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

Fig. 3 
Monthly averaged ambient temperature and accumulated global solar radiation in Shenzhen 
Table 1
Settings of the comparative simulation cases 
Inlet water temperature of internal window 
cavity f5 (°C) 
Case no. 
Window 
composition 
Flow rate of 
water within Cir1 
and f2 (kg/s) 
Inlet water temperature 
of external window 
cavity f2 (°C) 
Flow rate of 
water within Cir2 
and f5 (kg/s) 
January, February,
and December 
Other months 
1 L+A+C 
— 
— 
— 
— 
— 
2 
C+W+C+A+C+
W+C 
0.005 
Same as ambient 
temperature 
0.005 34 
Same as ambient 
temperature 
3 
C+W+C+A+C+
W+C 
0.005 
Same as ambient 
temperature 
0.005 37 
Same as ambient 
temperature 
4 
C+W+C+A+C+
W+C 
0.005 
Same as ambient 
temperature 
0.005 40 
Same as ambient 
temperature 

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Li et al. / Building Simulation / Vol. 13, No. 3 
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Table 2 
Optical properties of the glass panes in the comparative 
simulation cases 
Glass type 
Clear glass 
(PLANILUX_6) 
Low-e coated glass 
(PLANITHERM 
ONE 2) 
Thickness (m) 
0.0059 
0.006 
Solar transmittance at normal 
incidence 
0.806 0.489 
Solar reflectance at normal 
incidence (front side) 
0.072 0.390 
Solar reflectance at normal 
incidence (back side) 
0.071 0.447 
Emissivity (front side) 
0.84 
0.84 
Emissivity (back side) 
0.84 
0.022 
(f2) is taken the same as ambient temperature, based on the 
assumption of thorough heat transfer with municipal feed 
water at the tank. For Cir2, the flowing water layer (f5) 
releases heat to the room space during heating season and 
collects solar thermal energy in the remaining seasons. 
Therefore, the inlet temperature of the internal water layer 
(f5) is higher than indoor air in heating season, which 
includes January, February and December for Shenzhen.
In order to evaluate the influence of water temperature on 
system energy and economic performance, the inlet tem-
peratures of the internal water layer (f5) is set to be 34 °C in 
Case 2, 37 °C in Case 3 and 40 °C in Case 4. In the remaining 
period, the inlet water temperature of f5 is set the same as 
ambient temperature.