Building Services Engineering 5th Edition Handbook

Ventilation and air conditioning 151
Supply air
Condenser coil and
propeller fan in
outside air duct
+
+ Electronic heater
– Refrigeration coil
Drip tray
Fan
Filter
Recirculated room air
Refrigeration compressor
5.15 Packaged air-conditioning unit.
and have a change-over valve to reverse the refrigerant flow direction. This enables the unit to
cool the internal air in summer and the external air in winter.
Heat rejected from the condenser is used to heat the internal environment in winter. In this
mode of operation it is called a heat pump. A separate ventilation system may be needed.
Compressor and fan noise levels are compared with the acceptable background acoustic environment.
Maintenance requirements are filter cleaning, bearing lubrication and replacement of
the compressor when it becomes too noisy or breaks down.
Split system units have a separate condenser installed outside the building. Two refrigerant
pipes of small diameter connect the internal and external equipment boxes. This allows
greater flexibility in siting the noise-producing compressor. Ducted models provide conditioning
and ventilation and are often sited on flat roofs. Figure 5.15 shows a typical through-the-wall
installation.
Vapour-compression refrigeration
The electrically driven vapour-compression refrigeration system is the principal type used. Its rival,
the absorption cycle, burns gas to produce cooling but has a coefficient of performance of
around 1, whereas vapour compression has a coefficient of performance in the range 2–5, and
so it is cheaper to operate. Compressor types are as follows.
1. Single- or multi-cylinder reciprocating piston compressor with spring-loaded valves: domestic
refrigerators and small air conditioners have hermetically sealed motor–compressor units
which are sealed for their service period, that is, about 10 years.
A condensing unit comprises a sealed compressor, a refrigerant condenser, a liquid receiver,
pipework and controls. Refrigerant pipework is installed on site from this unit to a finned
pipe forced-draught air-cooling coil in the air-conditioning system.