Potential use of evaporator coils for water extraction in hot and humid areas

Limits of water production from atmospheric water vapor are investigated for cases where fresh hot humid air is cooled over evaporator coils of refrigeration machines and then directed to open localized areas. This application may be considered as a source of limited amounts of potable water at a free cost since the water is a by-product of the climate conditioning process. For high air velocities, water yield was found to diminish due to insufficient evaporator capacity. On the other hand frosting effect was found to bind the vapor condensation process due to coolant starvation. A working chart was developed for quick prediction of water yield for any combination of atmospheric air temperature in the range (25 < Ta < 40°C) and relative humidity in the range 30% < ϕ < 100%. The water yield due to air dehumidification on finned evaporator coils was calculated using a developed model that relates the surface efficiency to the enthalpy change of cooled moist air. The surface was treated as an extended finned coil with mean efficiency for wet and dry conditions. For typical hot humid weather (Jeddah, Saudi Arabia, 21°23'N and 39°E), the daily variation of water yield showed to follow the relative humidity pattern with minimum during midday hours. The maximum water yield for August 1st was predicted as 17.6 kg/m2 day for an air speed of 2.25 m/s. On the basis of actual climatic data, the monthly estimated average water yield during August and February were 509 and 401 kg/m2, respectively.