Glass has two core energy-saving parameters: Shading Coefficient (SC) and Thermal Transmittance (U-value). The extent to which each parameter contributes to building energy efficiency depends not only on the climate conditions of the region where the building is located but also on the building’s functional use.

Building energy efficiency design standards specify limit values for energy performance of doors, windows, and glass curtain walls based on different climate zones. On the premise of meeting these limit values, glass selection should prioritize the corresponding parameter according to the local energy consumption characteristics:

  • For regions where air conditioning (cooling) accounts for a larger proportion of energy consumption, glass with a lower SC should be prioritized. Take Hot Summer and Warm Winter Regions as an example: studies show that solar radiation-induced energy consumption accounts for approximately 85% of the annual total energy consumption in these areas, while energy consumption from temperature difference heat transfer only accounts for 15%. Clearly, maximizing the reduction of solar radiation penetration into the room is essential for achieving optimal energy-saving effects in such regions.

  • For regions where heating energy consumption dominates, glass with a lower U-value should be prioritized. In Severe Cold Regions, for instance, summer is short, while winter is long with extremely low outdoor temperatures. Building thermal insulation becomes the core energy-saving requirement here, and a lower U-value can effectively reduce heat loss from the interior to the exterior, making it more conducive to energy conservation.

In fact, across all climate zones, a lower U-value theoretically means better thermal insulation performance of the glass. However, reducing the U-value incurs additional costs—if its contribution to local energy savings is minimal (e.g., in Hot Summer and Warm Winter Regions), there is no need to deliberately pursue an extremely low U-value.

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The picture is sourced from https://www.energystar.gov/products/res_windows_doors_skylights/key-product-criteria

In summary, we can draw the following conclusions:

1.  A lower U-value indicates better thermal insulation performance. Its contribution to building energy efficiency decreases gradually from north to south in China. On the premise of meeting energy efficiency standards, whether to pursue a lower U-value can be determined based on cost factors.

2.  A lower SC is more beneficial for energy savings in summer but has a negative impact on energy efficiency in winter. Currently, there is more debate around whether to further enhance shading for residential buildings in Hot Summer and Cold Winter Regions and public buildings in Cold Regions. Such decisions require analysis based on the building’s functional use to select the option where benefits outweigh drawbacks.


How to quickly measure the SC (Shading Coefficient) and U-value (Thermal Transmittance) of glass?

1.  Aoptek GlasSmart1000 On-site Optical and Thermal Parameters Measuring System for Insulating Glass

GlasSmart1000 is a portable measuring system suitable for on-site measurement of installed building glass. It can quickly measure the glass structure, non-destructive measure U value, SHGC, Spectral Transmittance and Reflectance, and Total Solar Transmittance g of insulating glass.

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2.  AoptekGlasSpec2500 Optical and Thermal Parameters Measuring Instrument for Glass

GlasSpec2500 is a spectrophotometer which can test UV & Visible & NIR spectrum, and optical and thermal parameters of glazing. The instrument not only can measure the single pane, but also can directly measure the insulating glass without separating.

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