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Indoor Pool Ventilation
Indoor swimming pools continuously produce large quantities of chlorine laden water vapour through the process of pool evaporation.

The effects of this evaporation are magnified by the fact that the construction industry keeps building more energy efficient tighter structures.

When water vapour has no escape from these air tight structures, it causes numerous problems such as:
blistering of paint,
deterioration of structural supports
and many other negative comestic effects on your building.

As a result repair or replacement of damaged items can be very costly and time consuming. Patrons and staff of indoor pools must also endure an unpleasant environment. They are surrounded in the physical discomfort of high humidity. The mould, mildew, bacteria and fungi that grow in these moist conditions can effect their health. These growths give off low-molecular weight volatile organic compounds (VOCs), many of which are poisonous and have potent odours.
Bathhouses, mechanical equipment rooms, storage areas and indoor swimming pool enclosures shall be ventilated, either by natural or mechanical means. Room ventilation shall prevent direct drafts on swimmers and shall minimize condensation. A minimum of two air changes per hour shall be provided for indoor pool areas. Heating units shall be kept from contact with swimmers. Fuel-burning heating
equipment shall be installed and vented to the outdoors in accordance with the Uniform Code.


In general , it may be said that a mechanical ventilation rate of 1 ACH (one air change per hour) of the
pool enclosure will be sufficient to maintain reasonable relative humidity levels when a pool cover is
used regularly. However, the ventilation system should be capable of supplying 2 (two) ACH for maintenance of good air quality in all operating conditions.


The amount of water evaporated from a pool depends on:

a) the surface area of the pool;
b) the water temperature;
c) the indoor air temperature and relative humidity;
d) the amount of air movement over the pool surface.

In short, the following principles apply:

1) The larger the water surface area, the greater the amount of water evaporated. Therefore,

using a pool cover to reduce the surface area of water exposed reduces the amount of water evaporated;

2) The higher the water temperature, the higher the evaporation rate;

3) The lower the indoor air temperature, the higher the evaporation rate;

4) The lower the indoor relative humidity the higher the evaporation rate;

5) The greater the air movement over the pool area, the higher the evaporation rate. Thus,
activity in the pool area will increase the evaporation rate.



After calculating the mechanical ventilation rate required for the pool enclosure, it is necessary to
consider the distribution network for both the supply and exhaust air streams.

Proper duct design will:

1. minimize air flow requirements;
2. ensure a comfortable recreation environment;
3. optimize humidity control , including elimination of condensation on windows.
Please refer to Sketch I and 2, enclosed, for typical layouts.
In general, please note that:

1. The airflows and duct lengths Indicated on the sketches are meant as examples only - actual
performance may differ;


2. Supply air should be discharged near exterior windows. If the supply air is being heated, the
supply grills may be close to the ground - otherwise, discharge height should be at least
eight feet.
3. Return grills and lines should be located near the ceiling;
4. Maintain a reasonable distance (at least eight feet) between supply and return grills, to
prevent short circuiting.
R eheating of Supply Air:

Although the air-to-air heat exchanger will recover up to 80% of indoor air temperature , the incoming
fresh air supply may be uncomfortably cooI. Therefore it may be desirable to add an
heater to heat the incoming air.

Rules for economical solution of residential pool design

choose a building envelope with the best thermal insulation and technical parametersavoid unnecessary large glazing (mainly in pool roofs)
totally eliminate thermal bridges
design perfect vapor barriers for walls and roofs
design rectangular pool shapes to easily install rolling foil covers, possibly insulating cassettes made of polyurethane
design connections to house only through a tight door, preferably through separately ventilated corridor
in respect to possible losses and condensation in ducts locate the ventilating unit as close as possible to pool

Rules for ventilation and heating of residential pools
The rules come fromexperience with many newly built or retrofitted pools in recent years:

ensure thorough ventilation of the whole space; avoid poorly ventilated corners with possible condensation
always ensure supply of dry warmair with low RH value on glazing with sufficient speed and reach
keep the whole space in negative pressure (min. 95 %) to avoid risk of water vapor escaping into adjacent spaces or into a structure through an incorrectly made vapor barrier
always design the ceiling distribution ductwork in the pool made of stainless material with slot or nozzle outlets; possibly of aluminumfinished polyurethane, with slot outlets without control (due to complicated access)
ensure perfect tightness of stainless floor ductwork, sloping towards a condensate drain, access for cleaning and excelent thermal insulation
design air distribution ductwork outside the pool of tight duct (e.g. Polyurethan), sloping towards a condensate drain, and thermaly insulated. Never install exhaust grilles in false ceiling through a cut vapor barrier!
design suction grille centrally opposite the glazing, under the space ceiling
design the air distribution for very small spaces (e.g. with only one window or in a basement) only by a central jet air outlet (adjustable)
always isolate the pool air-handling systemfromthe one serving the house, including supply and exhaust ducts, to avoid drafts (backdraft dampers do not guarrantee continuous and trouble-free opeartion)
due to unsteady residential pool opeartion (e.g. 1 – 2 hours a day) it is ideal to install the air-handling systemwith warm-air heating to achieve required air temperature quickly, in just several dozens of minutes (with thermal insulation and vapor barrier on the wall inside).
air-handling units for pools must be suitable for aggresive environmet (chlorine), i.e. With heat recovery core made of stainless or plastic material, condensate drain pan of stainless steel or with a special finish
it is recommended that as a basic heating system a floor distribution system be installed with connection to a low-temperature heat source (HP, solar energy), possibly a system of floor-standing convectors under windows, with excelent anticorrosive finish with a special design to avoid human injury

Another sample pool air change calculation

Another sample pool air change calculation (excel table by GEA)

Pool Dehumidifiers




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