This study investigates the potential for waste water heat recovery in a residential application.A heat exchanger is utilized to transfer heat from the waste water drain line of a residence to the incoming water supply line.An experiment is conducted on the University of Illinois 2009 Solar Decathlon competition home to quantify the benefit of a heat recovery system that utilizes a counter flow flat plate heat exchanger in a balanced flow configuration.This system recovers heat in a non-regenerative scheme (meaning that it does not retain the discharge water for batch heat recovery) and is capable of reducing the hot water energy demand the home.This system is designed to benefit appliances like showers and sinks that drain simultaneous to the make-up water demand.The results of the experiment indicate that up to 37% of the thermal energy used by a shower can be recovered with the system developed in this study.These results are based on a drainage water temperature of 101 °F (38 °C) and a supply water temperature of 76 °F (24 °C) at an average effluent mass flow rate of 6.74 kg/s.Flow rate is determined to have a positive correlation to the magnitude of recoverable heat, although the heat recovery percentage has marginal difference for the low, medium, and high flow rates tested.The heat recovery percentage was 34%, 37%, and 33% for the low, medium, and high flow rates tested.It is further estimated that the heat recovery percentage would increase as the supply water temperature decreases.An estimate is conducted that shows the heat recovery percentage for each flow case would increase to 41%, 44%, and 38% respectively if the supply water temperature was reduced to 55 °F (12.8 °C).
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Domestic graywater heat recovery from the UIUC 2009 solar decathlon house