Recovery of greywater thermal energy with a wire on a tube heat exchanger attached to a dishwasher.

Heat recovery and energy savings from the graywater of household appliances, such as dishwashers and washing machines, can encourage people to avoid the unhealthily long hours of hand dishwashing. In this experimental study, the size of energy saving that could be obtained from a domestic dishwasher with a wire on a tube heat exchanger attached was investigated. The study results validated that heat recovery from graywater is possible and equivalent to annual electricity savings of 53.48 kWh. The efficiency of the dishwasher can be increased to approximately 16% by saving energy, and the economic value of efficiency increase can be $5.88 per year. With all fittings, pipes, and fixing equipment, the heat exchanger cost was also calculated to be $35 per machine, and the payback period is 5.94 years per machine. The payback period can be shortened by achieving lower production costs with mass production. Furthermore, the possible reduction of CO emission by saving electrical energy was estimated to be 26.74 kg. In Turkey, nearly 8 million units of dishwashers are in domestic use, the size of the annual energy saving can be 427.84 GWh, and the economic value is $47.04 M. By energy saving, approximately 213.92 kt/year less CO released. PRACTITIONER POINTS: Graywater heat recovery with a wire on a tube heat exchanger was studied experimentally. The energy consumption and processing time of a household dishwasher is shortened by graywater heat recovery. With the decrease in energy consumption, a reduction was achieved in the CO emission released during the energy generation.