Solar thermal is approximately four times more efficient at converting solar radiation to energy than photovoltaic panels.  However, to make solar thermal a viable renewable energy source the building needs to have a large domestic hot water or radiant heating to use the water.  Laboratory buildings with their large domestic hot water usage are a great fit for solar thermal installations, as was recently installed at the Marshall Conant Science and Mathematics Building at Bridgewater State University. Designed to meet the required load, a closed loop solar preheat water system was custom-built on the roof. The two solar thermal systems use evacuated tube collectors in a forty panel array for the protected hot water and a nine panel lineup for the domestic water. Mounted at an angle of 45°, the panels face due south. Estimated peak demands are 590 gph and 145 gph, respectively. In both systems, incoming cold water enters the respective storage tank (2,000 gallons for protected, 750 gallons for domestic). For anti-bacterial purposes storage tank water circulates through plate type solar heat exchangers in order to maintain 140°F in the tanks.



The panel circulating systems supply the other side of the heat exchangers with glycol. When the temperature falls below 140°F, and the sun cannot provide the necessary heat, steam heat exchangers (from the central plant) boost hot water exiting the tank to 140°F. This temperature regulation occurs before introducing the water to mixing valves to drop the temperature for end use. These systems run continuously during daylight, with the glycol routing to heat dump systems in case of low demand or excessive panel output. To allow for the release of heat and reduce the overheating of the system, the design respectively use 990 and 220 linear feet of 3/4 inch copper pipe embedded in the concrete foundation mat below the building.



Implementing this technology is ideal in science buildings where demand for hot water impacts energy costs and consumption. Additionally, hydronic space heating utilizes this technology if the building design is appropriate. Water heating systems with high operating costs frequently benefit from solar water heating systems due to their cost effectiveness.

by Todd Sloane

from → Sustainable Design