Solar Pool Heating
Solar pool heaters are the simplest and least expensive solar water-heating systems to install and use in a home. The only components needed are solar collectors and some additional valves and piping. Solar heating systems make use of the pump and filter already needed for pool operations.
Solar collectors, typically mounted on the home's roof, absorb heat from the sun. The pool pump pulls water from the pool and forces it through the pool filters, a pressure-relief valve, a check valve, a bypass valve and then through the solar collectors for heating. Once heated, the water flows through piping to the chlorinator (if used) and back into the pool. The solar collectors raise the temperature of the pool water 5 to 10 degrees Fahrenheit between the inlet and the outlet of the collector. The collector transfers most of the solar energy that strikes it to the water, often operating at 80 percent efficiency or higher. The series of valves added for a solar pool-heating system is important, too. The check valve prevents backflow of water from reentering the filter, and the bypass valve controls water flow to the solar collectors as needed when the pool reaches the appropriate temperature and when it needs servicing.
Various types of solar collectors are available for pool-heating systems. Site-specific factors, such as climate and the amount of space available for the collectors as well as the homeowner's preference, usually drive the choice of solar collector.
If a pool needs to be heated year-round and is located in a cold climate, the collectors need to be glazed—encased in a glass-covered insulated box—to prevent freezing. Glazed collector systems typically use an antifreeze solution and a heat exchanger to transfer heat to the pool water rather than heating the pool water directly. This setup is similar to that used for a solar domestic hot-water system, in which the water temperature needs to be raised a significant amount.
Most solar pool-heating systems use unglazed collectors, however, because the water temperature does not need to be raised a significant amount. The most popular unglazed collectors include rigid polypropylene panels, EPDM (ethylene propylene diene monomer) rubber mats, ABS (acrylonitrile butadiene styrene) pipes, and metal tube-on-sheet panels consisting of copper tubes on a copper or aluminum sheet.
Metal tube-on-sheet collectors conduct more heat per square foot of collector area than plastic or rubber collectors, but they are more expensive. When using copper collectors, monitor the pH level of the pool water carefully. If the water becomes too acidic (lower than 7.2 pH), the chlorine in the pool water will react with the copper pipe, causing the water to leave a dark film on the pool walls. Metal is more susceptible to freezing than plastic or rubber, although if properly maintained, metal collectors will last for 30 years or more.
Plastic and rubber solar collectors are more popular than metal collectors because they are less expensive per square foot. More are needed, however, because the thermal conductivity of plastic is lower than that of metal. Unlike metal collectors, plastic and rubber collectors are not susceptible to corrosion from pH variations in the pool water. The life expectancy of plastic and rubber collectors is 10 to 15 years as long as ultraviolet inhibitors have been added to the materials to prevent damage from the sun.