Balancing variable-flow circuits

Guidance for designers in harnessing the energy-saving potential of variable-speed pumps is available from SAV Valve Modules. Research by the authors of ‘Variable-volume pumping systems’ shows that most heating and chilled-water systems in the UK operate at peak demand only 10% of the time. Pumping less water at all other times can achieve major reductions in pump energy consumption. Because of the cube-law relationship between pump speed and energy consumption, annual pump-energy savings of 60 to 70% have been predicted. The key to exploiting the benefit of variable-speed pumps is to achieve thermal balance in a system. The solution is to use differential-pressure-control valves (DPCVs) to maintain a constant pressure difference between two points in a pipework system that are either side of a variable resistance. The SAV guide argues that rather than using one large DPCV per floor, it is more effective to have more smaller valves controlled by pump sensors close to the system extremities.