Abstract
Hot water heating accounts for about 7% of the energy demand in South Africa and about 30% in the residential sector. The most common heating method electrical resistance water heaters (geysers) are inherently fossil-fuel driven and thus responsible for carbon emissions. In this paper, the potential application of a direct-expansion solar-assisted heat pump water heater (DX-SAHPWH) system in South Africa was investigated. The DX-SAHPWH combines the beneficial characteristics of both the solar thermal collector and heat pump, however, the performance of a DX- SAHPWH system is significantly influenced by the changes in meteorological conditions. A quasi-steady state mathematical model was developed and theoretical simulations were conducted using meteorological data of Cape Town. The results indicated an hourly average COP of was 4.9, collector efficiency of 50 %, solar fraction and heating times of 68 % and 192 minutes for average temperature, solar radiation and wind speeds of 23 °C , 700 W/ m2 and 3.3 m/s. The annual average COP was 5.3, collector efficiency 48 %, solar fraction 66% and heating time of 127 minutes. Furthermore, a parametric study indicated that the ambient temperature, solar radiation and wind speeds influence the system performance.
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