HIGHLIGHTS OF SEVERAL COMMERCIAL DRAINBACK SOLAR HOT WATER INSTALLATIONS IN 16 TO 52 UNIT APARTMENT BUILDINGS, ALL USING LARGE NON-PRESSURIZED EPDM LINED TANKS

摘要

The author feels that simple Bulk Drainback systems using economical non-pressurized tanks and simple single pass submersed heat exchangers, can be the most economical and effective solar hot water preheat system for many buildings that use large quantities of domestic hot water. This paper goes into some of the reasons for this belief, and highlights some examples of such systems that have been installed in the Philadelphia area. Bulk drainbacks are somewhat different in design from typical residential size solar hot water systems. The heart of each system highlighted in this paper is a large EPDM lined tank that holds up to several thousand gallons. Single family size solar hot water systems typically utilize pressurized steel tank storage somewhere in the 60 to 120 gallon (227 to 454 ltr.) range. Steel pressure tanks in that size range can usually fit through standard doorways and stairways by 2 workers with a hand truck. One of the challenges with very large solar hot water systems are the very large tanks required. Even if one had means to move around very heavy multi-thousand gallon steel tanks, doorway and stairway limitations of existing buildings will rarely permit entry of such sizes. Rows of 120 gallon (454 ltr.) steel tanks could potentially be used, however these tanks are not cheap, plus considerable plumbing, labor and materials are involved to plumb them together, further adding to cost. From a heat loss standpoint, the extra surface area of multiple tank systems increases heat loss and decreases system efficiency. In contrast, a large multi-thousand gallon non-pressurized EPDM lined tank can be brought in, one component at a time, through standard stairs and doorways and site assembled at a cost per gallon less than the cost of multiple steel tanks. In summary, a single large EPDM lined tank can store more water for less cost, with less surface area, with less heat loss, on a smaller footprint, than the alternate approach of multiple steel tanks.