Green Pumping Solutions for Energy-Efficient Water Circulation

Green Pumping Solutions

After chillers, water circulating pumps consume substantial plant energy. Use of modern devices for pump speed control has provided great opportunities to save energies consumed under this account. Traditionally, pumps are oversized to avoid failures. Additional pump head which is non existent in the system wastes energy. Constant volume of flow through system and equipment is no longer required. Volume flow can be varied saving pumping energy.

Electronics is being successfully utilized for pump speed control. Digital controls like variable frequency drives bring pump speed down to thirty percent of maximum speed. Reducing pump speed saves electric energy consumed by the pump.

Manufacturers of boilers and chillers have improved internal safeties to a level where they allow water flow rate through equipment to be reduced. When flow requirement in the system is reduced, water flow through equipment is also reduced to match with the loads. Pump VFD tracks system water flow requirement. It reduces speed and consequently water flow, according to actual demand in the building. Power of the pump varies as the cube of the pump speed. At reduced demand in the buildings, energies are proportionately reduced.

Pump impeller is trimmed when balancing valves are required to be partially closed during balancing of the pump. Closing balancing valves means putting additional pressure drop in the system. It is done to balance water flow, when pump is oversized. Trimming impeller under these conditions is energy efficient way of treating this issue. Pump impeller size is reduced one or two size smaller for the range of impeller sizes for same casing. During pump selection, it is better to use impeller size in the middle of the range offered by the manufacturer. This selection provides opportunity to go for larger or smaller size impellers during balancing, when required.

Pump fittings to isolate the pump from the system are selected for low pressure drops to save energy. Strainer at pump inlet is kept clean of debris and foreign materials. Pump suction line is selected larger than discharge line to keep flooded impeller. Sharp bends and undue restrictions in the suction line are avoided to prevent cavitation. Positive suction head is required for satisfactory operation of the centrifugal pumps. This is published for each model by the manufacturer. This suction head is always maintained during operation. Pump level can be lowered when suction head is not sufficient for open systems.