SUSTAINABLE ARCHITECTURE
Energy Efficiency - II
DR AVLOKITA AGRAWAL
DEPARTMENT OF ARCHITECTURE AND PLANNING
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Energy Performance Index
• Energy Performance Index (EPI) is a metric to understand the annual energy
consumption of a building per unit area.
• Units: kWh/ m2/ Annum
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Source: Energy technology Perspective 2016
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Building Envelope
• THE BUILDING ENVELOPE refers to the
exterior façade, comprised of
opaque components and
fenestration systems. components
include walls, roofs, slabs on grade
touch with ground), basement walls,
and opaque doors.
• Fenestration systems include
windows, skylights, ventilators, doors
that are more than glazed. The
envelope protects building’s interior
and occupants from the weather
conditions shields them from other
factors e.g. noise, air pollution,
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Building Envelope Design Considerations
• Climate & microclimate
• Temperature, humidity, solar radiation, wind speed/direction, landform, vegetation, water bodies,
open spaces, etc.
• » Building Orientation & Form
• Orientation of the building, surface−to−volume ratio and exposed surface area
COMPOSITE MODERATE HOT-DRY COLD
CLIMATE CLIMATE CLIMATE CLIMATE
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Insolation
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1. Efficient Building Envelope
(a) North- South Orientation for longer occupied spaces
When Larger façade facing North-South When Larger façade facing East-West
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(d) Adjacent shading through trees
Source : https://prezi.com/me5usbe9ciid/
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Source : ECBC
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Fenestration
Glazing
Covers most of the area
and thus most
important part to Frame
achieve energy Important to optimize
efficiency the overall energy
efficiency of the window
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Window to Wall Ratio
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Window to Wall Ratio
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(c) High Performance Glass
Source : Skyviewwindows.ca.
N.p., 2016. Web. 31 Dec. 2016.
Source : Ksg.com.my. N.p., 2016.
Web. 31 Dec. 2016.m
SHGC
SHGC refers to the ratio of the solar heat that passes through the glazing to the total
Source : ECBC
incident solar radiation, the lower the SHGC, the lesser the direct incident heat gains from
the glazing surfaces.
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Source : GRIHA
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Source : GRIHA
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Window Shading
Direct Solar rays incident on the window. Incident solar rays blocked by solar shading.
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(e) Fenestration Shading
Source : Image.slidesharecdn.com. N.p., 2016. Web. 31 Dec. 2016.
Source : Greenpassivesolar.com. N.p., 2016. Web. 31 Dec. 2016.
Source : Energy-models.com. N.p., 2016. Web. 31 Dec. 2016.
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Cool Roofs
• “Cool roofs” are roofs covered with a reflective coating
with a high emissivity property that is very effective in
reflecting the sun’s energy away from the roof surface.
– Known to stay 10˚C to 16˚C cooler than a normal roof
under a hot summer sun
– Reduced Urban Heat Island Effect
• Ideal Exterior Surface in hot climates
– Reflectance near 1 & Absorptance near zero to
minimize solar gain
– Emissivity near 1 to radiate absorbed heat back to the
sky.
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Significance of Cool Roofs
Gray Roof Cool Roof
Average daily maximum roof−surface 52˚C 32˚C
temperature
• Effect of Solar Reflective Roofs
• Case study: Satyam Technology Center, Hyderabad, India
– By International Institute of Information Technology (IIIT), Hyderabad, with Lawrence Berkeley National Lab,
California
• Measured daily electricity savings = 30 kWh (Building operation: 25 days/month, 12 month = 300 days)
• Estimated annual electricity savings = 9,000 kWh
• Annual savings per square meter = 13 kWh/m2
• Monetory savings at Rs. 5 /kWh = Rs. 65 /m2/year
• Incremental cost of cool roof = Rs. 700 /m 2
• Total discounted savings over the expected life of the roof = Rs. 430,000
100 m2 of a white roof, replacing a dark roof, offset the emission of 10 tons of CO2
Source: http://cbs.iiit.ac.in/Cool%20Roof/index.htm
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Blinds & Shading
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Blinds & Shading
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Sky lights
• U−Factor and SHGC requirements according to
• Installation of skylight (Flush mounted/curb mounted)
• Skylight Roof Ratio (SSR)
SOURCE: ECBC User Guide, USAID ECO−III Project, New Delhi
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ECBC Building Envelope Requirements: Overview
Building Component Mandatory Requirements Prescriptive Requirement
OPAQUE CONSTRUCTION Building Envelope Sealing Maximum U−factors & Minimum
(Roofs and Walls) Requirements R−values of roofs & walls
Cool Roof Specifications
FENESTRATION Calculation of U−factors & Solar Heat Maximum U−factors & SHGC,
(Doors, Windows and Skylights) Gain Coeficient (SHGC) of glazing Wall−Window Ratio (WWR), &
Visible Transmission (VLT) of
Air Leakage Maximum Limits Glazing
Skylight Roof Ratio (SSR); Maximum
U−factors & SHGC of glazing
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Thank you
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