By reducing the approach temperature between water and refrigerant, compression pressure differential can also be reduced. One way to effectively increase evaporation temperatures is to install a chilled water reset. This type of control will allow chilled water temperature to climb when less load is present. Table 2 summarizes the effect of reducing head pressure or increasing suction pressure to the COP of the compressor. As seen from Table 1, all compressors are not created equal.
Some compressors operate better than others when only partly loaded.
Reciprocating compressors generally operate better when partly loaded while screw compressors operate best under fully-loaded conditions.