Experimental analysis of energy performance f a ventilated window for heat recovery under controlled conditions

A ventilated window in cold climates can be considered as a passive heat recovery system. This study carried out tests to determine the thermal transmittance of ventilated windows by using the Guarded Hot Box. By testing under defined boundary conditions, the investigation described the heat balance of the ventilated window and clarified the methodology for thermal performance evaluation. Comparison between windows with and without ventilation using the window-room-ventilation heat balance revealed that a ventilated window can potentially contribute to energy savings. In addition, it was found that a significant part of preheating occurred through the window frames, which positively influenced the heat recovery of the window but increased the heat loss. Results also showed that increasing air flow decreased the recovery efficiency until the point when the additional thermal transmittance introduced by the ventilation was higher than the effect of heat recovery. Accordingly, the use of the ventilated windows might be most suitable for window unit with low ventilation rates. The results correlated with theoretical calculations in standards and software. However, the concept of a window thermal transmittance (Uw) value is not applicable for energy performance evaluation of ventilated window and requires deeper analysis.

► We tested a ventilated supplied window and compared it with a traditional window.
► The test was performed in the Guarded Hot Box under a controlled environment according to the standards.
► We found out that the ventilated window can reduce energy consumption.
► The efficiency of the ventilated window was highly dependent on the ventilation air flow rate.