Effect of Climatic Loads on IGU
The climatic load is a specific internal load of insulated glass. The insulated-glass effect acts on the panes due to changes in the climatic conditions surrounding it.?
During the production of insulated glass units, each glazing cavity is sealed hermetically, and the current state of the gas in production (volume, pressure, and temperature) defines the properties of the IGU. A pressure difference between the glazing cavity and the environment occurs if the gas temperature or atmospheric pressure changes. The pressure balance can be restored by an increase in the volume in the glazing cavity, according to the ideal gas law.?
The isochoric pressure expresses the magnitude of the climatic load. The isochoric pressure is defined as the pressure difference between the glazing cavity and the immediate environment that develops if the glass panes are rigid and cannot deform. It can be calculated by adding up three separate terms: the elevation difference, air pressure difference, and temperature difference between the conditions at production and installation.?
Further definition, climatic load also refers to the forces exerted on IGU (Insulated Glass Unit) due to weather-related conditions, such as loads coming from wind and temperature fluctuations.?
The wind load is a force exerted by the wind on the building facade surface, which has a positive and negative pressure effect on IGU. It is positive pressure when the wind creates positive pressure on the windward side of the building, pushing against the IGU and the framing system, including the IGU seals and the pressure plate. On the other hand, the negative pressure is when the wind creates a suction effect on the leeward side. During these two wind load scenarios, the IGU has two possible responses:?
Temperature-related load is when glass expands and contracts with temperature changes that will induce thermal stresses on the IGU and its supporting elements. In principle, when the IGU is exposed to high temperatures, it will expand and increase its stress. On the other hand, when the IGU is exposed to low temperatures, it will shrink/contract and can similarly induce stress.?
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During these temperature fluctuation events, the IGU seals shall be designed based on the expected temperature variations, including the expansion and contraction, without compromising the performance and integrity of the IGU and its structural stability. In the experiment performed (1), the edge seal is observed to be more flexible with rising load cycles until a constant level has been reached.
In real-world scenarios, the wind load and temperature-related load often act simultaneously. For example, during summer, the glass expands due to high temperatures while the wind exerts additional pressure on the IGU.?
It is the facade designer's responsibility to ensure that the IGU seal is designed to withstand climatic loads and ensure the long-term performance and safety of the IGU panel. The factors, such as local weather conditions, production sites, temperature changes, building height and locations, and applicable codes and standards, shall be considered in the early design stage in determining the appropriate loads and their effect on manufacturing IGU and the long impact of those factors in the overall performance, operation, and maintenance of the building facade.
Footnote:
(1) Budenberg, Hof, Oechner, 2016, Climate load in insulating glass units: comparison of theory and experimental results, Springer Link, DOI:?https://link.springer.com/article/10.1007/s40940-016-0028-z