Step by step method to calculate the daylight factor

Daylight simulation can also be conducted manually for projects that adopt the prescriptive compliance approach. The following example demonstrates how to calculate the daylight extent factor (DEF) for a building located in Delhi and how to use this factor to determine the area that complies with the Uniform Daylight Illuminance (UDI) requirement.

Step 1: Determine the DEF for each orientation From Table 4-3 in the ECBC code, the DEF for a building located in Delhi with glazing of VLT ≥ 0.3, shading PF ≥0.4 shading and light shelves in windows are as follows:

• North = 3.5
• South = 3.0
• East = 2.1
• West = 1.8

Step 2: Calculate the daylight area for each orientation Using the DEF values and the fenestration dimensions, calculate the daylight area for each orientation as follows:

• North façade: The length of the glazing on the north-facing façade is 45 meters, and the head height of the fenestration is 3 meters. Therefore, the area perpendicular to the fenestration is 3.5 x 3 = 10.5 meters. The distance parallel to the fenestration is 45 meters + 2 meters (1 meter on each side), which is equal to 47 meters. Therefore, the total daylight area on the north façade is (47 x 10.5) = 493.5 square meters.
• South façade: The length of the glazing on the south-facing façade is 45 meters, and the head height of the fenestration is 3 meters. Therefore, the area perpendicular to the fenestration is 3.0 x 3 = 9 meters. The distance parallel to the fenestration is 45 meters + 2 meters (1 meter on each side), which is equal to 47 meters. Therefore, the total daylight area on the south façade is (47 x 9) = 423 square meters.
• East façade: The length of the glazing on the east-facing façade is 25 meters, and the head height of the fenestration is 3 meters. Therefore, the area perpendicular to the fenestration is 2.1 x 3 = 6.3 meters. The distance parallel to the fenestration is 25 meters + 2 meters (1 meter on each side), which is equal to 27 meters. Therefore, the total daylight area on the east façade is (27 x 6.3) = 170 square meters.
• West façade: The length of the glazing on the west-facing façade is 0 meters (service zone). Therefore, there is no daylight area on the west façade.

Step 3: Calculate the total daylight area meeting the UDI requirement Add the daylight area for each orientation to determine the total daylight area meeting the UDI requirement during 90% of the year. In this case, the total daylight area is 1086.5 square meters per floor. Since the building has four floors, the total daylight area meeting the UDI requirement during 90% of the year is (1086.5 x 4) = 4346 square meters.

Step 4: Calculate the percentage of area meeting the UDI requirement The total area of the building above grade is 7200 square meters. Therefore, the percentage of area meeting the UDI requirement during 90% of the year is (4346 / 7200) x 100 = 60.3%. This is above the minimum requirement of 40%, so the building complies with the UDI requirement.