Talking About Green

Installing a swimming pool is a big investment. Consequently, anything you can do to extend your enjoyment of the pool is appealing. That’s why so many pools are heated. The only problem is the expense. In many parts of the country, the cost of heating a pool with a conventional heater can be several times the cost of heating the house. There are two cost-effective alternatives to conventional pool heaters: solar pool covers and solar thermal pool heating system.

Regardless of the pool type, conservation should be your first step since it will reduce the size of the solar system required to keep the pool comfortable. They include planting low shrubs around the pool perimeter to reduce pool water evaporation and the heat loss that goes with it, and cutting away tree limbs that shade the pool. If you’re building a pool, choose a sunny but protected site.

A passive approach: solar pool covers

Sun shining on a pool’s surface will heat up the water, but when the sun goes down much of that heat will be lost. One remedy is a solar pool cover, also called a pool blanket or solar cover. A pool blanket helps to retain heat that would otherwise be lost to radiation, convection, and evaporation. Even in cool climates, a cover will extend the swimming season by four to six weeks. And because they reduce evaporation, pool blankets also reduce the need for make-up water by 30% to 50% and cut consumption of pool chemicals by 35% to 60%, according to the U.S. Department of Energy. To be effective, the blanket should fit tightly at the pool’s perimeter.

Pool blankets are available in several types, including bubble, vinyl, and insulated vinyl. Vinyl is the preferred choice because it can be used all year and its operation can be automated, helping to ensure its use.  As a bonus, they make your pool safer when it’s not in use. When secured by tracks along the sides of the pool or to the pool decking, a vinyl cover can easily support the weight of a person.

Solar thermal pool heating

Solar thermal pool heating systems have a proven track record of over 40 years and are a low-cost way to heat a pool. Like solar domestic water heating systems, they use liquid-cooled collectors (collectors that transfer heat to a liquid) to heat water or glycol. But instead of storing the captured heat in a tank, the swimming pool itself stores the heat. The collectors are usually unglazed and made of a lightweight, durable polymer. In many cases, pool water is circulated directly through the collectors, and no antifreeze or heat exchanger is needed.

Solar systems for above-ground pools

Solar thermal pool heating systems for above-ground pools are generally quite simple, relatively inexpensive, and are often designed for do-it-yourself installation. A typical system for an 18-ft. to 24-ft. diameter above-ground pool consists of two or three flexible 4-ft. by 20-ft. unglazed solar panels that connect to the filter pump with flexible hoses and hose clamps. The panels typically rest directly on the ground beside the pool. Before the first frost, the panels must be drained or blown out with compressed air, rolled up, and stored in the basement or the garage.

The pool’s existing filter pump is typically sufficient for circulating water between two or three collectors and the pool. A manual bypass (diverting) valve allows the homeowner to bypass the solar array when the pool water is too warm. In general, pool water should pass through the collectors when the array is in the sun. If the filter pump is running at night, or when it is raining or the pool water is too warm, then the pool water should bypass the solar collectors. Passing pool water through the collectors at night will cool the pool.

Solar systems for in-ground pools

Solar thermal systems for in-ground pools are more elaborate but similar in concept to those for above-ground pools. The pool filter pump draws water from the pool, usually from the skimmers, forces it through the filter, and then through an array of unglazed liquid-cooled solar collectors. From the collectors, the sun-heated water returns to the pool water return pipe and from there flows to the pool supply jets.

When compared to collectors for outdoor above-ground solar pool heating, collectors for outdoor in-ground systems tend to be more substantial, larger in area, and permanently mounted to a roof- or ground-mounted frame. Collectors are designed so they can be connected in parallel flow arrangement rather than in series. Where the piping runs above grade, rigid plastic piping connects the filter outlet to the array rather than the flexible tubing used for above ground pools. Piping runs below grade are usually made with flexible polyethylene tubing, similar to that used for well water lines.

Plumbing for an in-ground pool is more involved than for an above-ground pool. Because the collectors and piping may be subject to freezing temperatures, the array and piping must be pitched so they can be easily drained at the end of the season.

Although a separate collector loop pump is not required for solar heating outdoor in-ground pools, the filter pump must have sufficient capacity to lift the water from the poolto the top of the solar array. In retrofit situations, if the array is only one story above the pool water, the existing filter pump may be able to do that. If the solar array is higher than one story, the existing pump may need to be replaced.

Solar collectors can be used in conjunction with an existing pool heater. The solar system should be plumbed as a pre-heater. In most cases where solar pool heating systems have been added, homeowners soon stop using the conventional heater and eventually have it removed.

Joe Provey is the co-author of Convert Your Home to Solar Energy (Taunton), from which this article was adapted. He lives in Bridgeport, CT where Long Island Sound serves as his swimming pool. Joe also writes for Dr. Energy Saver, an energy efficiency company that provides customers with affordable home energy audits.

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