Journal
APPLIED ENERGY
Volume 242, Issue -, Pages 27-45Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.apenergy.2019.03.029
Keywords
Triple-glazed airflow window; Numerical modelling; Heat and mass transfers; Experimental validation; Energy efficiency; Building
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In this paper, we numerically investigate thermal characteristics and performances of a triple-glazed airflow window, by comparison to conventional double and triple-glazed ones. Numerical simulations were performed with a nodal model of the airflow window, which has been first validated from experiments. Both experimental and numerical results show that the air supply preheating through the airflow window is significant, ranging from approximately 10-20 degrees C without solar radiation and during sunny periods, respectively. In the first case, the energy gain comes from both solar radiation and heat loss recovery through the window, while only from heat loss recovery in the second one. Then, additional simulations have been performed in order to compare the airflow window to a conventional airflow ventilation system combined to conventional double and triple-glazed windows. Numerical results point out that, due to the entering fresh outdoor air, the airflow window causes a stronger cold wall effect. However, at the same time, it reduces cold draught risks (air supply preheating of about 10 degrees C) and heat losses too. Indeed, for the same reason, the outer face temperature of the airflow window glazing is low and subsequently external heat transfers by convection and radiation reduced. Results also show that, in comparison to conventional windows, energy needs to heat a room are lower if this one is equipped with an airflow window. The reduction approximately ranges from 5% for night-time to 90% for daylight conditions. The main reason is the significant reduction in energy needs to heat the fresh air entering the room, by 36% and 79%, respectively. For an entire day, we found that the energy balance sheet is approximately neutral for an airflow window (-70 Wh), while negative for conventional double and triple-glazed ones (-572 Wh and -653 Wh, respectively). Finally, we compare and discuss the airflow window performance in terms of thermal transmittances, U-g and U-w values, and solar heat gain coefficients, g(g) and g(w) values. Results obtained for the airflow window point out that U-g and U-w significantly decrease when the airflow rate increases, due to an increase in the air supply preheating, especially until 15 m(3) h(-1). Results also show that it outperforms the double-glazed window at any airflow rate and the triple-glazed one for airflow rates from just 3 m(3) h(-1). At the opposite, g(g) and g(w) increase with the airflow rate, especially until 15 m(3) h(-1) and the comparison points out that the airflow window out-performs both the double and triple-glazed ones at any airflow rate. As an example, for an airflow rate of
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