Pool Water Heating & 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.

I. 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.

II. Ideal Water / 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°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)
• 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/diving, fitness swimming, training: 26°C to 28°C
• Recreational swimming, adult teaching: 27°C to 29°C
• Leisure waters: 28°C to 30°C
• Children’s teaching: 29°C to 31°C
• Babies, young children, disabled and infirm: 30°C to 32°C
• Hydrotherapy: 30°C to 35°C
• Spa pools: 30°C to 40°C

What Type of Heater?

Traditionall pool water was heated by a gas or oil fired boiler but the high carbon output of these has resulted in a situation where most operators are considering their replacement with more sustainable heating powered by electricity.

The options invariably narrow down to Air Source or Ground Source Heat Pumps.

Ground Source Heat pumps are more suitable for district heating schemes and most Commerical Pools will be best suited by replacing the boilers with a bank of Air Source Heat Pumps that feed the hot water into a buffer tank that also acts as a heat exchanger with the pool water.

Bluepools can provide all the advice required in terms of the best option and the most economic way to upgrade the old heating system.

Water and Air Temperatures in Domestic Pools:

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

It is preferable for the Air Temperature 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.

The boilers that are needed to feed the heat to the Air Handling Unit can be most easily replaced with one or two air source heat pumps and a buffer tank / heat exchanger.