A versatile computer program was developed to simulate five typical solar domestic hot water systems. These systems include both thermosyphon and pumped designs. These systems were assembled and tested in the present work. Numerical simulations of these systems were verified by comparison to experimental results. Predicted thermal performance, i.e., collector inlet and outlet temperatures, and auxiliary energy requirements were found to be in excellent agreement with experiments. The computer program was then used to predict the long-term annual performance of the various systems at 14 different locations throughout California. Load size and load distribution were also varied. Economic analyses were performed on each system with the goal of identifying the most economical system at each location under a prescribed load (gallons/day) size and distribution pattern (time of day for hot water use). It was found that in almost all cases the Two-Tank Thermosyphon system was the most cost effective system for all locations, load sizes and distributions. For a large all day-time load ((GREATERTHEQ) 100 gallons (378.50 liters) per day of hot water during the day-time) the Two-Tank Pumped system was found to be the most economical system at all locations investigated. Tables are presented that show which systems are the most cost effective for each of the 14 locations given a particular load size and distribution pattern. It was also found that the collector circulation flow-rate could be reduced from typically used values of 1.50 gpm (5.678 liters/min) to 0.30 gpm (1.136 liters/min) with annual system performance unaffected. This points out the need for a low flow-rate pump that could possibly be powered by a solar cell(s). A reduction in auxiliary pump energy along with the possible elimination of pump safety devices (e.g., pump-off alarms when the sun is shining and/or auxiliary battery packs to make up for pump power losses) could be accomplished if a smaller capacity pump powered by a solar cell(s) is utilized.; The Two-Tank Thermosyphon system shows promise of being the most widely used solar domestic hot water system. Numerical and experimental results for thermosyphon systems show comparable performance between a One-Tank system with a horizontal storage tank and a Two-Tank system with a vertical storage tank. The horizontal storage tank has some advantages over conventional vertical tanks. These are: (1) reduction of tank height protruding above roof line and (2) possible elimination of added roof members to support the storage tank. An experimental investigation of a 20-gallon (75.70 liters) (12 in x 40 in or 30.48 cm x 103.188 cm) horizontal tank was performed under typical solar operating conditions. Thermocline break-up was noted when loads were taken. A diffuser manifold on the cold make-up water inlet can prevent smearing of the temperature profile when a load is removed. A diffuser manifold design is presented. An analytical model was developed to simulate the thermal performance of a horizontal storage tank when a diffuser manifold is used on the make-up water inlet. Agreement between theory and experiment was found to be good. The model can be used for long-term annual performance simulations of One-Tank Horizontal systems.
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