SWIMMING POOLS | INSULATION Table 1: Conductive heat losses typical and good practice Envelope material Thermal transmittance Wm-2K-1 Area m2 Heat loss kW Solid brick 2.00 672 26.9 Single glazing 5.80 168 19.5 Concrete roof 1.00 800 16.0 0.70 800 11.2 Total Annual heat loss kWh per year 73.6 644,736 Annual heat loss kWh per year Typical practice 523,000kWh per year, saving heating costs by about 22,300 per year. This is rather small compared with the cost of the work. Many pool halls are not very well for installing additional insulation and double glazing is usually not very strong. We came to realise, however, that improved insulation would have a dramatic secondary effect. Better insulation allows the pool to operate at a much higher level of RH and, so, with a much lower ventilation rate, without causing condensation. We can see from the characteristic curves for a typical pool that raising the RH from 50% to 60% saves about 10,000 per year in (gas) heating costs. Our model showed that operating the pool hall at 70%, rather than 50%, would save 550,000kWh per year, worth about 23,400 per year. (At lower outdoor temperatures the RH would need to be lower.) These savings arise through blowing out less warm, energy-rich air containing all the latent heat of the evaporated water. This insulation. Figure 4 shows the hypothetical wall with and without insulation. When we looked at the temperature see that such a rise in humidity levels is possible. So, the energy savings achievable from insulation could be roughly double the savings in conductive heat losses alone. This makes the case for improved insulation and double glazing much more attractive. It also highlights the need for new buildings to be very well insulated, and have no thermal bridges, exposed steelwork or crevices where condensation can accumulate. Envelope material Thermal transmittance Wm-2K-1 Area m2 Heat loss kW Insulated cavity 0.25 672 3.4 Double glazing 1.90 168 6.4 Insulated roof 0.25 800 4.0 0.16 800 0.1 Total 13.9 121,764 Good practice Insulation Air boundary layer 30C 20C Inside Inside With insulation It highlights the need for new buildings to be very well insulated, and have no thermal bridges, exposed steelwork or crevices where condensation can accumulate Dew point RH 70% Dew point RH 50% 10C Without insulation Summary Modelling has shown that most of the energy used is extracted from a pool in the ventilation, and the more this can be reduced without condensation taking place, the better. The positive impact of pool covers, deployed overnight, has also been demonstrated. Modelling has highlighted the enormous variation in the evaporation rate during the day and throughout the year, and that a variable-speed ventilation system is needed to accommodate it. However, the important point is that the best results will arise when well-designed ventilation systems and controls are combined with good building insulation. CJ MIKE HANCOCK is a director at Dee Associates References: 1 Charles C Smith, George O E Lf, Randy W Jones, Rates of evaporation from swimming pools in active use, ASHRAE Transactions 1998 vol 108, pt 1, item 4146, pp1-9, American Society of Heating, Ventilation and Air Conditioning Engineers, Atlanta, USA. 50 October 2021 www.cibsejournal.com CIBSE Oct21 pp48-50 Energy savings swimming pools Supp.indd 50 24/09/2021 15:24