Solar Air Heating Roof for Army Office Building

DATE: Fall 2011

American Solar recently commissioned the solar air heating roof retrofit at an Army Office Building at the Army Research Lab in MD. The solar roof retrofit involved installation of a solar air heating metal roof, outside air-preheat of roof top units, air-to-water preheat system for domestic hot water, and a high-temperature solar assisted heat pump for VAV reheat.

The system included re-roofing 11,700 square feet of low slope metal roof over with 4,000 square feet of membrane roof around the perimeter. The standing seam metal roof is designed to last for 40 years and outlast 2 built up roofs.

Solar heated air from the roof is used for: ventilation preheating of outdoor air at the roof top units, domestic water preheating using an air-to-water heat exchanger inside the building, and high-temperature heating of the VAV reheat loop using a solar assisted air-to-water heat pump. It is the largest solar air heating roof on an office building in North America.

The solar air heating metal roof was installed over the existing, worn out, built- up roof. No tear-off or disposal of the old roof was required. The old roof’s insulating value was preserved, so the final roofing R-value increased from 20 before, to 50 after the re-roof. Monitoring of the system showed domestic water was preheated to 40+F degrees above incoming cold water, outdoor air was preheated of 42+F warmer than outdoor air, and the solar assisted heat pump maintained a water temperature of 130F for the VAV loop. All these were achieved with less energy use and a better, longer life roof.