Geothermal heaters are being called a ‘renewable heat source’ by the U.S. Department of Energy. This is the fastest growing segment in the heating industry. It’s becoming more popular for pool and spas worldwide.
Reviewing Heat-Pump Technology
In the pool industry a heat pump is simply a system that removes heat from a source. That source can be water or ground, and it transfers to pool or spa water. If we want to be technical, all refrigeration systems (refrigerators, water coolers, air conditioners) are heat pumps. All of these things move heat from one place it is not needed to another place where it is useful or can be wasted.
Heat pumps have the same technology as refrigeration and have the same basic components: a compressor, an evaporator heat exchanger, a condenser heat exchanger/coil, and a metering device that controls the flow through the system.
In a refrigerator, the compressor is the pump of the system. The pump moves refrigerant through the condenser, metering device, and the evaporator. The evaporator and condenser coil are heat exchangers. The evaporator is the location heat is absorbed by the refrigerant coming from the heat source. In the condenser, collected heat in the evaporator is rejected into the pool or spa water.
The design of the evaporator and condenser heat exchanger varies on what will be transferring heat to or from. If the heat source happens to be the air, the evaporator coil design is usually an aluminum copper tube design. This is what you would see in your home air conditioning system. Because the home air conditioning system transfers heat from air inside the home to air outside, the evaporator and condenser are very similar in design.
The air-source heat pump pool heater (commonly referred to as HPPH) uses a very similar coil design for its evaporator. With an HPPH, warm air is pulled across the aluminum copper tube heat exchanger by a fan. The heat is absorbed by the refrigerant flowing through the tubes. It uses a different type of condenser coil because it will reject the collected heat into the pool water. This specific condenser/heat exchanger is usually a tube inside of a plastic shell. In an HPPH warm refrigerant flows through a titanium tube which then travels through the plastic shell. It works by flowing pool or spa water through the plastic shell and over the titanium tube. It transfers heat from refrigerant to water.
This is known as ‘air to water’ refrigeration.
Now, back to geothermal pool heat pumps. They are refrigeration systems that have components to help the transfer of heat from a water source to a pool or spa. The water source can come from a well, lake, or even a closed-loop system of plumbing buried into the ground.
This type of heat system is gaining popularity because it is reliable. The ground temperatures and water temperatures are constant and stay much warmer than the air above ground.
If you have an air-source heat pump, heat is drawn from the outside air. If the air cools, there is less and less heat available. the efficiency rate (COP) falls with decreasing air temperatures.
Geothermal (water to water systems) depend entirely on a more stable source- water. Fluctuations in temperatures in lakes, rivers, or ground loops are much more stable. If you have a properly designed heat pump, you can have very efficient and reliable operation with a very small amount of variability.
Proper sizing of the geothermal HPPH is important and will need to be fitted according to the pool size.
A geothermal heat pump is about the same cost per Btu as an air source. If you choose to go with a ground-loop water supply it will be an added expense. However, with the extra reliability and efficiency from a geothermal HPPH is well worth the investment.
Because the geothermal units are not depended on air flow they are entirely enclosed and completely silent- who wouldn’t want that? They can be installed anywhere- indoors or outdoors. Also, they tend to last an extra 50% longer compared to air pump heat sources.
Another option is using an unheated pool as a source for the heat pump itself. This method would transfer heat from the pool to the heat pump to a spa. This is not a geothermal method, it still can work.
Have questions? Contact someone at Ask the Pool Guy!