation through grills

• Collecting the used air through exhaust and mixing Juo nie with the outside air and sucking again the air through