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Introduction to Skylighting in eQUEST
Quick Energy Simulation Tool
Introduction to Skylighting in eQUEST
Quick Energy Simulation Tool
an energydesignresources.comSkylighting
Design Tutorial
22Why Consider Skylights?Why Consider Skylights?
•
Inexpensive method of bringing daylight into the core of low rise buildings
•
Reliable form of energy savings•
SCE study found actual energy savings 98% of predicted savings (3% of systems failed)
•
Aesthetically pleasing•
Link to productivity and sales increases
•
In general, people like daylight
33Some of the largest retailers use skylightsSome of the largest retailers use skylights
•
WalMart
has over 1,500 skylit
stores•
Building 250 more per year
•
Dimming fluorescent on photocontrols
•
Cost-effective
44Skylights can be main source of lightSkylights can be main source of light
•
Primary source of light in this school library•
Note troffers
in ceiling are turned off
66Sacramento Municipal Utility District Sacramento Municipal Utility District
Skylights with splayed light well
77Skylighting design principlesSkylighting design principles
•
Provide enough skylight area to provide sufficient light for most day-time hours
•
… while not providing too much area to cause excessive heat gains and losses
•
Skylights spaced close enough together to provide reasonable uniformity•
Just like electric lighting design
•
Energy savings accrue only if electric lighting turned off!•
Thus the need for automatic daylighting
controls
88eQUEST has the answers to …eQUEST has the answers to …
•
How much skylight area should I install?•
How much energy savings do I get from using a “high performance”
skylight?
•
Which type of lighting controls yield the most energy savings?
•
What is the HVAC impact of skylighting?•
With and without photocontrols
•
Will peak loads increase or decrease?
1010Download eQUESTDownload eQUEST
•
eQUEST
is a free whole building energy simulation tool
•
Detailed simulation model with easy to use graphical interface
•
Available from energydesignresources.com•
eQUEST
is listed under “software”
•
This tutorial steps you through a skylighting simulation
1212Start-up OptionsStart-up Options
•
Two primary choices•
Simulate a new or pre-existing building model•
Multiple pages of inputs
•
Create a weather file for the SkyCalc
skylighting spreadsheet
•
One page of inputs
1313Generating weather files for SkyCalc3Generating weather files for SkyCalc3
•
SkyCalc3 also available at www.energydesignresources.com
•
Simple skylighting spreadsheet
•
Not the subject of this tutorial
•
Select climate file, energy code, and roof U-factor to generate a SkyCalc
Weather file
1414Start eQUEST Schematic Design WizardStart eQUEST Schematic Design Wizard
•
Design Overview•
Location
•
Building Type•
Area
•
Utility rates•
Heating and cooling?
•
Select “Create a New Project Via the Wizard”
Select Daylighting Controls to “Yes”
1515Building FootprintBuilding Footprint
•
Select floor to floor & floor to ceiling height
•
Plenum and suspended ceiling assumed if Flr-to-
Flr
> Flr-to-Ceil
NOTE: Unless Flr-to-
Flr
height exceeds Flr-
to-Ceil height by > 1.0 ft., no separate above ceiling zone will be modeled
1616
LightWell
skylightglazing
skylight framecurb
lightwelldepth
ceiling
roofdeck
Dome-depth
Skylight ComponentsSkylight Components
1717Rule of Thumb for Spacing SkylightsRule of Thumb for Spacing Skylights
•
Daylit
zone around skylights is•
35
degree angle from edge of skylight opening
•
Or 70% of ceiling height (skylight edges spaced no more than 1.4 x ceiling height)
•
Daylit
area reduced by partitions
•35 •35
•H
•H x 0.7
•DAYLIT AREA
•Gap
•> 0.7 x Gap
•Permanent partition
•< 0.7 x Gap•35 •35
•H
•H x 0.7
•DAYLIT AREA
•Gap
•> 0.7 x Gap
•Permanent partition
•< 0.7 x Gap
1818Adjust no. of skylightsAdjust no. of skylights
•
For uniform daylighting, skylights should be spaced no further than 1.4 times the ceiling height•
For our 20 ft. ceiling height, skylights should be a maximum of 28 ft. apart from edge-to-edge.
•
Using typical 4 ft x 8 ft skylights, this results in a minimum requirement of 4 skylights or a 2.5% coverage (or Skylight to Roof Ratio –
SRR).
•
If space below has partitions or shelving, space skylights closer together for full daylighting•
In this example we choose 8 skylights or 5% coverage
1919Adjust no. of skylightsAdjust no. of skylights
•
To adjust skylight spacing, change the “% Coverage”
or “Skylight Dimensions” •
In this example, 4 ft x 8 ft skylights and 5% coverage result in 8 skylights
•
Decrease skylight size or increase % coverage to increase number of skylights or vice-versa.NOTE: If Core / Perimeter zoning pattern is used, % coverage refers to daylight zone area not floor area.
2020Select Glazing TypeSelect Glazing Type
Frames are ordered in terms of their conductivityMetal – most conductive (low R-value)
Wood or vinyl least conductive(high R-value)
•
“Category” defines frame
and shape (Dome vs. Flat)
2121Select Skylight PropertiesSelect Skylight Properties
Ordered by visible transmittanceClear highestGrey lowest
Clear skylights:Clear, bronze, grey
Diffusing skylights:Clear (crystal), White, all acrylic/fiberglass
•
“Type”
defines glazing visible transmittance, solar gain and clarity
2222Select Skylight PropertiesSelect Skylight Properties
Different skylight types default to diffusing or domed, based on typical skylight configurations
•
Choose if your skylights are diffusing or dome shaped.
2323Define Light WellDefine Light Well
•
The default light well depth = plenum depth
•
Choose inside reflectivity
If no plenum, the default size is 1 ft which accounts for depth of a generic curb, and roof deck.
2424Skylight properties by NFRC ratingsSkylight properties by NFRC ratings
•
You can also specify the NFRC rated properties of the skylight by selecting “Specify Properties”
under
“Category”
Specify:- U-factor- SHGC- Visible Transmittance
2525Skylight properties by Window 4/5Skylight properties by Window 4/5
•
You can also specify a skylight designed in LBNL’s
Window
software v. 4/5.•
See eQUEST
help
for more details on this method
2626Daylight Zoning (simplified)Daylight Zoning (simplified)
•
Define fraction (%) of lights controlled by photosensor
•
Define your desired light level at the level of your working plane.
•
Input height of working plane under “Height Above Floor”
2727Photosensor (CA, Title-24)Photosensor (CA, Title-24)
•
eQUEST calculates Daylit
Area (as defined in Title-24 2008)•
Below the Daylit
Area Method pull-down menu, eQuest
shows
the total Daylit Area and fraction
of lights controlled
•
The next slide shows Title-24 calculation method
Daylit Area Calculation MethodDaylit Area Calculation Method 2828
14 ft14 ft
Example: A 20’
tall space (14’
zones around skylights)
Green – Overlapping sky-lit areas
Pink or Grey – Area not within Title-24 day-lit area (upper right corer)
Lighting in Green areas are controlled, those in Pink area are uncontrolled.
28 lights controlled2 lights uncontrolled
Fraction controlled28/30 ~ 94%
2929Lighting ControlsLighting Controls
•
Lighting controls determine the method of reducing the lighting in the space when sufficient daylighting
is available.
Choose your lighting control type from choices given here
3030Dimming and Switching ControlsDimming and Switching Controls
•
For a dimming control, the Minimum Power and Minimum Light inputs determine the lowest level of light output and the corresponding power usage by the electric lights when sufficient daylight is present.
3131Dimming ControlsDimming Controls
10% min-light, 20% min-power
0%
20%
40%
60%
80%
100%
0% 20% 40% 60% 80% 100%
Daylight illuminance (fc) / Lighting setpoint(fc)
Frac
tion
Max
imum
Pow
er
10% min-light20% min-power
When daylight is providing 90% or more design illuminance, electric lighting is dimmed to 10% of light output,while consuming 20% of rated power.
3232Switching ControlsSwitching Controls
•
For a switching control, the number of control steps determine the stages between on and off.
3333Switching ControlsSwitching Controls
0
0.2
0.4
0.6
0.8
1
1.2
0 20 40 60 80 100
Daylight illuminance(fc) / Design illuminance (fc)
Frac
tion
of m
axim
um p
ower
1-step2-step3-step
Separate circuiting and separate setpoint required for each step 3 steps = 100% power, 66% power, 33% power and 0% power (off)
3535Skylight Parametric AnalysisSkylight Parametric Analysis
•
This analysis feature helps you identify the Skylight to Roof area Ratio –
SRR, that will
maximize savings for your building
3636Skylight Parametric AnalysisSkylight Parametric Analysis
•
The Parametric Runs screen lets you choose the number of parametric runs.•
0% -
represents 0 SRR
or no skylights•
100% -
represents
design SRR, or the number of skylights currently specified in your model
Click on “Perform SRR Parametric Runs” to start the parametric runs.
Review results once all simulations are done
3737Skylight Parametric AnalysisSkylight Parametric Analysis
•
The result output from the analysis is a graph that shows Total Annual Energy Savings, and Total Energy Cost Savings. •
With these graphs it is easy to spot the optimum SRR from maximum energy and cost savings
•
Dashed lined in the graph represents design case (shown here at 5%)
Energy and Cost Savings Report
3838Skylight Parametric AnalysisSkylight Parametric AnalysisDaylight Illuminance
Report
Dark shaded values show lower than acceptable daylight levels
Light shaded values show acceptable daylight levels
•
This report shows the average daylight illuminance
at the reference point for each hour of the day (columns) and each month of the year (rows)
3939Output ReportsOutput Reports
•
With Parametric Analysis, results from up to ten cases can be compared on a single graph. However, to view energy use by end use, for any of the cases, you can use eQUEST’s
Results Output Mode.•
To view output reports select View| Results Output Mode
4040Output ReportsOutput Reports
Graphic results of monthly electric and gas energy consumption
Breakdown of energy use by end use, and month.
4141Comparing Output ReportsComparing Output Reports
Without Skylights
With 5% Skylights
Electric Lighting energy use decreases with skylights
Space Heating energy use increases with skylights
Cooling energy use increases with skylights
Note that the Y-axis gets re- scaled for each run
4242Example 1 – Conditioned WarehouseExample 1 – Conditioned Warehouse
•
For this example we will consider:•
An air conditioned warehouse
•
50 ft x 100 ft in plan and with 20ft ceilings•
5% Double glazed, white acrylic domed skylights (VT=0.5, U=1.14, SHGC=0.47)
•
Lighting setpoint: 10 fc•
Lighting Power Density (LPD): 0.75 W/sf
•
Space has racks: 15’
height, 8’aisle width•
Lighting controls: 2 level + Off
•
Location: Riverside, CA (CA Climate Zone 10)•
Utility rates: $0.12/kWh and $0.90/therm
4444Example 1 – Conditioned WarehouseExample 1 – Conditioned Warehouse
•
Using the Skylight Parametric Analysis we will identify the optimum Skylight area to Roof area Ratio (SRR)
•
We will also consider two other skylight choices:•
Clear prismatic, double glazed, domed acrylic skylights (VT=0.88, U=1.14, SHGC=0.78)
•
Clear Low-E coating (0.20 on surface 1), double glazed, flat glass skylights (VT=0.44, U=0.43, SHGC=0.39)
VT = visible light transmittanceSHGC = solar heat gain coefficientU = conductive thermal transmittance, (1/R-value)
4545Example 1 – Conditioned WarehouseExample 1 – Conditioned Warehouse
•
The energy savings parametric analysis shows that maximum savings are at 6.3% SRR. The designed case at 5% SRR is close to maximum
•
View Output Reports to see whether thermal loss, excessive solar gain or heat loss causes savings to decline
Energy Savings ReportNot enough daylight with only 1.3% skylights to turn off all lights resulting in very little savings.
Maximum savings at 6.3% SRR
After the peak, the thermal losses begin to offset lighting savings
4646Example 1 – Conditioned WarehouseExample 1 – Conditioned Warehouse
•
The energy cost savings parametric analysis also shows the optimum SRR to be 6.3% as it gives the maximum savings ~ $2,000.
Energy Cost Savings Report
4747Example 1 – Conditioned WarehouseExample 1 – Conditioned Warehouse
•
Comparing the two other skylight types, we find that with a low-e glazing skylight, the max savings are reached at 6.3% as compared to 2.5% for clear prismatic .
•
Furthermore, the max savings for both skylights are almost the same (~14,000 kWh)
Clear Prismatic
Low-e Clear
4848Example 1 – Conditioned WarehouseExample 1 – Conditioned Warehouse
RESULTS•
With this example, it is clear that same max savings can be achieved using a much cheaper skylight (clear prismatic vs
low-e glass), and also by using a smaller
area of the cheaper skylights (2.5% SRR)•
Other non-energy considerations may still motivate the selection of glass skylights
•
These results are specific to the conditions defined for this particular case and the result will differ if any of them are changed.•
The eQUEST
tool allows you to consider what is
important for your building in your climate•
Using eQUEST’s
Skylight Parametric Analysis Tool it
becomes possible to compare various scenarios over a broad range of skylight areas
4949Example 2 – Retail StoreExample 2 – Retail Store
•
For a second example we will consider:•
An air conditioned retail store
•
100 ft x 100 ft in plan and with 20 ft ceilings, 5 ft wells
•
5% Double glazed, white acrylic domed skylights (VT=0.5, U=1.14, SHGC=0.47)
•
Fluorescent lighting •
Lighting setpoint: 60 fc, LPD: 2.18 W/sf
•
Space has racks: 10’
height, 10’aisle width•
Lighting controls: Dimming to 10% light output
•
Location: Riverside, CA (CA Climate Zone 10)•
Utility rates: $0.12/kWh and $0.90/therm
5151Example 2 – Retail Store: ControlsExample 2 – Retail Store: Controls
•
We will consider choices for controls and determine the one with the most savings:•
Dimming 10%
Dimming min 10% light
0%
20%
40%
60%
80%
100%
0 10 20 30 40 50 60 70 80 90
Daylight Foot-Candles
Lig
htin
g Po
wer
Two level + off switching
0%
20%
40%
60%
80%
100%
0 10 20 30 40 50 60 70 80 90
Daylight Foot-Candles
Lig
htin
g Po
wer
•
2 level + Off
5252Example 2 – Retail Store: DimmingExample 2 – Retail Store: Dimming
•
The energy savings parametric analysis shows that maximum savings are at 4.7% SRR.•
At design case (6.3% SRR), adding more skylights increases heating and cooling loads more than additional lighting savings. Total savings are reduced.
Energy Savings Report
Maximum savings at 4.7% SRR
5353Example 2 – Retail Store: Energy SavingsExample 2 – Retail Store: Energy Savings
•
Comparing between the lighting control strategies, two level + off controls save ~6000 kWh more energy than dimming controls.
•
Dimming max savings occurs at 4.7% SRR
•
Max savings for 2 level switching occurs at 6.3% SRR
Dimming Controls
2Level+Off Controls
5454Example 2 – Retail Store: Cost SavingsExample 2 – Retail Store: Cost Savings
•
Switching controls max savings is ~ $800/yr higher than dimming
•
With dimming controls, max savings can be achieved at a lower SRR (4.6%), but at same SRR, switching controls still have greater savings.
•
Designer may still choose dimming for non-energy reasons
Dimming Controls
2Level+Off Controls
5555Example 2 – Retail StoreExample 2 – Retail Store
RESULTS•
Relative savings from different control strategies depend upon rest of the design including the SRR.•
eQUEST’s
Skylight Parametric Analysis Tool allows
quick evaluation of savings over a broad range of SRR’s•
In this case with 6.3% SRR, 2 level switching saved more energy than dimming.•
Under full daylit
conditions, fully dimmed system is
consuming 20% power while switched system is off.•
Often retailers leave some lights on to show they are open. The likely switching control would leave 10% of the lights on. Now which system saves more?•
You can answer this question using eQUEST!
5656Daylighting resourcesDaylighting resources
•
www.energydesignresources.com•
eQUEST
software and this tutorial
•
SkyCalc
skylighting
design spreadsheet•
Skylighting
Guidelines (100 pages)
•
detailed skylighting
design handbook•
Daylighting
Guidelines
•
Design Briefs (20 pages)•
Skylights with Suspended Ceilings
•
Lighting Controls
5757Daylighting Resources: Savings By DesignDaylighting Resources: Savings By Design
•
California statewide nonresidential new construction energy efficiency program •
http://www.savingsbydesign.com/
•
Administered by California investor owned utilities (SCE, PG&E SDG&E and SCG)
•
Program features:•
Design assistance
•
energy information and analysis tailored to the needs of your project
•
Owner incentives•
help offset the initial costs of energy-efficient buildings •
Design team incentives
•
reward designers who meet ambitious energy efficiency targets
5858AcknowledgementsAcknowledgements
•
This tutorial and skylighting
upgrades to eQUEST were funded by California utility customers under the
auspices of the California Public Utilities Commission•
Project management: Southern California Edison
www.sce.com•
Diane McLean & Shelley Baumgardner
•
Technical content: Heschong Mahone Group www.h-m-g.com
•
Jon McHugh & Mudit Saxena•
Technical content: JJ Hirsch Associates www.doe2.com•
Jeff Hirsch, Paul Reeves, Scott Criswell & Marlin Addison