INDOOR SWIMMING POOL DESIGN
Answers to the most common questions:
Planning Permission: If the pool is in a standalone building in the garden more than 5 meters away from the house, there may be a chance that you will not need planning permission for your indoor swimming pool, but in all other cases, including extensions and basements, you will most definitely need it, so do check with the council before you go too far in the process.
Timelines: A bespoke indoor pool in a standalone building will take between 20 months and 24 months to build, but a pool project in an extension or a basement will depend on the general program of the overall works.
Pool Heating: In the case of outdoor pools it's just the pool water that needs to be heated, but indoor pools also need the air in the pool hall to be heated to 1ºC above the pool water to control evaporation when the pool is in use. In addition to that, due to constant evaporation when the pool is open the pool hall air also needs to be dehumidified to keep the RH levels below 60% in order to protect the pool hall finishes. So all indoor pools need a dehumidifier preferably with air heating built in, and if there are skylights or external facing glass involved, ducting with grilles to serve these glass areas.
Pool Covers: Yes, indoor pools also need covers. The water evaporates from the free water surface causing a lot of energy wastage and slatted covers that float on water are the most effective in indoor pools. Without a pool cover, the dehumidification system will work overtime to keep the humidity in control.
Indoor Deck Level Swimming Pools with perimeter circulation
Deck-level swimming pools, as shown below and also in the main pic got their name from the fact that the level of water is the same as the level of the surrounding pool deck. This creates an effect of continuity that makes the pool area look larger than it is actually, so a deck-level pool is ideally suited for indoor installation. The deck-level pool effect also makes the pool look more modern, so it also goes well with new build development properties where a contemporary look and clean lines are a big advantage.
The overflow channel associated with a deck-level pool can be covered in many ways. The conventional method, and still popular, is plastic grating which is economical and low maintenance. For modern effect stainless steel grating works well, and if you have a traditional setting you can opt for purpose-made stone grating that will match the pool surround. In modern deck-level pools, we sometimes also use a continuous slot around the pool that makes the channel very discreet and offers a very minimalist look. The tiles or stone used for making the slot can be matched to the pool surround making the transition from pool to surround very elegant.
Because the water level in a deck-level pool is the same as the pool surround, there is a need to construct a balance tank to take the water displaced by a swimmer entering the pool. Due to this extra structure and also extra detailing required for the overflow channel and associated gratings, deck-level swimming pools usually are more expensive than skimmer-type pools but are well worth the price.
Indoor Pool Heating & Ventilation Systems
The H&V design basis for indoor swimming pools is to keep the pool hall surfaces above the 'Dew Point' and prevent any moisture to condense on these surfaces. Air distribution also plays a key role in this and the objective is to completely blanket the area with warm dry air supplied by the dehumidifier, thereby increasing the surface temperature to above the Dew Point*. This requires competent knowledge of air handling, heating & ventilation as well as swimming pool construction.
*Dew Point: As the air temperature drops, its capacity to hold water vapour decreases, so as a result it becomes saturated and the moisture begins to condense on any adjacent surface below a certain temperature (Dew Point). Indoor swimming pool environments are often designed with a room temperature of 30ºC and a relative humidity of 60%. These conditions have an associated dew point of about 22ºC.
We always specify the installation of a central air handling and dehumidification plant within the pool plant room or anywhere adjacent to the pool hall. The most suitable units are refrigerant-based dehumidification units with built-in heat recovery air-to-air heat exchangers, that using proven refrigeration technology, chill the room air to remove the water vapour that has been absorbed by the air. Removing this water vapour releases energy that the dehumidification unit can then reuse to heat both the pool water and the air within the poolroom. The dehumidification process should be automatically controlled by a digital humidity “hygrostat” and the refrigerant used should have high efficiency and low GWP (Global Warming Potential).
A competently designed and installed dehumidification unit should also extract stale air from the poolroom, whilst balancing this with fresh air introduction. The stale air extract rate should be varied according to the prevailing room humidity and occupancy. If the pool is unoccupied and the humidity is satisfactory, then the stale air extract rate should be set to a minimum, to reduce the system running costs. If the use of the pool leads to a raised room humidity, then initially the heat recovery refrigeration system should operate and then, after a period of time, the extract and fresh air introduction rates should be increased in an effort to assist the heat recovery system.
The stale air and fresh air rates can be inherently balanced by the dehumidifier's design, which should provide slightly greater extraction than supply. This will ensure that the poolroom is always maintained at slightly negative pressure when compared with surrounding rooms and the atmosphere. This feature obviously would depend on well-constructed buildings with the use of draught strips etc. The negative pressure should ensure the minimum egress of vapour and odours to adjacent areas. When the heat recovered by the dehumidifier is not sufficient to provide pool water and pool room heating, then “backup” heating must be called for, by way of the boiler plant or geothermal heat pump.
Pool Hall Air Heating
The pool air “backup” heating should be controlled by a calibrated digital thermostat on the dehumidifier's control panel. According to the mode of use, the boiler system should be called to operate when the air temperature drops below the set temperature.
Pool Water Heating
The pool water temperature should also be controlled by a digital display. This should start the backup boiler unit and allow hot water to flow to a stainless steel or titanium heat exchanger. Connections to the pool water filtration scheme are therefore required to make use of this feature. An internal pressure switch should act as a safety device to prevent water heating if for some reason the filtration system is inactive.
Pool Hall Air Distribution
The pool hall environment should be designed with a room temperature of 1ºC above the pool water temperature or 30ºC whichever is lower and relative humidity of 60%. In these conditions, the condensation will occur at around 22ºC, and conventional double-glazing will reach this when the external temperature is as high as +9ºC...!
So by forcibly delivering the warm dry air onto the glass, condensation can be limited to only occasions when sub-zero conditions exist.
To make the most effective use of the dried and heated air produced by the air-handling scheme, this air needs to be distributed around the pool hall. The air should be delivered primarily to the sections of external glass, which are undoubtedly the coldest and hence most vulnerable part of the building. This dried air should then pass back over the pool, and through the poolroom, collecting moisture from the evaporating pool surface. The humid air should be then returned to the dehumidifier unit where the drying process can be repeated.