Light Load/Peak Load Control

The low capacity chiller is commanded as light load chiller and as peak load chiller. The next figure shows an example of a typical light load/peak load chiller application with 1 low capacity chiller and 3 high capacity chillers. The low capacity chiller (light load) is started when there is a cooling demand. If the low capacity chiller is not able to cover the need for cooling demand, the low capacity chiller will be switched off and a higher capacity chiller will be started. If all higher capacity chillers are in operation and there is still a need for more cooling, the low capacity chiller is commanded again (peak load).

Fig. 1.   Light Load/ Peak Load Control

The total number of stages to control all chillers is equal to

Number of stages = number of high capacity chillers + 2

(1 light load chiller + 1 peak load chiller). The total number of stages must be incremented by 1 when the chiller plant uses free cooling/ ice storage.