In this paper, different kinds of water heating systems are analyzed for hot water production in Hong Kong in terms of economic
characteristics and global warming impacts.
The economic comparison results show that a solar thermal system has greater economic benefits than an electric water heater
and a towngas water heater. Accordingly, its payback period is
much shorter than a towngas water heater. Further analysis demonstrates that the solar fraction of a conventional SWH system is
much lower than a SAHP system when the solar collector area is
less than 4 m
2
. Conversely, while the solar collector area is larger
than 4 m
2
which means the solar fraction of a conventional SWH
system is above 50%, both the cost saving and payback period of
a conventional SWH system are comparable with that of a SAHP
system.
From analysis on the sensitivity of TEWI of different solar thermal systems, it is concluded that the towngas boosted SWH system
has the greatest potential in reducing greenhouse gas emission under any design conditions. While the electricity boosted SWH system has the comparative TEWI with the SAHP systems if its solar
collector area is larger than 4 m
2
. As for the SAHP systems, the
SA-ASHP system has evident advantage considering its global
warming impact.
All investigation results demonstrate that solar thermal systems have greater application potential under Hong Kong weather conditions. In order to utilize solar thermal energy more
efficiently, the system selection should depend on the available
space for solar collector arrangement. If there is enough space
to ensure that the solar fractions of the conventional SWH systems are above 50%, the conventional SWH systems, especially
the towngas boosted SWH system, are preferred compared with
SAHP systems. Otherwise, SAHP systems are proposed, especially
the SA-ASHP system.