Open AccessHigh performance in low-flow solar domestic hot water systems
Author(s) -
Myrna Dayan
Publication year - 1997
Language(s) - English
Resource type - Reports
DOI - 10.2172/578464
Subject(s) - volumetric flow rate , mechanics , flow (mathematics) , heat exchanger , environmental science , water flow , materials science , flow coefficient , nuclear engineering , engineering , mechanical engineering , environmental engineering , physics
Low-flow solar hot water heating systems employ flow rates on the order of 1/5 to 1/10 of the conventional flow. Low-flow systems are of interest because the reduced flow rate allows smaller diameter tubing, which is less costly to install. Further, low-flow systems result in increased tank stratification. Lower collector inlet temperatures are achieved through stratification and the useful energy produced by the collector is increased. The disadvantage of low-flow systems is the collector heat removal factor decreases with decreasing flow rate. Many solar domestic hot water systems require an auxiliary electric source to operate a pump in order to circulate fluid through the solar collector. A photovoltaic driven pump can be used to replace the standard electrical pump. PV driven pumps provide an ideal means of controlling the flow rate, as pumps will only circulate fluid when there is sufficient radiation. Peak performance was always found to occur when the heat exchanger tank-side flow rate was approximately equal to the average load flow rate. For low collector-side flow rates, a small deviation from the optimum flow rate will dramatically effect system performance