This column
features helpful information,
innovative equipment, systems
and applications utilities
around the nation can use
to save energy and improve
service.
Calculating energy savings of indoor swimming pool measures
Residential, commercial and municipal indoor swimming pools require significant energy to heat. IndoorPoolCalc, an online spreadsheet from the Washington State University Extension Energy Program, estimates the savings of several energy conservation measures for pools. Use the accompanying instruction sheet to get the most accurate results.
Swimming pool heat loss basics
There are two forms of heat loss from a swimming pool and the pool house: sensible and latent heat loss. Sensible heat loss is due to temperature difference, such as the temperature difference across the building envelope or the difference between make-up ventilation air and exhaust air. Latent heat loss is caused by exhausting moisture evaporating from the pool surface and or by expending energy to dehumidify the air. Almost all the heat loss from the pool itself is due to surface evaporation.
You can reduce sensible heat loss by adjusting the indoor air temperature, insulating the building and using heat exchangers. To reduce latentheat loss for indoor pools, adjust temperatures and humidity, use a pool cover during unoccupied hours and install a heat pump dehumidifier. Installing an efficient water heater and adjusting the circulation pump's operating hours can also be effective measures.
To estimate energy savings from these measures, you will need to know, at least approximately:
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water surface area
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water temperature
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room air temperature during occupied and unoccupied periods
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room relative humidity
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hours per year the pool is uncovered (8,760 if no pool cover is used)
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typical number of people using the pool, typical type of use (recreation, training, etc.)
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use schedule
Energy conservation measures
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Adjust the pool temperature, indoor air temperature and humidity — As a no-cost step, investigate adjusting the pool temperature, indoor air temperature and indoor relative humidity. In IndoorPoolCalc, pass your mouse over the input cells of the base case to view comments with recommended ranges for air and water temperatures and indoor air relative humidity. If the air temperature is set back during unoccupied hours or for the heating vs. cooling seasons, in IndoorPoolCalc run each shift or season as a separate case.
It is possible to reduce evaporation from a pool surface to a low level or even zero by this strategy. Be careful to stay within recommended ranges for temperature and relative humidity. A compromise must be found between energy efficiency, swimmer comfort and building maintenance through humidity control.
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Cover the pool consistently during unoccupied hours — Other than adjusting air and water conditions, this is usually the most cost-effective energy conservation measure for both indoor and outdoor pools. A pool cover can result in energy savings of 50 to 70 percent and also saves water. Estimate the savings of a pool cover with IndoorPoolCalc by reducing the number of hours the pool is uncovered.
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Install a heat pump water heater — heat pump pool heaters are more efficient than electric resistance heating as long as the outside temperature remains above the 45 to 50 degrees Fahrenheit range. To estimate the savings of a heat pump water heater using IndoorPoolCalc, enter its average coefficient of performance.
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Install a heat pump water heater and dehumidifier with heat recovery — A heat pump water heater may also include heat pump dehumidification and heat recovery. The dehumidification process recovers latent heat from condensing moisture in the air and uses it to heat pool water. To estimate the savings of a heat pump dehumidifier using IndoorPoolCalc, enter its COP for both the water heater and dehumidifier and adjust the percent of heat recovery. You may also reduce the fraction of "other heat losses" to roughly account for recovery of sensible heat.
Heat pump dehumidifiers with heat recovery are available from at least three companies: PoolPak, Desert Aire and Calorex. All three offer commercial and municipal systems, but PoolPak also offers the "PoolComPak" for residential applications.
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Install a solar pool heater — Significantly reduce swimming pool heating costs with a solar pool heater. RETScreen International has developed a spreadsheet-based application, SWH3, for sizing solar water heating systems for indoor and outdoor pools.
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Reduce the circulation pump's operating hours — When the pool is closed for the season, filtration can be reduced by as much as 50 percent. During swimming season, try reducing filtration by three to six hours per day. Adjust operating hours as necessary to maintain water quality.
More resources
DOE's Office of Energy Efficiency and Renewable Energy is a good resource for additional information. Learn tips for improving the energy efficiency performance of swimming pool heating systems. Calculations are also available for estimating costs and savings for gas-heated pools.
