The heating of water for domestic purposes presently accounts for 24 percent of Canadian residential energy consumption (Natural Resources Canada, 2006). This energy demand is primarily met by conventional sources such as electricity, natural gas and oil. Recent changes in fuel availability and price as well as environmental concerns lead consumers to give further consideration to the use of solar energy for heating water. The objective of this paper is to simulate the different domestic hot water (DHW) systems to examine their fuel consumption, greenhouse gases (GHG) emissions, life cycle costs and pay back periods. In this case study, seventeen different DHW systems were simulated using TRNSYS as simulation engine. These include solar-based models (with electric and natural gas backup tanks), electric and natural gas tank models (with and without gray water heat recovery), on-demand and combo-boiler systems. This paper will discuss three solar-based systems in detail, however their result comparison with other systems will be discussed. Three different solar-based systems are: I) Solar pre-heat with .56 efficiency natural gas back up tank; II) Solar pre-heat with .94 efficiency electric back up tank; III) Timers (off during peak times 7am till 10 pm) with solar pre-heat and electric (.94 efficiency) secondary. Results indicate that solar alternative having timers with solar pre-heat and electric secondary gives best results in terms of annual fuel consumption ($93) and GHG emissions (266 kg). However on demand modulating gas combo boiler (0.78 efficiency) with gray water heat recovery (0.6 efficiency) has best 30-year life cycle cost ($12332).

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