How to improve energy efficiency in a pool system

Filter flow rates

Pool filters are rated with a maximum designed flow rate which should not be exceeded. Doing so can cause failure of the filter’s internal components, as well as poor water filtration. The pump’s flow rate needs to be less than the maximum design flow rate for the filter. Many new pumps can easily output enough water to exceed designed flow rates for pool filters, especially sand filters. Cartridge filters are much more capable of handling higher flow rates due to the lack of a multi-port valve, which can be a significant restriction to flow.

Improving flow rates on existing systems

There are many pump and filter combinations that can work on a given pool with the pipe size being a limiting factor. A pump and filter installation that can meet the turnover requirement for the pool, while not exceeding 1.8 m/s (6 fps) velocity, or the maximum design flow rate for the filter, is ideal. This is the reason why two-speed and variable-speed pumps provide such improved efficiency over single-speed pumps. The same can be said as to why more horsepower is not any better, either.  For existing systems struggling to meet the pool’s circulation and filtration demands, the following changes should be considered:

• Re-plumb the equipment pad entirely using 51-mm (2-in.) pipe. This will reduce velocity as water travels through the highest concentration of flow restrictions. Even if the system uses 38-mm (1.5-in.) plumbing lines underground, reducing the water velocity through the equipment pad will have a net positive change on friction loss in the system.
• Allow for an absolute minimum of five times the pipe diameter in a straight run directly into the suction port and out of the pressure side of the pump. Elbow fittings directly into the suction side of the pump should be re-plumbed wherever possible.
• Replace all sharp bend (i.e. street elbow) fittings with sweep elbow fittings. Each sharp-bend elbow is a significant flow restriction and should seldom be used. Any interior fit-barbed fittings on the equipment pad should be replaced with glued slip connections where possible.
• Replace single-speed pumps with variable-speed pumps to allow greater control over flow rates and to experience a marked increase in system efficiency and electrical savings.
• Replace small/older sand filters with cartridge filters that are better suited to accommodate the flow rates provided by powerful pumps. This is especially important when a system has been retrofitted with a pump larger than the filter is rated to handle.

In the field it will not always be possible to meet ideal installation requirements. Still, it is important to understand the limitations of plumbing size, the nature of how friction loss reduces efficiency, and how to minimize these losses by removing unnecessary restrictions to flow. Understanding these principles will not only help to ensure pool equipment is sized correctly, but also has the ability to keep the water clear. Further, it will also be installed in such a way as to get the maximum efficiency and service life out of each system component.

Steve Goodale is a second-generation pool and spa expert from Oakville, Ont. In addition to owning Green Pools and A Better Pool Company, Goodale is also a web developer and author of www.swimmingpoolsteve.com. He can be reached at swimmingpoolsteve@gmail.com.