introduction to unit skylights for daylighting of ... to unit skylights for daylighting of...
TRANSCRIPT
Introduction to Unit Skylights for Daylighting of Commercial Buildings 2
AIA/CES Continuing Professional Education
This program is registered with the AIA/CES for continuing professional education.
As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at your request.
AAMA is a Registered Provider with The American Institute of Architects Continuing Education Systems.
Credit earned on completion of this program will be reported to CES Records for AIA members. Certificates of Completion will also be provided.
Introduction to Unit Skylights for Daylighting of Commercial Buildings 3
Copyright Materials
This presentation is protected by US and International copyright laws. Reproduction, distribution, display and use of the presentation without written permission of the speaker is prohibited.
© AAMA/HMG 2008
Introduction to Unit Skylights for Daylighting of Commercial Buildings 4
Learning ObjectivesWhat is daylighting? Daylighting design strategiesBenefits of unit skylightsElectric lighting with daylight controlsEnergy savings Specification issues Case StudiesAdditional Resources
Introduction to Unit Skylights for Daylighting of Commercial Buildings 5
Why use Skylights?
Art FormMeans for sustaining life and growthColor enhancement and high illumination Add life and variability to a dull space
Add high quality, dependable illumination for indoor spaces
Introduction to Unit Skylights for Daylighting of Commercial Buildings 6
Skylights – why do we use them?Design feature
Enhance the building appearance
Enhance the performance of the people inside…Today’s focus is on the use of unit skylights* for uniform lighting in commercial and industrial spaces
Introduction to Unit Skylights for Daylighting of Commercial Buildings 7
Recent studies have shown that…Retail stores with unit skylights sell more
One Chain achieved 40% higher sales with unit skylights
Another chain of retail stores received up to 6% higher sales in those stores with unit skylights
Students perform better in daylight
Students progressed 21% faster in classrooms with daylight compared to those without daylight
1. PG&E (1999). Skylighting and Retail Sales – http://www.pge.com/003_save_energy/003c_edu_train/pec/daylight/daylight.shtml
2. CEC PIER (2003). Daylight and Retail Sales: Replication Study – http://newbuildings.org/technologies/lighting‐solutions
3. PG&E (1999). Daylighting in Schools ‐ http://www.pge.com/003_save_energy/003c_edu_train/pec/daylight/daylights.html
Introduction to Unit Skylights for Daylighting of Commercial Buildings 8
…all buildings were daylit.
Just 50 years ago, almost all
workplaces and schools were daylit !
Before electric lighting….
Introduction to Unit Skylights for Daylighting of Commercial Buildings 9
The resurgence of interest in daylighting design.
There are two basic strategies:
Side-lighting Top-lighting
Introduction to Unit Skylights for Daylighting of Commercial Buildings 10
Potential for unit skylight useWe often think of daylighting only through windows…But the majority of commercial buildings in the U.S. are two stories or less
•Where is the most surface area?
• Where is it easiest to collect and control daylight?
Introduction to Unit Skylights for Daylighting of Commercial Buildings 11
Daylight illumination patterns from windows vs unit skylights
Daylight from windows is limited
Clerestory can increase penetration, but non-uniformity in illumination
Unit skylights with splayed light wells provide the most uniform light
Clerestory with light shelf and blinds
Skylights with splayed light wells
View window with blinds
Introduction to Unit Skylights for Daylighting of Commercial Buildings 12
Unit skylights provide more uniform illumination that extends deeper into a room than windows
0
50
100
150
200
250
0.5 4.5 8.5 12.5 16.5 20.5 24.5 28.5Distance from Exterior Wall (ft)
Illum
inan
ce (f
c)
window w/ blinds
window + clerestory
splayed skylights
Source – Sectional analysis of a 30 ft wide space using Lumen Micro
Introduction to Unit Skylights for Daylighting of Commercial Buildings 13
How much light?Windows provide daylight from the skyUnit skylights use sunlight in addition to daylightThus, a unit skylight can easily be three to ten times smaller than a window or roof monitor* while collecting the same amount of daylight
Blue Sky, 1000-3000 fc
Bright sunlit clouds, 3000-5000 fc
Dark, heavy clouds, 1000 fc
Direct sun, 5,000-10,000 fc
Two to ten times more light!
fc = foot candles – a measure of illumination from a light source
*A roof monitor is vertical or near vertical glazing above the level of the adjacent roof.
Introduction to Unit Skylights for Daylighting of Commercial Buildings 14
Effective Aperture = 2.50%, Skylight to Floor Ratio (SFR) = 5.00%Average daylight foot-candles
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24Jan 0 0 0 0 0 0 0 2 8 19 32 42 45 39 27 14 5 0 0 0 0 0 0 0Feb 0 0 0 0 0 0 0 3 14 29 47 55 57 55 45 27 11 3 0 0 0 0 0 0Mar 0 0 0 0 0 0 2 9 25 42 57 66 70 67 59 41 20 6 0 0 0 0 0 0Apr 0 0 0 0 0 1 6 20 45 65 79 88 90 84 70 55 29 11 3 0 0 0 0 0May 0 0 0 0 0 3 12 33 56 75 89 98 99 93 85 63 39 17 5 0 0 0 0 0Jun 0 0 0 0 0 4 14 32 55 75 93 103 107 102 89 71 46 22 8 0 0 0 0 0Jul 0 0 0 0 0 3 11 31 57 81 98 110 113 108 95 75 50 23 9 1 0 0 0 0Aug 0 0 0 0 0 1 8 22 46 68 90 101 105 101 85 64 39 16 5 0 0 0 0 0Sep 0 0 0 0 0 0 4 17 41 64 84 93 96 88 72 50 23 8 1 0 0 0 0 0Oct 0 0 0 0 0 0 2 10 29 46 64 69 71 63 47 26 10 2 0 0 0 0 0 0Nov 0 0 0 0 0 0 0 5 15 29 42 48 48 42 26 12 4 0 0 0 0 0 0 0Dec 0 0 0 0 0 0 0 2 8 18 29 40 39 33 22 11 3 0 0 0 0 0 0 0
Design Illuminance = 50 fc < 5 fc; < 25 fc; < 50 fc; > 50 fc;
Unit skylights provide more useful daylight for more hours of the year than roof monitors
The yearly hours of sunlight that can be collected by the vertical glazing of a roof monitor varies by orientation and seasonA unit skylight, such as a dome or pyramid, collects sunlight throughout the year and for almost all of the daylit hours
Eas
t fac
ing
roof
mon
itor W
est facingroof m
onitorSkylight
South facing roof monitor
This diagram shows the available sunlit hours by month and time of day for roof monitors versus unit skylightsSource: SkyCalc ®
Introduction to Unit Skylights for Daylighting of Commercial Buildings 15
This is because unit skylights receive both sunlight and daylight all day long, especially in the more critical early morning and late afternoon hours
Early morning, low in the east
Late afternoon, low in the west
Mid-day, high in the south
Photograph – Lisa Heschong
Introduction to Unit Skylights for Daylighting of Commercial Buildings 16
The Skylighting SystemA successful skylighting system
Unit skylightsBuilding characteristicsElectric lighting systemLighting controls
Introduction to Unit Skylights for Daylighting of Commercial Buildings 17
But don’t skylights leak?Not any more!
In the old days, when skylights had to be custom built on-site, some of the glazing joints did not age well and eventually leaked
Modern unit skylights use factory-formed components that are designed, tested, and certified to resist uncontrolled water infiltration
Often, water stains from condensation dripping off the glazing is mistaken for a leak
Introduction to Unit Skylights for Daylighting of Commercial Buildings 18
LightWell
Skylight Aperture skylightglazing
skylight framecurb
condensationgutter
lightwelldepth
ceiling
roofstructure
Nomenclature: Unit Skylight System Components
Introduction to Unit Skylights for Daylighting of Commercial Buildings 19
Unit skylight shapes
Unit skylights come in various shapes and sizes:
1. Flat2. Parabolic3. Domed4. Vaulted5. Ridge6. Smoke Vents7. Custom geometry
1 2
6
5
3 4
7
Introduction to Unit Skylights for Daylighting of Commercial Buildings 20
Unit Skylight Glazing MaterialsCommon glazing materials for unit skylights include:
GlassTemperedLaminatedSand BlastedLow-eChemical EtchedCeramic Frit
PlasticsAcrylicPolyCarbonateFiberglass
Molded SheetInsulated panel
Co-polyesters
Introduction to Unit Skylights for Daylighting of Commercial Buildings 21
Unit Skylight Glazing PropertiesThe choice of glazing material can have enormous impact on the quality of light provided and energy efficiency of designFactors to consider include:
Visible Transmittance (Tvis or VT) – Measures how much light comes through a product; an optical property that indicates the amount of visible light transmitted.Haze Factor – Haze is the ratio of diffusely transmitted light (scattered more than 2.5º) to the total transmitted light of a glazing. Diffused light provides more even light dispersion.
Introduction to Unit Skylights for Daylighting of Commercial Buildings 22
Unit Skylight Glazing PropertiesAdditional factors to consider:
Solar Heat Gain Coefficient (SHGC)A measurement of how well a product blocks heat from the sun The lower a product’s SHGC, the less solar heat it transfers
Thermal Conductance (U-factor)A measurement of how well a product prevents heat from being transmittedThe lower the U-factor, the better the product’s insulating value Skylights with unique
glazing options may require physical testing as shown in
this solar calorimeter.
Introduction to Unit Skylights for Daylighting of Commercial Buildings 23
To achieve efficient illumination in a space, the designer should:
Diffuse the light uniformly
Insist upon light colored surfaces throughout the building
Size the unit skylights appropriately
Space unit skylights evenly
Use an efficient light well design when needed
Consider ways to avoid glare and “dim the daylight” when necessary
Introduction to Unit Skylights for Daylighting of Commercial Buildings 24
Why is diffusion so important?Natural sunlight is too bright for comfort
“Hot spots” of excessively bright non-difused light will cause thermal discomfort, local melting of frozen products, and interference with laser scanners
Introduction to Unit Skylights for Daylighting of Commercial Buildings 25
A diffusing unit skylight provides high quality, uniform light throughout the space
There are many ways to achieve diffusion:
Glazing properties
Louvers
Light well shape
Diffuser at bottom of well
Banners
Structural elements
Introduction to Unit Skylights for Daylighting of Commercial Buildings 26
Paint Your Ceilings WhiteWhite ceilings greatly increase the light levels, increase system efficiency and reduce contrast glare
Introduction to Unit Skylights for Daylighting of Commercial Buildings 27
In buildings with a dropped ceiling, unit skylights require a “skylight well”
Skylight wells have two essential parts:1. A “throat” that helps to move the light as efficiently
as possible through the plenum space, between the top of the roof and the bottom of the ceiling
Examples of pre-manufactured “throats”
Introduction to Unit Skylights for Daylighting of Commercial Buildings 28
The second part of a light well, the “splay,” allows the daylight to spread as broadly as possible
And reduces glare by creating a surface similar in brightness to the ceiling
For more information download Modular Skylight Well Guidelines- http://www.energydesignresources.com
Introduction to Unit Skylights for Daylighting of Commercial Buildings 29
Unit Skylight Size Rules of ThumbThere are many tradeoffs between more but smaller, vs. fewer and larger unit skylights Size selection depends on the
Height of the daylit space
Tasks performed in the daylit space
Daylighting requirements of the space
Construction and cost constraints
The ratio of skylight area to floor area is called the…
Skylight to Floor area Ratio (SFR)
Introduction to Unit Skylights for Daylighting of Commercial Buildings 30
Unit Skylight Spacing Rules of Thumb
The general rule of thumb is to space skylights at 1.0 to 1.5 times the ceiling height(center-to-center in both directions)
Actual designs can vary considerably based upon:
Skylight type
Light well depth and splays
Furniture or shelves in the space
Introduction to Unit Skylights for Daylighting of Commercial Buildings 31
So what is an optimum skylighting layout?
The optimum sizing and layout of a skylight system is dependent on many variables:
Preferences for illumination levelsUniformityEnergy savingsCost savingsCost of installationCode compliance
Introduction to Unit Skylights for Daylighting of Commercial Buildings 32
Optimizing Unit Skylighting Layout
SkyCalc® is a Microsoft Excel ® based application
It is a simple, free, publicly available tool that calculates energy impacts and illumination levels in a space for a given skylight and building design using typical hourly weather information for a nearby city
See the ‘additional resources’ slide at the end of this module for how to receive a free copy
Introduction to Unit Skylights for Daylighting of Commercial Buildings 33
SkyCalc® predicts average hourly illumination, by month and time of day, for your given design
Hint: The more hours you can turn off or dim
the electric lights per year, the better your energy savings
Introduction to Unit Skylights for Daylighting of Commercial Buildings 34
Well Designed Systems = Net Energy Savings
More skylights (bigger SFR) can provide ever greater lighting energy savingsBeyond a certain SFR, increases in heating and cooling loads can outweigh lighting energy savings and thus increase the total energy use of the building
Energy Savings from Skylights
-80,000
-30,000
20,000
70,000
120,000
0% 2% 4% 6% 8% 10% 12%SFR
kWh/
yr
Lighting Cooling Heating Total Energy
Optimal savings Positive Savings Negative Savings
The above diagram illustrates the energy savings information, as calculated by SkyCalc, for a particular building design in a particular climate
Introduction to Unit Skylights for Daylighting of Commercial Buildings 35
Why unit skylights can reduce cooling loads
Unit skylights save energy by reducing electric lighting usage
Daylight is inherently more efficient than electric light
Too much daylight will, however, result in excessive heat gain
Unit skylights have the potential, if not carefully chosen, to increase heating loads in a building
Introduction to Unit Skylights for Daylighting of Commercial Buildings 36
Unit Skylight Energy SavingsYou may not save energy when the electric lights are not properly dimmed or switched in response to daylight!Automatic photocontrols guarantee the energy savings
i.e. lighting controls for electric lighting based on daylight availability
Fresno Skylit Store
($0.40)($0.30)($0.20)($0.10)$0.00$0.10$0.20$0.30$0.40
0% 1% 2% 3% 4% 5% 6% 8% 10% 12%
Skylight to Floor Ratio
Ann
ual E
nerg
y C
ost
Savi
ngs
($/S
F)
DimmingNo Control
Introduction to Unit Skylights for Daylighting of Commercial Buildings 37
Lighting Control Strategies
1. Open loop controlsThe sensor responds to daylight illumination levels and reduces electrical lighting usageThe photosensor typically faces upwards looking out of the skylight or mounted on the outside of the building
fieldof
view
Open Loop Controls
There are two main control strategies
Introduction to Unit Skylights for Daylighting of Commercial Buildings 38
Lighting Control Strategies
2. Closed loop controlsThe sensor responds to both daylight and electric light in the space
The photosensor is typically placed on the ceiling looking down upon the task area
Closed Loop Controls
There are two main control strategies
Introduction to Unit Skylights for Daylighting of Commercial Buildings 39
Lighting Control OptionsON/OFF
This is the simplest form of control where all of the controlled lamps are turned OFF when there is adequate daylight
Multi-level switchingIndividual lighting circuits, fixtures or lamps are controlled separately
Dimming All the controlled lamps are dimmed with the help of dimmable ballasts to achieve lower light output and energy consumption
Introduction to Unit Skylights for Daylighting of Commercial Buildings 40
How well do the photocontrols really work?
Very well! Especially in skylit applications!Some urban myths around photocontrols operation were debunked:
The photocontrols performed very wellUsers were generally happy with their performanceBut savings depend on the control equipment being commissioned correctly
1. Check additional resources slide for the SCE Photocontrols Effectiveness Study
Introduction to Unit Skylights for Daylighting of Commercial Buildings 41
Skylights and Energy CodesCalifornia’s Title 24 requires skylights and photocontrols in single story buildings 25,000 square feet or largerASHRAE/IESNA 90.1-2006 limits skylight area to 5%
Glazing must have a 90% minimum haze factorVLT must be greater than 0.40Energy Cost Budget (ECB) Method: Any area can be used
International Energy Conservation Code (IECC) 2003IECC recognizes ASHRAE/IESNA 90.1
Introduction to Unit Skylights for Daylighting of Commercial Buildings 42
Skylights also need to meet various criteria
Building CodesSafety StandardsRating Standards
Introduction to Unit Skylights for Daylighting of Commercial Buildings 43
Additional ResourcesNow that we have given a brief overview of the skylighting design issues and specifications, you are ready for more detailed information.
1. The AAMA Web site is a great resource for skylight specifications and manufacturer information. It also has a sortable product finder.
www.aamanet.org
2. The Skylighting Guidelines have detailed information on skylighting design issues that we have introduced in this module.
www.energydesignresources.com
Introduction to Unit Skylights for Daylighting of Commercial Buildings 44
Additional Resources3. Skylights in spaces with suspended ceilings present
unique challenges. The Modular Skylighting Guidelines are a great design and specification guide.
www.h-m-g.com/projects/skylights/main.htm4. Download SkyCalc™ at
www.energydesignresources.com or www.h-m-g.com
5. The Advanced Lighting Guidelines are an excellent reference on lighting quality and design issues
www.newbuildings.org/lighting.htm#guide
Introduction to Unit Skylights for Daylighting of Commercial Buildings 45
Additional Resources6. The Photocontrols Effectiveness Study and
Installation Guidelines has excellent data on photocontrol system operation in the field and guidelines for proper commissioning
http://www.calcodesgroup.com/database/download/CalCodes_Report_48.pdf
7. Lighting knowhow™ Series Design Guides from the Design Lights Consortium have case studies and sample design layouts for skylighting in retail and warehouse buildings
www.designlights.org/skylighting.html
Introduction to Unit Skylights for Daylighting of Commercial Buildings
Thank you for your kind attention. Are there any questions?