Quantifying residential hot water production savings by retrofitting geysers with air source heat pumps

Inefficient geysers remain South Africans´ most popular and conventional modes of hot water production Today, the air source heat pump (ASHP) water heater is used in the residential sector as energy efficiency technology for sanitary hot water production. It is capable of supplying sanitary hot water with 30 to 40% of the total thermal energy generated from electrical energy; the rest emanates from ambient aero-thermal energy. Sanitary hot water is set at a threshold temperature of 55°C to prevent growth of legionella (bacteria).Therefore, employing this technology could result in a substantial reduction in Eskom peak demand and global warming hazards. This research focused on designing and building (DAS housing) various temperature sensors, power meters, flow meters, relative humidity and ambient temperature sensors, to determine electrical consumption and useful thermal energy gained by the hot water in the geyser and the storage tank of the ASHP water heater. In addition, an empirical calculation of the co-efficient of performance of the ASHP water heater was reached. Furthermore, the amount of aero-thermal energy extracted was evaluated based on the temperature difference between the warm air in the vicinity of the evaporator and the cold, dehumidified air expelled from the duct space of the ASHP unit. Finally, results of the electrical energy consumption from sanitary hot water production showed a reduction from 60% to 31% by the retrofitting of the geyser with ASHP.