In cooling systems that have fan coil units or similar devices with three-way valves, and therefore almost constant system characteristics, adjusting the pump performance based on the differential pressure will be impossible. In such systems, another control parameter must be used. The best choice is to control the circulator pump according to temperature. The return pipe temperature of the system signals changes in the system load. A decrease in the return pipe temperature (i.e., the temperature approaches the supply pipe temperature) indicates that a large amount of the circulated flow is bypassed in the control valves due to a reduced cooling demand in the system. In such situations, the circulated flow in the system should be reduced to lower the power consumption of the pump.
A differential temperature control could be used as an alternative to the constant temperature control of the return pipe temperature. The temperature control provided by the intelligent pump offers the same operational advantages as that of differential pressure control.
Intelligent Pumps and Three-Way Valves
September 1, 2008