The human body is sensitive to water temperature. It can even discern a water temperature differential as small as .5°F. Thus, the temperature of water varies between pools to correlate with the aquatic activity that will occur in the pool. This may be a temperature of 80°F for a 50-meter competition pool, 84°F for an activity pool, 95°F for a therapy pool, or 104°F for a spa. Regardless of the pool function or water temperature, from an operational perspective, it is imperative to easily and efficiently heat the pool.
The work horse for pool heating over the years has been the gas-fired pool boiler. Boilers have increased in efficiency over the years as there have been advancements in burner technology. A generation ago, atmospheric pool boilers were 80%-82% efficient. Today, atmospheric boiler efficiency has incrementally increased to 84%-85%. When additional air is provided to the combustion process (similar to a turbo charger on an automobile), the boiler efficiency increases to 88%-89%. The inefficiency of atmospheric boilers has been reduced from 18%-20%, down to 11%-12%. A 40% improvement is pretty substantial.
Additionally, the gas-fired boiler industry has worked out how to incorporate condensing boilers into the swimming pool market. With a condensing boiler, the boiler has a second stage that extracts additional heat from the exhaust, further increasing the overall efficiency of the boiler. Condensing boilers run at efficiencies of 95%-98%. With condensing boilers, the inefficiency of gas-fired pool boilers has been reduced from roughly 20% down to 2%, which represents a great leap forward for efficiency and sustainability of gas-fired pool boilers.
Heat pumps are also a reliable source for pool heating. Two common types of heat pumps are air and water source heat pumps. Air source heat pumps exchange heat with the ambient air around the pumps, while water source heat pumps exchange heat with a water source (pond, a cold pool, etc.). The beauty of a heat pump system is that the energy consumed by the system is only that which is required to run the pump and the compressor. The heat (or energy) transferred or moved from one body to another can be a significant multiple of the energy used to run the system. This is called the coefficient of performance (COP), which can easily be above five. Heat pumps do face geographical limitations as they need air and water temperatures to be reasonable (above freezing) to work efficiently, but where ambient temperatures are available, they are a great sustainable system for both heating and cooling if needed.
Other sustainable systems include the harnessing of solar power to heat a pool. Passive solar pool heating is accomplished when the sun is shining, which is the primary heat source for many seasonal pools. Active solar heating harnesses additional heat from the sun through an array of panels that collect and transfer the heat to a fluid system. The fluid then transfers the heat to the pool water, providing a sustainable heating solution that efficiently extends the outdoor pool season.
With indoor natatoriums, it is very common to adapt the sustainable strategy of rejecting waste heat from the HVAC units to the pool water. If a system is rejecting heat, it is always wise to determine if another system might benefit from gaining that heat. Implementing a second use for waste heat is a great strategy for minimizing operational costs. It also reflects a holistic approach to sustainability for a project.
Similar to how the sun is the silent provider of heat to many seasonal pools, wind and evaporation are the silent thieves that rob pools of heat. Water loss through evaporation continually cools a pool. If cooling is desired, as is needed in some hot climates, agitating the water to increase evaporation is a sustainable way to cool the pool. In most of the United States, however, there is no need for that. Therefore, minimizing evaporation helps keep heat in pools. The use of pool covers is the easiest way to minimize water evaporation from the pool. It takes some manual labor to install and remove pool covers, but they are fantastic at reducing heat loss.
There are additional strategies for providing sustainable practices and good stewardship when heating a pool. Technology continues to open new doors and provide new solutions to the market. By using sustainable pool heating solutions, one can be cool while providing heat to the pool.