Sunrooms are made of over 80% glass, and if the wrong glass is chosen, the room will not only be bright, but it will also absorb heat, making it uncomfortably hot in the summer and cold in the winter. This is a common and persistent problem with sunrooms. What are the limitations of insulated glass units (IGUs), which are commonly used in sunrooms?

Limitations of IGUs in Sunroom Roofs

Sunrooms have two types of glass: vertical glass for the walls and horizontal or sloped glass for the roof. While IGUs work well for the vertical walls, similar to how they're used in windows and doors, they have significant drawbacks when installed horizontally or at a large angle on a sunroom roof.

The heat transfer coefficient (U-value) of an IGU is determined by three main factors: conduction, convection, and radiation. The convection of the gas inside the sealed air space is the most critical factor affecting the U-value.

Heat buildup: When glass is installed horizontally on a sunroom roof, it receives far more direct sunlight than a vertical window. The air inside the IGU's cavity accumulates a lot of heat, with temperatures soaring to over 70°C in the summer. This intense heat increases both convective and conductive heat transfer between the inner and outer panes, causing the temperature inside the sunroom to rise dramatically. As a result, the inner pane of glass can get quite hot, often exceeding 40°C in the summer.

Angle-dependent convection: When an IGU is not installed vertically, the convection environment on its surface and within the cavity changes. While inert gases like argon can reduce convective heat transfer, the effect of the angle change on gas movement is still dominant. The U-value of an IGU changes significantly with the tilt angle.

Vertical installation: The gas layer is stable due to gravity, forming a distinct stratification of cold and hot air. This results in weak convection, high thermal resistance, and a low heat transfer coefficient.

Horizontal installation: Gravity causes vertical convection currents (e.g., cold and hot air circulating between the top and bottom glass surfaces), which increases turbulence and intensifies heat exchange. This leads to a significant increase in the convective heat transfer coefficient and a higher overall U-value.

According to Table 1, the U-values for single-cavity IGUs and double-cavity IGUs increase by 41% and 33%, respectively, when installed horizontally on a sunroom roof compared to a vertical installation.

However, because LandVac titanium vacuum insulated glass has a vacuum cavity, there is virtually no convective or conductive heat transfer. This means its U-value remains a consistent 0.48 W/m²·K, regardless of the installation angle. It also doesn't experience the same heat buildup within the cavity, which prevents excessive heat transfer to the indoors and the associated increase in the inner glass surface temperature.

The inherent properties of the gas in IGUs are a primary cause of discomfort in sunrooms. For this reason, LandVac titanium vacuum insulated glass is an ideal solution for sunrooms, skylights, and glass roofs.