Energy-efficiency strategies and proper siting can increase the effectiveness of solar pool heating systems or sometimes make them unnecessary.
Solar pool heating (SPH) is cost-effective for extending the swimming season and increasing comfort in outdoor swimming pools. But, as with any heating system, addressing energy losses first will maximize the system’s efficacy and performance, and provide additional savings.
Pools themselves are solar collectors. According to NREL’s Conserving Energy and Heating Your Swimming Pool with Solar Energy, between 75% and 85% of the sun’s energy that strikes a pool’s surface is converted to heat energy. Many seasonal pool owners capitalize on this and use their pools without supplemental heat. In hot climates, pools may need shade to prevent overheating.
The best opportunity to reduce a pool’s energy use is proper siting. The pool should be placed in an area that maximizes the solar gain when it is most needed. In climates with a short swimming season, such as those in northern areas, it is best for the pool to receive unimpeded sunlight from 8 a.m. to 4 p.m. during summer. In hot climates, it can work out best to site for maximum passive gain during the spring and fall, when the pool’s heat loss is more significant.
Shading assessment tools can be used to find the best pool siting. Tools like the Solar Pathfinder ($259) or SunEye (starting at $1,995) can assist with this task. A smartphone application that costs $20 to $40 (such as Comoving Magnetics Solar Shading application for Android and Solmetric’s iPV application for iPhone) can provide sufficient information for pool siting.
Pools are often sited for aesthetics and accessibility, which may limit opportunities for energy efficiency. While an aboveground pool could be relocated if there is a more appropriate location, in-ground pools do not have such luxury. Instead, tree removal may be the only option for increasing an existing in-ground pool’s passive solar gain.
Heat can flow into and out of a pool through conduction, evaporation, convection, and radiation. If there is a difference in temperature between the pool water and the earth (for an in-ground pool) or the air (for an aboveground pool), heat will flow through the pool walls. As pool water evaporates, heat is lost from the pool. Additionally, wind blowing across the pool’s surface can extract heat through convection and the surface of the pool will radiate heat to a colder sky.
Climate has a significant impact on a pool’s heat loss. For example, evaporation is more pronounced in dry climates. Areas with clear, cold nights will experience increased radiation from the pool surface. At higher latitudes, the earth’s cooler temperature will lead to greater heat loss through the walls of an in-ground pool.
Conduction through pool walls. In typical situations, the desired pool temperature ranges from 78°F to 82°F. Therapy pools are warmer, between 92°F and 94°F. Since there is often a temperature difference between the pool water and the surrounding earth or air, heat is transferred through the pool walls.