Performance of double-circulation water-flow window system as solar collector and indoor heating terminal Chunying LI 1

2 System configuration and operation mode 
Figure 1 presents the outlook of water-flow window (on the 
right side), which is quite similar to common double-pane 
glass window (on the left side). The photo was taken during 
the water-flow window experiment carried out in Hong

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Li et al. / Building Simulation / Vol. 13, No. 3 
577
Fig. 1 
Outlook of water-flow window (the right side) in comparison 
with common double-pane glass window (the left side) (Li 2012) 
Kong. Municipal water is preheated by solar energy in the 
system. The pipework above the window can be fabricated 
in the window frame or the false ceiling in practical for 
better appearance.
The proposed double-circulation water-flow window 
system contains 2 independent water circulations. The 
schematic structure and operation modes of the system in 
both heating and cooling seasons are also demonstrated. 
As illustrated in Fig. 2, the window part is composed of 
4 glass panes, which forming 3 cavities filled with running 
water or sealed air. The external water circulation (Cir1 in 
short) serves as solar collector throughout the year. Cir1 is 
formed with the external window cavity (filled with flowing 
water, and shortened as f2), the adjacent glass panes (g1, 
g3), the heat exchanger, as well as the circulation pump and 
pipework. Water collects infrared solar energy when flowing 
through the window cavity (f2), it gets warmer and releases 
heat to the cool feed water in the tank. The feed water gets 
preheated and flows to gas/electrical water-heating device 
and then to the hot water spot.
The internal water circulation (Cir2 in short) provides 
indoor heating in heating season and collects solar energy 
in the remaining seasons.Cir2 is formed with the internal 
window cavity(filled with flowing water, and shortened as 
f5), the adjacent glass panes(g4, g6), the heat source, the 
circulation pump and pipework. In heating season, warm 
water from heat source is supplied to the internal window 
cavity (f5) and it releases heat to adjacent glass panes (g4, 
g6). The temperature of g6 rises and warms up room air 
through convective and radiation heat transfer. There is a 
sealed air layer in between g4 and g6. It provides better 
thermal insulation to prevent warm water from losing heat 
to the cold environment in heating season. At the end of 
heating season, the heat source is turned off. Water stream 
in the internal window cavity (f5) and water flow from
the external window cavity (f2) are parallel connected, the 
heated circulation water in the window cavity flows to
the heat exchanger within the tank to preheat feed water. In 
this way, both water circulations perform as solar thermal 
collector and larger amount of renewable solar energy can 
be utilized.