The Changes in Thermal Transmittance of Window Insulating Glass Units Depending on Outdoor Temperatures in Cold Climate Countries

Karolis Banionis, Jurga Kumžienė, Arūnas Burlingis, Juozas Ramanauskas and Valdas Paukštys
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Karolis Banionis: Institute of Architecture and Construction, Kaunas University of Technology, Tunelio st. 60, LT-44405 Kaunas, Lithuania
Jurga Kumžienė: Institute of Architecture and Construction, Kaunas University of Technology, Tunelio st. 60, LT-44405 Kaunas, Lithuania
Arūnas Burlingis: Institute of Architecture and Construction, Kaunas University of Technology, Tunelio st. 60, LT-44405 Kaunas, Lithuania
Juozas Ramanauskas: Institute of Architecture and Construction, Kaunas University of Technology, Tunelio st. 60, LT-44405 Kaunas, Lithuania
Valdas Paukštys: Institute of Architecture and Construction, Kaunas University of Technology, Tunelio st. 60, LT-44405 Kaunas, Lithuania

Energies, 2021, vol. 14, issue 6, 1-22

Abstract: Windows, which have a U-value that is governed by an insulating glass unit (IGU) U-value, must be a building’s only enclosure element, which has no design value concept. The declared U-value, which is calculated or measured with 0 °C of external ambient temperature, is used instead of the design value. For most of a building’s elements, its thermal transmittance with a decrease in the external temperature diminishes a little, i.e., improves. However, for modern window IGUs with Low-E coatings, it is the opposite: the thermal transmittance with a lowering external temperature increases. Therefore, for calculating the peak power for the heating of buildings it is necessary to pay attention to this phenomenon and, therefore, it would be wise to introduce the concept of design U-value for windows, recalculation rules, or affix their declared U-values. This is especially the case in modern times with the prevailing architectural tendencies for enlargement of transparent building elements. For IGUs with Low-E coatings and inert gas fillers, the thermal transmittance depends on the temperature difference between warm and cold environments. When the external temperature is −30 °C instead of 0 °C, the thermal transmittance of the IGU can increase by up to 35%. This study presents the thermal properties of windows’ IGUs depending on the changes in outdoor temperatures by using guarded a hot box climate chamber and presents the proposed simplified methodology for determining the thermal properties of windows’ glass units. The accuracy of the composed simplified methods, comparing the calculated thermal transmittances of IGUs with those measured in the “hot box”, were up to 1.25%.

Keywords: window; insulating glass unit; thermal transmittance; Low-E coatings (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (1)

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