Parallel operation of variable speed pumps in chilled water systems
In the last two to three decades the cost of variable speed devices has come down considerably and their energy consumption has improved to the point that they no longer waste energy. Additionally, speed control of the circulating pumps in variable volume flow hydronic systems permits matching the head generated by the pumps to the frictional resistance to flow in the system. This will improve the operation of the control valves and save energy. In view of these advantages, the use of variable speed pumps has become widespread. Nevertheless, the speed control devices are costly, and the question arises whether all pumps in a given installation need be equipped with them. This article will explore the interaction between multiple speed pumps operating in parallel and their interface with the hydronic system they serve. It will specifically address two questions: can one pump be operated at varying speed in parallel with another pump at fixed speed? Also, what is the most economical method of applying variable speed pumping in a given chilled water system? It will be seen that the benefits to be gained from unequal speed operation of parallel pumps are minimal and the benefits are outweighed by the danger inherent in such operation. This practice must be discouraged. The study also will show that in a correctly engineered and analyzed system the number of parallel pumps can be reduced and that not all need be provided with speed control. However, all pumps in parallel operation must be run at the same speed.
- OSTI ID:
- 124481
- Journal Information:
- ASHRAE Journal, Vol. 37, Issue 10; Other Information: PBD: Oct 1995
- Country of Publication:
- United States
- Language:
- English
Similar Records
A simulation-based study on different control strategies for variable speed pump in distributed ground source heat pump systems
Using blending pumps to increase individual facility supply water temperatures and total system differential temperatures ({Delta}Ts)