Gujarat – Eco Niwas Samhita platform G-ENS

 

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Window to Floor area Ratio (WFR)

WFR is the ratio of window area to that of the floor area. ENS requires the building to comply with a minimum WFR. Ensuring minimum WFRop helps in ventilation, improvement in thermal comfort, and reduction in cooling energy

How to calculate WFR?

The openable window-to-floor area ratio is calculated as shown

Where,

A openable = Area of the opening

A carpet = Area of the space (net)

The following threshold needs to be met for WFR compliance:

Climatic Zone Composite Hot-Dry Warm-Humid Temperate Cold
Minimum WFR 12.50% 10.00% 16.66% 12.50% 08.33%

Source: Adapted from Bureau of Indian Standards (BIS). 2016. National Building Code of India 2016. New Delhi: BIS.

Identify your climatic zone as per the map below:

Guide to calculate WFR

Openable area: The openable area in WFR includes all openable areas that open directly to external/ outside air.

What can be considered as Openable area: Window, ventilator, an open balcony, ‘verandah’, corridor or shaft; and the openable area of the doors opening directly into an open balcony.

Exclusions in Openable area:

  • All doors opening into corridors are excluded.
  • External doors on ground floor, for example, ground-floor entrance doors or back-yard doors are excluded

Carpet area: The carpet area of dwelling units is the net usable floor area of a dwelling unit.

What can be considered as Carpet area:

  • Usable area in a space/ room
  • Area covered by the internal partition walls of the dwelling unit

Exclusions in Carpet area:

  • Area covered by the external walls,
  • Areas under services shafts, exclusive balcony or verandah area
  • Exclusive open terrace areas,

Quick Calculators/ Resources

 

 

How to calculate window area?

 

How to calculate floor area?

Note: The areas entered above should be of same units.

 

Note: The results displayed here are based on the inputs provided by the user. This implies compliance/ non-compliance to this particular parameter only.

Visible Light Transmittance (VLT)

VLT of non-opaque building envelope components (transparent /translucent panels in windows, doors, ventilators, etc.), indicates the potential of using daylight. Ensuring minimum VLT helps in improving daylighting, thereby reducing the energy required for artificial lighting. The challenge with VLT is that less VLT can lead to less daylight and more VLT can lead to glare. Optimization is thus crucial.

How to determine VLT?

The glass used in non-opaque building envelope components (transparent/translucent panels in windows, doors, etc.) shall comply with the requirements given in the following table. The VLT requirement is applicable as per the window-to-wall ratio (WWR) of the building. Hence, it is essential to calculate WWR first.

The following threshold needs to be met for VLT compliance:

WWR 0-0.30 0.31-0.40 0.41-0.50 0.51-0.60 0.61-0.70
Minimum VLT 0.27 0.20 0.16 0.13 0.11

Source: Bureau of Indian Standards (BIS). 2016. National Building Code of India 2016. New Delhi: BIS.

The Window-to-Wall-area-Ratio (WWR) should be calculated first to understand the minimum VLT requirements. Check out the ‘Guide to calculate VLT’ to understand calculation of WWR followed by VLT

The Window-to-Wall-area-Ratio (WWR) should be calculated first to understand the minimum VLT requirements.

 

Calculating WWR

WWR is the ratio of the area of non-opaque building envelope components of dwelling units to the envelope area (excluding roof) of dwelling units.

Based on this WWR, the minimum VLT as required for compliance (as shown in Compliance threshold ) should be met

Selecting glass with the required VLT

  • You can explore various glazing types (single, double or triple glazing) by various brands.
  • Ensure to request for ‘Specification sheet’ for the product
  • The Specification sheet has a list of parameters and their measured/ calculated number (For eg- U-value, SHGC etc.)
  • Ensure that ‘Visual Light Transmittance’ (or VLT) is mentioned there. Additionally, ensure that the VLT mentioned is as required for ENS compliance as per Compliance threshold

Quick Calculators/ Resources

 

How to calculate wall area?

 

How to calculate window area?

Note: The areas entered above should be of same units.

 

Great! Now you can correlate this with the table under ‘Compliance threshold’ to understand the minimum VLT to be achieved!

Note: The results displayed here are based on the inputs provided by the user. This implies compliance/ non-compliance to this particular parameter only.

Thermal Transmittance (U-value)

Thermal transmittance of a material assembly is its ability to conduct heat through the assembly. Limiting the U value helps in reducing heat gains or losses through the material assembly, thereby improving the thermal comfort and reducing the energy required for cooling or heating.

The ENS categorizes the requirements of U-value under the following:

  • Thermal Transmittance of Roof (Uroof)
  • Thermal transmittance of building envelope (except roof) for cold climate (Uenvelope, cold)

U-value (roof)

Limiting the Uroof helps in reducing heat gains or losses from the roof, thereby improving the thermal comfort and reducing the energy required for cooling or heating.

U-value (envelope, cold)

Limiting the Uenvelope,cold helps in reducing heat losses from the building envelope, thereby improving the thermal comfort and reducing the energy required for heating.

The following threshold needs to be met for U-value compliance:

U-value (roof)

Thermal transmittance of roof shall comply with the maximum Uroof value of 1.2 W/m2.K.

U-value (envelope)

The thermal transmittance of the building envelope (except roof) for cold climate shall comply with the maximum of 1.8 W/m2.K.

U-value of roof (or) envelope- Calculation guidance

Uenvelope,cold takes into account the following:

  • Heat conduction through opaque building envelope components (wall, opaque panels in door, window, ventilators, etc.)
  • Heat conduction through non-opaque building envelope components (transparent/ translucent panels in windows, doors, ventilators, etc.).

The following are links to reliable external tools:

Quick Calculators/ Resources

U-value calculator

 
Material Name
(Outer layer to Inner layer)
d (thickness)
in metres (m)
K (Conductivity)
in (W/mK)
R= d/k
(m2K/W)
Action
Outermost layer
Material-2
Material-3
Innermost Layer  
 
m2K/W
W/m2K

Note: The results displayed here are based on the inputs provided by the user. This implies compliance/ non-compliance to this particular parameter only.

Residential envelope transmittance value (RETV) for building envelope (except roof) for four climate zones, namely, Composite Climate, Hot-Dry Climate, Warm-Humid Climate, and Temperate Climate

RETV is the net heat gain rate through the building envelope (excluding roof) of the dwelling units divided by the area of the building envelope (excluding roof) of the dwelling units. Its unit is W/m2

The following threshold needs to be met for RETV compliance:

The RETV for the building envelope (except roof) for four climate zones, namely, composite, hot-dry, warm- humid and temperate shall comply with the maximum RETV of 15 W/m2.

RETV formula takes into account the following:

  • Heat conduction through opaque building envelope components (wall, opaque panels in doors, windows, ventilators, etc.),
  • Heat conduction through non-opaque building envelope components (transparent/ translucent panels of windows, doors, ventilators, etc.),
  • Solar radiation through non-opaque building envelope components (transparent/ translucent panels of windows, doors, ventilators, etc.)

The RETV calculation of the building envelope (except roof)

shall be carried out as shown below:

Aenvelope : envelope area (excluding roof) of dwelling units (m2). It is the gross external wall area (includes the area of the wall and the opening such as windows and doors).
Aopaquei : area of different opaque building envelope components (m2)
Uopaquei : thermal transmittance values of different opaque building envelope components (W/m2.K)
Anon-opaquei            : area of different non-opaque building components (m2)
Unon-opaquei : thermal transmittance values of different non-opaque building envelope components (W/m2.K)
SHGCeqi : equivalent solar heat gain coefficient values of different non-opaque building envelope components 
𝜔i : orientation factor of respevtive opaque and non-opaque building envelope components; it is measure of the amount of direct and diffused solar radiation that is received on the vertical surface in a specific orientation. 

Submit for compliance - Guidance

The following steps can be followed to submit your building for compliance:

  • 1. SignUp/ Login
  • 2. Register yourself as a building owner. If an ENS Expert is working with you, he/ she can use the building owner’s credentials or register on the owner’s behalf
    Note: Architects/ Developers/ Builders can register themselves as ‘Professional/ Student’ and proceed to the next stages.
  • 3. Register your building
  • 4. Utilize the guidance provided in the Certifications page
  • 5. Use the tools under Resources > Tools for exploring building features through quick simulations. This will help you finalise design decisions.
  • 6. Use the Desktop tool in the end to input all finalized decisions. Ensure that the final results are ‘Compliant’ according to the report generated.
Sl.No. Compliance Parameter & supporting documents
1 Architectural drawings with plans, sections & elevations clearly indicating the following
  (i) Position and sizing of opening
  (ii) Building materials used in various envelope components
  (iii) External and internal walls
2 Bill of Quantities (BOQ) with all materials purchased
3 Construction photographs
4 Specification sheets with mentioning parameters for compliance
5 Narrative elaborating compliance to ENS Part-1 with calculations (wherever relevent)