Air conditioning is the process by which
the air in a space is modified to make it comfortable for the occupants. The
primary function of air conditioning is cooling although all systems filter the
air and some also provide heating and adjustments to the humidity levels.
Cooling is needed when the room air
temperature rises above a comfort threshold of 27oC. Temperatures rise
above this level due to a combination of high outside temperatures and internal
heat gains. For example, in summer the outside air temperature may be 22oC
or above. When this warm air enters the building its temperature will be
further increased by heat gains from people, artificial lighting, appliances and
the sun. Increases of 6oC due to these casual gains are not uncommon
pushing the incoming air temperature above the comfort threshold. Even in winter
when outside air temperatures are low, office buildings may experience
sufficiently high casual heat gains that cooling is required.
Many of the situations need a degree of
air conditioning. To summarize, those situations most likely to require air
conditioning are;
-
Rooms subject to
high solar gains, such as south facing rooms especially those with large areas of
glazing
-
Rooms with high
equipment densities such as computer rooms and offices which make extensive use
of IT
-
Rooms in which
environment (temperature, dust or humidity) sensitive work is being carried out
such as operating theatres and microprocessor manufacturing units.
Air conditioning systems can be categorized into
three main types:
the air in a room to bring its
temperature down to acceptable levels. The cooling equipment is located
in the room itself. The main forms of local
comfort cooling system are:
· Window sill air conditioners
· Split systems
· Multi split systems
· Variable refrigerant flow split systems
Centralized air systems - All of the heating or cooling
is carried out in a central air handling unit. Room by room
is carried out in a central air handling unit. Room by room
control of temperatures is achieved
using the following systems:
· Constant volume systems
· Variable air volume (VAV) systems
· Dual duct systems
Centralized air systems do not just
provide heating or
cooling but can filter, humidify or
dehumidify the air as
required. The central plant is usually in
a ground floor
plant room or may be a packaged unit
situated on the
rooftop.
Partially centralized air/water systems - A central air handling unit is used first to filter and
then heat or cool an air-stream. Final adjustment of
temperatures is carried out using room based equipment. System
types are:
· Terminal re heat or fan coil systems
· Induction systems
· Chilled ceilings and displacement
ventilation