Domestic hot water heating in zero net energy homes

The objective of this paper is to examine different means of producing domestic hot water (DHW) in Zero net energy homes (ZNEH). Four alternatives are examined : i) a regular electric hot water tank; ii) the desuperheater of a ground-source heat pump with electric backup; iii) thermal solar collectors with electric backup; iv) a heat pump water heater (HPWH) indirectly coupled to a space conditioning ground-source heat pump. Energy simulations, using TRNSYS as the simulation engine, are performed to evaluate each alternative. The house simulated has 156 m2 of conditioned space and is located in a northern climate (Montréal, Canada). On site electrical production is accomplished using efficient photovoltaic (PV) modules generating 197.3 kWh/m2-year. Space conditioning is accomplished using an Energy Star 2.5 tons ground-source heat pump (GSHP). Results indicate that the alternative that uses thermal solar collectors is the best solution as it requires only 8.05 kW of peak PV power (compared to 8.75 kW for the next best solution). The total house energy requirements are around 11000 kWh. This amount of electricity has to be produced by the PV modules in order to achieve the ZNEH target.