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ABSTRACT
The rates of water evaporation from indoor and outdoor swimming pools in active use have been measured and compared with evaporation rates from unoccupied pools and with values calculated by the equation W=(95+0.425 v) (pwpa)Y, where W is evaporation rate, Ib/h ft2; v is air velocity at water surface, ft/min.; pw is saturation vapor pressure at water temperature, in. Hg; pa is saturation vapor pressure at air dewpoint, in. Hg; and Y is latent heat at pool temperature, Btu/ lb. In undisturbed pools, evaporation rates were measured and found to be 74% of the rates obtained by use of the equation. Rates of evaporation from pools in active use increase with the number of swimmers, rising 40% to 70% above the rates from a quiet water surface. Measurements of evaporation from a pool in use by 15 IS to 20 swimmers per 1,000 ,OOO ft2 were found to average 26% higher than the rate calculated by the equation.
INTRODUCTION
The design of equipment for heating water in indoor and outdoor swimming pools and for heating ventilation air in indoor pools requires reliable information on rates of heat loss from the pools. Such information is also needed for predicting energy quantities and costs and for estimating the savings obtainable by use of energy conservation measures. Proper sizing of water heaters, air heaters, ventilation fans, heat exchangers, dehumidification systems, and numerous accessories and the evaluation of heat recovery systems, pool covers, and other energy saving equipment are directly involved.
In indoor pools, virtually all the heat supplied to the pool water is dissipated to air in the natatorium by evaporation. Radiation and convection transfers are usually negligible. Moisture entering the air must be removed either by ventilation (requiring fresh-air heating when outdoor temperatures are appreciably below 80F) or by condensation in a dehumidification system. Heat losses from outdoor pools are also largely by evaporation, but radiation and convection to the surroundings are typically 30% to 40% of the total loss.
Prior to the current investigations, there have been no measurements of energy supply to swimming pools under well-controlled conditions. Equipment designers have commonly relied on a relationship originally formulated by W. H. Carrier (1918) and presented in ASHRAE Applications (1995, 1991, 1987). The equation...