Understanding the daylighting requirement as per ECBC

Daylighting is the use of natural daylight to light up the interior of a building, reducing the reliance on artificial lighting sources. It is a vital aspect of sustainable building design, and it has several benefits, including energy conservation, improved occupant health and well-being, and increased productivity. Many countries have incorporated daylighting requirements into their building codes to ensure that buildings are designed and constructed with an adequate amount of natural light.

In India, the Energy Conservation Building Code (ECBC) has established minimum requirements for daylighting in above-grade floor areas. The code requires that at least 40% of the above-grade floor area in business and educational buildings meets the useful daylight illuminance (UDI) area requirements listed in Table 4-1 for 90% of the potential daylit time in a year. The requirements are higher for hotels, resorts, and healthcare buildings.

The UDI is a measure of the illuminance received at a point on the workplane, taking into account the position of the point and the orientation of the workplane. The UDI requirement is expressed as a percentage of the above-grade floor area that should meet or exceed the UDI requirement listed in Table 4-1.

Calculating the UDI requirement can be done through daylighting simulation or manual calculations. Daylighting simulation involves using specialized software to simulate the amount of natural light entering a building under various conditions. Manual calculations involve using equations to determine the amount of natural light entering a space based on the building’s orientation, the size and location of windows, and the shading provided by exterior elements.

To calculate the UDI requirement using manual calculations, follow these five steps:

Step 1: Determine the minimum illuminance requirement The minimum illuminance requirement depends on the function of the space. For example, an office requires a minimum illuminance of 300 lux, while a classroom requires a minimum of 500 lux.

Step 2: Determine the window area Measure the area of all windows in the space.

Step 3: Determine the visible transmittance (VT) The visible transmittance (VT) is the fraction of visible light that passes through a window. It can be obtained from the manufacturer’s specifications or measured using a spectrophotometer.

Step 4: Determine the daylight factor (DF) The daylight factor (DF) is the ratio of the interior illuminance to the exterior illuminance. It can be calculated using the following equation:

DF = (0.318 x VT x A) / (W + D)

Where: A = window area W = perimeter of the window opening D = distance from the window opening to the workplane

Step 5: Determine the UDI requirement The UDI requirement is the percentage of the above-grade floor area that meets or exceeds the minimum illuminance requirement. It can be calculated using the following equation:

UDI = (DF x 100) / minimum illuminance requirement

Compliance with the daylighting requirements in the ECBC can be demonstrated through either daylighting simulation or manual calculations. However, compliance is required for most above-grade floor areas, except for assembly buildings and other buildings where daylighting will interfere with the functions or processes of 50% or more of the building floor area. By incorporating daylighting into building design, building owners and occupants can benefit from a healthier and more sustainable indoor environment.

Here are the daylighting requirements for different types of buildings as per the ECBC:

• Business and educational buildings: The above-grade floor area should meet or exceed the UDI requirement for 40% (ECBC), 50% (ECBC+), or 60% (SuperECBC) of the potential daylit time in a year.
• No star hotels: The above-grade floor area should meet or exceed the UDI requirement for 40% (ECBC), 50% (ECBC+), or 60% (SuperECBC) of the potential daylit time in a year.
• Star hotels: The above-grade floor area should meet or exceed the UDI requirement for 30% (ECBC), 40% (ECBC+), or 50% (SuperECBC) of the potential daylit time in a year.
• Healthcare buildings: The above-grade floor area should meet or exceed the UDI requirement for 30% (ECBC), 40% (ECBC+), or 50% (SuperECBC) of the potential daylit time in a year.
• Resorts: The above-grade floor area should meet or exceed the UDI requirement for 45% (ECBC), 55% (ECBC+), or 65% (SuperECBC) of the potential daylit time in a year.
• Shopping complexes: The above-grade floor area should meet or exceed the UDI requirement for 10% (ECBC), 15% (ECBC+), or 20% (SuperECBC) of the potential daylit time in a year.
• Assembly buildings: These buildings are exempted from meeting the UDI requirement if daylighting will interfere with the functions or processes of 50% or more of the building floor area.

In summary, the ECBC sets specific requirements for daylighting in different types of buildings to ensure visual comfort, energy efficiency, and occupant health. Compliance with the UDI requirement can be demonstrated through either daylighting simulation or manual methods.