Development of a wastewater heat recovery unit for residential buildings in New Zealand

Abstract Electric hot water cylinders account for a significant portion of residential building energy consumption. This is while most of this energy is wasted through the drainage water from showers and baths. Using a Waste Water Heat Recovery (WWHR) system to recover the waste heat is a viable solution to improve the energy efficiency of residential buildings. This would reduce the carbon emissions, and also help in adopting solar water heaters for domestic water heating systems. Due to the orientation of the drain pipes in the existing buildings, most of the systems proposed in the literature are vertical, which makes it difficult and costly to install on existing buildings. On the other hand, the impurities in the residential wastewater could lead to fouling of the heat recovery units. Therefore, this work is aimed at the development of a low-maintenance horizontal economizer that can be installed in various construction types. It was shown that the proposed economizer has the potential to increase the water inlet temperature of the hot water cylinder by 8℃. This is a reduction of 20% in energy consumption, equivalent to 0.912 kWh of energy, per shower, resulting in an annual reduction of 50 kg of CO 2 equivalent per shower in New Zealand. This is in alignment with the mission to achieve net zero carbon emissions by 2050.