PRB Articles

New Heat Beneath Our Feet

High energy costs and environmental concerns are mobilizing the aquatic industry to engineer more efficient ways to heat pool facilities. While gas, electric, boiler and heat exchanger technologies are making strides to enhance their efficiency, it appears that geothermal and solar alternatives are gaining public support and financial stimulus incentives.

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 makes sense to tap into these resources to provide cleaner, greener facilities. Enhancing the aquatic facility with a renewable energy source does involve a cost, but the ability to capture the sun’s rays and earth’s water offers a substantial payback over the long run.

A Closer Look

Heat-pump use is gaining momentum at aquatic facilities because it effectively meets clean energy initiatives. Air-source heat pumps do not actually burn energy to create heat--they only use energy to transfer heat from the outside air to the pool water. Geothermal heat pumps extract heat from ground wells, earth loops, surface water or cooling towers. The energy is absorbed and collected from underground. With the utilization of a heat exchanger, the heat is transferred to the pool water. While this is not a fast heat--as one would gain from a traditional gas (fossil fuel) heating system--the heat from a geothermal heat pump is available year-round.

A noteworthy installation captured the interest of the geothermal industry with a hybrid geothermal system in Pensacola, Fla. Albert Barfield presented a beachfront HVAC system in the June 2008 issue of the American Society of Heating, Refrigerating and Air-Conditioning Engineers Journal, ( This heat-pump system combined the resources of the HVAC system in heating the pool and spa. At the historic Fontainebleau Hotel in Miami Beach, management recently retrofitted the heating and cooling system to incorporate the pool heat-pump system with the air-conditioning cooling towers. While some people may perceive that geothermal is only from inground waters, these two installations show the versatility of geothermal heat-pump systems for aquatic facilities and water parks--both indoor and outdoor.

The region of the country plays a major role in the viability of geothermal heat pumps. A case study, titled “Residential Swimming Pool Heating with Geothermal Heat Pump Systems,”(GHC Bulletin, 2004), by Andrew Chiasson of the P. E. Geo-Heat Center, stresses that cooler climates require additional ground loops because the air extracts heat from the earth; however, in warmer climates, the economic feasibility of payback is approximately five years. While this study was based on residential-pool installations, it is evident that those involved in public-pool green initiatives should review these findings. There is a caution that any geothermal heat-pump installation must be engineered prior to taking on such an expansive project; technologies must be specific when transferring heat from a water source. These specifics include the distance from the water source to the equipment room, desired temperatures, recovery of heat and piping requirements.

Identifying Source Water

To further explain the technology being implemented in the water-source heat-pump applications, there are four types of source water commonly available:

1. Open loop

2. Closed/group loops

3. Surface water

4. HVAC loops.

Open Loop

The majority of pool-heating applications utilize the open-loop design. This requires two wells--one to supply warm water to the heater and the other to return the water to the extraction depth in the ground. These must be “deep” wells, which are characterized by their reliability and longevity. Typically, the extraction point is within porous, rock-based soil.

Closed Loop

A closed-loop system uses heat from the ground as its source. This system is designed using piping filled with a mixture of water and glycol that absorbs the heat from the ground. The heat energy is then brought to the heat pump to be utilized as the heat-supply source. This is a highly specialized application, and only professionals versed in this type of engineering should install this system.

Surface Water

The third source of heat energy may be obtained from surface water--either a lake or pond near the aquatic facility that has been examined and approved for the water-to-refrigerant heat exchangers. The approved water source should be examined to eliminate any damage to the heat exchanger by organic materials that can clog the system. A variation of this system utilizes a closed-loop piping placed under the surface water (pond or lake) in an attempt to capture the heat beneath. In order to protect the heat-pump system, saltwater and coastal wells can be used if there is a secondary heat-exchanger system installed to prevent corrosion from the saltwater sources.

HVAC Loops

Recent applications--such as at the Fontainebleau in Miami--have used HVAC loops, which utilize the building’s existing cooling-tower system. The cooling towers are designed to “reject” the heat extracted from the building with the air-conditioning system. These loops will typically have a gas boiler connected to supply heat to the building in the winter months. Such types of heat sources are high-water pressure systems, and require specialized plumbing accommodations.

At low-temperature conditions, the equipment can freeze the heat exchanger, causing damage. Thus, whichever type of source water is selected, it is evident that special equipment-design considerations must be applied. The region of the country and the freeze line should be considered during the design phase of these systems. The benefits to the aquatic facility include a reduced operating cost, product longevity and reliability. This equipment is still in its infant stage in the aquatic industry, but green initiatives provide an alternate and reliable heating application.

Proof Positive

In the July issue of PRB, “Seeing Green.” written by Tammy York, demonstrates the acceptance of solar energy as an economic and environmentally friendly initiative to sustainable energy implementation. The efficiency of a solar system depends on how the sun reaches panels. Solar panels are designed to tilt based on the latitude of the pool’s geographic region. The panels should face south to achieve the strongest sun rays and maximum solar efficiency. While solar panels collect the heat during the day, the night hours tend to pull the pool heat from the water. A pool blanket covering the pool’s surface area will prevent heat loss.

A hybrid version utilizing solar energy with air/water-source heat pumps provides an excellent alternative to eliminating the carbon footprint in aquatic facilities, and is gaining acceptance. The advantage of combining solar with heat pumps is the continuous supply of heat.

Technological advancements in pool heating are evolving. The marriage of the sun’s rays with air- and water-heat will make for a pool-heating system that provides a much cleaner source of comfort for bathers as well as a greener environment.

Thanks to the engineering and design staff at AquaCal Heat Pumps for sharing their expertise in the development of this article.

Connie Sue Centrella is a professor and Program Director for the online Aquatic Engineering Program at Keiser University eCampus. She was twice-honored with 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.


What's Hogging All The Energy?

What's Hogging All The Energy?