Step by Step Calculation of SHGC for ECBC Compliance
As buildings account for a significant portion of energy consumption, it is essential to ensure their energy efficiency. The Energy Conservation Building Code (ECBC) is a set of guidelines that aim to optimize energy performance and reduce greenhouse gas emissions from buildings. The ECBC has provisions for various building components, including fenestration. In this article, we will go through a case study that demonstrates the calculation of SHGC for ECBC compliance.
A two-story office building in Delhi, with a rectangular layout of 90m x 30m, is trying to achieve ECBC level compliance. The building’s floor to floor height is 4.0m, and the floor area is evenly distributed over the two floors. The windows are either east or west facing and equally distributed on the two floors. The windows are all 1.85m in length and 2.165m in height with an overhang of 0.85m, and the cill level is 1.385m above floor level. The overall glazing area is 384m2. The SHGC of the glazing in the East/West Fenestration is 0.30, the area-weighted U-factor is 3.0 W/m2.K, and the VLT of the glazing in all orientation is 0.5. The question is whether the vertical fenestration will comply with the ECBC from the prescriptive approach.
The first step is to refer to Table 4-10 and §4.3.3 of the ECBC guidelines, which list the U-factor, SHGC, and VLT requirements for vertical fenestration. Since the building is in Delhi (Latitude: 28070’ N, Longitude: 77010’E), which falls under the composite climate, as per Appendix B, Table 12.1, we need to ensure compliance with the requirements for this climate zone.
According to the prescriptive requirements, the Window to Wall ratio should be ≤ 40%, SHGC ≤ 0.27, U-factor ≤ 3.0 W/m2.K, and VLT ≥ 0.27. Let’s calculate the Window to Wall Ratio (WWR) for this building:
Total Floor area = 5400 m2 Total wall area = 2 x (2x ((90m x 4m) + (30m x 4m))) = 1,920 m2 Total Fenestration area = 384 m2 WWR = Fenestration area / Wall area WWR = 384 / 1920 WWR = 0.20 or 20%
As the WWR is less than or equal to 40%, the building satisfies the prescriptive requirement for the Window to Wall ratio.
Next, let’s check the SHGC requirement. The SHGC of the glazing in the East/West Fenestration is 0.30, which is greater than the maximum permissible value of 0.27. Therefore, the building does not comply with the SHGC requirement from the prescriptive approach.
In conclusion, the step by step calculation of SHGC for ECBC compliance for the given case study shows that the vertical fenestration of the two-story office building in Delhi does not meet the prescriptive SHGC requirement of 0.27. The building owner can explore alternative compliance paths, such as using high-performance glazing or opting for the trade-off approach, to meet the ECBC guidelines. These measures will not only reduce energy consumption and operating costs but also contribute to the sustainable development of the built environment.