Trane TRG-TRC016-EN manual Control of Primary-Secondary System

period two

Chilled-Water System Design

notes

Control of Primary-Secondary System

condition	response
deficit flow for	start another
specified period of	chiller and pump
time
excess flow greater	turn off next chiller
than 110% to 115% of	and pump
next pump to turn off
neither	do nothing

Figure 62

Starting and stopping of pump-and-chiller pairs in a primary-secondary system depends on the direction and quantity of water flow in the bypass pipe.

nWhenever there is deficit flow through the bypass pipe for a specified period of time (typically 15 to 30 minutes in a comfort-cooling system), another pump-and-chiller pair started.

nWhenever there is excess flow through the bypass pipe that is greater than the flow being produced by the next pump-and-chiller pair to be turned off, that pump and chiller are turned off. To prevent short cycling as the result of a slight increase in load, the chiller-plant control system will typically allow excess flow of from 110 to 115 percent of the flow produced by the next production pump to be turned off.

nIf neither of the above conditions exist, no action is taken.

56 TRG-TRC016-EN