The benefits of parallel pumping and how cost-effective and efficient it can be for a wide variety of applications. Yet, for some reason, the benefits of parallel pumping seem to be known mainly for large flow rate applications such as chilled water distribution systems. This is unfortunate because there are many benefits to be realized for the “smaller” applications as well.
In fact, once you look closely at parallel pumping and how to apply it properly, you will find that you don’t need to use bigger in-line or base-mounted pumps as often because two smaller pumps in parallel will handle the job just as well. Not to mention that if you get stuck in a jam and cannot find the big pump you need to do the job; by applying parallel pumping you will be able to use two smaller stock pumps.
Here are some ‘refresher’ truths about parallel pumping:
For any given discharge head, flows for parallel pumps are additive
The system flow rate will be determined by the intersection of the system-head curve and the performance curve of the parallel pumps
Pumps of different hydraulic characteristics may be operated in parallel to the extent that they share common discharge head characteristics
Pumps of different hydraulic characteristics may encounter severe problems when operated in parallel
All pumps have different hydraulic characteristics
To produce flow, a pump must generate a greater discharge pressure at start-up than the pressure already present in the system
When two pumps are better than one
As you know, parallel pumping involves installing two circulating pumps in a piping system in parallel with each other. When selected properly, each circulator will pump half of the total required flow rate at the design head loss. This means that each pump is capable of pumping half of the gallons per minute needed at the total designed pressure drop for an application.
Why Bother With Parallel Pumps?
Using parallel pumps can be beneficial because installation often costs less to buy, install, and maintain compared to a single large pump
Takes less space in the equipment room (especially if one utilizes in-line pumps that may be stacked)
Uses less energy
Provides better than 50 percent flow redundancy during single pump operation
However, small systems or systems that rarely change flow may not be good candidates for parallel pumps. Of course, if the system requires 100 percent redundancy, the designer must provide a single pump system with another 100 percent standby pump.