The low capacity chiller is commanded first and stays commanded.
The next picture shows an example of a light load/peak load chiller application with 1 low capacity chiller and 4 high capacity chillers.
Fig. 3. Keep Low Capacity Chiller Enabled
The total number of stages to control all chillers is equal to
Number of stages = number of high capacity chillers + 1
(1 light load chiller). The total number of stages must be incremented by 1 if the chiller plant uses free cooling/ice storage.