Development of a virtual pump water flow meter with a flow rate function of motor power and pump head

Water flow rates are key operating variables in chilled and hot water systems. The water flow rate through a pump can be virtually measured using available motor power and pump head with projected motor and pump efficiencies. In general, motor efficiency is implicitly determined by motor power while pump efficiency is given as a function of water flow rate. As a result, the water flow rate has to be calculated through a numerical method, which is difficult to apply in building automation systems (BAS). The objective of this paper is to develop a virtual pump water flow meter, which can be implemented in BAS with an explicit expression of motor power and pump head. First, motor efficiency is regressed as a function of motor power by consolidating multiple dependent factors, then pump efficiency function is reconstructed with pump shaft power and head, and finally experiments are conducted to develop and validate a virtual pump water flow meter on a chilled water pump. The experimental results show that the virtual flow measurements agree well with the flow measurement by a physical meter. The measurement standard deviation is 0.5 L/s for a pump with the design flow rate of 37.9 L/s.