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

Double-circulation water-flow window is a novel-designed solar-building-integrated energy saving system. The window part is composed of four layers of glass panes and 2 layers of flowing water, which contributes to building energy conservation by utilizing solar energy for domestic hot water preheating and regulating indoor heat gain through window. In heating season, warm water is supplied to the water-flow window cavity and it releases heat to the room through the innermost glass pane. Thermal, energy and economic performance of the compact double-circulation water-flow window was numerically analyzed in the present study. Results showed that direct solar transmission could be largely reduced with water-flow window, compared with common curtain wall. The year-round solar collection efficiency was 16.2% for the external water circulation and 4.3% for the internal water circulation. The predicted static payback period was around 7 years, with the extra investment of water-flow window over common curtain wall and the saving in electricity charge taken into consideration. For higher inlet water temperature at the internal window cavity during heating season, the predicted payback period was slightly longer, since part of the heat was lost to the outdoor environment. The results showed preferable potential of double-circulation water-flow window system in buildings with stable hot water demand and high-density energy demand.