Calculating Effective SHGC for Windows in Commercial Buildings: A Step-by-Step Guide with Sample Calculation
Introduction: Windows play a critical role in the energy performance of commercial buildings, affecting factors such as daylighting, thermal comfort, and solar heat gain. Solar Heat Gain Coefficient (SHGC) is an important parameter used to quantify the amount of solar heat that enters a building through windows. However, the effective SHGC takes into account the shading devices or window attachments used in the building design, and is a more accurate representation of the actual solar heat gain. In this article, we will explore how to calculate the effective SHGC for windows in commercial buildings, along with a sample calculation.
Step 1: Gather Information To calculate the effective SHGC, you will need the following information:
- SHGC of the window without shading devices (SHGCwoSD): This is the original SHGC value provided by the window manufacturer for the window unit without any shading devices.
- SHGC of the shading devices (SHGCsd): This is the SHGC value of the shading devices or window attachments used in the building design.
- Area of the window (A): Measure the total area of the window, including the glass and framing, in square feet or square meters.
- Area of the shading devices (Asd): Measure the total area of the shading devices or window attachments, in square feet or square meters.
Step 2: Calculate the Effective SHGC The formula to calculate the effective SHGC (SHGCEff) is as follows: SHGCEff = ((SHGCwoSD x A) – (SHGCsd x Asd)) / A
Sample Calculation: Let’s consider an example where a commercial building has windows with an original SHGC of 0.70, and shading devices with an SHGC of 0.30 covering 50% of the window area. The window area is 1000 square feet.
SHGCwoSD = 0.70 SHGCsd = 0.30 A = 1000 sq ft Asd = 0.50 x 1000 = 500 sq ft
Plugging these values into the formula: SHGCEff = ((0.70 x 1000) – (0.30 x 500)) / 1000 SHGCEff = (700 – 150) / 1000 SHGCEff = 0.55
So, the effective SHGC for the windows with shading devices in this example is 0.55.
Conclusion: Calculating the effective SHGC for windows in commercial buildings is an important step in accurately assessing the solar heat gain and energy performance of the building. By taking into account the shading devices or window attachments used in the design, the effective SHGC provides a more realistic representation of the actual solar heat gain through windows. Understanding how to calculate the effective SHGC and incorporating it into building design can help optimize the energy performance of commercial buildings and improve overall comfort for occupants.
Note: The values used in the sample calculation are for illustrative purposes only and may not represent real-world conditions. Actual calculations should consider specific window and shading device characteristics, climate conditions, and other relevant factors. Always consult applicable building codes, standards, and guidelines for accurate and up-to-date information.
According to the Bureau of Energy Efficiency (BEE) in India, the Shading Equivalent Factor (SEF) is a coefficient that is used to account for the effect of shading devices or window attachments on the solar heat gain through windows. The SEF takes into consideration the type, size, and orientation of shading devices, as well as their location with respect to the window. The BEE provides recommended SEF values for different types of shading devices as follows:
| Type of Shading Device | SEF (Shading Equivalent Factor) |
|---|---|
| Exterior horizontal shading | 0.40 – 0.60 |
| Exterior vertical shading | 0.60 – 0.80 |
| Exterior overhangs | 0.50 – 0.70 |
| Interior horizontal shading | 0.50 – 0.60 |
| Interior vertical shading | 0.60 – 0.70 |
| Interior venetian blinds | 0.30 – 0.40 |
| Interior roller blinds | 0.30 – 0.50 |
| Interior cellular shades | 0.40 – 0.50 |
| Interior pleated shades | 0.30 – 0.40 |
| Interior fabric curtains | 0.30 – 0.40 |
| Interior metal blinds | 0.50 – 0.60 |
Note: The SEF values provided above are approximate ranges and may vary depending on specific design parameters, location, and other factors. Always refer to the latest guidelines, standards, and regulations from the BEE or other relevant authorities for accurate and up-to-date information.
These SEF values can be used in conjunction with the original Solar Heat Gain Coefficient (SHGC) of windows to calculate the Effective SHGC (SHGCEff), as discussed in the previous blog article. By multiplying the SHGC of the window by the corresponding SEF value for the shading device used, the effective SHGC can be obtained, providing a more accurate assessment of the solar heat gain through windows in commercial buildings.