Evacuated-tube (ET) solar water heaters are popular in China. Both single-phase and two-phase thermosyphon ET collector systems
are available in the market. However, the system energy and economic performance has not been evaluated systematically. In this paper,
the numerical evaluation of these two types of solar water heaters in different climate zones of China was reported on the aspects of
system energy performance and economical return. The single-phase system is found having better cost payback period in all these cities,
and can be a suitable choice except for locations with extreme cold weather. The two-phase design is an attractive and sustainable alter-native since its thermal efficiency is higher under the same weather condition and this is important for supporting zero-carbon building
design. On the other hand, it can be readily used to enhance the outside appearance of a building. Hence when considering climate adapt-ability and aesthetic compatibility, the potential of the two-phase system is higher.