daylighting buildings

Daylighting BuildingsNexus | November 12, 2009

Holly Wasilowski, Registered Architect, LEED AP

Doctor of Design Student in Sustainable Design Harvard Graduate School of Design

Daylighting Buildings

Nexus | November 12, 2009

Agenda:

Introduction

Rules of Thumb

Metrics

Case Study Using Metrics

Software Overview

Daylighting and LEED

Introduction

What is daylighting?

What are some of the potential benefits of

daylighting?

Introduction

What are some of the potential benefits of

daylighting?

reduced electric lighting load

reduced internal gains

reduced cooling loads

improved lighting conditions

color rendition

color temperature

“sparkle”

occupant satisfaction

occupant comfort

reduced cooling loads

connection to nature

time orientation

health: circadian rhythms…

etc.

Introduction

What are some of the potential drawbacks of

daylighting?

Introduction

What are some of the potential drawbacks of

daylighting?

increased heat gains

increased cooling loads

glare!

increased electric lighting load – how?

functional interference (example: projectors)

More is not always better.

Introduction

Some Resources

Heating, Cooling,

Lighting –

Norbert Lechner

Sun, Wind &

Light – Brown

and DeKay

Environmental

Control Systems

– Fuller Moore

Green Studio

Handbook

- Kwok and

Grondzik

Introduction

http://www.amazon.com/gp/reader/0471241431/ref=sib_dp_pt



Rules of Thumb

For other Rules of Thumb and Tutorials Go to:www.gsd.harvard.edu/research/gsdsquare/tutorials.html

Rules of Thumb



Rules of Thumb

Sun angles

Rules of Thumb

Sun angles

Opinion poll: Would you rather have your office

window facing north, south, east, or west?

Rules of Thumb

Sun angles



What about your bedroom?

Rules of Thumb

Sun angles



What about your bedroom?

Would you rather have your outdoor swimming pool on

the north, south, east, or west of your Boston

apartment building?

Rules of Thumb

Sun angles

Rules of Thumb

Sun angles

Quiz question:

Does an east-facing surface in Boston receive more

solar radiation in the summer or the winter?

A horizontal surface?

A south-facing surface?

Rules of Thumb

Sun angles

Rules of Thumb

Sun angles

VS.

south

Rules of Thumb

Building orientation: north/south +/- 15 degrees

Carmax Headquarters by ADD Inc

Rules of Thumb

Façade Design and Building Massing

Carmax Headquarters by ADD Inc

Rules of Thumb

External Shading

Why is EXTERNAL shading so important?

Rules of Thumb

Lighting Controls and Interior Design

Rules of Thumb

Lighting Controls and Interior Design

Interior light shelf

photosensors

zoning of electric

lighting

reflective colors

low/translucent

partitions

Rules of Thumb

Some definitions

Illuminance

Luminance

Rules of Thumb

Some definitions

Illuminance Units: lux

(SI), footcandles (IP)

(1 fc = about 11 lux)*

Luminance Units:

candela/m2 (SI),

candela/ft2 (IP)(1 candela/ft2 = about 11

candela/m2)*

*Use a conversion

factor of 10 today, for

convenience.

Rules of Thumb

Falsecolor Luminance Image from Radiance

Rules of Thumb

Illuminance Image from Ecotect(calculations performed in Radiance)

Rules of Thumb

What are some typical light levels?

Office:

Classroom:

Parking lot at night:

Overcast day outside:

Sunny day outside:

Rules of Thumb

What are some typical light levels?

Office: 50 fc, 500 lux

Classroom: 30 fc, 300 lux

Parking lot at night: 1 fc, 10 lux

Overcast day outside: 1500 fc, 15,000 lux

Sunny day outside: 8000 fc, 80,000 lux

Rules of Thumb

Illuminance meter

$60 to $500 +/-

Rules of Thumb

Glare

direct glare

discomfort glare -

physical discomfort

disability glare – reduced

visual performance

indirect glare

veiling reflections

Rules of Thumb

Maximum Recommended Brightness Ratios for

Indoor Lighting1

1 From Heating, Cooling, Lighting, Lechner 2009

Ratio Areas Example

3:1 Task to immediate

surroundings

Book to desk top

5:1 Task to general

surroundings

Book to nearby

partitions

10:1 Task to remote

surroundings

Book to remote wall

20:1 Light source to large

adjacent area

Window to adjacent

wall

Rules of Thumb

Maximum Recommended Luminance Ratios for

Indoor Lighting1

1 From Heating, Cooling, Lighting, Lechner 2009

Ratio Areas Example

3:1 Task to immediate

surroundings

Book to desk top

5:1 Task to general

surroundings

Book to nearby

partitions

10:1 Task to remote

surroundings

Book to remote wall

20:1 Light source to large

adjacent area

Window to adjacent

wall

What is wrong with these rules of thumb for daylighting?

Rules of Thumb

A Glare Study

Classroom renderings from Radiance

Rules of Thumb

A Study of Contrast Ratios in a Daylit Space

Rules of Thumb

Daylight Penetration

X

How far can daylight

penetrate into a space?

Rules of Thumb

Daylight Penetration1

1 From Christoph Reinhart, Harvard Graduate School of Design 2009

In a sidelit space with a standard window and

venetian blinds, the depth of the daylit area usually

lies between 1.5 and 2 time the window-head-

height. If a space does not require the use of a

shading device the ratio can increase up to 2.5.

X

1.5X 2 X 2.5 X

Rules of Thumb

For other Rules of Thumb and Tutorials Go to:www.gsd.harvard.edu/research/gsdsquare/tutorials.html

Current Tutorials:

Daylighting Rules of Thumb

Getting Started with Ecotect/Radiance/Daysim

From Rhinoceros to Ecotect

Getting Started with DesignBuilder/EnergyPlus

Daylighting Metrics



Daylighting Metrics

Daylight Factor (DF)

Ratio of Outside

Illuminance to Inside

Illuminance

DF = 100 * Ein / Eext

From: www.learn.londonmet.ac.uk/packages/clear/visual/daylight/analysis/hand/daylight_factor.html

Daylighting Metrics

Daylight Factor (DF)

Widely used metric

Easy to understand

2% or 5% DF are 2 common thresholds for

daylighting

Limitations:

Overcast sky only!!!

More is not always better

Daylight Factor Image in Ecotect(Calculations Performed in Radiance)

Daylighting Metrics

Daylighting Metrics

Dynamic Climate Responsive Daylight Metrics

Consider daylight over a period of time, such as

a year

Use actual occupied hours

Use actual climate conditions

TMY weather files

Daylighting Metrics

Daylight Autonomy (DA)

Percentage of working hours when a minimum

work plane illuminance (example, 300 lux or 28

fc) is maintained by daylight alone

Daylighting Metrics

Useful Daylight Illuminance (UDI)

Divides working hours into three bins:

% < 100 lux (insufficient daylight)

% between 100 lux (9.2 fc) and 2000 lux (186 fc)

(useful daylight)

% > 2000 lux (186 fc) (too much daylight)

A Case Study Using Daylighting Metrics



Case Study Using Daylight Metrics

Case Study

Academic Building in Northern Kentucky

West-facing Laboratories

South-facing Classrooms

East-facing Offices

Comparing Design Alternatives for Each


Case Study Variant A: “No Shade” Same as

E but without sun shelf.

Variant B: “Different Glass”

60% visible transmittance rather

than 72%

Variant C: “Horizontal Louvers”

6” deep louvers at 6” O.C. for

portion of windows above 7’

Variant D: “Interior/Exterior

Shelf” 24” exterior shelf plus 36”

interior shelf at 10’

Variant E: “As Designed” 3’ or

7’ sill, 12’-6” head, 24” deep

exterior sun shelf at 10’

AB

C

D

E


Case Study: Daylight Autonomy (DA)

A

B

C

D

E

Here all the variants show that there

is plenty of daylight in the space.


Case Study: Useful Daylight Index (UDI)

A

B

C

D

E

The UDI for all 5 variants indicates that glare

control near the windows is a concern. Variant B

shows that glass with less visible transmittance is

actually beneficial from a daylighting perspective.

This would allow for a lower solar heat gain

coefficient, which would be beneficial from an

energy stand-point as well.


Case Study: Direct Shading Studies

South-Facing Classroom: June 21, noon

South-Facing Classroom: March 21, noon

South-Facing Classroom: Dec 21, noon

The louvers of variant C and the deep

lightshelf of variant D help control

glare; however, interior blinds will be

needed during low sun-angles for

each of the current variants.


Case Study: Conclusions

The classroom receives plenty of daylight. If the window sizes could

be reduced it would likely be beneficial from an energy stand-point

as well as cost. The lower glazing provides the least lighting benefit

but the best view.

Use photo-controlled dimmers throughout the space. Zone

perimeter space separately if possible.

A glass that provides more shade is recommended for this space.

Consider 0.6 visible transmittance or higher and 0.35 shading

coefficient or lower (instead of 0.7 and 0.43 respectively.)

Add an interior sun shelf if possible or consider horizontal louvers.

Provide as much depth as feasible for the shading devices.

Software Overview



Software Overview:

Direct Shading

Solar Position

Static Simulations

Dynamic Simulations

Glare Probability

Software Overview

Direct Shading:

SketchUp, Ecotect…

Any other 3D modeling program in which you

can accurately set:

Your location (longitude/latitude or city)

Your orientation (face your building the

right direction)

And the time of day and year

And which accurately positions the sun

Software Overview

Solar Position:

Climate Consultant (freeware)

http://www.energy-design-tools.aud.ucla.edu/

Software Overview

Solar Position:

Ecotect / Ecotect Weather Tool

Software Overview

Radiance:

Accurate, physically-based renderings

Static (one moment in time) Calculations

Luminance values

Illuminance values

Freeware:

http://radsite.lbl.gov/radiance/download.html

Software Overview

Radiance Rendering

From: www.artifice.com/radiance.html

Software Overview

Radiance Illuminance Images

Exporting to Radiance in Ecotect

Software Overview

Radiance Calculations Visualized in Ecotect

Software Overview

Software Overview

Daysim:

Dynamic, Climate-Based Calculations

UDI

DA

Uses Radiance Engine

Can Model Blind Operations

Freeware: http://www.nrc-

cnrc.gc.ca/eng/projects/irc/daysim/versions.html

The Daysim GUI

Software Overview

Software Overview

Evalglare: For Calculating Glare Probability

A classroom rendering in Radiance

A glare study in Evalglare

Software Overview

Evalglare: For Calculating Glare Probability

http://www.sbi.dk/download/pdf/Evalglare.pdf

Freeware (Site in German. Look for evalglare v0.9f –

Windows Version in lower right)

http://www.ise.fhg.de/radiance


LEED 2009 IEQ Credit 8.1

75% of Occupied Spaces Daylit = 1 point

90% of Occupied Spaces Daylit = 2 points

Option 1: Simulation

Option 2: Prescriptive

Option 3: Measurement

Option 4: Combination


Option 1 Simulation

To qualify as daylit, space

must meet a minimum of 25

fc and max of 500 fc on

September 21 at 9am and

3pm under clear skies

Automated shades exempt

you from the maximum

illuminance limitations


Option 2 Prescriptive

To qualify as daylit, the visible light transmittance (VLT)

times the window-to-floor area ratio (WFR) must be

between 0.150 and 0.180

And the space must meet this ceiling height

requirement…

0.150 < VLT X WFR < 0.180


Option 2 Prescriptive

0.150 > VLT X WFR < 0.180


Option 3 Measurement

To qualify as daylit, space must meet a minimum of

25 fc measured on a 10 foot grid


Option 3 Combination

To qualify as daylit, each space

must meet one of the methods

described above

In all cases (Options 1-4)

provide glare control

Questions?



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