Thermal characterization of a novel heated glass element

Abstract

Although the U-value of glazing has improved significantly in the last decades, the thermal transmittance of windows remains relatively high compared to opaque elements of the thermal shell. Consequently, glazing has a relatively low interior surface temperature in the heating season, which can cause thermal discomfort. A novel heated glass element has been developed, allowing for the control of its interior surface temperature. In-situ measurements were conducted on a heated glass element, with the objective to (i) characterize its thermal behaviour, (ii) assess its thermal performance and (iii) to assess its impact on thermal comfort. The examination of heating-up and cooling-down curves of the heated glass element revealed that cooling-down is a slower process (τ2 of 100 - 145 minutes) than heating-up (τ2 of 70-85 minutes). In terms of thermal performance, it is shown that most of the heat provided by the heated glass element is effectively directed towards the room, rather than lost to the outdoor environment. The efficiency depends on the temperature difference between interior glass surface and the room, with efficiencies of 58 - 65% reached at surface temperatures of 23 - 25 °C, and efficiencies of 90% reached at surface temperatures of 39 - 43 °C. Comparative measurements of thermal comfort in a room with the heated glazing, and in a room with conventional triple glazing show an improvement in operative temperature.