It demonstrates these new and advanced technologies in an unobtrusive way within the conventional construction of a small 400-square-foot building.
The guard station solar project incorporates the following 12 technologies:
1. Solar thermal tile air heating roof system.
2. Reflective roofing laminates and selective surface absorbers to boost solar roof air temperature.
3. High temperature, multi-stage solar roof with peak operating temperatures above 212 degrees F.
4. Photovoltaics (PV) beneath solar thermal tiles for electricity generation and heat production.
5. PV panels separate from the solar roof for grid independent power generation and operation.
6. Grid connected, off-peak, supplemental battery charging controlled by PV-sensing relays.
7. PV-powered cooling fans for PV temperature control, switch gear cooling, and solar roof heat recovery.
8. Desiccant dehumidification of outside air using solar "waste heat" in the summer.
9. Solar heat driven desiccant-evaporative cooling of outside air.
10. Solar pre-heating and pre-cooling of a heat pump to boost heat pump performance and cut electrical energy use.
11. Rainwater recovery from the solar roof to supply the indirect evaporative cooling stages.
12. Automatic winter tank drain-down to prevent freezing.
Many of these features have never before been demonstrated, such as the solar air heating tiles with PV absorbers below for simultaneous electricity and heat production in one weather-tight roof. The desiccant evaporative cooling system is also a unique development, since it relies on solar air heating to drive a desiccant air conditioning system. The high temperature summer airflow from the solar roof is an ideal energy source for the desiccant regeneration, which is accomplished with hot air. In the wintertime, the solar roof supplies heating energy to the guard station. The electric power produced drives the heating and cooling system fans and pumps throughout the year and provides security lighting at night.
The solar-desiccant-evaporative system has reduced dew point temperatures by as much as 16 degrees and reduced dry bulb temperatures by 10 degrees F during a mid-day test in July. When minor adjustments are made to the water flow and airflow between stages, a 20+ degree drop in dry bulb temperature is expected. At peak performance, the existing system has demonstrated 3.6 units of cooling/dehumidification output for every 1 unit of electrical input and all of the electrical input from the utility grid is at night, during "off-peak" hours.
During cold weather, heat pump energy use can be cut by 35 percent or more with the addition of solar air pre-heating systems. In many cases, solar heated air from the roof or walls can be readily directed to the nearby rooftop or ground mounted heat pumps. Similarly, cooler air supplied to the heat pump in summer will cut electricity use by the heat pump in delivering air conditioning. The Pentagon system was designed to demonstrate how solar air pre-heating and pre-cooling of heat pumps can cut high electricity use in the winter and summer.
The PV system is sized to supply all the power needed during the winter months. During the peak air conditioning season in the summer, the solar-desiccant-evaporative system will often consume more power than the PV panels can generate. The batteries provide the necessary capacity to operate the solar-desiccant-evaporative system throughout the day. When the sun sets, the PV system activates a "110 Volt AC to 24 Volt DC" battery charger that brings the batteries up to full charge during the nighttime hours. This hybrid battery charging approach makes the maximum use of the PV output during peak electric demand and shifts the grid connected battery charging to an "off-peak" period when electrical demand on the utility grid is lower.
The project was initiated in 2003 and the system began automatic operation and testing in the summer of 2004. Dr. Get Moy, director of Installations Requirements and Management for the Office of the Under Secretary of Defense (Installations and Environment), said, "I am excited that the Pentagon has demonstrated the successful application of these advanced energy technologies, where they will be visible to energy users across the Department of Defense and the federal government."
Reprinted from FEMP Focus, Winter/Spring 2005, a publication of the office of Federal Energy Management Programs, U.S. Department of Energy. For additional information contact Terri Robertson, Pentagon energy manager, at 703-695-8004 or John Archibald of American Solar Inc. at 703-346-6053 or download the Summary Report at www.americansolar.com/techpapers.html.
Publication date: 05/16/2005