Differences in heat losses between glazing of various emissivities related to night sky radiation: Experimental and numerical analysis

Radiation from cloudless night skies causes significant heat loss through glazing, resulting in higher heating costs. This study investigated the heat loss of glazing due to night-sky radiation as a function of its emissivity. A measuring apparatus comprising measuring stations mounted with glazing and two different emissivities was set up. The glazing losses and amount of energy radiated from the sky in the infrared region were measured. Additionally, to indicate the impact of other factors, a numerical model of glazing heat loss was prepared. A difference in temperature and heat losses between conventional glazing with an emissivity of 0.89 (29.47 W/m2) and coated glazing with an emissivity of 0.14 (5.43 W/m2) was observed. The temperature difference and heat losses were 54.26 % (1.28 °C) and 81.6 % (24.04 W/m2), respectively, in favour of the coated sample. The novelty of this study is the determination of heat losses from glazing of different emissivities due to radiation in the night sky under real conditions, with the indication of other factors. These results motivate further research on coated glazing to reduce heat loss. This numerical model can serve as a blueprint for examining similar applications.