In some applications, a number of units are not needed and a mechanical center is not called for. Then an outdoor condensing unit is used (see Figure 8-21). These units come as a factory package. They are easily hooked up with the refrigeration unit inside the store or office or factory. They may be located on the roof or on a slab outside the building they are serving. Possible loss of head-pressure control (caused by the wind) is prevented by enclosing the underside of the unit.
It has been generally believed that it is necessary to artificially maintain summer-like conditions on the condenser of refrigeration systems. This was because a large pressure difference had to exist between the high and low sides. It has been found, however, that if adequate measures are taken to ensure a solid column of liquid refrigerant to the expansion valves of cases located inside the building, no problems will be experienced. The advantage is in lowering the condenser temperature. This makes the compressor run more efficiently, saving on energy costs.
Liquid lines exposed to temperatures above 60◦F (15.6◦C) must be insulated. This also applies to any lines that run overhead and to some lines close to the floor.