The economic and environmental impact of replacing geyser with air source heat pump water heater

The study focused on the evaluation of the energy cost saving and greenhouse gas emission reduction when a 3.0 kW electric geyser is replaced by a 1.2 kW split type ASHP water heater. Both hot water devices were of 150 L capacity and are set up to operate simultaneously under specific volumes of hot water drawn off (150, 50 and 100 L) in the morning, afternoon and evening each day over a year. The data acquisition system comprising of flow meters, temperature sensors, power meters, ambient temperature and relative humidity sensor and a data logger. The data acquisition system was built and installed to monitor the performance of the hot water devices. The results depicted that the average monthly energy saving and CO2 reduction achieve with the ASHP system due to the 300 L of daily volume of hot water drawn off was 203.67 kWh and 201.63 kg, respectively for the summer season. The average monthly cost saving for the summer period based on the flat rate tariff (FR) and the time of use (TOU) tariff was R25S.66 and R 296.35. In addition, the average monthly energy and CO2 impact of the ASHP water heater due to the daily 300 L of hot water drawn off was 249.24 kWh and 246.74 kg, respectively for the winter season. The corresponding average monthly flat rate and time of use cost saving for the winter season was R 378.84 and R 719.26. The average month-day COP for both the summer and winter seasons was 2.90 and 2.49, respectively. A firm conclusion can be established that the time of use cost saving is higher than the flat rate cost saving due to the relatively higher electricity tariff structure attributed to the time of use electricity plan especially during the peak periods. Despite, the low average month-day COP experienced by the ASHP water heater in the winter as opposed to the COP for the average month-day in the summer period, the electrical energy saving of the ASHP water heater was higher due to the lowered makeup water temperature. These lowered makeup water temperature is associated with a greater electrical energy consumed and thermal energy gained before hot water set point temperature is attained after the hot water drawers.