Positioning of Low-E Coating: Surface #2 VS Surface #3
The answer depends on the different climate zones and customer's specific requirements.
In practical applications, in hot areas, if more sunlight needs to be reflected and the heat insulation effect needs to be improved, the Low-E coating should be placed on the #2 surface; if the climate is severely cold in winter and more sunlight is desired to enter (for example, more solar radiation needs to be introduced into the room in winter), the coating can be placed on the #3 surface. In other words, if heating costs exceed cooling costs, the Low-E coating should be placed on Surface #3 to allow more solar heat gain in winter, thus resulting in lower heating costs; if cooling costs exceed heating costs, it should be placed on Surface #2.
Different SC Value
It can be seen from Table 1 that the shading coefficient (SC) of the glass varies significantly with the position of the Low-E coating, and thus we can adjust the position of the Low-E coating according to the different climate zones and their requirements for the glass shading coefficient. As for thermal transmittance (U-Value), it remains unchanged when the Low-E coating surface is at Position #2 or #3, regardless of whether the Low-E glass is single-silver, double-silver or triple-silver type.
Surface Temperature Comparison
From the above data, regardless of being single-silver, double-silver or triple-silver Low-E glass, when the coating surface is at Position #2 or #3, the indoor-side glass surface (i.e., Position #4) varies drastically in temperature, by more than 10℃ at maximum. Therefore, to meet the requirements for indoor comfort (Eg. 3.5℃ Passive House Institute standard1) and reduce thermal radiation, it is preferable to place the coating surface at Position #2.
Conclusion
It can be seen from the above analysis that the placement of the Low-E coating on Position #2 and Position #3 results in the following differences:
The shading coefficient (SC) differs, while the thermal transmittance (U-Value) remains the same.
When the Low-E coating is applied on Position #3, its shading coefficient (SC) is higher than that on Position #2.
The indoor-side glass surface temperatures are different, leading to a significant variation in indoor thermal comfort.
When the Low-E coating is applied on Position #3, the indoor-side glass surface temperature is higher than that on Position #2.
From both indoor and outdoor perspectives, the glass exhibits different colors and visual effects.
Another point to note is that after the glass arrives at the construction site and before installation, the actual position of the coating must be strictly identified and inspected to ensure that the final performance parameters of the glass are consistent with the design values.
The instrument we use in this video is GlassMeter800K. This instrument is used to directly measure the glass thickness, air space, detect the Low-E side of DGU or TGU, and then calculate the E value and U value , which has the characteristics of portable design, simple operation and fast measurement. It is especially suitable for on-site measurement of installed building glass, doors and window.
Reference:
1. Based on Passive House Institute (PHI) standards, the difference between the temperature of any cold surface (like a window) and the average indoor air temperature should not exceed 3.5°C.
https://passipedia.org/basics/building_physics_-_basics/thermal_comfort/thermal_comfort_in_passive_house_building
