Application of VSD (Variable Speed Drive) in Chilled Water Pumps

This article describes the application of variable speed driver in chilled water pump

Primary pumps in a primary pumping can be used to maintain a constant flow through chillers that encounter operation or control difficulties when exposed to variable flow.

In chilled water systems, the primary loop consists of primary pumps sized to handle the chillers designed flow rate at a discharge pressure just high enough to circulate the water through the chiller and the rest of the primary piping loop. Chilled water loop is a variable flow system consists of pumps sized to circulate chilled water to handle full capacity of the cooling loads connected on the circuit. During light load condition, most of the two-port control valves on the loads are not fully open resulting in pressure rise in the chilled water loop. In a conventional system, a by-pass valve connected across the cooling loads will be used to by-pass the water flow and regulate the flow to loads and balance the water pressure in the system. A differential pressure sensor normally controls the by-pass valve.

The figure shows an arrangement of the primary chilled water circuit with VSD and by-pass valve for regulation chilled water flow according to the actual loading requirement. Energy saving is achieved in pump motors in most of the time when the cooling loads are not at full capacity and maximum chilled water flow is not required.