Refrigeration Controls
Refrigeration and air conditioning systems are essentially the same in that they both involve removing heat from the surrounding air. The differences that occur are in the amount of heat removed and the operating environment. Air conditioning systems operate at a higher temperature and are used for comfort cooling and humidity control. They generally operate only in the warmer months and the condenser units are located outside the structure being cooled.
Refrigeration systems are intended to produce colder temperatures and generally operate through- out the year. Some are intended to produce temperatures that range from 35°F to 45°F for food storage and others produce temperatures of 0°F or lower for hard freezing. Probably the greatest difference between air conditioning and refrigeration, as far as controls are concerned, lies in the fact that refrigeration systems operate at lower temperatures and must employ some method for defrosting the evaporator.
Many refrigeration systems, such as open freezers in supermarkets, are intended to operate inside an air conditioned building. It is this operating environment that can create some special problems. The cold ambient air temperature in winter or the cool air inside an air conditioned building can cause the compressor head pressure to drop below a point such that the pressure differential between the high and low side of the system is insufficient for the unit to operate efficiently. When this is the case, some method must be employed to raise the temperature of the condenser and permit the compressor head pressure to increase. Some common ways of accomplishing this are fan cycle control, shutters, and condenser flooding. Refrigeration and air conditioning units that employ water-cooled condensers control the flow of cooling water to maintain head pressure.