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A windbreak around the pool can also reduce evaporation, and make pool "lounging" more comfortable and private. A 7-mph wind at the pool surface can increase heat loss by 300 percent. A windbreak could include a fence or vegetation. It needs to be high and close enough to the pool so that it effectively blocks wind from moving across the pool surface, but doesn't block beneficial solar energy.

Heating the Pool Efficiently: If you are selecting a pool heater, ask for as energy efficient model as you can afford. Several heat pump manufacturers make retrofit desuperheater coils for pool heating, and several make heat pumps for pool heating. These may be cost effective relative to natural gas heaters.

Besides that, the easiest way to save energy is to lower the thermostat on your pool's heater so that it heats the pool no higher than the temperature that you feel comfortable with. Every 1 degree reduction can cut your energy usage by between 5 and 10 percent. Once you have lowered the thermostat, keep the remaining heat from escaping by using a pool cover when the pool is not in use.

Solar Pool Heaters: If you have taken steps to retain your pool's heat but are still not happy with your heating bills, or if you plan to install a new pool, a solar pool heater may be a good investment. Such heating systems are one of the most cost-effective applications of solar energy. It is relatively simple to integrate a solar water heater since most pools require a pump, filter, and plumbing. With a solar energy system, the pool's water is pumped through the filter and then through a solar energy collector(s) instead of directly back to the pool. The sun heats the water in the collector(s) before it returns to the pool.

If you add a solar heater, you may need a pump larger than your present one, or a separate, smaller pump to pump the pool's water to and through the solar collectors. Adding any heater, solar or otherwise, will preclude selecting the smallest pump. Nevertheless, you also may reduce pumping time to help cut costs.

Unlike solar domestic water heating systems, which raise a small amount of water to a high temperature of about 140°F, pool heaters raise the temperature of several thousand gallons of water to about 80°F by circulating the water at a relatively fast rate through the collectors. This allows most of the solar energy falling on the collectors to transfer to the pool water.

Solar energy not only can be used for heating residential pools but also for larger commercial and public pools. One such application is the International Swim Center in Santa Clara, California. Heaters using solar energy heat three pools-a 50-meter racing pool, a 25-yard and 17-foot deep diving well, and a 25-yard training pool. Nearly 13,000 square feet of flat-plate collectors heat 1.2 million gallons of water. Since the project was completed in February 1979, solar energy has been providing 60 percent of the energy required to heat the pools. The pool used for the 1996 Summer Olympics in Atlanta is heated with solar energy as well.

Solar collectors can also be used to cool the pool in hot climates or during peak summer months by circulating the water through the collectors at night. The collectors lose heat by radiation to the night sky.

Solar Pool Collectors: Collectors for heating a pool normally do not require glazing or insulation because they operate during warmer months when solar radiation and ambient temperatures are relatively high. This allows for a simpler design that is usually less expensive than collectors for domestic hot water. Many pool collectors are made of heavy-duty rubber or plastic treated with a UV light inhibitor to extend the life of the panels. The advantages of plastic collectors are that they're usually less expensive and weigh less than metal collectors.

Metal collectors generally are made of copper tubing mounted on an aluminum plate. The advantage of glazed metal collectors is that they are more efficient at capturing the sun's heat on colder days. Swimming pools that require heat on a year-round basis, especially in colder climates, may be best suited for this type of system. Both glazed metal and unglazed plastic panel systems should include freeze protection if they'll be used in colder conditions.

The area needed for collectors to heat your pool depends on many factors. A general rule of thumb is that the collector surface area should equal at least one half of the pool's surface area. In a relatively sunny climate, this additional heating helps extend the swimming season into spring and autumn. In cooler and cloudier areas, you may need to increase the collectors surface area to equal the entire surface area of the pool.

Collectors can be mounted on roofs or anywhere near the pool that provides the proper exposure, orientation, and tilt toward the sun. The optimum collector orientation is south, but west-facing orientations are good if the collectors surface area is increased to at least 75 percent of the pool's surface area. East-facing orientations are marginally good. The tilt of the collector is as important as the orientation. For heating primarily in the summer, the tilt should equal the latitude where the pool is located minus 10 to 15 degrees. Where optimizing the tilt is not possible, for example on an existing roof with a high slope or on a flat roof, increasing the collector area may be necessary to achieve the desired pool temperature.

One potential benefit of roof installation is that it may reduce the cooling load of the building that it's located on, since it puts the solar heat into the pool water and keeps it from radiating into the attic and the conditioned space below.

There is a company that makes a heat exchanger, which is placed in the attic, for heating pool water. This "collector" absorbs heat that builds up in the attic and transfers it to the pool water.

Because swimming pools include a pump and related plumbing, adding on a solar heater can be relatively simple. Unless you have experience with plumbing and electrical wiring, however, have a professional install your system. Often the pump circulates the pool water enough, but be sure it maintains a high flow rate to keep the panels operating at optimal efficiency. Your collector should require little maintenance if the pool's chemical balance and filtering system are checked regularly.

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Figure 120: Roof-mounted solar collectors are used to heat this pool, reducing energy costs.

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