daylighting: accident or technology? marc schiler schiler & associates / university of southern...

Daylighting: Accident or Technology?

Marc SchilerSchiler & Associates /

University of Southern California

Technical Approach to Natural Lighting Provide the light:

• Building plan, section and orientation• Fenestration location and sizing

Lighting circuits and controls• Balance the availability of natural light• Shutoff in stages

Sensors• Occupancy sensors• Photosensors

Aesthetic Approach to Natural Lighting Provide the space:

• Building plan, section and orientation• Fenestration location and sizing

Colors, reflective forms and gradation• Show the sensuous nature of the space• Reinforce the design concept and parti

Reinforce the function• Avoid glare• Provide visual terminus(humans are phototropic)

Five Topics: Topic One: Technical

– Concepts and Strategies

Topic Two: Aesthetic– Examples and Images

Topic Three: Models– Simulating Daylight with Physical Models

Topic Four: Calculations– Rules of Thumb and Calculations

Topic Five: Equipment– Sensors and Controls

Topic One

Technical: Concepts and Strategies

Agenda for Topic One

Benefits Strategies and Elements Definition of Terms Design Guidelines

Benefits

Quantitative– Cost savings for

user– Peak Reduction– Sustainability

Qualitative– Color Rendering– Productivity– Connection

Prototype Strategies

Foot Prints Clerestories Sawtooth Skylights Light Shelves Atria Exotica

Foot Prints

Clerestories

Sawtooth

Skylights

Caveat: – Lower winter angles = less light– Higher summer angles = more heat

Light Shelves

Light Pipes

Atria / Light Wells

Fresnel Lenses and Holographic Films

Design Guidelines Basic Principles

– illuminance vs. luminance

Glare– discomfort glare vs. veiling reflections

Vertical vs. Horizontal Tips

– Bring it in high– Bounce it or filter it– Control it – Harvest it

Vertical vs. Horizontal

Solar Control vs. Lighting per glazing area– more light from horizontal glazing, more heat

gain in summer, less heat gain in winter– less light from vertical, better distribution,

overhang controls for southern orientations, fins for eastern and western orientations (and northern)

Single Story

WarehousesSupermarkets Bldgs.Light IndustrialSuburban sites

Multiple Story

OfficesCity Bldgs.Urban sites

Summary (of Topic One)

Strategies and design elements

Design “Tips”

Break

Take a break– Stretch your legs– Get some coffee– Get rid of some coffee– Call home

Topic Two: Aesthetics

Classics– Older buildings with natural

lighting often stand the test of time very well.

Current Examples– Newer buildings enjoy the

technique and the technical.

Good Examples, Old to New

St. Gallen Abbey Library, Peter Thumb Bradbury Building Ventura Coastal Building by Scott

Ellinwood Mt. Airy Library by Ed Mazria Boy’s / Ralph’s Supermarket Lyons School of Architecture by Jourda

and Peroudin

Examples for Varying Functions and Climates

Arab Center, Paris, Jean Nouvel Episcopal Church, Phoenix MIT Chapel, Boston, Aero Saarinen Wells Branch Bank, Minnesota BRF Office Building, Copenhagen

More Examples

Crystal Cathedral, Philip Johnson North Jutland Art Museum, Alvar Aalto Menil by Renzo Piano Kimbell Museum, Louis Kahn Ronchamps, Le Corbusier La Tourette, Le Corbusier

Note -

The preceding three pages refer to 35mm slide

collections of each building.

Summary of Part Two

The greatest designs include natural lighting.– Natural light saves energy– Natural light can project in dramatic fashion– Natural light can be bounced and diffused to fill a

space

This has proven true throughout history– Rather than fight the architecture, we wish to work

with the architecture in the designing the natural and “artificial” lighting to work together.

Topic Three: Models

Using Scale Models to Study Light Distribution

Daylight Harvesting

Provide the light:– Building plan and orientation– Fenestration location and sizing

Test the design– Physical models– Computer simulations

Lighting circuits and controls– Balance the availability of natural light– Occupancy sensors, Photosensors

Agenda for Topic Three

Scales Examples Model Craft Measurement Photography Computations

Scale #1 - Quick and Dirty

Simple question: – skylight in middle or by the wall?– horizontal skylight or monitor?– eyeball assessment of question

Small Scale: – 1/16”=1’-0” to 1/2” = 1’-0” or about

1:200 to 1:20

Quick and Dirty (cont’d)

Construction – time: one hour or less– foamcore or chipboard, approximate

reflectances– tacky glue, masking tape or even pins – scissors, scrap materials at hand

Time and cost– 1/2 hour, $0 - $20

Scale #2 - Developmental

Developmental issues:– Sizing issues: “How big should the skylight

be?”– Placement/Light distribution: “How close to

the wall?”– Details: “How wide or deep should the light

well be?”– Actual measurements taken at different

times and seasons

Middle Scale: – 1” = 1’-0” or about 1:10

Developmental (cont’d)

Construction– Correct reflectances, some details like

baseboards – simple furniture, critical objects to be lit– more detail, such as mullions to show shadow

patterns– specular and diffuse surfaces are differentiated

Time and cost– 2 to 4 hours, $30 - $100

Scale #3 - Presentation

Qualitative issues:– Calibration against existing space to test

proposed renovations– Color interaction, mood, ambience,

personal reactions– Search for glare sources, veiling reflections– Photographs taken at different times and

seasons

Large Scale: – 2” = 1’-0” or about 1:5 or larger

Presentation (cont’d)

Construction– Correct colors, complete details like return

air grills, blackboards– Complete furniture, with simulated textures– Ceiling treatments, light fixtures, ducts– Dirty surfaces, where appropriate

Time and cost– 20 to 100+ hours, $100+

Review - Solar Angles

Altitude Azimuth

Solar Gnomons

One for each latitude, gnomon at correct height

Glued to model in relation to model compass

Manipulated to get shadow in the correct position– Azimuth first– Altitude second

Solar Gnomon Example 1

Model Craft

Joints must be sealed– electrical tape, or aluminum foil taped over all

corners and seams

Walls must be opaque– construction paper, opaque internal surface

treatments glued to internal surfaces– aluminum foil covering all exterior surfaces

(exception: any surface which might reflect light into the model, such as a roof adjacent to a roof monitor or sawtooth)

Model Craft (cont’d)

Replaceable parts or oversized parts– Whatever is being tested should fit into a light-

leak-proof slot– Prepare modules for each variation in

developmental or presentation models– In some cases, testing skylight placement can be

done by making an oversize roof, and then sliding it around so that the skylight sits over different areas. One roof and skylight can then simulate many positions without any cutting.


Portholes for measurement– allow access for meters and wires, if

necessary, and cover the hole if it is possible to read the meter from somewhere else.

– if necessary, cut holes in the floor to allow the meter surface to be at the workplane height in the scale of the model


Portholes for photography– plan the access for the camera from the

desired viewpoints– place portholes at in scale eye position,

e.g. 5’-3” in model scale– if multiple views are desired, cover

portholes with scale blackboards or paintings so that one porthole is not visible from the other camera angle

Review - Measurement

Footcandle or Lux Suggested Daylight Factors

(DF)– What the heck is a daylight

factor? Ein / Eext hor

Measurement Procedures

Grid Record Sheet– Draw a grid of expected measurement

points on a sheet of paper, along with headers recording actual time of day and simulated time of day

– Xerox enough copies of the sheet for different date or design variations

– Record each set of readings onto separate sheets

Measurement (cont’d)

Don’t let light in over your shoulder– shade the meters from direct beam for DF

values– Don’t let light in through the measurement

port (it screws up the measurement)– put a shroud over your head, and tape it

to the model, if necessary (black plastic trash bag, double thick, is usually sufficient)

Measurement (cont’d)

Do let light in over your shoulder!– when measuring through the active

window, be sure that your body stays below the field of view of the window and the meter

– don’t shade the meters from direct beam for absolute values

Photography

Record date and time– Include the date and time you

are simulating within the image itself

Photography (cont’d)

Provide a porthole Don’t let light in over your

shoulder– again, put a shroud over your head,

and tape it to the model, if necessary (a black plastic trash bag, double thick, is usually sufficient)

Slides

Note. At this point the presentation proceeds to proof that this can be done at each scale in the form of a series of 35mm slides of the interiors of real buildings followed by models of the same space, generally indistinguishable.

Summary of Topic Three

Scales, costs and functions Examples Model Craft Measurement Photography

Break


Topic Four: Calculations

Rules of Thumb and Calculations

Agenda for Topic Four

Rule of Thumb Computations– Width to Depth– Percentage Glazing

IES calculation methods– sidelighting– toplighting

Design Guidelines (Reminder) Basic Principles

– illuminance vs luminance

Glare– discomfort glare vs veiling reflections

Vertical vs. Horizontal Tips

– Bring it in high– Bounce it or filter it– Control it – Harvest it

Reminder of Application Guidelines

Different functions and building forms will require different calculation methods.

Vertical vs. Horizontal

Solar Control vs. Lighting per glazing area– more light from horizontal glazing, more heat

gain in summer, less heat gain in winter– less light from vertical, better distribution,

overhang controls for southern orientations, fins for eastern and western orientations (and northern)

Single Story

WarehousesSupermarkets Bldgs.Light IndustrialSuburban sites

Multiple Story

OfficesCity Bldgs.Urban sites

Rules of Thumb for Aperture Sizing

Suggested Daylight Factors (DF)– What the heck is a daylight factor?

Sizing to obtain the suggested DF– What glazing area in which kind of

element

Computer Programs– If the client’s got money

Suggested Daylight Factors

Function DF Comment

Circulation 1% vertical surfaces are importantPublic Spaces >1% more light, more dramaWarehouse 1.5% higher for tightly packed shelvesOffice area 2-4% filing, reception, general area

Detailed office work 5% focus on work surfaceFactory work 2-4% dependent on function and dangerDetailed manf’g 5% tasks requiring high visual acuityManual drafting, color comparison 6% provide one area within the space

Sizing

From Sidelighting (d < 2.5 x h) Suggested Glazing Areanear the front of the space DF x Af / 0.5Tgat the middle of the space DF x Af / 0.2Tgnear the back of the space DF x Af / 0.1Tg

From Toplighting Suggested Glazing AreaVertical monitors DF x Af / 0.2TgNorth facing sawtooth DF x Af / 0.33TgHorizontal Skylights* DF x Af / 0.5Tg

Example #1

2,000 sf of warehouse, toplighting – forklift access, generous aisles– suggested DF = 1.5%– Transmissivity of glazing = 62%– Horizontal skylights

Go for uniform 1.5% – Ag = DF x Af / 0.5 Tg – = .015 x 2,000sf / (0.5 x .62)– = 96 sf

Example # 2

Go for 3% at middle

–Ag = DF x Af / 0.2 Tg

– = .03 x 2,000sf / (0.2 x .75)

– = 400 sf

Go for 3% at back

–Ag = DF x Af / 0.2 Tg

– = .03 x 2,000sf / (0.1 x .75)

– = 800 sf

2,000 sf of simple office space, sidelighting – non strenous tasks, filing, some computer terminals– suggested DF = 2-4%– depth within 2.5h of window (20 ft of 8 ft window)– Transmissivity of glazing = 75%

Do layout, decide desired daylit depth

IES Lumen Method

Tracks light from sky and sun separately

Applies form and reflectance factors to light from ground

Assumes a strip window for the entire length of one wall (as might be found in an office.)

IES Lumen Method (cont’d)

Calculates a Coefficient of Utilization (CU) for five locations within the cross section of the space

Basic Equation

Ei = Ex NT CU where

Ei = interior illuminance in lx, Ex = exterior illuminance in lx,

NT = net transmittance, CU = coefficient of utilization.

Sidelighting

Ei = Exv τ CU

where Ei = interior horizontal illuminance on a

reference point from sidelighting, in lx, Exv = exterior vertical illuminance on the window wall in lx, τ = net transmittance of the window wall, CU = coefficient of utilization.

Ground Exitance

Mg = ρg (Exh sky + Exh sun)

where

Mg = exitance from the ground in lm/m2, ρg = reflectance of the ground, Exh sky = horizontal illuminance from the sky in lx, Exh sun = horizontal illuminance from the sun in lx.

Illuminance from Overcast Sky Refer to IESNA Lighting Handbook, Ninth Edition for complete

tables

Illuminance from Clear Sky

Refer to IESNA Lighting Handbook, Ninth Edition for complete tables

Illuminance from Sun


Net Transmittance

τ = T Ra Tc LLF

τ = net transmittance of windowLLF = light loss factor representing dirt accumulation Ra = the net-to-gross window area ratio representing such elements as mullions and glazing bars; Tc = other elements such as shades and drapes

Light Loss Tables (used to be slide 87)


CU Sky Component = 0.75


CU Ground Component


Clear Window Illuminance

Ei = τ (Exv sky CUsky + Exv g CUg)

Ei = interior illuminance at a reference point in lx, τ = net transmittance of the window wall, Exv sky = exterior vertical illuminance from the sky on the window in lx, CUsky = coefficient of utilization from the sky, Exv g = exterior vertical illuminance from the ground on the window in lx, CUg = coefficient of utilization from the ground.

Diffusing Window Illuminance

Ei = 0.5 τ (Exv sky + Exv g ) ( CUsky + CUg)

Ei = interior illuminance at a reference point in lx, τ = net transmittance of the window wall, Exv sky = exterior vertical illuminance from the sky on the window in lx, CUsky = coefficient of utilization from the sky, Exv g = exterior vertical illuminance from the ground on the window in lx, CUg = coefficient of utilization from the ground.

Toplighting

Ei = Exh τ As / Aw

Ei = average incident illuminance on the workplane from skylights in lx, Exh = horizontal exterior illuminance on the skylights in lx, As = gross projected horizontal area of all the skylights in m2

Aw = area of the workplane in m2, τ = net transmittance of the skylights and light well, including losses because of solar control devices and maintenance factors, CU = coefficient of utilization.

Toplighting (cont’d)

TDM = 1.25 TFS (1.18 - 0.416 TFS)

TDM = dome transmittance, TFS = flatsheet transmittance.

Toplighting (cont’d)

T = (T1 T2) / (1 - ρ1 ρ2)

T1, T2 =diffuse transmittances of the individual domes, ρ1 = reflectance from the bottom side of the upper dome, ρ2 = reflectance from the top side of the lower dome.

Light Well Equation

WCR = 5h(w +l) / wl WCR is the well cavity ratio, used to

look up the well efficiency Nw

h is the well height, w is the well width,l is the well length. (The dimensions h, w, and l must be expressed in the same units.)

Light Well Cavity Ratio

Table from IESNA Lighting Handbook, Ninth Edition

Diffuse Transmittance

τd = Td Nw Ra Tc LLF

Td is equal to the diffuse transmittance

Nw is the well efficiency

Ra = ratio of net to gross skylight area Tc = transmittances of diffusers, lenses, louvers, or other controls LLF = the light loss factor from IES tables.

Direct Transmittance

τD = TD NW Ra Tc LLF

TD is equal to the direct transmittance of the dome

Nw is the well efficiencyRa = ratio of net to gross skylight area Tc = transmittances of diffusers, lenses, louvers, or other controls LLF = the light loss factor from IES tables.

Room Cavity Ratio

RCR = 5 hc (l + W) / lw

hc is the height from the workplane to the bottom of the skylight well, l is the length of the room,w is the width of the room. (All three parameters must have the same units.)

Room Cavity CU Tables


Wall Reflectance (%) Ceiling Reflectance

RCR 50 30 10

0 1.19 1.19 1.19

1 1.05 1.00 .97

2 .93 .86 .81

3 .83 .76 .70

4 .75 .67 .60

5 .67 .59 .53

6 .62 .53 .47

7 .57 .49 .43

8 .54 .47 .41

9 .53 .46 .41

80

10 .52 .45 .40

Overcast Sky

Ei = Exh sky τd CU N (A / Aw) Exh sky = exterior horizontal illuminance due to the

sky only, in lx, τd = net diffuse transmittance, τD = net direct transmittance,CU = coefficient of utilization, N = number of skylights, A = area of each skylight in m2, Aw = area of the workplane in m2.

Clear Sky

Ei = (Exh sky τd + Exh sun τD) CU N (A / Aw) Exh sky = exterior horizontal illuminance due to the sky

only, in lx, Exh sun = exterior horizontal illuminance due to the sun only, in lx, τd = net diffuse transmittance, τD = net direct transmittance,CU = coefficient of utilization, N = number of skylights, A = area of each skylight in m2, Aw = area of the workplane in m2.

Daylight Factor

CIE (European) methods Less accurate, more flexible, in

allowing asymmetrical window placement

PSALI Some methods only account for

overcast conditions

Computer Programs

More accurate predictions or renderings– Lightscape– Radiance– Lumen Micro (et al)– Superlite

Payback period, including effect of HVAC– DOE2.1E– MicroDOE, PowerDOE, CECDOE, etc.– HEED, Solar 5

Summary of Topic Four

Computational Rules of Thumb IES Lumen Method

– sidelighting– toplighting

Daylight Factor Computer programs

Break


Part Five: Equipment

Natural Lighting:Control Devices and Systems

Daylight Harvesting

Provide the light:– Building plan and orientation– Fenestration location and sizing

Test the design– Computer simulations– Physical models

Lighting circuits and controls– Balance the availability of natural light– Occupancy sensors, Photosensors

Agenda for Topic Five

Controls California Codes Typical Circuits Demonstration Possible Savings Dangers and Pitfalls Walkthrough

Review - Terms

Design Level Circuits Devices

– sensors– power packs– switches

Basic Strategy Circuit layout and sensor

placement, daytime

Basic Strategy Circuit layout and sensor

placement, nighttime

California Code

Must provide possibility for 50% reduction in any room over 100 sq. ft.

Provide separate switching for daylit areas, to allow harvesting

Allowable Lighting Power Density and Actual Lighting Power Density– Credits for daylight sensors– Credits for occupancy sensors– Credits for automatic time controls, etc.

California Code (cont’d) Credit factors for occupancy sensors

Type of Control Type of Space Factor

Occupant Sensor any space 251 square feet enclosed 0.20with separate sensor for eachspace

by opaque floor to ceiling partitions; any size classroom, corridor,conference room or waiting room

rooms of any size that are used solely for storage 0.60

other spaces greater than 250 square feet 0.10

Occupant sensor with a separatesensor for each space used inconjunction with daylightingcontrols and separate sensor foreach space

any space 250 squarefeet within a daylight areaand enclosed by opaquefloor to ceiling partitions

0.10 (may be addedto daylighting controlcredit)

California Code Required Layouts

Control types

Occupancy Sensors Photosensors Continuous Dimming vs. Step

Dimming Occupancy and Photosensor

Interaction

Occupancy Sensors

Ultrasonic– sees around corners– quartz crystal oscillator– multiple receivers– sees inanimate movement, sometimes vibrations

Infrared– line of sight only– ignores movement of same temperature objects– can be aimed and masked

Comparison

Function or characteristics ultrasonic infraredpartitioned areas good badrestrooms with stalls good badlong enclosed hallways good OKvery large low ceilinged areas good OKsmall enclosed offices OK goodareas with high ceilings OK goodareas with high vibration or airflow bad goodopen areas which need to be subdivided bad good

Ultrasonic

Infrared

Photosensors

Ceiling mounted, viewing workplane

Continuous Dimming vs. Step Dimming

Low natural light + single step = no savings (single step is never activated, light too low)


Continuous dimming harvests immediately (begins @ 100%, reduces to 30%*)


Large natural light + single step = big savings (single step is activated, goes to zero)


Plentiful daylight + single step = best value Lower natural light levels require

continuous dimming

Typical circuits

Power Pack Separate low voltage signal RS-232, EPROM, Carrier Wave and

X-10

Power Pack Switches, sensors and outside sources

Staged Signals

Interim logic box collects signal data

“Intelligent Ballasts” Separate low voltage signal from sensor to ballasts

Possible savings

DOE2.1E– STEPPED vs.CONTINUOUS– LT-REF-PT-1 ( x, y, z)– LT-FRACTION-1– DESIGN LEVEL– Lighting ->HVAC -> plant -> Economics

HEED, DAYLIT– STEPPED vs. CONTINUOUS– 3 zones– DESIGN LEVEL

Dangers and Pitfalls

Users– Sensitivity and Time Delay– Incorrect Placement– “Know it All”

Contractors– Upside Down– Wrong Voltage– Passive Circuit to Active Circuit– No Calibration

Summary

Controls– Occupancy Sensors– Photosensors– Continuous Dimming vs. Step Dimming– Occupancy and Photosensor Interaction

Code Requirements and Benefits

Summary (cont’d)

Typical Wiring Diagrams– Power pack vs. “intelligent ballasts”

Typical Pitfalls Energy saved Quality Environment!

Overall Summary

Natural Light in Buildings– Provide the light:

• Building plan, orientation and section• Fenestration location and sizing

– Lighting circuits and controls• Balance the availability of natural light• Shutoff in stages

– Sensors• Occupancy sensors• Photosensors

Sources for further study Books:

– Ander, Gregg; Daylighting Performance and Design, Van Nostrand Reinhold, New York 1995

– Kaufman, John, et al; IES Handbook; Illuminating Engineering Society (IESNA), New York

– Schiler: Simplified Design of Building Lighting, Wiley & Sons, New York 1992

– Schiler et al: Simulating Daylight with Architectural Models, DNNA report

Sources for further study (cont’d)

Monographs:– ____; RP-5 Recommended Practice of

Daylighting; Illuminating Engineering , Society (IESNA), New York

– ____; RP-21 Calculation of Daylight Availability; Illuminating Engineering Society (IESNA), New York

– ____; RP-23 Calculation of Daylight; Illuminating Engineering Society (IESNA), New York

Finis


Marc SchilerSchiler & Associates / University of Southern California

daylighting: accident or technology? marc schiler schiler & associates / university of southern...

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