When considering the performance of building materials in relation to solar energy, the concept of G-value becomes critical. Often referred to as the Solar Heat Gain Coefficient (SHGC), G-value is a key factor in evaluating how much solar energy is transmitted through glazing, affecting the internal temperature and comfort of a space. This becomes especially relevant when designing skylights, facades, tensile membrane structures or any building elements exposed to significant sunlight, particularly in climates that demand constant temperature regulation.
What is G-value?
The G-value refers to the proportion of solar energy that passes through a material, such as glazing or ETFE (Ethylene Tetrafluoroethylene) structures, and is expressed on a scale between 0 (complete blockage of solar energy) and 1 (transparent to solar energy, such as 3mm clear glass). The higher the G-value, the more solar energy enters a building, directly impacting its cooling and heating requirements.
ETFE G-value in Hot Climates:
In hot climates, where cooling is a constant concern, the G-value of ETFE plays a significant role in managing internal temperatures. ETFE cushions can achieve G-values as low as 0.22, providing significant control over solar heat gain. The G-value’s impact is especially pronounced when compared to the conductive properties (U-value) of the material. While U-value measures heat transfer through materials (important for insulation), the G-value directly influences the amount of heat that enters a building due to solar radiation.
In hot climates, the transmission of heat through ETFE materials (G-value) can contribute up to 10-20 times more to the cooling load than the material’s conductive properties. As such, it is crucial to prioritize reducing G-value, for example, by using frits or coatings, to minimize solar heat gain rather than focusing primarily on lowering the U-value by adding more layers of ETFE.
The Role of G-value in Cold Climates:
In contrast, the role of G-value becomes less important in cold climates, particularly during winter months. During this time, the focus shifts to managing heat loss, where U-value becomes a much more significant factor. G-value is not as critical in these situations because solar radiation is minimal or irrelevant at night and early morning when heating demands are highest. In fact, in cold climates, increasing G-value may even be beneficial to harness free natural heating through solar gain, especially when the building’s orientation is optimized for sunlight exposure.
Why G-value is Negligible in Heating Load Calculations:
In cold climates, heating load calculations typically focus on steady-state conditions, assuming no solar radiation or transmission and steady outdoor temperatures. The primary concern is to estimate heat loss, and internal heat sources are generally sufficient to offset some of this loss. Since G-value has no impact during the night or early morning when the heating demand is greatest, it is generally neglected in heating load estimations. Instead, thermal conductivity and convective heat transfer dominate the calculations.
ETFE G-value and Sky Visibility:
One of the trade-offs of reducing G-value is the potential loss of visual connection with the sky. To achieve lower G-values, ETFE cushions are often treated with frits or special coatings, which reduce the material’s transparency. While this helps to reduce cooling loads, it can limit the view of the sky. The optimal range for balancing cooling efficiency and sky visibility in ETFE cushions is typically between G-values of 0.33 and 0.40.
Finally in warm climates, G-value plays a critical role in managing cooling loads, as it directly impacts the amount of solar energy entering a building. By reducing G-value, especially through the use of frits or special films, cooling efficiency can be significantly improved. However, in colder climates, G-value has little effect on heating loads, and U-value becomes the primary factor in maintaining comfort. In such cases, increasing G-value may even contribute to natural heating, reducing reliance on mechanical systems.
While G-value is an important consideration, it is just one factor in the broader landscape of HVAC performance. Other variables such as insulation, thermal mass, and internal heat sources must also be taken into account for a comprehensive energy efficiency strategy.
TE Membrane’s reputation in tensile fabric structures and ETFE structures in Southeast Asia is built on a foundation of design innovation, engineering excellence, and a commitment to sustainability and quality. Their present in across Singapore, Malaysia, Thailand, Indonesia, Vietnam, the Philippines, Cambodia, and Myanmar. To showcases their ability to adapt and excel in diverse environments, making them a trusted partner for any tensile membrane project.
