Introduction to basics of energy efficient building design. Basics of Energy Efficient... ·...
Transcript of Introduction to basics of energy efficient building design. Basics of Energy Efficient... ·...
Introduction to basics of energyefficient building design
Pierre Jaboyedoff
Seminar onEnergy Efficient & Thermally Comfortable Buildings
in AmravatiFor CRDA, Andhra Pradesh
May 2nd 2017
Indo-Swiss Building Energy Efficiency ProjectProject Management and Technical Unit (PMTU) 1 of 21
Thermal Comfort
Mean radiant temperature
Air temperature
Air velocity
Relative humidity
Clothing
Metabolic rate
Factors influencing the Thermal Comfort of the human body
Source: ASHRAE Handbook _2009
Personal Factors
Environmental Factors
Short wave (solar
radiation)
Long wave (surface
temperature)
Main factors influencing the comfortin a building
• Air temperature▪ Inside the building
• Humidity
• Radiant temperature▪ Surface temperature
• Air velocity▪ Low velocity for «cold» air
▪ Higher velocity for «warm air»
• Solar radiation▪ Direct on the body
▪ Diffuse or re-radiated
▪ Solar protection
▪ Daylighting
• Clothing
• Activities
Climate-Responsive Architecture?
Environment (Climate)-responsive architecture can be defined as
architecture aimed at:
• achieving occupant thermal and visual comfort with
• little or no recourse to non-renewable energy sources
(Simos Yannas, 2003)
Temperature Humidity Wind Rain
Solar Radiation-
Direct & Diffused
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BRIEF HISTORY OF THE DESIGN PRACTICES AND OF THE TECHNOLOGY PROGRESSES
Passive design of the building envelope versus time
0
20
40
60
80
100
120
1940 1950 1960 1970 1980 1990 2000 2010 2020 2030
Passive
«modern» architecture70-100% glazed, no naturalventilation, all air systems
Ancient architecture(low window to wall ratio, naturalventilation, …
«sustainable» architecture, 25-40% window to wallratio, naturalventilation, externalmovable solarprotection
Insulation of the walls
• Insulation did always exist
• Became an industrial product in the 1950’s
• Reduction of the heat (in/out) across the walls
• Typical values▪ Brick 9 inch U~2 W/m^2-°C
▪ 20 cm insulation U~0.2 W/m^2-°C
▪ Reduction of the losses/gains of a factor ~10
Insulation characteristics of glazing systemshave improved significantly in the 1970-2010
• Single glass U~6 W/m^2-°C
• Triple glass with selective coating U~0.6
W/m^2-°C
• Reduction of the losses by a factor 10
• Partly solar protection by reduction of
the solar radiation passing through by 60%
• Daylighting compromise by a reduction of
the visual light transmission of ~30%
Heat gains by ventilation
• Infiltration▪ Building tightness has improved during the last 40
years
▪ Reduction of the gains/losses by a factor ~5
• Mechanical ventilation▪ Reduction of the fresh air flow rate to the hygienic
need
▪ Addition of heat and humidity recovery heat
exchangers
▪ Reduction of the gains/losses by a factor 4-5
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CLIMATE ANALYSIS
Climate analysis
• Temperature evolution▪ Dry bulb
▪ Wetbulb (humidity)
• Solar radiation▪ Direct
▪ Diffuse
• Wind regime▪ Velocity
▪ Direction
▪ Fluctuation (gust)
• Time analysis▪ Over 24 hours
▪ Over seasons
Example: Wind on a specific site
Strategies for Climate Responsive Design
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CLIMATE RESPONSIVE BUILDING MASSING
Building Orientation and Massing
N
S
E
W
• Massing is the overall shape and size of the building
• Orientation is the direction the building faces
Good building massing and orientation helps minimise external
energy loads and harness solar and wind energy for human comfort
Solar Heat Gains
N
S
E
W
South façade is
highly exposed in
winter, but less in
summer.
North façade
receives very
little direct
radiation. Only
in summer
mornings and
evenings
Winter
21st Dec
Summer
21st Jun
Horizontal surface
receives the greatest
intensity
East and West façades
receive high amount of
radiation both in
summer and winter
Access to Daylight and Natural Ventilation
Daylight
Ventilation
Orientation: Effect on Cooling Load
Total cooling
load (kWh) on
an
intermediate
floor for
March to May
(BELGAVI)
3677
4305
-15%
• Linear building form in which the longer sides oriented the north
and south will have less solar heat gains in summer.
Effect on Daylight Access
< 100 lux
100 – 200 lux
• Linear building form in which the longer sides oriented the north
and south will have better daylight access.
• Shallow floor plate (14m – 18m) deep allows maximum daylight
penetration.
Effect on Natural Ventilation
• Linear building form with a shallow floor plate (14m – 18m) deep
allows better natural ventilation potential.
Air velocity < 0.1 m/s
Air velocity < 0.1 m/s
Conclusions on Building Massing and Orientation
Linear building form with shallow floor plates (14–18 m)
and with the longest façades towards north and south
preferable
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DESIGN OPENINGS FOR DAYLIGHT
Daylight Factor
Daylight Factor= Ii / Io
Illumination
available inside
Ii
Illumination
available outside
Io
Daylight Autonomy
TIME-IN-USE:
Time when building is being
used. For e.g. 9 am to 6 pm
Daylight Autonomy:
Percentage of the time-in-use that the daylight levels exceed a
specified target illuminance or lighting set-point.
TARGET ILLUMINANCE / LIGHTING SET
POINT:
Recommended illuminance (lux) levels.
For e.g. lighting set-point for standard
offices is 300 – 500 lux.
Daylight Autonomy: the percentage of time that an occupant can work through the
use of just daylight without supplemental electric lighting
Designing for Good Daylight
• Keep Window-to-Wall Ratio (WWR) around 20%–30%.
• Keep most of the windows OR Design larger windows on the north and
south faces
• Openings for daylight should be close to the ceiling
• The space depth should not generally exceed 2.5 times the floor to
lintel height. Usually, daylight is available up to 6 or 8 metres from the
window.
• For good daylight, the visual light transmittance (VLT) of the glazing
should be high. In most cases, the VLT of clear float glass is high. A
balance has to be made in the daylight and heat gain through
windows. This can be further controlled by the use of external
movable shading
• The room finishes should be white or in light shades
• Shallow floor plates are better for daylighting and natural ventilation
Placement & Area (Window-Wall-Ratio)
N
S
E
W
East and West façades
receive high amount of
radiation. Difficult to
shade. Hence less
windows here.
South façade is
highly exposed in
winter, but less in
summer.
Windows can be
easily shaded here.
North façade
receives very
little direct
radiation. More
windows here.
Winter
21st Dec
Summer
21st Jun
Windows closer to the Ceiling for daylight access
H
Daylight penetrates into a room roughly 2.5 times the height
of the top of the window from the ground.
2.5 H
• Higher the window, deeper the daylight penetration in the room
• Usually, daylight penetration in the room is between 6m to 8m
from the fenestration
2.5 H
Building Massing and Zoning for Daylight
Shallow floor-plates provide daylight access to
greater floor area
Building spaces can be zoned to place areas
requiring more daylight near the perimeter.
Areas requiring less daylight placed in the
centre of the floor-plate
Visible Light Transmission (VLT) of Glass
VLT is the ratio of visible light that passes through a glazing unit
to the total visible light incident on it.
FACTORS INFLUENCING VLT:
- Colour of glass
- Tints & Coatings on the glazing
- Number of glass panes
Design features for better daylight access
Light shelves help better day light distribution while also
providing shading
• Lighter colours on interior surfaces reflect light better.
• Helps in daylight distribution and reducing glare.
INFOSYS, HYDERABAD
Very high daylight autonomy
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DESIGN FOR NATURAL VENTILATION
What is Natural Ventilation?
Natural ventilation is the process of supplying and removing air
through an indoor space without using mechanical systems.
Wind driven natural
ventilation
Buoyancy driven natural
ventilation
Purpose of Natural Ventilation
• To provide an acceptable indoor air quality (IAQ)
• To provide thermal comfort by providing a heat transport
mechanism
▪ Cooling of indoor air by replacing or diluting it with outdoor
air as long as outdoor temperatures are lower than the indoor
temperatures.
▪ Cooling of the building structure i.e. Thermal mass of
building.
▪ A direct cooling effect over the human body through
convection and evaporation.
Natural Ventilation Potential (example in Karnataka)
Semi arid climate: Vijayapura
Nearly 40% of annual hours below 26°C
Natural Ventilation (example in Karnataka)
Temperate climate: Bengaluru
Nearly 65% of annual hours below 26°C
Wind Driven Natural Ventilation
Cross ventilation
Single sided ventilation
When possible, cross ventilation is more efficient than single sided
Wind Driven Natural Ventilation
• Cross ventilation works well up to building depths of around 15 m
and when the predominant wind direction is ± 60° from the axis
perpendicular to the building façade
Wind Driven Natural Ventilation
• If the predominant air direction is parallel to the building façade,
the use of deflectors is helpful in increasing the flow.
Stack Ventilation
Night Ventilation
Night Ventilation keeps windows and other passive ventilation
openings open at night to flush warm air out of the building and cool
thermal mass for the next day.
For night cooling to be efficient, it requires a building with large
areas of exposed internal thermal mass
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CLIMATE-RESPONSIVE BUILDING ENVELOPE
Significance of building envelope
The building envelope is first a protection and shelter.
It should meet this need of the occupants while reducing energy
consumption.
The building envelope is the boundary between the conditioned
interior of a building and the outdoors.
Energy Loads: Building Envelope Components
Roof
Wall
Fenestration
Air leakage
Floor
Heat gains through building envelope components
• Heat gain from windows is much
higher compared to the heat gained
through walls
• Heat gain from the roof is highest
• Heat gain from windows is also
significant
Reducing heat gains from the roof and windows should be
a priority
Recommended Roof Insulation as per ECBC
Envelope
component Climate Zone
Day-time use buildings
& other building types
Max U-value Min. R-value of insulation alone
W/(m²K) m² K/W
Roofs All 0.409 2.1
Over deck insulation, e.g., with 10 cm of extruded
polystyrene or 7.5 cm of polyurethane
foam, is a standard suitable solution for roof insulation
Wall Insulation as per ECBC
Envelope
component Climate Zone
Day-time use buildings
& other building types
Max U-value Min. R-value of insulation alone
W/(m²K) m² K/W
Walls
Tropical wet, wet and dry,
semi-arid, andtemperate climates
0.440 2.1
The contribution of heat ingress from walls generally
smaller than the contribution of solar energy through
glazing
Heat transfer through Windows-Single Glazing
Incident solar radiation
TransmittedReflected
Absorbed
Re-emittedRe-emitted
Conducted
Conducted
Convection
Infiltration
Design decisions for windows
Placement and Area (Window-Wall-Ratio)
Solar Protection
Glazing and Frame Properties
Window Glazing & Frame
Heat transfer through
• Conduction
Heat transfer through
• Conduction
• Convection
• Radiation
U factor
SHGC
Light VLT
Solar radiation is the largest contribution to heat gains
through windows and often of the total heat gains
Solar Heat Gain Coefficient (SHGC)
SHGC is the ratio of solar (radiant) heat gain that passes through
the fenestration to the total incident solar radiation that falls on it.
SHGC is a dimensionless number between 0 and 1.
FACTORS INFLUENCING SHGC:
- Solar protection or shading
- Type of glass & number of panes
- Tints & Coatings on the glazing
- Gas fill between glazing layers
U Factor
As with opaque envelope components, U-factors measure thermal
conductivity through the window components.
FACTORS INFLUENCING U FACTOR:
- The size of the air gap between glass panes
- Coatings on the glazing
- Gas fill between glass panes
- Frame construction
Visible Light Transmission (VLT)
VLT is the ratio of visible light that passes through a glazing unit
to the total visible light incident on it.
FACTORS INFLUENCING VLT:
- Colour of glass
- Tints & Coatings on the glazing
- Number of glass panes
Different Glazing Types
Glazing type Glass pane
thickness
(mm)
U factor
W/(m²K)
SHGC VLT
Single clear glazing 6 6 0.81 0.89
Double glazing (clear) 6 2.7 0.7 0.79
Double glazing (low-e) 3 1.8 0.71 0.75
Triple glazing (clear) 3 2 0.67 0.74
Double glazing, argon
filled (low-e)
6 1.4 0.57 0.73
Source: www.wbdg.org/resources/windows.php, Whole Building Design Guide
Double glazing (low-e)
SKN Envision
6 1.5 0.33 0.55
Source: Saint Gobain
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SOLAR SHADING SOLUTIONS
Solar Protection
• North-facing windows receive direct sunlight in summer mornings
and evenings.
• Vertical fins can shade adequately
N
S
E
W
Summer
21st Jun
Winter
21st Dec
Static Solar Protection
Horizontal overhangs can effectively cut
direct solar radiation on the south façade
in summer but not the diffuse radiation
Summer
Winter
IRRAD, Gurgaon
Solar Protection
N
S
E
W
Summer
Winter
• Low sun on east west facades
• Solar azimuth angle also changes
Dynamic shading most effective on east west facades
Summer
21st Jun
Winter
21st Dec
Interior Blinds
SHGC > 40%
Inside Outside
Exterior Blinds
SHGC ~ 12%
External movable shades can reduce solar heat gains by
60 % - 80%
External Movable shades
External Movable shades
External Movable shades
ROLEX LEARNING CENTRE, EPFL,
LAUSANNE
COMMUNICATION BUILDING, EPFL,
LAUSANNE
External Movable shades: India
GOLCONDE, PONDICHERRY
External Movable shades: India
SABARMATI ASHRAM, AHMEDABAD
External Movable shades: India
SAFAL PROFITAIRE, AHMEDABAD
External Movable shades: India
SAFAL PROFITAIRE, AHMEDABAD
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RECAP
Recap
• Orient the building and organise the spaces and forms so as to
minimise the heat gains from solar radiation, provide good
daylight access, and facilitate natural ventilation.
• A linear building form with shallow floor plates (14–18 m) and
with the longest façades towards north and south fulfills the 3
criteria mentioned above.
1 CLIMATE RESPONSIVE BUILDING MASSING
Recap
• For a typical office building in Karnataka, WWR of 20%–30% is sufficient to provide good daylight (daylight autonomy of around 75%).
• To achieve good daylight, the building shape should be linear (14–18 m width) in which the longer sides are oriented towards the north and south and the windows are provided only on the north and south façades.
• Use of clear glass for best VLT in combination with adequate shading devices to cut off glare and heat and use of light-coloured finishes
• Zone building spaces to place areas needing daylight at the perimeter
• Place windows higher up on the wall, near the ceiling for better daylight distribution
2 DESIGN OPENINGS FOR DAYLIGHT
Recap
• Cross ventilation works well up to building depths of around 15 m and when the predominant wind direction is ± 60° from the axis perpendicular to the building façade.
• If the predominant air direction is parallel to the building façade, the use of deflectors is helpful in increasing the flow.
• In certain cases, stack effect can be used to enhance natural ventilation. However, to be effective, due care should be exercised in designing the height and dimensions of the opening of the stack.
• Night ventilation takes advantage of lower night-time temperatures to flush heat out of the building and precool the building structure. For night cooling to be efficient, the thermal mass of the building structure needs to accessed by the air flowing through the building and thermally closed false ceilings should be avoided.
3 DESIGN FOR NATURAL VENTILATION
Recap of Passive Design Measures
• Roof needs to be insulated and treated to reflect the solar
radiation. The ECBC for Karnataka recommends roof insulation to
reach U values of 0.4 W/m.K.
• Buildings should have an optimum WWR, which helps in admitting
adequate daylight yet limits heat gain. WWR of around 20%–30%
may be adequate.
• The U value of the windows should be low and a trade-off is to be
made between SHGC (heat gains) and the VLT (for daylight).
4 CLIMATE RESPONSIVE BUILDING ENVELOPE
Recap of Passive Design Measures
• The best solutions for solar shading are exterior dynamic shading
solutions such as shutters or external movable blinds. The major
advantage of such solutions are listed below:
▪ Flexibility of use according to weather conditions and seasons
▪ Provide good daylight, when opened
▪ Effectively cut 80% to 90% of the solar gains
▪ Can be applied on any façade, which gives more flexibility for
the orientation of the building.
5 SOLAR SHADING SOLUTIONS
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THANK YOU