How RoofShade Works:

Most methods for reducing air-conditioning expense use costly insulation to delay the solar heat that is absorbed by the rooftop from entering the building. These methods do nothing to protect the building from harmful radiation and drastic temperature changes. The RoofShade uses a more basic approach by preventing the heat and solar radiation from reaching your building.

The conclusion of various studies by Cullin, Shirtleefe, Bliss, Yellott, and others is that between 3.5 and 4.0 BTUs per square foot per hour per degree (F.) difference between the surface temperature and inside temperature is transferred into the building. These figures assume a non-insulated roof. The temperature of a dry roof surface is dependent on the absorption of radiant solar energy and the equilibrium reached as the roof radiates the heat back into space or into the building, or loses heat through some other mechanism. On a clear day, the BTUs from the sun vary from 0 BTUs/hour/sq. ft. at dawn to 300+ BTUs/hour/sq. ft. in the middle of the day. The roof temperature is usually below ambient until the radiant energy absorbed by the roof reaches 30 BTUs/hour. The eventual temperature reached is dependent on how much of the sun’s energy is absorbed by the roof. A typical gravel-covered roof absorbs approximately 80% of the sun’s radiation, or 240+ BTUs/ hour/sq. ft., during the middle of the day. This yields a temperature rise of approximately 80 degrees F. above ambient air temperature. During daylight hours, a typical non-insulated, gravel-covered roof will transfer an average of 190 BTUs/ hour/ sq. ft. into the building. Insulating the roof, or the area that needs to be cooled, is one way to partially alleviate the transfer of heat into the building. However, as long as the roof temperature is higher than that of the inside of the building, heat transfer will occur.
Using a light colored, or reflective membrane on the roof is another method that is sometimes used to reduce heat transfer. This method can reduce the temperature of the roof, but still leaves the roof temperature well above ambient temperature. The reflective index of the coating is also damaged by dirt and stains, and requires consistent maintenance to be effective.

RoofShade, Inc. has developed a patent-pending system to keep the temperature of the roof surface below the ambient temperature, and often below the thermostat setting inside the building. TheRoofShade also prevents the major causes of roof failure from affecting your building by blocking 95% of the UV radiation, and reducing the contraction and expansion of the roof membrane due to extreme temperature changes. The main component of the RoofShade system is a reflective shade fabric that is mounted eight inchesabove the rooftop. This shade fabric prevents 90% of the heat from reaching the roof, and air is allowed to circulate between the RoofShade fabric and the roof. Instead of 300+ BTUs per hour per sq. ft. from full sunlight, only 30 BTUs per hour per sq. ft. reach the rooftop. This brings the roof temperature to within 5 to 10 degrees of ambient, depending on wind. In buildings which are minimally insulated, or where power costs are high, a timed water spray system that dampens the RoofShade fabric can be added to further reduce the rooftop temperature. The evaporation of this water lowers the temperature of the air and the rooftop below the fabric another 20 to 30 degrees, or to near that of the wet bulb temperature. Since it is not necessary to remove the entire solar heat load from the roof, but only the 10% that penetrates the RoofShade, our patent-pending system requires a relatively small amount of water. In practice, we have found that the amount of water required to maintain the roof temperature 15 degrees F. below ambient temperature is about 0.008 gallons per hour per sq. ft. In the hottest climates, a 10,000 sq. ft. building would require about 480 gallons of water per day, at a cost of less than a dollar/day. The RoofShade system completely eliminates the solar heat load that would usually be transferred into the building from the roof. In fact, during those times when the temperature of the roof is below the thermostat setting inside the building, the roof acts as a large cooling surface.

A detailed study of a computer simulation was conducted by the U.S. Department of Energy, discussing some of the methods used by the RoofShade system.