ROLE OF GLASS IN GREEN BUILDINGS

“A green building uses less water, optimises energy efficiency, conserves natural resources, generates less waste and provides healthier spaces for occupants, as compared to a conventional building.”

Buildings across the world create a tremendous environmental impact. Globally, buildings are responsible for at least 40% of the total energy use. The construction of new buildings generates a large amount of solid waste, and in turn, disturbs the natural habitat and vegetation.

In contrast, green buildings offer immense potential to reduce energy consumption while regenerating resources from waste and other renewable sources.

WHAT IS A GREEN BUILDING?

A green building is a building that incorporates environmental-friendly features. Even though the building might appear the same as other buildings, it is different in its approach.:

Salient features of a green building are:

• An envelope-like design
• Efficient system design (HVAC, lighting, electrical and water heating)
• Integration of renewable energy sources to generate energy on-site
• Efficient use of water as well as water recycling and waste management
• Use of ecologically sustainable materials (with high recycled content, rapidly renewable resources with low emission potential)
• Use of energy-efficient and eco-friendly equipment
• Maintain indoor thermal and visual comfort and air quality
• Effective control and building management systems

BENEFITS OF GREEN BUILDINGS

A green building offers significant benefits, both tangible and intangible. The most prominent tangible benefit is the reduction in water and operating energy costs right from day one. The benefit accrues for the entire lifecycle of the building.

Tangible benefits:

• Green buildings consume 40% ~ 60% lesser electricity as compared to conventional buildings.
• Green buildings consume 40% ~ 80% lesser water as compared to conventional buildings, by utilising ultra-low fixtures, rainwater harvesting, wastewater recycling, etc.
• Green buildings generate lesser waste by employing waste management strategies on-site.

Intangible benefits:

• Enhanced air quality.
• Excellent daylighting.
• Improved health and well-being of the occupants.
• Conservation of scarce national resources.
• Enhanced marketability of the project.

GREEN BUILDING DESIGNING and RATING SYSTEM

A green building rating system is an evaluation tool that measures the environmental performance of a building through its life cycle. It usually comprises a set of criteria, covering various parameters related to the design, construction and operation of a green building. Rating programmes help projects to address all aspects related to the environment. Moreover, they are an effective tool to measure the performance of the building/project.

Two rating systems mainly followed in India, include:

• LEED India (Leadership in Energy & Environmental Design)
• GRIHA (Green Rating for Integrated Habitat Assessment) National Rating System

IGBC, which is a part of CII-Godrej GBC, is responsible for promoting the green building concept in India. The council is represented by all stakeholders of the construction industry, including corporate, government and nodal agencies, architects, material manufacturers, institutions, etc.

As part of the indigenisation of the LEED rating system, IGBC has been working on LEED India for the past three years.

LEED India was formally launched in October 2006 but became operational from January 2007.

LEED India has incorporated a few changes like more emphasis on water conservation and adoption of local Indian codes and standards like NBC guidelines and MoEF guidelines for large projects, CPCB norms for DG set emissions, ECBC for energy efficiency, etc.

LEED® India

The Leadership in Energy and Environmental Design (LEED INDIA) green building rating system is a nationally and internationally accepted benchmark for the design, construction and operation of high-performance green buildings.

LEED INDIA promotes a whole-building approach to sustainability by recognising performance in the following five areas:

• Sustainable site development
• Water savings
• Energy efficiency
• Indoor environmental quality

Specific LEED-INDIA programmes include:

IGBC, in its endeavour to extend green building concepts to all building types, has developed the following rating programmes to cover commercial, residential, factory buildings, SEZ, etc.

Specific IGBC programmes include:

• IGBC Green Homes
• IGBC Green SEZ
• IGBC Green Factory Building

IGBC Green Homes Rating System

Indian Green Building Council (IGBC) Green Homes is the first rating programme developed in India, exclusively for the residential sector.

• Sustainable site development
• Water savings
• Energy efficiency
• Indoor environmental quality

IGBC Green Factory Building rating system

IGBC Green Factories rating system is a first of its kind, addressing sustainability in industrial buildings. The programme is fundamentally designed to address national priorities and quality of life for factory workmen.

GRIHA

Green Rating for Integrated Habitat Assessment (GRIHA) is the national rating system of India. It has been conceived by TERI and developed jointly with the Ministry of New and Renewable Energy, Government of India. It is a green building ‘design evaluation system’, and is suitable for all kinds of buildings across different climatic zones in the country.

The rating applies to new building stock, including commercial, institutional and residential functions. As of November 7, 2007, the system is being endorsed by the Ministry of New and Renewable Energy, Government of India.

GRIHA is a five-star rating system for green buildings, which emphasises passive solar techniques for optimising indoor visual and thermal comfort.

The rating system evaluates some credit points through a prescriptive approach and other credits via a performance-based approach. Over the years, the rating system has become more comprehensive and user-friendly.

While LEED/IGBC or GRIHA systems do not certify specific building (glass) products, these systems do recognise that the selection of glass products plays a significant role in fulfilling LEED/IGBC or GRIHA point requirements.

GLASS SELECTION

Glass plays a unique and important role in the design of the building and the environment. It affects the design, appearance, thermal performance and comfort of the occupant. Selecting the right glass is a crucial component of the design process.

India being a tropical country, we need to be careful while selecting a glass. The selection of glass has become more complex because of the availability of a variety of glasses, ranging from performance to aesthetics.

The properties of glass have also become multifaceted and can perform a variety of functions from solar control to thermal insulation. The solar and thermal performance will often be a high priority decision, along with appearance (colour, transparency and reflectivity).

AIS products can help architects achieve LEED/IGBC or GRIHA certification for their projects in several areas, such as energy performance, recycled content, regional material, daylight and views.

ENERGY MANAGEMENT

Key factors that play an important role in designing the building envelope with glass, are as follows.

• Solar Factor (SF)/Solar Heat Gain Coefficient (SHGC)
• U-Value
• Relative Heat Gain (RHG)
• Visual Comfort

Solar Factor (SF)/Solar Heat Gain Coefficient (SHGC)

A combination of the directly transmitted solar and radiant energy and the proportion of the absorbed solar energy that enters the building. The lower the number, the better the solar control.

U-Factor (U-Value)

This is the measurement of air-to-air thermal conductance or insulation between indoors and outdoors through the glass. The lower the number the better the insulation or thermal control.

Relative Heat Gain (RHG)

RHG is calculated as: (Solar heat gain factor (ASHRAE) 630° W/m2 X shading coefficient of the glass) + ( Temperature Difference x U value)

• Heat gain due to solar factor contributes to 80% of the RHG value
• Heat gain due to U-value contributes to 20% of the RHG value

Visual Comfort

Visual Light Transmission

It is defined as the percentage of light transmitted through the glass. It does not determine the colour of the glass.

The glass should provide for optimum daylight inside as per the condition outside. Excessive daylight creates glare and can make the occupant uncomfortable.

Energy Conservation Building Code

Energy Conservation Building Code prepared by the Bureau of Energy Efficiency sets minimum standards for external wall, roof, glass structure, lighting, heating, ventilation and air conditioning of a commercial building. ECBC provides a minimum requirement for the energy-efficient design and construction of the building.

Scope

The ECBC covers buildings with an:

• Electrical connected load of > 500 kW or
• Contract demand of > 600 kVA and/or
• Building or complexes with air-conditioned area > 1000 SQM

The ECBC provides design norms for:

• Building envelope
• Lighting system
• HVAC system
• Electrical system
• Water heating and pumping systems

The code provides three options for compliance:

• Prescriptive (component-based approach): Each system and sub-system must comply with the minimum performance requirement as laid down by the code.
• The Trade-off (system-based approach): This method offers more flexibility than strictly following the prescribed values for an individual element. Trade-offs typically occur within building envelope system – roofs, walls, fenestration, overhangs, etc.
• Whole Building Performance: This method helps the designer to evaluate the energy performance of a building, making it more energy efficient by introducing necessary modifications in the design.

Climatic Zones

As per the climatic conditions, India is divided into five climatic zones and the ECBC considers these zones for the building envelope design:

*SRR:Skylight roof ratio is the ratio of the total skylight area of the roof, measured to the outside of the frame and the gross exterior roof.

PRESCRIPTIVE REQUIREMENTS

In the prescriptive approach, the ECBC sets values of the light transmission, solar factor and U-value for the different climatic zones and the designed window-wall ratio of the building.

Table 1.2: Vertical Fenestration U-Factor (W/ m2K), SHGC requirements and Minimum VLT requirements

Composite / Hot & Dry / Warm & Humid	Window Wall Ratio (WWR)
	0 ~ 30%	31% ~ 40%	41% ~ 50%	51% ~ 60%
MINIMUM Light Transmission (%)	27	20	16	13
Maximum Solar Factor / SHGC	0.25	0.25	0.20	0.20
Maximum U-VALUE (W/SQMK)	3.3	3.3	3.3	3.3
Moderate	Window Wall Ratio (WWR)
	0 ~ 30%	31% ~ 40%	41% ~ 50%	51% ~ 60%
Maximum Light Transmission (%)	27	20	16	13
Maximum Solar Factor / SHGC	0.4	0.4	0.30	0.30
Maximum U-value (W/SqmK)	6.9	6.9	6.9	6.9
Cold	Window Wall Ratio (WWR)
	0 ~ 30%	31% ~ 40%	41% ~ 50%	51% ~ 60%
Maximum Light Transmission (%)	27	20	16	13
Maximum Solar Factor / SHGC	0.51	0.51	0.51	0.51
Maximum U-value (W/SqmK)	3.3	3.3	3.3	3.3

TRADE-OFF APPROACH

The trade-off is permitted only between building envelope components. With the trade-off approach, the prescriptive requirement of SHGC can be a trade-off with shading devices/overhangs and/or side-fins

• Shading for all the fenestration getting direct solar radiation by using Sun Path analysis or shading norms
• Internal Shading Devices (Overhangs and/or Side Fins)

Adjusted/Effective SHGC is calculated by multiplying the SHGC of the unshaded fenestration product by a multiplication factor (M)

SHGC Effective = SHGC Glass X M

Multiplication Factor (M)

(M) Is taken out from table 1.2 based on the projection factor (P)

Projection Factor (Overhangs/Side Fins)

EXCEPTION TO ECBC

SHGC requirement of a window can be affected by overhangs on a building. The term called projection factor determines how well the overhangs shade the building’s glazing.

The Projection Factor is calculated by

PF = Ratio of projection divided by height from the window sill to bottom of overhang (must be permanent)

ECBC provides modified SHGC values where there are overhangs and/or side-fins. An adjusted SHGC, accounting for overhangs and/or fins, is calculated by multiplying the SHGC of the unshaded fenestration product by a multiplication factor (M).

Table 1.3: SHGC ‘M’ factor adjustment for Overhangs & Side FinsTable 1.3: SHGC ‘M’ factor adjustment for Overhangs & Side Fins

		Overhang M factors for 4 PF				Side fins M factors for 4 PF				Over hang + Side Fins M factors for 4 PF
Project Location	Orientation	0.25  0.49	0.50  0.75	0.76  0.99	1.00 +	0.25  0.49	0.50  0.75	0.76  0.99	1.00 +	0.25  0.49	0.50 0.75	0.76  0.99	1.00 +
North latitude 15* or Greater	North	0.88	0.8	0.76	0.73	0.74	0.67	0.58	0.52	0.64	0.51	0.39	0.31
	East/West	0.79	0.65	0.56	0.5	0.8	0.72	0.65	0.6	0.6	0.39	0.24	0.16
	South	0.79	0.64	0.52	0.43	0.79	0.69	0.6	0.56	0.6	0.33	0.1	0.02
North latitude less than 15°	North	0.83	0.74	0.69	0.66	0.73	0.65	0.57	0.5	0.59	0.44	0.32	0.23
	East/West	0.8	0.67	0.59	0.53	0.8	0.72	0.63	0.58	0.61	0.41	0.26	0.16
	South	0.78	0.62	0.55	0.5	0.74	0.65	0.57	0.5	0.53	0.3	0.12	0.04

EXCEPTION TO SGHC

Vertical fenestration areas located more than 2.2m (7 ft.) above the level of the floor are exempt from the SHGC requirement in (Table 1.2) if the following conditions are complied with:

• Total Effective Aperture: The total effective aperture for the elevation is less than 0.25, including all fenestration areas greater than 1.0m (3 ft) above the floor level.
• An interior light shelf is provided at the bottom of the fenestration area, with an interior projection factor not less than:

1.0 for E/W. SE, SW, NE, and NW orientations
2. 0.5 for S orientation, and
3. 0.35 for N orientation when latitude is <23

WHOLE BUILDING PERFORMANCE APPROACH

This method involves developing the computer model (for thermal, visual, ventilation and other energy-consuming processes) of the proposed design and comparing its energy consumption with standard design.

• Energy simulation software is necessary to show the ECBC compliance. Energy simulation is a computer-based analytical process that helps designers to evaluate the energy performance of a building and make necessary modifications before construction.
• Perform hourly analysis of the whole year.
• Used to simulate air-conditioned building and predict annual energy consumption under various head.

This simulation process takes into account:

• Building geometry and orientation
• Building material
• Building facade design
• Climate indoor environmental condition
• Occupant activities and schedules
• HVAC and lighting system and other parameters to analyse and predict the energy performance of a building