Turn Up the Heat

In order for a sustainable swimming pool to use less energy and emit fewer pollutants, it requires a balancing act that harmonizes design, installation and environmental and operational considerations.

Energy conservation in new construction or renovation requires an understanding of hydraulics, while lower velocities, larger pipe diameter, larger filters and backwash valves are all critical when developing a plan.

Pool-heating efficiencies that are environmentally friendly require proficient technology to keep patrons happy.

Swimmers want a specific temperature for comfort–typically between 80 F and 84 F–while those who enjoy vertical exercise prefer the pool warmer–between 84 F and 86 F. Pool heating is traditionally the greatest expense for aquatic facilities and these will continue to face the challenge of maintaining a preferred temperature without prostrating their budgets. Thus, energy-efficient heaters are one way to make facilities more profitable, while keeping customers happy.

In both indoor and outdoor pools, maintaining the temperature depends on eliminating heat losses. There is much the aquatic director can do to manage costs and at the same time achieve a “greener” pool. Understanding advancements in swimming-pool heating helps management meet its goals.

Factors To Consider

The environment plays an important role in swimming-pool heating, and minimizing evaporation is necessary to conserve heat and energy. Relative humidity–defined as the amount of water vapor in the air–has a direct effect on evaporation and heating efficiency. When the air temperature is high, this gaseous mixture of air and water is low, and evaporation increases. Conversely, with high air temperatures and high relative humidity, evaporation is low.


Outdoor pool efficiency is influenced by wind, rain and ground temperatures. In addition, the heat of the sun and UV diffusion affect pool-water temperatures. Evaporation accounts for 50 percent of heat loss in pool environments; the more water lost to the atmosphere, the higher the heating costs based on the cooling effect of replacement (fill) water as well as night temperatures.

Indoor pools must control humidity and air temperatures to manage patron comfort and health, as well as to extend facility life. A healthy indoor environment should have a relative humidity of 40 to 60 percent and indoor air temperature of 2 to 5 degrees above the water temperature to reduce the chill factor. The ventilation system should have eight to 10 air exchanges per hour. With these parameters, evaporation can be minimized.

Heat-Pump Technology Gains Momentum

Heat pumps are gaining acceptance at aquatic facilities because they effectively meet clean-energy initiatives. Also called “proactive collectors of solar energy,” heat pumps use the naturally heated air or water and then transfer that heat to the pool. The only energy consumed is running the compressor and fan. No natural gas or propane gas is required to run the units, so no pollutants or carbon emissions are forced into the atmosphere. The only limitation is that heat pumps must be installed outdoors to obtain air for operation. Also, a heat pump does not heat as quickly as gas; however, once it heats up, the water temperature remains stable.

Research Reinforces Retrofits

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