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

3 Characteristics of the proposed system 
Performance evaluation of the innovative double-circulation 
water-flow window system with multi-functions of room 
heating and solar thermal collection was executed through 
Fig. 2
Schematic structure of double-circulation water-flow window system 

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Li et al. / Building Simulation / Vol. 13, No. 3 
578 
numerical simulation. Typical Meteorological Year (TMY) 
weather data of Shenzhen, China (obtained from http:// 
apps1.eere.energy.gov/buildings/energyplus/cfm/weather_
data.cfm) was used in the present investigation. Shenzhen 
is located in southeast China, with longitude of 114.1°E and 
latitude of 22.5°5N. The monthly averaged ambient tem-
perature and accumulated global solar radiation values are 
shown in Fig. 3. Its year-round average ambient temperature 
is 22.9 °C, with the highest/lowest temperatures to be 38.0 °C/ 
4.0 °C throughout the year. The accumulated global solar 
radiation is as high as 1509.1 kWh/m
2
. With rapid economic 
growth and ever-growing living standard, more and more 
buildings are equipped with air-conditioning devices and 
are consuming larger amount of energy, which leaves great 
potential for energy saving in building sector. 
The proposed double-circulation water-flow window
is applied to an air-conditioned room with dimensions of
3.0 m (length) ×3.0 m (width) ×3.0 m (height). The room is 
located at the south side of the building, with south-facing 
water-flow window as curtain wall. The composition of
the window is shown in Fig. 2, with dimensions of 3.0 m 
(height) ×3.0 m (width). The other walls, floor and ceiling 
are adjacent to rooms with the same indoor temperature, 
i.e. there is no extra external heat sources. The room is 
assumed to be occupied from 8 a.m. to 8 p.m., with indoor 
temperature preset to be 26 °C in cooling season (from 
May to October) and 21 °C in heating season (January, 
February and December). 
The settings of comparative simulation cases are listed 
in Table 1. Case 1 is taken as the base case, with common 
curtain wall configuration composed of double glass panes, 
i.e. L+A+C, in which L, A and C represent Low-e glass pane, 
sealed air and clear glass pane, respectively. The investigated 
double-circulation water-flow window is applied to Cases 2–4, 
with window composition shortened as C+W+C+A+C+W+C, 
in which W represents the flowing water layer. Water flow 
rates within both Cir1 and Cir2 are 0.005 kg/s.
The clear glass panes (g1, g3, g4 and g6 in Fig. 2) in these 
comparative cases are PLANILUX_6 and the Low-e coated 
glass in Case 1 is PLANITHERM ONE 2. Their optical 
properties (obtained from https://windows.lbl.gov/software/ 
window) are listed in Table 2. The thickness of the flowing 
water layers (f2 and f5) in Cases 2–4 are 0.01 m, with direct 
solar absorption rate of 0.1357 at normal incidence (Otanicar 
et al. 2009). 
For Cir1, the water circulates with power provided
by the pump for the purpose of solar energy collection.
The inlet temperature of the external flowing water layer