Heat Transfer Through Insulating Glass Units Subjected to Climatic Loads.

Zbigniew Respondek

doi:10.3390/ma13020286

Abstract

One of the structural elements used in the construction of insulating glass units (IGUs) are tight gaps filled with gas, the purpose of which is to improve the thermal properties of glazing in buildings. Natural changes in weather parameters: atmospheric pressure, temperature, and wind influence the gas pressure changes in the gaps and, consequently, the resultant loads and deflections of the component glass panes of a unit. In low temperature conditions and when the atmospheric pressure increases, the component glass panes may have a concave form of deflection, so that the thickness of the gaps in such loaded glazing may be less than its nominal thickness. The paper analyses the effect of reducing this thickness in winter conditions on the design heat loss through insulating glass units. For this purpose, deflections of glass in sample units were determined and on this basis the thickness of the gaps under operating conditions was estimated. Next, the thermal transmittance and density of heat-flow rate determined for gaps of nominal thickness and of thickness reduced under load were compared. It was shown that taking into account the influence of climatic loads may, under certain conditions, result in an increase in the calculated heat loss through IGUs. This happens when the gaps do not transfer heat by convection, i.e., in a linear range of changes in thermal transmittance. For example, for currently manufactured triple-glazed IGUs in conditions of “mild winter”, the calculated heat losses can increase to 5%, and for double-glazed IGUs with 10–14 mm gaps this ratio is about 4.6%. In other cases—e.g., large thickness of the gaps in a unit, large reduction in outside temperature—convention appears in the gaps. Then reducing the thickness of the gaps does not worsen the thermal insulation of the glazing. This effect should be taken into account when designing IGUs. It was also found that the wind load does not significantly affect the thickness of the gaps.

Highlights

Used in the building industry as a filling of windows or glass facades, insulating glass units (IGUs) consist of two or more component glass panes, connected at the edges with a glass spacer.The space between the component glass panes forms a tight gap filled with gas
Further improvement of the performance is achieved by the use of component glass panes with a low-E coating—such a coating must be located on the side of the gap because it corrodes quickly when exposed to weather conditions
The results of calculations presented in this paper were obtained using the author’s analytical model proposed in the article [13], which allows to calculate the load and deflection of component glass panes in units with any number of tight gaps

Summary

Introduction

Used in the building industry as a filling of windows or glass facades, insulating glass units (IGUs) consist of two or more component glass panes, connected at the edges with a glass spacer. The space between the component glass panes forms a tight gap filled with gas. Howthe theaffects pressure gas gap, and increased thickness of the component glass plates. It is important that under conditions of low air temperatures, i.e., during the heating season, insulating glass units tend to take conditionsof oflow lowair airtemperatures, temperatures,i.e., i.e.,during duringthe theheating heatingseason, season,insulating insulatingglass glassunits unitstend tendto totake take conditions the concave form of deflection. Component glass panes indicates the concave form of deflection of the unit. It was found that a 20 ◦ C temperature difference reduces thermal performance by 4.6% for double-glazed IGUs and by 3.6% for triple-glazed IGUs. Penkova et al [5] presented examples of numerical analysis and experimental research regarding both parameters related to heat flow and climate loads. An example of an IGU in which the component panes came into contact due to climatic loads is presented

Methodology for the Calculation of Static Quantities in IGUs

Materials and Methods

Notes on IGUs Wind Load

Static quantities in IGUs loaded with wind

Findings

Conclusions