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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

55Oak Ridge High SchoolOak Ridge High School

Skylights balance light from windows

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?

99Design it right the first time!Design it right the first time!

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

1111eQUEST start-up screeneQUEST start-up screen

Start-up screen choices

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

http://www.energydesignresources.com/

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)

3434Lighting LoadLighting Load

•

Define lighting load in Watts per sq.ft. for every area type.

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


•

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


•

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


•

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)


•

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


•

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


•

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


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


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

http://www.savingsbydesign.com/

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

http://www.sce.com/

http://www.h-m-g.com/

http://www.doe2.com/

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