Quantification of the viability of residential air source heat pump water heaters as potential replacement for geysers in South Africa
Authors: Tangwe Stephen loh , Simon Michael 
Published: January 2019

Purpose
This paper aims to compute demand, consumption and other avoidance saving by replacing existing geysers with split and integrated type air source heat pump (ASHP) water heaters, to prove the potential of both ASHP water heaters in both winter and summer by virtue of their coefficient of performance (COP) during the vapour compression refrigeration cycles and to demonstrate that despite the viability of both split and integrated ASHP system, the latter exhibits a better performance in terms of its COP and achievable savings and load factor.

Design/methodology/approach
This research emphasised the use of the data acquisition system housing various temperature sensors, power metres, flow metre, ambient temperature and relative humidity sensor to determine electrical energy consumption and useful thermal energy gained by the hot water in a geyser and storage tanks of residential ASHP water heaters. The load factors, average power and electrical energy consumptions for the 150 L high-pressure geyser, a 150 L split and integrated type ASHP water heaters were evaluated based on the controlled volume (150, 50 and 100 L) of daily hot water drawn off.

Findings
The results depicted that the average electrical energy consumed and load factors of the summer months for the geyser, split and integrated type ASHP water heaters were 312.3, 111.7 and 121.1 kWh and 17.9, 10.2 and 16.7 per cent, respectively. Finally, the simple payback period for both the split and integrated type ASHP water heaters were determined to be 3.9 and 5.2 years, respectively. By the application of the Eskom’s projected tariff hikes over the years, the payback periods for the split and integrated ASHP water heaters could be reduced to 3.3 and 4.1 years, respectively.

Research limitations/implications
The experiments were conducted in a controlled outdoor research facility as it was going to be of great challenge in conducting both experiments simultaneously in a specific home. The category of the different types of ASHP water heaters was limited to one due to the cost implication. The experiment was also conducted at a single location, which is not a full representation of all the ambient conditions of the different regions of South Africa.

Practical implications
The experiments were done with a specific controlled volume of hot water drawn off from each of the three hot water heating devices. The experiments was structuring controlled to a specific volume of hot water drawn off and at specific period of the day and hence to not cater for random drawers and intermittent drawn off.

Social implications
The findings help to assure homeowners that irrespective of the type of ASHP water heaters installed in their residence, they can be guarantee of year-round performance and a favourable payback period provided their hot water consumption is over 200 L per day. Also, although the split type ASHP water heater performed better than the integrated system the cost of installation and maintenance will be higher in a split type in comparison to the integrated type. Finally, by successful implementation of either of the ASHP water heaters the home owner can substantially save of his hot water bill.

Originality/value
The experimental design and methodology is the first of its kind to be conducted in South Africa. The results and interpretation were obtained from original data collected from the set of experiments conducted. Also, the authors are able to show that the introduction of back up element in an ASHP unit to run simultaneously with the vapour compression refrigeration cycles of the ASHP can reduce the COP of the overall system.