WhiteCap™ Roof Spray Cooling in Nogales, Arizona

In 1996 a WhiteCap™ roofing system, which enables the downsizing of conventional cooling equipment, was installed on a General Services Administration (GSA) Port of Entry station building in Nogales, Arizona. The building was built in 1974 and has concrete walls and built-up roof construction. It is used to regulate and process commercial transport between the United States and Mexico and houses approximately 30 people during the day. The WhiteCap™ system is a night-sky radiant cooling system that is suitable only in warm, dry climates. The WhiteCap™ system consists of a piping grid and conventional water spray nozzles which are installed on a roof surface and connected to a water pumping and filtration system. Water is sprayed over the roof at night and is cooled by evaporation and by radiation to the night sky. The water cycles through this process until it reaches a temperature of 45-50° F (7.2-10°C) and is stored for later use in cooling the building. In Nogales, 44 spray heads and piping were installed as a retrofit on top of a parking canopy with the cooling benefit going to the neighboring building. A water tank was constructed nearby to store the water until it is needed for cooling purposes.

Technical data

In dry western and south-western US climates, where hot days are followed by cool nights with minimum temperatures below 65°F (18°C) typical capacities are 25 ton-hours per 1,000 square feet (93 square meters) of roof surface in peak conditions. Typical capacities tend to be higher in medium weather. For well-designed buildings with moderate loads, this typical capacity is sufficient to provide all cooling. For buildings with peak loads exceeding 25 ton-hours per 1,000 square feet, WhiteCap™ capacity allows significant downsizing of conventional cooling equipment.

Energy data

Water usage is approximately 1.7 to 2.6 litres/kWh (0.15 to 0.20 gallons/kBtu) cooling. The installation saves about 1020 kWh/week in cooling energy.

Economic data

Cost for design and construction of the system was approximately USD 28,500 (Note that the cost was relatively high because of the small scale of the project.) The system saves cooling energy worth USD 56 /week. Therefore in this case the WhiteCap™ system has a pay-off period of about 9.8 years.

Contacts:

Davis Energy Group 123 C Street Davis, CA 95616 916-753-1100 916-753-4125 (fax) http://www.davisenergy.com

US GSA Tucson Field Office/9PMM-28 300 West Congress Street Tucson, AZ 85701 520-670-4738 520-670-4752 (fax)

See also: Nightsky System Cools Roof Tops

“NightSky” natural cooling system saves energy

Night Sky Radiant Cooling System

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