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Pool Heating and Air Circulation

Maintaining satisfactory environmental conditions in the pool hall and all other areas of the building is essential for the comfort of pool users, staff and spectators—and for the pool to operate successfully over a reasonably extended working life.

The heating and ventilation of the pool hall needs to take into account a wide range of factors. These include: bathing load; water temperature and quality; plant room location; integration with the building structure; materials and insulation of the pool hall envelope; capital; operating; and life cycle costs.

The temperature of the air and the water need to be linked and balanced so as to get the right humidity, optimise user comfort and minimise evaporation from the pool water. It is also necessary to ensure that the air circulation system distributes the air effectively over the whole of the pool hall area. This is necessary in order to:
• Provide comfortable conditions for occupants
• Remove any chlorinous odours
• Reduce the risk of condensation
• Control air movement within the occupied area so it does not produce uncomfortable draughts.

Pool Water Heating
The actual heating of the pool water is a relatively simple operation. It is generally carried out by either a closed-loop heat exchange system, or through direct heating of the pool/spa water using a pool/spa heater (and/or solar energy). Sometimes heat recovery systems are used as the primary source of heat.
The heater is generally sized on the basis of raising the pool water temperature by 0.5˚C per hour. If a pool is being heated from cold, the rate must be no more than 0.25˚C per hour, otherwise rates of expansion of materials may cause problems to the pool structure or lining. Particularly in a new pool, designers need to determine the precise rate of temperature rise.
The heating control system must be capable of coping accurately with a wide range of temperatures. It may be possible, through the use of mixing valves and associated equipment, to serve different pools at different temperatures from a single heat exchanger. But it is recommended that a separate heat exchanger and controls be provided for each separate pool water area, so that different temperatures can be more easily achieved.

There has been a consistent trend towards higher water temperatures in recent years, encouraged by the substantial growth in aquatic leisure activities. The temperatures of multi-function indoor pools, however, need to reflect the aquatic activities being undertaken. Outdoor heated pools tend to operate within a range of 26–29˚C.
People with limited mobility may require higher water temperatures to gain therapeutic benefits from aquatic based activity. However, operators tempted to join the move towards higher temperatures should bear in mind that they do create a number of problems:
• Microorganisms multiply faster so filters are increasingly likely to become colonised.
• Pool users get hotter—limiting more vigorous swimming and increasing bather pollution through sweat and body oil contamination in the water.
• 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. This carries a risk of condensation, and possibly corrosion and deterioration of the building fabric, structure and equipment.
• Chloramines tend to form more rapidly.

With an increasingly wide variety of pool uses, and operators attempting to program more flexible pool operations, it is difficult to select a single appropriate or optimum operating temperature for any particular pool. Rather than catering to any single user group, it may be better to seek a happy medium. The large volumes of water involved make it impossible to vary water temperatures rapidly in any one water area. This means that the selection and accurate control of the optimum water temperature for each pool is essential to maintain operational efficiency and customer satisfaction.
The temperature of the pool hall air should normally be maintained at around the water temperature—no more than 1˚C above. However, it is recommended that an air temperature of 29˚C or more should generally be avoided. However, there may have to be compromises where, for example, the elderly or parents and toddlers have to be accommodated in the same area as fitness swimming.

Pool Hall Ventilation and Air Circulation
This is a complex and critical area. It is generally recommended that air is well distributed over the whole area, and that air movement within the occupied zone is maintained within acceptable conditions for bather comfort. The ventilation system is normally the primary means of removing contaminants from the air. It also
controls pool hall air quality, temperature, humidity, evaporation from the pool surface and condensation to maintain comfortable environmental conditions. It is generally recommended that the relative humidity be maintained between 50 per cent and 60 per cent throughout the pool hall area. Levels higher than 60 per cent produce a risk of discomfort and condensation, and levels lower than 50 per cent can increase evaporation
and energy use.

The ideal ventilation rate for a pool hall, taking into account varying external conditions, bather loads, evaporation rate and water quality, is very difficult to estimate. It will, by necessity, change with varying circumstances. Effective, well-distributed mechanical supply and extraction ventilation systems are,
however, essential to maintain satisfactory internal environmental conditions under all potential variations.
The Australian Standard AS1668.2—2002 can offer some guidance in this area. But it is generally recommended that advice is sought from a design engineer with experience in swimming pool and handling systems.

Separate Areas
Areas for eating and drinking within the pool building are a potential problem. Their individual requirements should be assessed carefully. These areas do not necessarily need to be physically separated from the pool hall, but environmental conditions which are different from those around the pool should be considered.

Sources of Ventilation
The best source for ventilation is fresh air. This should be the first consideration for new pools. A system with a high ratio of recirculated pool air increases the potential for deterioration of equipment and components made of metal or nylon (for example, structural steelwork, roof and ceiling fittings, air handling plant and equipment). Therefore, if an air recirculation system is used for energy efficiency, it should be possible to vary the ratio of fresh air to recirculated air. During periods of very high bather loads or if high levels of contaminants are present in the pool atmosphere, 100 per cent fresh air may be required. Air intakes should be located away and upwind from exhaust outlets.

Energy Management
Swimming pools are one of the few building types operating at high temperature and humidity throughout the year. This results in potentially high heat losses and means that all pool buildings should be well insulated—above basic building regulation standards if possible. They should also be well sealed from the outside and surrounding areas.

Heating the ventilation air will generally be one of the major energy loads for a pool. A simple heat exchange device, such as a plate heat exchanger or run-around coils, should generally be provided to reclaim as much energy as possible from the exhaust air, in order to optimise energy efficiency.
Other heat recovery devices and energy sources can be considered, such as thermal wheels (rotary heat exchanger), heat pumps, combined heat/power units, geothermal and solar energy. These should be carefully evaluated over the projected life cycle of the building services installation.
It may be necessary to run the pool ventilation system when the pool is not in use, to maintain environmental conditions within the pool hall and prevent condensation and possible building or equipment damage. An effective pool cover may reduce condensation, evaporation and pool water heat loss and minimise the need for the ventilation system to operate out of hours. This will also substantially reduce energy use.