Geothermal pool and water heating saves energy and increases efficiency

Have you stopped to notice all of the heat sources in your client’s’ homes and businesses? Things like desktop and laptop computers, appliances, lights and people all create heat and are a potential source of energy that can provide domestic hot water and can be used to heat spas and pools. With standard air-source air conditioners and heat pumps, all of the heat generated inside homes and commercial buildings typically goes up though the return air ductwork and is ultimately exhausted to the outdoors. 

You probably already know that geothermal heat pumps (GHPs) are the most efficient heating and cooling systems available. Here’s a big benefit of GHPs that you might not have thought about; because GHPs are “water-sourced,” they conduct all of the heat that is being pulled from your home inside a 1-inch liquid line. You can choose where you want that heat to be placed. It can go back into the cooler Earth, which is typically the way GHP systems are designed, or with a little modification, that heat can be transferred directly into a pool or spa. This is great news for plumbing professionals.  

﷯Take a look at the illustration, and you can easily see how amazing the benefits of reusing heat energy can be for you. For any who are not quite up to speed on geothermal technologies here’s a little refresher.

Outdoor temperatures fluctuate with the changing seasons, but underground temperatures don’t change as dramatically, thanks to the mass and insulating properties of the earth. Remember that Earth is a big solar collector, and stores solar-thermal energy. Four to six feet below ground, temperatures remain relatively constant year-round. A geothermal system, which typically consists of an indoor handling unit and a buried system of pipes, called an earth loop, and/or a pump to reinjection well, capitalizes on these constant temperatures to provide “free” energy. As a matter of fact, governments worldwide are making the switch to GHPs in order to eliminate the CO2 emissions that come from combustion heating. Geothermal replaces combustion heating and related emissions with renewable solar energy, pumped from the earth. 

﷯With some minor modifications, the waste heat from appliances and devices in the home can be channeled into usable heat for domestic hot water (DHW), swimming pools and spas. Let’s look at the different ways a pool is normally heated; fossil fuel (combustion heating), electric resistance, solar or a heat pump (either “air-sourced” or “geothermal-sourced”). Fossil fuel or combustion heating of potable water, pools and spas is an old favorite. First cost is relatively low, but that comes at a higher price environmentally and monetarily as you move forward (due to high CO2 emissions).  

The most energy-efficient and renewable source for potable water and pool heating is solar-thermal, but direct solar-thermal heating is dependent upon the cooperation of the weather. Cloudy and cool days can mean a cold pool, and may require need for backup heating sources much of the year. 

Electric resistance heating uses straight electricity through electrodes or heating elements over which the water passes, providing a clean and safe water heating alternative, but electric resistance can use a lot of electricity. Using the Coefficient of Performance (COP) rating system for heating equipment, electric heating has a COP of 1.0, meaning that 1 unit of heat is provided for each unit of electricity, a one-to-one ratio, or 100 percent efficient in the COP rating system. This is a little bit heavy on calculations; for those that like this kind of thing take a look at figures 4 and 5. It also gives a primer on Energy Efficiency Ratings (EERs) for cooling. 

Air-source heat pumps designed for pool and potable water heating use outside air, pumping heat out of the ambient air into your pool or hot water tank. However, they too rely somewhat on cooperative weather conditions; that is, air temperatures need to be warm enough to facilitate efficient extraction of heat to transfer to potable water and/or pool heating needs. Air-source heat pump (AHP) efficiencies are in the 3.0 COP ranges (300 percent efficient) when the outdoor air temperature is above freezing. If the temperature is much below freezing, AHPs don’t function.

For swimming pool and spa heating, the best scenario is attained with a geothermal heat pump, pulling heat from a dependable, steady and renewable energy source; the solar energy stored in the earth. Geothermalheat pumps (GHPs) can have a 5.0 COP (500 percent efficient) or more. While you’re paying for electricity to run your cooling system, you are also providing for the energy to run computers, lighting, blow dryers, ovens and domestic water heating. Your home’s cooling system must use electrical power to remove the heat created by all of these internal gains on top of the occupant loads. You end up paying for energy twice to remove this waste heat through the process of cooling your house. Going back to the first thought in this article, why not channel that heat somewhere else where it’s needed, like your pool, spa or DHW tank? 

There are tens of thousands of geothermal heated pools around in the U.S. There is a good chance that the local YMCA, hotel, health club or community pool near you already has geothermal-sourced pool heating. Surprisingly, many of these still have air-sourced cooling systems that could be converted to geothermal (and likely will be) during the normal course of HVAC equipment attrition and upgrade (another opportunity for income for plumbing and heating contractors).

Why not share with your friends and neighbors how they can stop paying two and three times to move energy, and share the loads in their homes and businesses; show them how you can help them to enjoy the savings of thermal load sharing with a geothermal HVAC system. n

Jay Egg is a geothermal consultant, writer and the owner of EggGeothermal. He has co-authored two textbooks on geothermal HVAC systems published by McGraw-Hill Professional. He can be reached at

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