Swimming pool water temperature

What is the best water temperature for children?

Low air and water temperature, insufficient drying and warm-up after swimming can lead to low child body temperature. Infants cool off much more quickly than adults because of the high body surface-body volume ratio. Adults and children (and babies in particular) have very different reactions to heat and cold. This happens because the body cools down by perspiring at a rate proportional to the area of its skin, but warms up in proportion to its mass (volume). The ratio of surface area to mass is much larger for babies, so they cool down faster than adults. It is recommended to set the pool heater to a warm water temperature above 33°C (91°F) for up to 3 years, and above 31°C (88°F) for between 3 and 6 years.

What is the reason for the decrease in temperature after heating the pool water?

The main reason why your swimming pool water loses temperature is evaporation mostly caused by wind. There are several other swimming pool water temperature reducing factors. Evaporation from the surface of the swimming pool lowers both pool water temperature and pool water level in the pool. Radiation causes heat loss in the pool by transferring that heat into the surrounding air. Convection of heat energy is the result of cool air blowing over the pool’s surface and lowering swimming pool water temperature. Heat loss is also attributed to conduction, which is a transfer of heat from the swimming pool water through the pool walls to the surrounding air or soil. But you can reduce the loss of water temperature for example by using isothermic swimming pool covers. Get some hints of how you can save swimming pool heating energy at Pool heating cost saving tips.

The loss in water temperature depend on where the swimming pool is installed. Open air above ground pools have nearly the same loss in water as inground pools. The only differences are the higher loss of swimming pool water through the wall and the wind that cools the outside of an above ground pool. Outdoor pools are subject to greater evaporation, radiation, and convection heat losses than occur with indoor pools. If the installed swimming pool is located indoors then the mentioned water reducing factors are reduced. The major difference is due to wind or air velocity.

Swimming pool water temperature also depends on the average air temperatures. The Zeroth Law of Thermodynamics states that whenever two or more objects are in thermal contact, they reach thermal equilibrium at the same temperature. Thus an aluminium cup holding a sample of water will be at the same temperature as the water. Swimming pool water that is exposed to solar radiation has a slightly higher temperature in contrast to the average air temperature. Water needs a longer time to acclimatise to the air due to its ability of saving a higher amount of thermal energy at higher quantity.

Average air temperatures in different parts of Europe

JAN.

FEB.

MARCH

APRIL

MAY

JUNE

JULY

AUG.

SEP.

OCT.

NOV.

DEC.

Lisbon

11°C

12°C

13°C

14°C

17°C

20°C

23°C

23°C

22°C

18°C

14°C

12°C

Rome

8°C

9°C

11°C

13°C

17°C

21°C

24°C

24°C

21°C

18°C

12°C

10°C

Barcelona

9°C

9°C

11°C

13°C

16°C

20°C

23°C

24°C

21°C

17°C

12°C

10°C

Madrid

5°C

7°C

9°C

11°C

15°C

21°C

24°C

24°C

20°C

14°C

9°C

6°C

Paris

4°C

4°C

7°C

10°C

14°C

17°C

19°C

19°C

16°C

11°C

7°C

5°C

London

5°C

5°C

7°C

9°C

13°C

16°C

18°C

18°C

15°C

11°C

8°C

6°C

Amsterdam

3°C

3°C

6°C

8°C

12°C

15°C

17°C

17°C

14°C

11°C

6°C

4°C

Berlin

-1°C

1°C

4°C

8°C

13°C

16°C

18°C

18°C

14°C

9°C

4°C

1°C

Prague

-2°C

-1°C

4°C

7°C

13°C

16°C

17°C

17°C

14°C

8°C

3°C

0°C

The amount of pool heating energy required by the swimming pool heater also depends on the geographical location of your swimming pool. Warmer climates have the advantage that you can save swimming pool heating energy. As we already stated the swimming pool water temperature depends on the surrounding air temperature. Lets pretend you live in Prague and your friend lives in Barcelona. You both have nice swimming pools each with a capacity of 50000 liters of water. It is June and you both want the swimming pool heater to heat the swimming pool water to a warm temperature of 25°C (78°F). Let us take a look at the table above:

The average temperature in June is 16°C (60°F) in Prague and 20°C (68°F) in Barcelona. That means a difference in average air / water temperature of about 4°C or 8°F. Now let us see how much more swimming pool heating energy you will need to heat your pool water:

The formula described in Heating swimming pool water :

Volume (Liters) x Temperature-Rise x Kilowatt-hour (unit of energy)

32000 x 4 x 0,001164 = 149 kWh

The result shows you that you would have to pay for an extra amount of about 149 kWh of swimming pool heating energy just because of your geographical location!

Why should a swimming pool used for competitive swimming be kept on a cooler water temperature?

If you are training vigorously your body generates an increased amount of heat energy. In air, this heat is dissipated by perspiring. The evaporation of the perspiration is the cooling mechanism to help control the body temperature at 37°C (98.6° F). In water, your body generates the same amount of heat, but there is no evaporation to provide cooling. Cooling is provided by conduction / convection of heat from your warm body to the cool water. This is roughly proportional to the temperature difference between your body and the water. The warmer the water the less heat is dissipated.