Results and discussions
The economic comparisons between different water heating
systems are performed by means of the aforementioned calcula-tion method and summarized in Table 1. The results show that
the solar thermal systems, especially the SA-ASHP system, have
great potential of saving energy. As a result, their payback periods
are much shorter than the towngas water heater compared with
the base case: the electric water heater. Among the solar thermal
systems, the conventional SWH system exhibits the shortest pay-back period. Although the SA-ASHP system has the highest annual
cost saving, its payback period is longer than the conventional
SWH system because of higher initial cost. Also, the payback peri-ods of other SAHP systems are much longer than the conventional
SWH system even though they have similar annual cost savings.
These analyses show that both the initial cost and the annual cost
savings have great effects on the payback periods of the systems.