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