Water On The Roof For Cooling

In the simplest form this involves placing a pond on the building roof.

Water on the roof for cooling.

Also called an evaporative cooling system a roof misting system lowers surface temperatures by spraying an extremely small amount of water across the roof allowing the water to cool the roof as it evaporates. As water evaporates from the pond heat is consumed. This cools the roof which acts as a heat sink and absorbs heat from the interior of the building. An evaporating layer of water on the roof approaches a wet bulb temperature of 12 c a typical roof reaches 60 100 c mitigating the albedo effect.

1 gallon of water consumes 8000 btu as it evaporates. A more refined method involves insulating the pond during the daytime to prevent solar gain. Cooling with liquid water running off from a sprinkler is not efficient but evaporative cooling from a small amount of water like a periodic sprinkle is very efficient. The majority of time older homes do not have enough roof vents to help cool the attic in summer.

Yes you can spray your roof to help cool it down but that will only cool the shingles for a short time and be a large waste of water. These systems provide cooling by spraying the water evaporates and cools the surface. At its lowest tech a roof misting system can be little more than a garden hose set to the mist setting and aimed across the roof. 50 radiant heat from surface radiation and 50 air temperature.

Areas where water is in short supply. Prototype for a evaporative roof for radiant cooling cherry valley ca usa reconsidering comfort. Ambient indoor temperature is approx.