Improving the energy consumption of a laundry washing machine through drain-water waste heat recovery

Abstract

In recent years, improving the energy efficiency of household appliances has become increasingly important due to rising energy costs and growing concerns about environmental sustainability. This study presents the use of waste heat recovery in a domestic laundry washing machine as a practical approach to reducing energy consumption and improving overall energy efficiency. A detailed investigation into the recovery of heat from drain water is carried out, focusing on the design, fabrication, and performance evaluation of a heat recovery unit used to preheat the incoming cold water. The study quantified the amount of heat lost in wastewater during a typical washing machine and designed a simple heat recovery unit (HRU) based on measured operating conditions. Baseline tests were first conducted under identical conditions to evaluate performance. The findings obtained indicate that the implementation of the HRU resulted in an average energy saving of 0.09 kWh per wash cycle, representing/corresponding to an approximate 14% reduction in total energy consumption on an annual basis. This translates to an estimated energy saving of 46.8 kWh per household and a reduction of 9.69 kg of CO₂ emissions. The system remains attractive due to its simplicity, low cost, and ease of implementation, despite the relatively modest annual cost savings per unit.