By running the model of the system for swimming pool operation with inputs from meteorological models, we can compare the calculated pool temperatures determined by different recommendations for the evaporation heat loss coefficient using different sources from relevant literatures.

Evaporation causes the dominating part of heat losses at swimming pools. It normally accounts for more than 60% of the total energy losses [6]. The mostly used equation for determining the evaporation heat loss power at the water surface is the following:

Q = A. h

z—eva pool /leva

where

evaporation heat loss power at the swimming pool, W, swimming pool surface area, m2, evaporation heat loss coefficient, W/(m2Pa),

vapour pressure of saturated air directly at swimming pool temperature, Pa, vapour pressure of ambient air, Pa.

The evaporation heat loss coefficient can be determined as

heva = a + b • W>t, (2)

where

w is the wind speed at the swimming pool, m/s, a, b and n are constants.

For the value of a , b and n different references [10], [11], [12] and [13] contain recommendations (see in Table 1).

Table 1. Recommendations with adequate sources for the constants of evaporative heat loss coefficient. a b n Source Height of relevant wind speed in meters 4,523 5,088 0,84 Richter, 1969 [10] 1,0 5,058 6,690 1 ISO TC 180/ SC 4 N 140 [11] 0,3 8,5 5,08 1 Rowher, 1931 [12] 0,3 8,866 7,813 1 HVAC Handbook, 1987 [13] 0 — on ground level

According to the descriptions in this paper the model have been run using meteorological models. Specifications for the calculations are as follows:

The modelled day is a clear day [3] with number 163 (12 June).

Irradiance, ambient temperature, wind velocity is determined by the model.

Air humidity is fixed to be constant, ф=0,65.

There is no auxiliary heating.

The initial swimming pool temperature is 25°C.

Fig. 6. Comparison of the swimming pool temperatures affected by the evaporation heat loss coefficient.

The biggest difference of the calculated swimming pool temperatures is in the cases of using the recommendations by Richter and by the HVAC Handbook. Namely the difference has a mean value of

0, 76°C, maximum value of 1,25°C, residual value, at the end of the modelled day, of 0,9°C.

References

[1] I. Farkas, Z. Rendik, International Journal of Ambient Energy, 14, 2 (1993) 59-68.

[2] J. A.Duffie, W. A.Beckman, (1991). Solar Engineering of Thermal Processes, John Wiley and Sons, New York.

[3] Gy. Szabo, Zs. Tarkanyi, (1969). Solar radiation data for the planning in building industry, Institute for Building Sciences, Budapest (in Hungarian).

[4] J. Buzas, I. Farkas, A. Biro, R. Nemeth, Mathematics and Computers in Simulation, 48, 1 (1998) 33-46.

[5] J. Buzas, I. Farkas, The 3rd ISES-Europe Solar Congress (EuroSun 2000), Copenhagen, Denmark, June 19­22, 2000, CD-ROM Proceedings, 9.

[6] E. Hahne, R. Kubler, Solar Energy, 53, 1 (1994) 9-19.

[7] B. Molineaux, B. Lachal, O. Guisan, Solar Energy, 53, 1 (1994) 21-26.

[8] I. Farkas, I. Vajk, Energy and the Environment, I /ed. by B. Frankovic/, Croatian Solar Energy Association, Opatija, October 23-25, 2002., 91-99.

[9] B. Bourges, (1991). European simplified methods for active solar system design. Kluwer Academic Publishers for CEC.

[10] D. Richter (1969). Ein Beitrag zur Bestimmung der Verdunstung von freien Wasserflachen dargestellt am Beispiel des Stechlinsees, Abhandlung des Meteorologischen Dienstes der DDR Nr. 88 (Band XI), Akademie- Verlag, Berlin.

[11] ISO/TC 180/SC 4 N 140, Solar Energy — Heating Systems for Swimming Pools — Design and Installations.

[12] Rowher, United States Department of Agriculture, Tech. Bulletin 271 (1931, December).

[13] HVAC Handbook (1987). Section 20.8.