A solar hot water heating system installed about a year ago in a ten unit apartment building has not yielded the anticipated reduction in energy consumption. The system has three tanks, two with heat exchangers to preheat the water, and a 100 gallon, 199,000 BTU/hour gas-fired tank to boost the temperature as required. Two preheat tanks were installed in parallel to insure an adequate flow rate; space constraints prevented the installation of a single large tank. The 1.5 inch diameter outputs of each pre-heat tank are combined to feed the 2.0 inch diameter input of the gas-fired temperature boost tank before the water is fed to the building.
The solar panel fluid is circulated in a separate closed system with a drain-back tank. Currently, the solar panel fluid is similarly divided and flows in parallel through both of the pre-heat tanks. Is that the optimum configuration? It seems to me that channeling the solar panel fluid through pre-heat tank heat exchangers connected in series would result in more efficient operation, while the pre-heat tanks remain connected in parallel for the delivery of water to the gas-fired temperature booster tank.
The solar panel fluid is circulated in a separate closed system with a drain-back tank. Currently, the solar panel fluid is similarly divided and flows in parallel through both of the pre-heat tanks. Is that the optimum configuration? It seems to me that channeling the solar panel fluid through pre-heat tank heat exchangers connected in series would result in more efficient operation, while the pre-heat tanks remain connected in parallel for the delivery of water to the gas-fired temperature booster tank.
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