Swimming Pool Energy Efficiency

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Inside this Article

Shading your pool to prevent overheating
In hot climates, shading your pool to prevent overheating from solar gain can be an effective passive strategy.
Siting the pool to receive as much sunshine as possible
In cooler climates, siting the pool to receive as much sunshine as possible will help maintain a more comfortable water temperature.
Above-ground pools may incur more heat loss
In cooler climates, above-ground pools may incur more heat loss through the pool walls compared to their in-ground counterparts.
Opaque pool cover
Opaque covers reduce heat loss and algae growth, but can reduce or eliminate solar heat gain.
Translucent solar pool cover
Translucent solar pool covers have bubble insulation to reduce heat loss, but can still admit solar gain.
Solar rings
Solar rings are touted as being easier to handle than a blanket cover, but can leave 25% to 30% of the pool’s surface uncovered.
Liquid pool cover
Liquid pool covers provide a very thin layer of solution that floats on the water’s surface to reduce evaporation.
Variable-speed pump
Variable-speed pumps are very energy-efficient and have built-in controllers for ease of function.
Shading your pool to prevent overheating
Siting the pool to receive as much sunshine as possible
Above-ground pools may incur more heat loss
Opaque pool cover
Translucent solar pool cover
Solar rings
Liquid pool cover
Variable-speed pump

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.

Siting

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.

Modes of Heat Transfer

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.

Comments (6)

Fred Golden's picture

By installing 3" supply and return lines to the pump instead of 1.5" or 2" lines, you can reduce the friction loss in the piping, and thus get the same flow with less feet of head pressure loss. Also increasing the filter square feet of surface area, the pressure drop across the filter becomes less and flow will increase.

To maintain water flow through a solar pool heater, it is more energy efficient to install a small pressure booster pump to run only in the daylight hours, instead of sizing the pool filter pump larger and then pushing water thought the heater when it might be colder than the pool water.

Changing from a 100 watt incandescent light to a low voltage LED pool light will also offer savings you can count on.

Jason Szumlanski's picture

"In Florida, a pool pump with a capacity greater than 1 hp must be multi- or variable-speed."

Per the Florida Building Code: Energy Efficiency, it is actually pumps greater than 0.75 HP that must be multi- or variable speed, and they must have controls that are capable of operating the pump at multiple speeds. We see a lot of pool builders designing pools to have very efficient flow now so they can get away with a 3/4 HP pump and reduce their proposed prices. That's great, but in some cases it makes solar pool heating a bit less efficient if the flow isn't sufficient. That's exactly why we switched to a very low resistance panel that works better with smaller and variable speed pumps.

Also, it was mentioned that variable speed pumps are more efficient than multi-speed pumps. It's important to note that this is not only because of the much more granular control over pump speed, but the inherently more efficient brushless motors found in pumps with variable frequency drives. This alone accounts for about 30% energy savings at the same flow rate as a single speed or two-speed pump. Sometimes pool features and heating sources require a certain flow rate for effective operation, so slowing the pump down is not a great option, but using an inherently more efficient pump is.

Fred Golden's picture

Tom M

Most of the heat loss is actually from water evaporation. Wind blowing across the pool can cause significant heat loss. Each pound of water lost through evaporation is 1,088 Btu's of heat loss.

Heat loss into the ground with little delta T is not nearly as much. If your local ground temperature is 55F, that is only 20F to 30F delta T. The ground next to the pool will eventually warm to about 70F, further dropping the delta T. When in a northern climate, where local ground temperatures can be below 45, that can increase the heat loss into the ground a bit.

Tom M's picture

Though the article mentions heat loss through the earth it does not mention that insulating this area is a big plus for keeping heat in a pool especially since this is 4/5 of the surface area through which heat can be loss and is usually the most overlooked.

Jason Szumlanski's picture

Your math is a little off. The surface area of a pool exposed to ground (the walls of the pool) is closer to 2/3 of the area. For example, for a 15x30 pool that is 5 feet average depth, the surface exposed to air is 450 sq ft and the surface exposed to ground is 900 sq ft.

But that doesn't really matter. Even though the ground exposure is double the air exposure, the evaporation will have a far, far greater effect on heat loss. The air will conduct a lot more heat away than the ground, especially in windy conditions. Ground loss is effectively ignored when sizing a solar pool heater. Sizing rules of thumb are done using the surface area without much respect to the volume of water or relative exposure to the ground.

Fred Golden's picture

Several municipal pools have started replacing the standard 1,000,000 Btu gas fired boilers with heat pumps. Heat pumps can be very cost effective in cooling the building as well as heating the pool. Some dedicated heat pumps look like the outside unit of a split heat pump, and only are used to warm the pool water, not providing cooling to the building. Others are combination heat pump and dehumidifier that both can cool the building as well as heat the water.

A 2-3 ton capacity heat pump can provide heat at a very cost competitive rate compared to a gas fired boiler - with todays high fuel costs. If the cool air from the heat pump can be used to cool a building, all the better!

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