Water On The Roof For Cooling

Areas where water is in short supply.

Water on the roof for cooling.

Yes water on the roof will help cool it. As water evaporates from the pond heat is consumed. Ambient indoor temperature is approx. One study indicates that water use is around 100 gallons per day per 1000 sqft of roof area.

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. 50 radiant heat from surface radiation and 50 air temperature. 1 gallon of water consumes 8000 btu as it evaporates. 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.

This cools the roof which acts as a heat sink and absorbs heat from the interior of the building. 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. A more refined method involves insulating the pond during the daytime to prevent solar gain. The majority of time older homes do not have enough roof vents to help cool the attic in summer.

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