notes on heating swimming pools and energy conservation

7/30/2019 Notes on Heating Swimming Pools and Energy Conservation

1/5

Chapter 9

Notes on heating swimming

pools and energy conservation

It is usual practice to provide heating for indoor swimming pools, both for the pool

water and for the pool hall, changing rooms etc. On the other hand, the heating of

the water in open-air pools is rather less common in the UK.In the UK and countries with a similar climate, an open-air pool can only be

used in reasonable comfort for about 45 months during the year, and during this

period there are many days when only the most determined swimmers will be

willing to use the pool unless the water is heated, and wind protection provided.

The termpool heating means a properly designed and installed heating system

connected to the water circulation system of the pool.

9.1Heating open-air swimming pools

By far the greatest loss of heat is from the surface of the water, with only a

comparatively small percentage through the walls and floor to the surrounding

ground, unless the ground water level is high. See Section 4.15.

The heat loss from the water surface depends on a large number of factors all of

which, except one, are closely associated with weather conditions. The exceptional

factor is whether the pool has a thermal insulating cover for use at night and other

times when the pool is not in use. Weather conditions include ambient air

temperature, wind velocity, and direction, hours of sunshine, all of which change

during the day and from day to day. A formula which seeks to take into account allrelevant factors may well turn out to be more inaccurate than a simplified version

and experience.

The simplified calculation which follows assumes that the pool is covered at

night with a proper cover and thus the fall in temperature during the time when the

heating is turned off is 3 C. The calculation is intended as an illustration, and the

selection of a suitable type of boiler should always be left to experienced firms.

If the pool is 16.67 m long, 8.0 m wide with a minimum depth of 0.90 m and a

maximum depth of 1.50 m, the water surface will be 133 m2 and the volume of

water about 160 m3. When the boiler is switched on in the morning, it will berequired to raise the temperature of the 160 m3 of water 3 C in, say, 3 hours, i.e. 1

C per hour. Boiler capacity, assuming 80% efficiency, is:

Copyright 2000 Philip H Perkin


2/5

(160l000l.00)4.180.80=836 000 kJ=836 0003600=232 kWh (1

calorie=4.18 J).

To this figure of 232 kWh should be added a percentage to cover heat loss during

the warming-up period of, say, 5%, thus making an estimated boiler capacity ofsay 245 kWh (or 924 000 Btu/hour).

The boiler would be gas or oil fired.

9.2Heating the water in indoor swimming pools

The temperature of the water in indoor swimming pools is generally higher than in

open-air pools. In private house, club and hotel pools, the temperature is often 30

C, while in public pools in the UK it is 2628 C; in hydrotherapy pools, the

water is usually maintained at about 32 C. In Europe, in public pools, a watertemperature of 28 C is considered a minimum.

9.3Heating and ventilation of pool halls andadjoining areas

9.3.1General considerations

For comfort, the air temperature in the pool hall and changing rooms should be at

least 1 C above the water temperature, assuming this is not less than 26C.

Mechanical ventilation is considered essential in indoor public swimming pools

as it helps to control condensation and adds to the comfort of the pool users. See

comments about roof construction inChapter 7.

The heating of the water and the heating and ventilation of the pool hall and

adjacent rooms are all part of the same problem which has to be resolved by

experienced firms of consulting engineers, or by experienced and reliable

contractors on a package deal basis.

In Europe, it is quite usual to find that benches around the pool are heated and

underfloor heating is provided to the walkways, and floors of changing rooms.

The details of heating and ventilating systems vary from one building to another

and to the requirements of the client who is naturally concerned with both the

capital cost and the operating costs.

In spite of the wide differences in design approach and client requirements, it is

generally agreed that the following principles apply:

1. Condensation should be reduced to the maximum practical extent.

2. Air pressure in the pool hall should be slightly lower than in adjoining areas

so as to induce a flow of air towards the pool hall. This will help reduce, but

will not eliminate the diffusion of chlorine smell to other parts of the building

when chlorine is used as the main disinfectant in the pool water. The smell of

http://tf5906_ch07.pdf/http://tf5906_ch07.pdf/http://tf5906_ch07.pdf/


3/5

chlorine is not caused by the presence of elemental chlorine, but by chlorine

compounds, such as nitrogen trichloride, and dichloramine.

3. When chlorine is used as the main disinfecting agent in the pool water, the air

should not be recirculated, but should be discharged, preferably in total, to the

external air.4. The air changes per hour (ventilation rate) will normally vary in different

parts of the building. For the pool hall, the ventilation rate will be closely

related to the area of the pool and the area of surrounding walkways as it is

from these areas that evaporation takes place.

Heat is a form of energy and exists in a body in the form of motion of the molecules.

Heat can be transferred from one body to another by conduction, when the bodies

are in direct contact, by convection through a liquid and by radiation by which

heat can be transferred through a vacuum.There are two forms of heat, the latent heat of the fusion of ice and the latent

heat of evaporation. The unit of heat is the amount of heat required to raise 1 g of

water 1 C and is known as a calorie, and this is equivalent to 4.18 J.

During the change of state (ice to water and water to steam), the temperature

remains constant. The latent heat of the fusion of ice is about 80 calories (360

J) and the latent heat of evaporation of water is about 540 calories or 2260 J

(2.26 kJ).

It can be seen that the amount of heat energy required to convert water to vapour/

steam is very high.All reasonable steps should be taken to reduce heat loss and thus reduce

energy consumption. The first principle is to ensure that the floor, walls and

roof have appropriate low Uvalues. The Building Regulations 1985 Approved

Document L Conservation of Fuel and Power requires that the U value of

exposed walls, exposed floors and ground floors for industrial buildings should

not exceed 0.45 (W/m2K). For semi-exposed walls and floors, the U value

should not exceed 0.6 (W/m2K).

As far as heating and ventilation is concerned, there are many systems available

to conserve energy. There is an excellent and comprehensive publication from theEnergy Efficiency Office entitledEnergy Efficiency Technologies for Swimming

Pools (details are given under Further Reading at the end of this chapter). It is

claimed in this publication that, in a typical indoor public swimming pool, the

annual cost of energy consumed can be reduced by a significant figure by the

adoption of well-tried techniques.

The main factor which controls the use of energy in maintaining satisfactory

conditions in an indoor swimming pool is the evaporation of water from the pool

surface. The energy used operates on two distinct levels, namely the heat used up

in the evaporation process, and the energy used by the mechanical ventilation systemwhich is needed to reduce the relative humidity to an acceptable level, say, 60

70%. It has been established that the energy used at these two levels is over 60% of

the total energy used for the whole building and its operation. There are a number



4/5

of methods which will make a material contribution to the conservation of energy

and these include the following:

1. The provision of a thermal insulating cover to the pool for use when the pool

is not in use, e.g. at night;2. The reduction of the mechanical ventilation (rate of air change) when the pool

is not in use and the pool hall not occupied. This can effect a saving of 10

12% in the energy consumed, with of course, a corresponding reduction in

operating cost. However, if the pool hall has a pressurised roof void, the closing

down of the ventilation system can cause problems (see Sections 7.147.16);

3. Accurate and effective control of temperature and humidity;

4. The use of heat recovery and/or heat reclaim techniques.

9.3.2Heat conservation techniques

Briefly, heat recovery uses heat exchangers, and heat reclaim uses heat pumps.

Heat exchangers collect waste heat for reuse, while heat pumps reclaim and

regenerate heat from lower energy sources. The installation of an efficient system

of energy conservation is said to reduce energy consumption for pool hall heating

by up to about 30%.

Heat pumps are ideal for heat energy conservation. A heat pump operates to

extract heat from a low temperature heat source and up-grade it to a higher

temperature. For example, a heat pump can be used to extract heat from a large

volume of relatively cool water and use this heat to raise the temperature of a

comparatively small volume of water.

A heat pump is similar in principle to a refrigerator, but working in the

reverse; it requires an external source of power, electricity or gas, to drive the

compressor.

A simple heat exchanger will extract heat from warm air which is being

discharged to waste, and transfer this heat to fresh incoming air, without external

energy input, and the same principle applies to out-going and incoming water.

More complex heat exchangers do the same thing but with an external energy

source in addition.

9.4Solar heating of swimming pools

The sun provides heat energy free of charge, the only cost being that required to

put this energy to practical use.

It appears that the large-scale use of solar energy to heat water for domestic use

was probably started in Israel in the 1950s. As far as the UK is concerned, it was

not until the oil crisis of the early 1970s that serious attention was given to the

possible use of solar heating for open-air swimming pools.

In 1986, the British Standards Institution published a Code of Practice for the



5/5

Solar Heating of Swimming Pools. The Code makes recommendations for

components, design and installation of equipment, performance and commissioning.

In addition, a great deal of useful information is included.

Contrary to general opinion, properly designed and installed solar panels can

collect a significant amount of heat energy on overcast days. The temperature ofthe water in an average unheated open-air pool in the UK during the four summer

months (mid-May to mid-September) is likely to be about 18 C. With properly

designed and installed solar heating, this could average about 23 C. This is

undoubtedly very useful from the point of conservation of energy (fuel) and money,

but for those people who like warmer water (the 23 C is an average figure), it is

necessary to install a conventional heating installation in addition to the solar heating.

The boiler can have a smaller output and the operating costs would show a

considerable saving compared with an installation without solar heating. The

conventional system should be considered as a back-up to the solar heating. Thetwo systems should be controlled thermostatically to obtain the best results.

The solar collectors are in the form of panels made from a patented form of

polypropylene which has a black matt surface. To secure the best results, they have

to be correctly sited and orientated; they are connected to the water circulation

system of the pool.

Further reading

Acoustics & Environmetrics Ltd. Some Ways of Saving Energythe Nature of Heat andCold Energy, 1988.

British Standards Institution. Code of Practice for the Solar Heating of SwimmingPools,BS6785, 1986.

Department of the Environment. The Building Regulations 1985, Approved Document L,Conservation of Fuel and Power, 1989.

Energy Efficiency Office and Sports Council.Energy Efficiency Technologies forSwimmingPools, January 1985.

Sports Council.Energy Data Sheets 121.Towler, P.A. Protection of buildings from hazardous gases,Journal of the Institute ofWater

and Environmental Management, 1993, No. 7, June, pp. 28394.


notes on heating swimming pools and energy conservation

Documents