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

Heat pumps have been manufactured for swimming pool usage since 1977. The market has seen significant growth recently with the increase in costs of natural gas and propane gas. At the 2008 World Aquatic Health Conference, research was presented on the energy-saving advantages of heat pumps, comparing three regions of the U.S. with three different size pools, with and without a pool blanket. The results were overwhelmingly positive, affirming that existing pools can become more efficient and environmentally friendly with conversion to heat-pump technology. One study included a 100,000-gallon pool in Oklahoma. This outdoor pool operated for eight months. Based on a natural gas cost per therm of $3 and electric kilowatt-hour rate of 11, the annual heating cost dropped from $50,900 to $6,985 by switching from gas to a heat pump. With a pool blanket, the savings were greater than 50 percent. It is important to note this research was completed in 2008; since that time, the price of natural gas has escalated.

Many heating manufacturers now offer energy-saving calculators on their Web sites so management can immediately see the energy-efficiency results of changing from gas to heat-pump technology.

Air-To-Air Technology

The use of air-source heat pumps is advancing in even cooler climates. These heat pumps do not burn energy to create heat; rather, the energy is only utilized to transfer heat from outside air to pool water. An air-source heat pump is actually a proactive collector of solar heat from ambient air. This is called air-to-air technology. The design is based on efficiency, which is denoted by the Coefficient of Performance (C.O.P.). The formula is the ratio of usable output to energy input. For example, a C.O.P. of 5.0 means that for every $1 of energy input, the pool will gain $5 in heat. The C.O.P. varies based on air temperature, humidity and pool-water temperature. Since the nomenclature between heat-pump manufacturers is different, Air-Conditioning, Heating and Refrigeration Institute testing standards were developed so all swimming-pool heat pumps meet specific standards. All testing is done with equal environmental parameters: water temperature of 80 F, relative humidity of 63 percent and air temperature of 50 F.

Protecting The Ozone Layer

Effective January 1, 2010, in accordance with Environmental Protection Agency (EPA) requirements, all heat-pump manufacturers are utilizing R410A (hydroflorocarbon) refrigerant. No more chlorodifluoromethane R-22 gas can be installed in new heat pumps. R410A refrigerant is a “near-azeotropic, homogeneous mix” that does not deplete the ozone layer.

Water-To-Water Technology

In an effort to utilize renewable energy to its fullest, geothermal or geosource heat pumps are being designed for pool heating and are considered the most environmentally friendly. In a water-source heat pump--also called water-to-water technology--the energy is generated by heat in the earth, and the absorbed heat is collected from underground. Geothermal heat pumps can also extract heat from ground wells, earth loops, surface water or cooling towers. It may sound simple; however, retrofitting to a water-source heat pump requires specific engineering technologies to recover the heat from the water source. Engineering water-source heat-pump technologies have now tapped into HVAC systems to combine energy efficiency for the entire facility. Combining facility cooling and transferring the heat to the pool is gaining attention as the most environmentally friendly application of water-source heating.

Looking Ahead

Heat is naturally abundant from the sun as well as within the earth. It is inexhaustible and renewable. Advanced technologies are underway to capture this abundance and divert it to heat aquatic facilities. It just makes sense to merge these resources to provide cleaner, greener facilities. Combining the use of the sun’s rays with the air and water heat will provide a pool-heating system that has a much cleaner source of comfort for bathers, as well as an environmentally sound technology to meet the future aquatic facility sustainability initiatives.

Connie Sue Centrella is a professor and Program Director for the online Aquatic Engineering Program at Keiser University eCampus. She is a four-time recipient of the Evelyn C. Keiser Teaching Excellence Award “Instructor of Distinction.” Centrella is an industry veteran with over 40 years experience in the pool and spa industry. She is a former pool builder with extensive knowledge in pool construction and equipment installation as well as manufacturing.