The function blocks “PmpFlowCalcHQ” and “PmpFlowCalcPQ” calculates the flow rate of pumps using the pump head flow (HQ) and pump pressure flow rate (PQ) curve characteristics respectively. These functions are applicable only for pumps run by variable frequency drives.

The flow calculation function provides a reasonably accurate calculation of the flow without the installation of a separate flow meter. The flow is calculated based on the pump characteristics. The user can define the PQ (Power vs Flow) or HQ (Head vs Flow) values for the performance curve at the inputs of the function block for the five coordinate points. The values of the PQ and HQ are generally provided by the pump manufacturer and all points defined must be within the operating range of the pump. These points are taken at the maximum operation speed and scaled down by the block according to the actual speed. By this method a good accuracy is achieved with limited parameterization effort.