Measurement and Analysis of Evaporation from an Inactive Outdoor Swimming Pool

Evaporation rates and total energy loads from an unoccupied, heated, outdoor pool in Fort Collins, Colorado were investigated. Pool and air temperatures, humidity, thermal radiation, wind speed, and water loss due to evaporation were measured over 2 1 test periods ranging from 1.1 to 16.2 hours during August and September, 1992. Data were analyzed and compared to commonly used evaporation rate equations, most notably that used in the ASHRAE Applications Handbook. Measured evaporation was 72% of the ASHRAE calculated value with near-zero wind velocity, and 82% of the ASHRAE value at 2.2 m/s wind velocity. A modified version of the ASHRAE equation was developed. Two overnight tests showed energy loss of 56% by evaporation , 26% by radiation, and 18% by convection. A correlation between radiation loss and temperatures was also found for the range of test conditions.