Pool water – heating and treatment

Water heating is essential for efficient operation of the pool, showers and other facilities in a pool building. Since the pool water itself is recirculated continuously, it needs to be disinfected. Although the chemical treatment of pool water is dealt with elsewhere in this website, its quality and the associated processes do have energy consumption implications.

Pool water heating

The heating of pool water is a relatively simple operation which is generally carried out by the introduction of a heat exchanger to transfer heat from the primary heating system, sometimes via heat recovery systems, to the pool water. The heater is typically sized, based on raising the pool water temperature by 0.5°C per hour (to adjust temperature and ‘make good’ heat lost by, for example, evaporation and backwashing).

If a pool is being heated from cold, the rate must be no more than 0.25°C per hour, otherwise the expansion of materials may cause problems to the pool structure or lining. Correctly specified and operated controls are the key to efficient pool heating.

Ideal water and air temperatures in Commercial Pools

There has been a consistent trend towards higher water temperatures in recent years to increase pool custom. Currently, main pool temperatures tend to be set around 29–30°C. Some pools do need to be this warm, for instance when catering for parents and toddlers or for rehabilitation purposes. However, operators tempted to increase temperatures should bear in mind that this creates a number of problems.

For example:

• Microorganisms multiply faster – up to twice as fast for a rise of 10 degrees C;
• Bathers get hotter – limiting serious swimming and increasing sweat and grease in the water;
• Increased perspiration will add to the levels of ammonia and urea in the pool, producing more combined chlorine. Chlorine demand will increase simply to maintain free chlorine levels;
• Raised urea levels will increase the production of irritant nitrogen trichloride. This will need to be dealt with;
• Dissolved gases become less soluble – more bad smells (chloramines) and potentially harmful trihalomethanes; and pH value rises as carbon dioxide escapes;
• Energy costs, direct and indirect, are higher – whatever efficiency or conservation methods are used;
• Air temperatures, which are linked to those of the water, rise too – making the atmosphere less comfortable for staff and others (as can the higher moisture levels); and
• There is more moisture in the pool atmosphere, even when relative humidity is controlled at the same level – with a risk of condensation and possibly corrosion and deterioration of the building fabric structure and equipment.

With an increasingly wide variety of pool activities taking place, and with operators attempting to introduce more flexibility into pool operation programming, it is difficult to select a single appropriate or optimum operating temperature for any particular pool. The large volumes of water involved make it impossible to vary water temperatures to a great extent in any one area. This means that selection and accurate control of the optimum water temperature for each pool is essential.

The air temperature in the pool hall should be similar to the water temperature – ideally 1°C above. This helps reduce evaporation and convection of heat at the pool surface. It also makes it more comfortable for bathers leaving the pool. Air temperatures of 30°C or more should generally be avoided.

Recommended water temperatures

Competitive swimming and diving, fitness swimming, training: 26oC to 28oC

Recreational swimming, adult teaching: 27oC to 29oC

Leisure waters: 28oC to 30o

Children’s teaching: 29oC to 31oC

Babies, young children, disabled and infirm: 30oC to 32oC

Hydrotherapy: 30oC to 35oC

Spa pools: 30oC to 40oC

 

Water and Air Temperatures in Domestic Pools

These can be set by the Pool Owner on the Air Handling Unit and can vary between 22oC to 29oC.

 

It is preferable for the Air Tmeperature to be set about 1°C above this to minimise evaporation and convection of heat from the pool surface - but many pool owners run their pool hall air at much higher temperatures.