Energy Efficient Glass Façade for building envelope Sri Ram.N – IGBC AP; GRIHA Trainer Saint Gobain Glass India 15 th June 2011

Glass for building envelope Indispensible construction material Freedom from conventional building shapes, with unmatched aesthetics. Transparent to visible light – daylighting of interiors Blending of interiors with exteriors Helps to maintain hygienic environment with easy maintenance Glass is 100% recyclable – Sustainable building envelope

Consumption Pattern RESIDENTIAL COMMERCIAL 80 % of Building Energy Consumption Source: Res :UNEP SBCI & TERI Study, Comm: IGDB Study

Key Performance Factors Lighting Energy Light Transmission Cooling Energy Total Heat Gain / Heat Transmission – SHGC or SF : Solar Heat Gain Coefficient or Solar Factor – U Value

Performance Parameter Light Factors

Visual Light Transmission (VLT) Percentage of incident light transmitted Percentage transmission depends Tint & Coating Light Transmitted out

Factors affecting Visual Light Transmission (VLT) Single Glazed Unit Clear VLT = 89% Single Glazed Unit Green tint VLT = 73% Single Glazed Unit Blue Tint VLT = 57% Single Glazed Unit Clear - Solar control VLT = 67% – 7% Single Glazed Unit Green - Solar control VLT = 54% – 6%

Energy Performance Factors Total Heat Gain / Heat Transferred -SHGC -U Value

UVVisible Far Infra RedNear Infra Red µ Electromagnetic Spectrum at Terrestrial Level TOTAL HEAT GAIN Heat Gain due to direct solar radiation Amount of heat Transferred due to temperature difference Total Heat Gain Wave Length

incident solar radiation 1#2# reflected energy re-emitted energy re-emitted energy directly transmitted energy Heat gain due to Direct solar radiation directly + re-emitted energy = S F / SHGC

Factors affecting SOLAR FACTOR (SF) or Solar Heat Gain Coefficient (SHGC) Single Glazed Unit Clear SHGC = 0.84 Single Glazed Unit Green SHGC = 0.56 Single Glazed Unit Blue SHGC = 0.56 Single Glazed Unit Clear –solar control SHGC = 0.15 – 0.68 Single Glazed Unit Green–solar control SHGC = 0.16– 0.47

Shading Coefficient Shading Coefficient (SC) = Solar factor of Glass Solar factor of 3.0mm Clear Glass (0.87) SC should be used if the solar value are through 3mm clear glass SF or SHGC should be used if it is direct solar value from sun Eg: Weather Files

Area = 1 m 2 T 1 = 1 o CT 2 = 0 o C U = 5.7 W/sqm K Amount of heat Transferred due to temperature difference U Value

Factors affecting U value Inert Gas Single Glazed Unit U value = 5.8W/SqmK Double Glazed Unit Low-e U value = 1.4 to 2 W/SqmK Double Glazed Unit Low-e + inert gas U value = 1.0 to 1.3 W/SqmK Double Glazed Unit U value = 2.9W/SqmK

ECBC – [Energy Conservation Building Code] Glazing Requirements for building envelope

ECBC Compliance Approach Prescriptive: component based approach (specs given for each) – Low Flexibility – Easy Approach Trade Off: system based approach (trade off between performance of envelope) – Moderate Flexibility – Comparatively Tedious Approach Performance Method: Whole Building Design Analysis Approach (overall building energy efficiency) – High Flexibility – Tedious Approach – High Detailing

Prescriptive Compliance Approach

Climatic zone map of India

WWR: Window to wall ratio WWR = Net Glazing area / Gross wall area – Net glazing area (window area minus mullions and framing) divided by – Gross exterior wall area (e.g., multiply width of the bay by floor-to-floor height) Spandrel Glass & Glass in front of dead wall are not considered as glass area Case 1 : WWR = X / Y Case 2 : WWR = (X+Z) / Y Z Z

Prescriptive Requirements ECBC Prescriptive requirements Light Transmission SHGC / U value

Light transmission Solar Control U Value 89% W/SqmK Clear Glass 73% W/SqmK Tinted Glass Greater than 20% Less than 0.25 Less than 3.3 W/SqmK ECBC Requirements Glass Performance Coated Glass with Solar / Thermal Insulation

Coating Technology - Glass Conforming to ECBC Compliance

Online Coating Manufactured during manufacturing of glass it self. Process of manufacturing known as pyrolysis Offline Coating Manufactured in a separate process (offline) by Magnetron sputtering on to raw glass COATINGTECNOLOGYCOATINGTECNOLOGY CVD Coating

Trade off Compliance Approach

Trade Off requirement Heat Gain Through Envelope – Covers: heat gain through: Wall, Fenestration, Roof EPF (Energy Performance Factor) – Calculate heat gain as per values specified by Prescriptive compliance for Glass, roof, wall – BASE CASE – Calculate heat gain as per actual performance of glass, roof wall – PROPOSED CASE – EPF of proposed case should be less than equal to base case

Trade Off Compliance: Envelope C = constant vale from ECBC table 12.1 to 12.4 – Appendix E

Performance Method Whole building Simulation Compliance Approach

Whole building Simulation Computer Simulation of annual energy performance using simulation software Hourly detailing & output result for base & proposed case is simulated Modeling & energy calculation is in accordance ECBC – Appendix D requirements encompassing details of: Design Model Space use / scheduling Building envelope Lighting HVAC SWH & miscellaneous loads

Choosing “Correct” Glass Energy EfficiencyDaylighting

Daylight Integration Sunlight aids in, – Reduction of Artificial lighting – Increasing Vitamin D level – Alleviate depression &anxiety – Eliminates Claustrophobic effect Glass, – Allows abundant natural sunlight – When compared to conventional brick-mortar building, daylight integration saves about 40 to 60% of the energy used for lighting – For a fixed lumen requirement, sunlight generates lesser heat in comparison to artificial lighting – reduce the A/C bill Light Heat ratio Heat Built up

Clear Glass Solar Control Coated Glass Light Transmission89%Light Transmission30% Average Lux Level430 lux Peak Lux level1680 lux Average Lux Level220 lux Peak Lux level670 lux Outdoor Lux level : 9000Lux Room Size : 4m X 5mWindow Size: 1.0mX 2.4m (WWR:20%)

Energy Efficiency

Air conditioned Spaces

Energy Analysis of air conditioned space CASESolar Factor U Value W/m2K Light Transmis sion HVAC Consumpt ion kWh Lighting Consumpt ion kWh Total kWh Savings / Year kWh 1. Single Clear % Base 3. Solar Control % Location: MumbaiFloor area : Sqft WWR – 20% Glass Performance on cooling & Lighting load Lower Solar Heat Gain coefficient significantly reduces the cooling Optimized light transmission of glass reduces lighting energy during daytime operation

Non - Air conditioned Spaces

Temperature Distribution Case 1: Double Glazed Unit – Clear Glass – Solar Factor : 0.71 – U value : 2.8W/SqmK Case 2: Double Glazed Unit – Single silver Low-e Glass – Solar Factor : 0.54 – U value : 1.8W/SqmK Case 3: Double Glazed Unit –Double silver Low-e Glass – Solar Factor : 0.32 – U value : 1.6W/SqmK Location :Mumbai Room Size :4m X 5m Glass Direction :South Glass Size :1.9m X 4.6m Over hang :1.0m Simulation :Ecotect Simulation hours :8760 Hrs

Temperature Distribution Duration Double Glazed Unit Clear Glass Double Glazed Unit Single silvered low-e Double Glazed Unit Double silvered low-e Temperature Range 20˚ – 30˚C Hours % 86%87.4%88.5% Increase in comfort hours Base122 Hrs299 Hrs Temperature 32˚C Hours % 11.7%11.6%10.9% Temperature Range 34˚ – 36˚ C Hours % 3.25%2.0%0.53% Comfort Temperature Range Discomfort Temperature Range

Go Green Do your little bit to the planet ! Every reduction in Unit of electricity (KwHr) means 1.4 kg (CO 2 e) per kWh* Every reduction in a single KWH, 1.4 Kg of CO2 emission is prevented Conversion factor includes GHG emission for handling, generation & transportation loss *Source: DEFRA – Dept of energy & climatic change