Tuesday, April 14, 2009

INDOOR DESIGN CONDITIONS

INDOOR DESIGN CONDITIONS

Indoor design parameters are those that the air conditioning system influences directly to produce a

required conditioned indoor environment in buildings. They are shown below and grouped as follows:

1. Basic design parameters

_ Indoor air temperature and air movements

_ Indoor relative humidity

2. Indoor air quality

_ Air contaminants

_ Outdoor ventilation rate provided

_ Air cleanliness for processing

3. Specific design parameters

_ Sound level

_ Pressure differential between the space and surroundings

The indoor design parameters to be maintained in an air conditioned space are specified in the

design document and become the targets to be achieved during operation. In specifying the indoor

design parameters, the following points need to be considered:

1. Not all the parameters already mentioned need to be specified in every design project. Except

for the indoor air temperature which is always an indoor design parameter in comfort air conditioning,

it is necessary to specify only the parameters which are essential to the particular situation

concerned.

2. Even for process air conditioning systems, the thermal comfort of the workers should also be

considered. Therefore, the indoor design parameters regarding health and thermal comfort for the

occupants form the basis of design criteria.

3. When one is specifying indoor design parameters, economic strategies of initial investment

and energy consumption of the HVAC&R systems must be carefully investigated. Design criteria

should not be set too high or too low. If the design criteria are too high, the result will be an excessively

high investment and energy cost. Design criteria that are too low may produce a poor indoor

air quality, resulting in complaints from the occupants, causing low-quality products, and possibly

leading to expensive system alternations.

4. Each specified indoor design parameter is usually associated with a tolerance indicated

as a _ sign, or as an upper or lower limit. Sometimes there is a traditional tolerance understood

by both the designers and the owners of the building. For instance, although the summer

indoor design temperature of a comfort air conditioning system is specified at 75 or 78°F

(23.9 or 25.6°C), in practice a tolerance of _2–3°F (_1.1 – 1.7°C) is often considered

acceptable.

5. In process air conditioning systems, sometimes a stable indoor environment is more important

than the absolute value of the indoor parameter to be maintained. For example, it may not be necessary

to maintain 68°F (20°C) for all areas in precision machinery manufacturing. More often, a

72°F (22.2°C) or even a still higher indoor temperature with appropriate tolerance will be more

suitable and economical.

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