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

Fig. 4 
Indoor heat gain through the window during heating season 
(per 1 m
2
window) 
Fig. 5 
Indoor heat gain through window during cooling season 
(per 1 m
2
window) 
gains through the window are as high as 161.6 kWh,
176.5 kWh and 191.4 kWh for Cases 2, 3 and 4, higher than 
the 141.7 kWh of Case 1. The increment percentages are 

---

Li et al. / Building Simulation / Vol. 13, No. 3 
581
14.0%, 24.6% and 35.1% respectively compared with Case 1. 
This means the water-flow window can provide room heating 
and partly replace the conventional air-conditioning terminals 
during heating season. 
As for the cooling season, the inlet water temperatures 
in both window cavities (f2 and f5) are preset at the same 
temperature of ambient, i.e. to use municipal water as cooling 
source to bring heat away from the room. Also, solar 
thermal energy is absorbed by the flowing water and 
exploited for water pre-heating. This energy transportation 
help to reduce indoor heat gain and achieve energy saving 
of Air-conditioning system. The monthly indoor heat gain 
from direct solar transmission and comprehensive indoor 
heat gain from window from May to October are shown
in Fig. 5. 
The cooling season is long and hot in Shenzhen, lasting 
from May to October every year. The accumulated incident 
solar radiation on every 1 m
2
of curtain wall during the 6 
months is 493.8 kWh, of which 150.9 kWh is transmitted 
into indoor environment directly in Case 1. The equivalent 
comprehensive transmissivity is 30.6%, which is slightly 
lower compared with heating season, mainly due to the 
larger solar elevation angle in summer. For double-circulation 
water-flow window, the direct solar transmission is 78.7 kWh 
for Cases 2–4, which is 47.9% lower compared with Case 1. 
The comprehensive indoor heat gain from window is
158.8 kWh for Cases 2, 3 and 4, which is 18.5% lower 
compared to the 194.9 kWh room heat gain in Case 1. The 
decrease in room heat gain means the cooling load of 
air-conditioning can be reduced by large scale, which is 
favorable for energy conversation. 
5.2 Solar collection rate and system efficiency 
A predominant advantage of water-flow window is the 
absorption and utilization of renewable solar energy. As
in Fig. 2, the flowing water in Cir1 keeps absorbing solar 
thermal energy during daytime throughout the year. As for 
the flowing water in Cir2, the solar energy is utilized from 
March to November, i.e. the months without room heating 
demand. The amount of monthly solar collection and the 
variation of system efficiency are given in Fig. 6 and Table 3.