Discussion on key issues of primary-secondary-tertiary pumping system design（1）—Head selection of pump and EC(H)R calculation

The primary-secondary-tertiary pumping system is divided into two types: decoupled system and non-decoupled system, according to the connection form between the user side branch pipe and the district distribution pipe. Based on the two system types, the number of differential pressure control points, and the relative position relationship between the differential pressure control point and the user side, classifies and determines the head selection of the secondary pump and the tertiary pump. Gives the actual calculation and selection results of seven cases for the non-decoupled primary-secondary-tertiary pumping system and proposes the key points for constant pressure design. Based on the determination method of pump head selection for the decoupled and non-decoupled systems, discusses the principle of loop selecting and pump head selection for calculating EC(H)R of the two type systems.