Pool heating is a requirement for all indoor pools and for outdoor pools that extend their season past the traditional summer season. When heating potentially hundreds of thousands of gallons of water, pool water heating can be a significant expense. Pool heating can come from a variety of sources and we will look at some of the most common sources for pool heating.
Stand-alone gas fired pool heaters have been the workhorse of the pool industry for decades and continue to be the heating source for a significant number of pools. The least efficient of these boilers is the atmospheric boiler which has efficiencies around 80-82%. The way to boost the combustion on atmospheric boilers is similar to boosting power from a car motor. Fan assisted atmospheric boilers provide additional air to the combustion process (that’s a supercharger in your car) and in the process increase the boiler efficiencies to 86-89%.
Condensing boilers further increase the efficiency of the pool heaters to 95-97% efficiency. The condensing cycle extracts heat from the waste heat being vented which captures the additional efficiency for these heaters. Additionally, some manufacturers have combined a heat exchanger with the condensing boilers so pool water is never processed through the coils of the pool heater itself. This significantly expands the life of a gas fired pool heater.
Things to keep in mind for gas fired pool heaters are the heaters need adequate combustion air and must be properly vented to maximize combustion. A lack of adequate air will lead to a loss of efficiency and an accumulation of soot in the vent. Additionally, for projects that are located at higher elevations - any location above 2,000 feet of elevation - the capacity of the heater is de-rated as the amount of oxygen in the air for combustion diminishes with the increased elevation.
It is also very common to have pools heated with domestic hot water to pool water heat exchangers or less commonly found is the steam to pool water heat exchanger. Heat exchangers have an almost perfect transfer of heat from one side of the exchanger to the other. Heat exchangers are used when there is significant capacity from the project or campus heating systems and pool heating is one of many heating requirements for the overall heating system.
On indoor pools the air within the natatorium is often controlled through the use of dehumidification air handling units. In the dehumidification process there is heat rejected from the process which then can be rejected into the pool water in a heat recovery loop. This is an efficient way to recover waste heat for use with the pool.
Waste heat can be recovered from other types of systems as well through the use of heat exchangers. The process for making and maintaining ice rejects considerable amounts of heat. Whether from an ice rink or from ice cubes used for convention center events, rejected heat from both situations has been used as sources of heat for pools. The use of heat pumps gather waste heat from either the air in the case of an air source heat pump or from water in a water source heat pump. Heat pumps provide a very efficient way to transfer heat into a system as the heat is being transferred from a medium to a medium.
The best source of heat is…free heat! For outdoor pools, the solar radiation from the sun is a daily source of free heat to the pool. Indoor pools with south facing glazed areas, protected from the summer sun by overhangs will admit heat and light during the winter months also utilizing the passive effect of solar heating.
Active solar heating systems employ solar panels, pumps, and heat exchangers to provide heat to the pool systems. Active solar systems are a low cost way to capture heat for pools, but remain challenged by the significant area required for the solar panels and often when the greatest amount of solar heat is available, the demand for heat from the pools is the lowest.
There are other heating systems also available for pools, but the main thing with pool heating is to have an efficient heating system as possible to control the expense side of pool heating. Then, in a perfect world all of your pool guests would be homogenous so there is never any complaints about the water temperature in the pool.