Water Roof Sky Cooling

Located on stanford university s campus in stanford ca the carnegie institute for global ecology built in 2004 makes use of a night sky cooling system.

Water roof sky cooling.

Showing cooling potential around the. Coatings are like very thick paints that can protect the roof surface from ultra violet uv light and chemical damage. Radiant cooling to the cool night sky during the day can add additional cooling and was used to make ice in ancient iran. A cool roof coating can benefit a building and its occupants by decreasing energy bills through the reduction of air conditioning needs.

A surface facing the sky will eventually eject some of its heat and that rejection takes the form of thermal radiation. These strategies can provide sufficient cooling for full comfort in virtually any climate. Radiative sky cooling is a method of transferring heat with little to no power cost. 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.

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. Night sky radiant cooling nsrc has been something of a lost art even though it has been documented and discussed by hvac and solar heating professionals for many decades. Instead of spraying water on the roof you should apply a cool roof coating to cool your roof down. This effect creates an effect equivalent of r 7 roof insulation during the day.

However this radiant heat is blocked by clouds and particulates and during the day the heat input by the sun far exceeds the heat released to space. 1 gallon of water consumes 8000 btu as it evaporates. Chilled water is supplied at between 55 and 60 degrees f. As ted van der linden director of sustainability for redwood city ca based dpr construction inc explains a night sky cooling system is essentially a rooftop sprinkler system.

The earth s surface constantly radiates heat into space simply due to the second law of thermodynamics. Cool roof coatings are white or special reflective pigments that reflect sunlight. For example the 1993 ashrae handbook of fundamentals mentions it nocturnal radiative cooling and provides a map of the u s. Radiative sky cooling occurs wherever there s a ground and a sky.

Evaporation of water in a fountain cool pool or roof pond can be used to provide powerful cooling. Yes water on the roof will help cool it. Heat is now transferred out of the building through the roof. Water is sprayed over a flat or sloping metal panel roof at night.

This cooling reverses the heat flow through the roof.