Lecture 9: Windows and Daylighting

Material prepared by GARD Analytics, Inc. and University of Illinoisat Urbana-Champaign under contract to the National Renewable Energy

Laboratory. All material Copyright 2002-2003 U.S.D.O.E. - All rights reserved

2

Importance of this Lecture to the Simulation of Buildings

Every building is different in many ways: Location/exterior environment Construction/building envelope Space usage/interior environment HVAC system

Building consume approximately one-third of all energy used nationally—lighting accounts for about one third of building energy use

Daylighting has the potential to significantly reduce the amount of energy spent on lighting

Proper modeling of windows is important to both daylighting studies and energy analysis since it has a significant impact on both of these areas

3

Purpose of this Lecture

Gain an understanding of how to Specify windows in EnergyPlus Specify and control daylighting

features within a zone

4

Keywords Covered in this Lecture

Material:WindowGlassMaterial:WindowGasMaterial:WindowGasMixtureMaterial:WindowShadeMaterial:WindowBlindWindowShadingControlWindowFrameAndDividerWindowGapAirFlowControlDaylighting:Simple and

Daylighting:Detailed

5

Windows

glass

gas

6

Material:WindowGlass

Non-opaque solid layer used to construct windows

MATERIAL:WindowGlass, SPECTRAL PANE, !- Name Spectral, !- Optical Data Type SpectralDataSet1, !- Name of Window Glass Spectral Data Set 0.0099, !- Thickness {m} 0.0, !- Solar Transmittance at Normal Incidence 0.0, !- Solar Reflectance at Normal Incidence: Front Side 0.0, !- Solar Reflectance at Normal Incidence: Back Side 0.0, !- Visible Transmittance at Normal Incidence 0.0, !- Visible Reflectance at Normal Incidence: FrontSide 0.0, !- Visible Reflectance at Normal Incidence: Back Side 0.0, !- IR Transmittance at Normal Incidence 0.84, !- IR Hemispherical Emissivity: Front Side 0.84, !- IR Hemispherical Emissivity: Back Side 0.80; !- Conductivity {W/m-K}

More examples from DOE-2 library in file WindowGlassMaterials.idf

7

Material:WindowGas

Non-opaque gaseous layer used to construct windows Gas type can be: Air, Argon, Krypton,

Xenon, or Custom Custom requires properties (curve fit

coefficients) for conductivity, viscosity, and specific heat as well as the gas molecular weight

MATERIAL:WindowGas, WinAirGap, !- Name AIR, !- Gas Type 0.013; !- Thickness {m}

More examples from DOE-2 library in file WindowGasMaterials.idf

8

Material:WindowGasMixture

Allows a custom mixture of gases to construct a non-opaque gaseous layer used for windows Gas type can be: Air, Argon, Krypton,

or Xenon User defines up to four gases in

mixtureMaterial:WindowGasMixture, MyWinGasMix, !- Name 0.0127, !- Thickness 2, !- Number of gases in mixture Air, !- Gas Type - Gas #1 0.5, !- Fraction - Gas #1 Argon, !- Gas Type – Gas #2 0.5; !- Fraction – Gas #2

9

Constructing Windows

Same as a regular construction definition except using window glass, window gas, and/or window gas mixture

CONSTRUCTION, ELECTRO-CON-DARK, !- Name ELECTRO GLASS DARK STATE, !- Outside Material Layer WinAirGap, !- Material Layer #2 SPECTRAL PANE; !- Inside Material Layer

10

Material:WindowShade

Allows specification of window shades Becomes part of window shading

control

MATERIAL:WindowShade, MEDIUM REFLECT - MEDIUM TRANS SHADE, !- Name 0.4, !- Solar transmittance 0.5, !- Solar reflectance 0.4, !- Visible transmittance 0.5, !- Visible reflectance 0.9, !- Thermal emissivity 0.0, !- Thermal transmittance 0.005, !- Thickness {m} 0.1, !- Conductivity {W/m-K} 0.05, !- Shade-to-glass distance {m} 0.5, !- Top opening multiplier 0.5, !- Bottom opening multiplier 0.5, !- Left-side opening multiplier 0.5, !- Left-side opening multiplier 0.0; !- Air-flow permeability

More examples from DOE-2 library in file WindowShadeMaterials.idf

11

Material:WindowBlind

Allows specification of window blinds Becomes part of window shading

control Example on next slide… More examples from DOE-2 library in

file WindowBlindMaterials.idf

12

Material:WindowBlind MATERIAL:WindowBlind,BLIND WITH HIGH REFLECTIVITY SLATS, HORIZONTAL, !- Slat orientation 0.025, !- Slat width [1"] (m) 0.01875, !- Slat separation [3/4"] (m) 0.001, !- Slat thickness (m) 45.0, !- Slat angle (deg) 0.9, !- Slat conductivity (W/m-K) 0.0, !- Slat beam solar transmittance 0.8, !- Slat beam solar reflectance, front side 0.8, !- Slat beam solar reflectance, back side 0.0, !- Slat diffuse solar transmittance 0.8, !- Slat diffuse solar reflectance, front side 0.8, !- Slat diffuse solar reflectance, back side 0.0, !- Slat beam visible transmittance 0.8, !- Slat beam visible reflectance, front side 0.8, !- Slat beam visible reflectance, back side 0.0, !- Slat diffuse visible transmittance 0.8, !- Slat diffuse visible reflectance, front side 0.8, !- Slat diffuse visible reflectance, back side 0.0, !- Slat IR (thermal) hemispherical transmittance 0.9, !- Slat IR (thermal) hemispherical emissivity, front side 0.9, !- Slat IR (thermal) hemispherical emissivity, back side 0.050, !- Blind-to-glass distance 0.5, !- Blind top opening multiplier 0.5, !- Blind bottom opening multiplier 0.5, !- Blind left-side opening multiplier 0.5, !- Blind right-side opening multiplier , !- Minimum slat angle (deg) ; !- Maximum slat angle (deg)

13

WindowShadingControl

Referenced by exterior window surface definitions

Shading types: Shade (interior, exterior, or between

glass)—WindowShade Blind (interior, exterior, or between

glass)—WindowBlind Switchable glazing

14

WindowShadingControl (cont’d)

Reference to either a construction or a material name

Many shading control variations: Always on or off or on as per schedule On if high solar, glare, air temperature,

cooling load, or combinations of these Meet daylighting illuminance setpoint On at night if heating required or low

temperatures with various daytime controls Off at night while on during daytime for

cooling conditions and high solar on windows

15

WindowShadingControl (cont’d)

Other controls Various setpoints Glare control Several control options for blind slat

angles WINDOWSHADINGCONTROL, WIN-CONTROL-GLARE, !- User Supplied Shading Control Name SwitchableGlazing, !- Shading Type ELECTRO-CON-DARK, !- Name of construction with shading OnIfHighGlare, !- Shading Control Type , !- Schedule Name 0.0, !- Solar/Load/Temp SetPoint {W/m2, W or deg C} NO, !- Shading Control Is Scheduled YES, !- Glare Control Is Active , !- Material Name of Shading Device , !- Type of Slat Angle Control for Blinds ; !- Slat Angle Schedule Name

16

WindowFrameAndDivider

Used to define information about frames and dividers

Can be significant portion of heat transfer characteristics of window

Includes physical properties (width, projections, number of dividers) as well as thermal properties

Example on next slide…

17

WindowFrameAndDivider (cont’d)

WindowFrameAndDivider, TestFrameAndDivider, !- User Supplied Frame/Divider Name 0.05, !- Frame Width {m} 0.05, !- Frame Outside Projection {m} 0.05, !- Frame Inside Projection {m} 5.0, !- Frame Conductance {W/m2-K} 1.2, !- Ratio of Frame-Edge Glass Conductance to Center-Of-Glass Co 0.8, !- Frame Solar Absorptance 0.8, !- Frame Visible Absorptance 0.9, !- Frame Thermal Hemispherical Emissivity DividedLite, !- Divider Type 0.02, !- Divider Width {m} 2, !- Number of Horizontal Dividers 2, !- Number of Vertical Dividers 0.02, !- Divider Outside Projection {m} 0.02, !- Divider Inside Projection {m} 5.0, !- Divider Conductance {W/m2-K} 1.2, !- Ratio of Divider-Edge Glass Conductance to Center-Of-Glass 0.8, !- Divider Solar Absorptance 0.8, !- Divider Visible Absorptance 0.9; !- Divider Thermal Hemispherical Emissivity

18

WindowGapAirFlowControl

Used to allow ventilation of air gap in windows with either inside or outside air

Air can be vented to inside or outside

Can be scheduledWindowGapAirflowControl, !- Used to control forced airflow through a gap !- between glass layers Zn001:Wall001:Win002, !- Name of Associated Window InsideAir, !- Airflow Source OutsideAir, !- Airflow Destination 0.008, !- Maximum Airflow (m3/s per m of glazing width) !- (5.2 cfm for 1m x 1m window) AlwaysOnAtMaxFlow, !- Airflow Control Type No, !- Airflow Has Multiplier Schedule? ; !- Name of Airflow Multiplier Schedule

19

Daylighting

DAYLIGHTING:SIMPLE Specify useful fraction of solar gain

DAYLIGHTING:DETAILED Calculates illuminance

Only one type per zoneMay use different types in same

run

20

Daylighting:Simple

Effectiveness method Fraction beam usable Fraction diffuse usable Schedule

LIGHTS Fraction replaceable All lights on one control

21

Daylighting:Simple

Sensible and Latent

Beam Solar

Sky Diffus

e

Ground

Diffuse

Light Contro

l

22

Daylighting:Detailed Methodology

Calculated illuminance levelExternal factors

Sky condition Sun position Ground reflectance External shading and obstructions

23

Daylighting:Detailed Methodology (cont’)

Window factors Size Position Transmittance Shades

Internal factors Interior surface visible absorptance Position of daylighting reference point

24

Daylighting:Detailed

Sensible and Latent

Beam Solar

Sky Diffus

e

Ground

Diffuse

Light Control

1

Light Control

2

Uncontrolled

Reference Pt 1

Reference Pt 2

25

Daylighting Calculation

Daylight factors Ratios of interior illuminance or luminance

to exterior horizontal illuminance Contribution of direct light from each

window to each reference point Contribution of reflected light from walls,

floor and ceiling Window luminance and window

background luminance used to determine glare

Factors calculated for hourly sun positions on sun-paths for representative days of the run period

26

Daylighting Calculation (cont’d)

Daylighting calculation performed each heat-balance time step when the sun is up

Daylight factors at each reference point interpolated using the current time step’s sun position and sky condition

Illuminance found by multiplying daylight factors by exterior horizontal illuminance

If glare control, then automatically deploy window shading, if available, to decrease glare below a specified comfort level

Similar option uses shades to control solar gain

27

Electric Lighting Control

Electric lights full-on assumed to provide the setpoint illuminance – regardless of schedule

Electric lighting control system simulated to determine fraction of lighting for each lighting zone

Based on daylighting illuminance level regardless of actual electric lighting input power

Zone lighting electric reduction factor passed to thermal calculation

Heat gain from lights and power input reduced

28

Continuous Dimming

Minimum input power fractionFractional input power

1.000

1.0

Minimum lightoutput fraction

Fractionallight output

Increasing daylightilluminance

Zero daylightilluminance

29

Stepped Lighting Control

Daylight illuminance

Fractionalinput power

1.0

00

Illuminance set point

Step 1

Step 2

Step 3

30

Daylighting:Detailed Inputs

1 or 2 illuminance reference points Specific point(s) in zone (X,Y,Z position) Zone coordinate system – relative to zone

origin If zone origins are all 0,0,0, then equivalent to

world coordinates1 to 3 lighting zones

Controlled by reference point 1 Controlled by reference point 2 Uncontrolled Specify fraction of lighting power for each

zone

31

Daylighting:Detailed Inputs (cont’d)

Illuminance setpoint(s) [lux]Lighting control type

Continuous – stay on at minimum Continuous – turn off at minimum Stepped – automatic Stepped – manual with probability Minimum lighting output and power

levels

32

Daylighting:Detailed Inputs (cont’d)

Glare control of window shades Direction of view Maximum glare level

33

Daylighting:Detailed Example

DAYLIGHTING:DETAILED,

Zone 2, !- Zone Name

1, !- Total Daylighting Reference Points

2.5, 2, 0.8, !- X,Y,Z-coordinates of first reference point {m}

2.5, 8, 0.8, !- X,Y,Z-coordinates of second reference point {m}

0.4, !- Fraction of zone controlled by first ref. point

0.4, !- Fraction of zone controlled by second ref. point

500, !- Illuminance setpoint at first reference point {lux}

500, !- Illuminance setpoint at second reference point {lux}

1, !- Lighting control type

0, !- Azimuth angle of view direction clockwise from

0, !- zone y-axis (for glare calculation) {deg}

22, !- Maximum allowable discomfort glare index

0.3, !- Minimum input power fraction for continuous control

0.2, !- Minimum light output fraction for continuous control

1, !- Number of steps (excluding off) for stepped control

1; !- Probability lighting will be reset in manual control

34

Ground Reflectance

GroundReflectance12 monthly valuesAffects:

Solar gains Daylighting

Snow Ground Reflectance Modifiers

35

Daylighting Modeling Guidelines

Do not use window multipliers Different window positions would be lost

Zone multipliers Beneficial to get room proportions correct Can only use if external shading not

affected by zone positionInterior surfaces within a zone do not

block direct light for daylighting calcs

36

Representative Room with Zone Multiplier

Zone Multiplier = 4

IW-1

Room-1

IW-2

IW-3

37

Model Unique Rooms as Individual Thermal Zones

A

B

C D

38

Multiple Lighting Zones

Second Reference Point

First Reference Point

Fraction of Zone Controlled bySecond Reference Point = 0.5

Fraction of Zone Controlled byFirst Reference Point = 0.5

39

Daylighting in Part of a Thermal Zone

First Reference PointA

B C D Interior window – no daylighting passes through

Exterior window

40

Shading Surfaces for Daylighting

Opaque No daylight transmitted

(according to manual, I/O ref. pp 191-192) However, shadowing surface transmittance

schedule does impact daylighting currently in some cases (may be a bug)

Black Do not reflect light For example, reflection from top of

overhang onto window above not calculated

41

Summary

Windows are a means of providing solar heat gain and natural lighting to spaces within a building

EnergyPlus requires specification of the composition of window components as well as any shading strategy being used

Daylighting calculations can show the possible reduction in electric lighting