AIR CONDITIONING UNIT
General Description
The computer rooms on the lower basement floor require cooling year-round because of the number of computers generating heat in these rooms. If the main air handling unit were expected to cool these rooms, cool air would have to be supplied year-round to the whole building. In the winter, this would then require wasteful reheat. Because of this, dedicated cooling systems using separate closed-loop refrigerant circuits are used to cool these rooms; i.e., the air conditioning unit.
The air conditioning unit provides cooling, heating and dehumidification using a refrigerant in a closed circuit.
The evaporator coil, compressor and fan are integral to the cabinet unit. The air-cooled condenser coil and fan are located outside. Condensed water from dehumidification is drained through a stainless steel drain pan and piping system.
A scroll-type motor-driven compressor compresses the gaseous refrigerant, which is then condensed in the outdoor condenser unit. Upon returning to the indoor unit, the liquid refrigerant passes through an expansion valve and into the evaporator coil, where it cools, providing a heat sink and thus cooling the air blown past the coil.
If the room requires heating, reheat is provided by a hot water coil (ACU-1) or electric heating coil (AHU-2), in which air is blown past the heating coil, heating the air.
A programmable microprocessor control on each unit indicates temperature, humidity, system status, setpoints and alarms. It also allows the operator to program daily and weekly operating schedules.
![[Schematic Diagram of the ACU Unit]](../../images/jpg/acu.jpg)
Operation
The computer room air conditioning unit runs continuously, but the dampers, or vents controlling the air flow through the unit, open and close depending on temperatures and schedules.
If the outside air temperature drops below 40°F, the outside air damper closes, the supply fan stops and the coil control valve opens. This prevents any water in the air (humidity) from freezing on the cooling coil and possibly damaging it.
The outside air damper will otherwise remain open during scheduled occupied hours.