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Commercial Pool halls Space heating and ventilation

Space heating and ventilation accounts for a large proportion of energy use in pool halls which means that there are big opportunities to make savings. However, it is important to ensure that the primary functions of the heating, ventilation and air conditioning system are not compromised.

Ventilating and heating pool halls can be rather complex and it is essential to manage these services correctly.

The control of evaporation from the water is a function not normally encountered in standard heating, ventilation and air conditioning (HVAC) systems, and can therefore be misunderstood by architects, pool designers and operators.

The ventilation system is normally the only means of:

Controlling the pool hall air quality,

Controlling temperature and humidity

Reduction of evaporation from the pool to prevent condensation and corrosion damage

Maintenance of comfortable environmental conditions for different occupants.

Removal of contaminants from the air.

Comfort requirements

Maintaining satisfactory environmental conditions in the pool hall and all other areas of the building is crucial to the comfort of bathers, lifeguards, staff and spectators. It is also essential if the pool is to operate successfully over its working life.

In addition to the fact that pool users are wet and wearing less clothing, they will also experience evaporation as they dry, which gives a cooling effect. As a result, higher than usual air temperatures need to be maintained. Evaporation also depends on the relative humidity in the air, but bathers are relatively tolerant of changes in humidity provided that air movement is minimised, for instance, by avoiding draughts.

Heating and ventilation of the pool hall has to account for a wide range of factors such as the number of bathers, water temperature, insulation of the pool hall and integration with the building structure. Air and water temperature should be set relative to each other to optimise user comfort and minimise evaporation from the pool water. Above all, humidity and moisture content in the pool hall needs to be controlled to avoid condensation.

Space heating and ventilation accounts for a large proportion of energy use in pool halls – which means that there are big opportunities to make savings. However, it is important to ensure that the primary functions of the heating, ventilation and air conditioning system are not compromised.

Air movement

A pool hall air circulation system needs to distribute air effectively so that:

There are three locations within the pool hall where these issues should be addressed and each one is examined in more detail below. These are: the pool surface, the poolside and other areas, such as upper walls and the ceiling void.

Pool surface

The key elements to be addressed at the pool surface are to remove contaminants if they could affect bathers, to provide bathers with oxygen for respiration and to control evaporation.

Poolside

The comfort of the bather (before entering and after leaving the pool) and on the poolside staff is the key elements to be addressed at the poolside.

Most of the people who use the pool hall will be wet, so the poolside temperature should be adjusted accordingly. This can be assisted, for example, by redirecting any grilles and jets near the poolside to avoid any direct air flow from the ventilation system.

Staff should also be discouraged from opening doors or windows, which creates draughts. Discourage poolside staff from opening emergency escape doors for their own personal comfort. If localised cooling is required, increased air movement can provide this, such as through simple overhead fans. Use controls to avoid increasing air movement at the pool surface or around wet bathers.

Temperatures elsewhere in the swimming pool building, such as café areas, the foyer, administration offices and plant rooms should be appropriate for the activities taking place.

Other areas in the pool building

Outside air normally has much less moisture in it than pool hall air as it has a lower temperature. Mixing outside air with pool hall air can reduce overall humidity. The key elements to be addressed in other areas of the pool hall are protecting the pool hall structure from condensation and providing comfort to non-swimmers.

One solution to both problems is to provide separate airflows for the pool and other areas to minimise mixing between areas. In a new pool building, the airflow could be directed upwards from a slot at the foot of the walls in ‘laminar flow’, so that it mixes as little as possible with the bulk of air in the hall. For existing pool buildings, inlet grilles and jets can be repositioned so that drier air entering the pool hall can be pointed towards the sides of the building rather than down on to the pool.

Comfort for spectators can be improved by having a similar arrangement to direct drier incoming air over them. It may also be appropriate to blow drier air into ceiling voids to ensure that condensation does not occur on hidden parts of the structure.

These approaches that separate air flow within the space have clear advantages over a traditional system in which all the air flows are mixed, demanding that all air in the pool hall be brought down to the limiting moisture content demanded for structural protection.

Ventilation rates and controls

The ideal ventilation rate for a pool hall varies in accordance with a number of factors such as the number of bathers, evaporation rate and water quality at any given time. A recommended guideline figure of 10 litres of ventilation air per second, per square metre of total pool hall area (water area plus all wet surrounds) is acceptable for a wide range of pool complexes. This normally results in an overall total of approximately 4–6 air changes per hour depending on the height of the pool hall.

Ideally, the speed of the ventilation fans should be controlled using variable speed drives (VSDs) linked to a dew point sensor. This optimises the speed of the fans to keep the moisture content of the air in the pool hall just above the dew point at which condensation occurs. Place the sensor so as to avoid condensation on the worst ‘cold bridge’ in the structure. A cold bridge is formed where the thermal insulation barrier is breached, leaving a bridge that short-circuits the thermal insulation and results in a colder surface than the surrounding area. In a pool building, this will usually be a window frame or structural steel. As an alternative to dew point sensors, a relative humidity sensor can be employed to control the air supply. It should be reset depending on the outside temperature. When the outside temperature is below freezing, for example, the relative humidity required to avoid internal condensation will be lower than in milder weather or summer. Note that these sensors require frequent recalibration.

Heat recovery

Heating the supply air is generally one of the major consumption areas for a pool building. Providing a simple heat exchange device, such as a plate heat exchanger or run-around coils, can optimise energy efficiency by reclaiming large amounts of lost energy from the exhaust air.

Fit heat exchangers with a bypass in the ductwork for occasions when heat recovery is not required. However, make periodic checks to ensure that they are not permanently bypassed and normally operate in the ‘heat recovery’ position.

Plate heat exchangers

Plate heat exchangers consist of glass, metal or plastic plates arranged in a stack with the exhaust air and incoming air flowing in the adjacent channels. Heat transfers from the outgoing air from the pool hall (which is warm and moist) through the plates to the cold incoming air. They are cheap and free from mechanical problems, although a limit on their application is that the incoming and outgoing air ducts must be adjacent to each other. If grease and grime are allowed to build up on the plates this will lead to a substantial reduction in their effectiveness, so the heat exchanger should be maintained in accordance with manufacturers’ specifications. If the plates are made of metal, chlorinated air can attack them. Inspect for signs of corrosion at least once a year.