Dedicated water-to-water heat pumps connected to a ground water source or a ground-coupled loop can be used for seasonally heating pools and hot tubs.
Catastrophic failure of the water-to-refrigerant heat exchanger can allow chlorinated water to enter the refrigeration circuit. This can destroy the compressor and other major components resulting in a very expensive replacement.
The heat pump's water circuit should take and return water from the piping between the pool pump and pool filter. A diverting valve can be used to assure a flow of 3 gpm per ton to the heat pump. A water thermostat can control the heat pump's operation to maintain minimum pool water temperature.
Water source heat pumps are used to heat indoor swimming pools and hot tubs and control the temperature and humidity of their enclosures. This equipment is specially designed and uses stainless steel to resist the corrosive effects of the chlorine in the air.
The specific equipment selected depends on site conditions. While not a geothermal application, there are situations where an outdoor pool can be used as a heat source and heat sink year-round for a water-to-air heat pump.
This application is limited to areas with very little heating load and high humidity, such as South Florida and the areas along the Gulf coast. With the exception of South Florida, these systems should not be installed more than 50 miles inland since the stabilizing influence of the ocean is reduced and the heating requirements become more demanding.
It's generally recommended that a minimum of 5,000 gallons of pool capacity per ton of nominal heat pump cooling capacity be used. For example, a pool with 15,000 gallons of water would be suitable for no more than a 3-ton heat pump.
During the heating season when the pool is not in use, it should be covered. This will prevent evaporation, but not substantially restrict solar gain. The heat pump's water circuit should take and return water from the piping between the pool pump and pool filter. A diverting valve can be used to assure a flow to the heat pump of 3-gallons per minute per ton.
To minimize pool overheating during summer months, several of the return nozzles in the pool may be converted to spray heads. Remember, the heat pump must be cooling the home in order to heat the pool.
A word of caution: Pool manufacturers may restrict their warrantees on their equipment on these applications.
Users must follow the instructions provided with the pool or hot tub for maintaining satisfactory water pH levels. If the pH is kept in the 6 to 8 range, preferably around 7, the heat pump should have a normal service life. If not, a separate water-to-water heat exchanger should be used. Otherwise, the heat pump service life will be much shorter.