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POOL HEAT LOSS

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Anything that eliminates evaporation will eliminate the largest single heat loss in a heated swimming pool.

The percentages of each heat loss mode will vary depending on the amount of wind, humidity and air temperature. Frequency of turbulance of water made by swimmers also have an influence on a heat loss.

EVAPORATION IS THE BIGGEST HEAT LOSS BY FAR IN ALL UNCOVERED POOLS.

Floating solar blankets have air pockets in them to make them float which also "insulates" your pool water from the air, reducing heat loss due to convection and giving you even more savings. Some solar blankets have an aluminized or foil bottom layer which also cuts down radiation losses at night.

Pool enclosures protect pools as good as flat pool covers but are multifunctional. Enclosures and pool covers save heat!

Climate conditions will cause your savings to vary (see below).

Swimming Pool Heat Losses

In order to maintain a heated pool at a given temperature, a heater must replace as much heat as the pool loses. Pools lose heat in four ways:

CONDUCTION - heat lost directly to the ground. Initially when a cold pool is being brought up to temperature, the ground and concrete or vinyl liner walls will absorb some heat. After they warm up, the soil around the pool actually insulates it slowing down the heat transfer to a minimal amount compared to total heat losses. Usually ground losses are negligible or less than 2% of all heat loss.

RADIANT COOLING - heat is lost by the warm water as it gives off infrared radiation back to the sky especially at night. Cloud cover will reduce this effect but the atmosphere will still absorb and scatter this thermal energy like light waves. This may account for 5 to 15 % of all heat loss.

CONVECTION - heat is lost to the air as it passes over the pool - this can usually account for 10 to 50% of the total heat loss.

EVAPORATION - for every gallon of water that is evaporated, approximately 8000 BTU is taken with the water vapor from the pool. This usually amounts to 50 to 95% of all losses. 50% if covered and up to 95% if uncovered.

Evaporation

The evaporation rate depends on the surface area of the pool, the temperature, and the relative humidity. Water evaporation is much greater in the autumn then the summer when water temps are high and air temps are cold (especially at night). This will just suck the water right out of the pool.

Variables of evaporation

The evaporation of water from a water surface, as a swimming pool, depends on the temperature in the water and the temperature in the air, the actual humidity of the air and the velocity of the air above the surface.

The greater the difference in temps, the greater the rate of evaporation.

"Splash-out" water is probably a much more significant source of water loss. There are a lot of variable as far as geographic location.

Determining heat loss

Trying to determine how much heat a swimming pool or spa looses is a very complicated technical problem requiring an understanding of heat transfer, thermodynamics, fluid flow and even meteorology. For example, evaporation is a function of pool water temperature, relative humidity and air temperature.

Radiation heat transfer is a function of pool temperature and cloud cover.