[BLDG-SIM] external louvres

Jeff Hirsch Jeff.Hirsch at DOE2.com
Fri Nov 19 17:03:41 PST 2004


eQUEST (or DOE-2.2) freeware can handle windows that include
one bind layer (outside, between glass or inside) that is either
louvers blinds or a pull-down shade.  These blinds interact with the
hourly thermal as well as daylighting calculation; included is the
effect of the slat angle on an hourly basis.  You could test this
model using a simple test zone with a window to decide for
yourself if the approach used is adquate to answer your
performance questions.  Like all modeling programs, many
simplifications are used; you can consult the complete documentation
to get a better idea of how the calculation is performed and which
effects are tracked at the level of detail you require.

At this time there is a limit of defining up to only 40 windows,
in a building model, that are layer-by-layer specified (but a
total of  8192 windows of all types, such as window5 library
imported glazing)

Below are some relevant pages from the DOE-2 Dictionary
with some information on specifying windows layer-by-layer to
use the hourly window4/therm detail calculation within DOE-2
(yes, it uses an older single band window4 based hourly calc
rather than multi-band window5 style hourly calc - EnergyPlus,
I believe, uses a Window5 based hourly calc - check its
documentation to be sure - but I do not recall if it has the
same type of blind capability, probably does or will soon )

---
Jeff Hirsch
James J. Hirsch & Associates
Building Performance Analysis Software & Consulting
12185 Presilla Road
Camarillo, CA 93012-9243 USA
phone: (805) 553-9000
fax: (805) 532-2401
email: Jeff.Hirsch at DOE2.com 
web: http://DOE2.com 

>From the DOE-2.2 Dictionary (Vol 2 of 6) Full set
can be downloaded from http://DOE2.com/DOE2   


Describing a Window Using Layers
A window can be described layer by layer using the following WINDOW-LAYERS keyword.

Example input:  A window consists of a layer of glass named GLASS-1, a gap named GAP-1 and a blind named BLIND-1.

GLASS-1 = WINDOW-LAYER ....

GAP-1   = WINDOW-LAYER ....

BLIND-1 = WINDOW-LAYER ....

WIN-1   =  WINDOW
WIN-SPEC-METHOD    = LAYERS-INPUT 
WINDOW-LAYERS      = (GLASS-1, GAP-1, BLIND-1) 
....

WINDOW-LAYERS keyword
Takes a list of up to nine U-names of WINDOW-LAYER commands or of window layers from the Library. This is a required keyword when WIN-SPEC-METHOD=LAYERS-INPUT. A U-name corresponds to a glass layer, a gap layer or a blind layer (see WINDOW-LAYER command). Figure 25 shows examples of layered windows for single- and double-glazed windows. 

Glass layers in the Library are shown in "Glass Layer Library," in the DOE-2.2 Libraries & Reports. Gap layers in the library are shown in Table 31. Blind layers in the library are shown in Table 32. Pull-down shade layers (pull-down shades modeled as closed blinds) in the library are shown in Table 33.

Notes:

·       The layers are entered from outside to inside. 

·       There can be up to five solid (i.e., glass or blind) layers. 

·       There can be at most one blind layer.

·       If there is a blind layer there must also be one or more glass layers; i.e., a layered window consisting only of a blind is not allowed.

·       Adjacent solid layers are not allowed; i.e., solid layers must be separated by one, and only one, gap layer.

·       Adjacent gap layers are not allowed; i.e., gap layers must be separated by one, and only one, solid layer.

·       A blind layer can be the first layer (exterior blind), the last layer (interior blind), or an intermediate layer (between-glass blind).

·       The gas in the gap on the inside of an exterior blind or the outside of an interior blind must be air.

·       The gaps on either side of a between-glass blind must have the same gas (but this gas does not need to be air).



Window Blind Control
The following keywords are used to control slat-type window blinds. They apply only if WIN-SPEC-METHOD=LAYERS-INPUT and one of the layers is a blind. See WINDOW-LAYERS keyword, above, and WINDOW-LAYER command.

BLIND-ADJ-TYPE
Takes a code-word that indicates how the blind coverage (the fraction of the window covered by a blind) is adjusted if a blind is present.

    NONE                              There is no adjustment; the blind coverage is fixed at the value of BLIND-COVER in the blind's WINDOW-LAYER command. 

    SCHEDULE                      The blind coverage varies according to a user-defined schedule given by BLIND-SCHEDULE.

    SOLAR-INTENSITY         If the direct plus diffuse solar radiation incident on the window exceeds the value given by BLIND-TRIGG-SCH, the blind coverage is set to the value of BLIND-COVER-MAX in the blind's WINDOW-LAYER command. Otherwise, the blind coverage stays at BLIND-COVER.

    ROOM-TEMP                   If the room temperature at the beginning of the hour exceeds the value given by BLIND-TRIGG-SCH, the blind coverage is set to the value of BLIND-COVER-MAX in the blind's WINDOW-LAYER command. Otherwise, the blind coverage stays at BLIND-COVER. [FOR FUTURE IMPLEMENTAITON]

BLIND-SCHEDULE
Takes the U-name of a schedule that adjusts the blind coverage between the values of BLIND-COVER-MIN and BLIND-COVER-MAX in the blind's WINDOW-LAYER command. This schedule is used only if BLIND-ADJ-TYPE = SCHEDULE. It should have TYPE = FRACTION. A schedule value of f , which should be between 0.0 and 1.0, gives 

            blind coverage = f * [BLIND-COVER-MAX] + (1-f) * [BLIND-COVER-MIN]

BLIND-TRIGG-SCH
Takes the U-name of a schedule of solar intensity values (if BLIND-ADJ-TYPE = SOLAR-INTENSITY) or room temperature values (if BLIND-ADJ-TYPE = ROOM-TEMP) that are used to adjust blind coverage. For solar intensity, the schedule should have TYPE = RADIATION and the schedule value should be the sum of direct plus diffuse solar radiation incident on the window (after shading by overhangs and other obstructions) per unit window area (Btuh/ft2 or W/m2). For room temperature, the schedule should have TYPE = TEMPERATURE and the schedule value should be in °F or °C. 

SLAT-ADJ-TYPE
Takes a code-word indicating how the slat angle is adjusted if a blind is present.

NONE                              There is no adjustment; the slat angle is fixed at the value of SLAT-ANGLE in the blind's WINDOW-LAYER command.

SCHEDULE                      The slat angle varies according to a user-defined schedule given by SLAT-SCHEDULE, below.

SOLAR-INTENSITY         If the direct plus diffuse solar radiation incident on the window exceeds the value given by SLAT-TRIGG-SCH, then:

The slat angle is adjusted to a value that just blocks direct sun if the sun is in front of the window and SLAT-SEPARATION is less than or equal to SLAT-WIDTH (the usual case).°F

If the sun is in front of the window but SLAT-SEPARATION is greater than SLAT-WIDTH, then the sun cannot be fully blocked and the slat angle is set to 90o, which maximizes blockage.

If the sun is in back of the window, the slat angle is set to SLAT-ANGLE.

The above adjustments are made even on overcast days when there is no direct sun.

ROOM-TEMP                   If the room temperature at the beginning of the hour exceeds the value given by SLAT-TRIGG-SCH, then the slat angle is adjusted as described for SOLAR-INTENSITY. [FOR FUTURE IMPLEMENTAITON]

SLAT-SCHEDULE
Takes the U-name of a schedule that adjusts the slat angle to a fraction of SLAT-ANGLE-MAX or SLAT-ANGLE-MIN. This schedule is used only if SLAT-ADJ-TYPE = SCHEDULE. A schedule value of f gives 

            slat angle           = f  * [SLAT-ANGLE-MAX], if f > 0

            slat angle           = f * [SLAT-ANGLE-MIN], if f < 0

The schedule should have TYPE = FRACTION if only positive values of f are used, in which case f should be between 0 and 1. If positive and negative values of f are used than the schedule should have TYPE = EXP-FRACTION, in which case f should be between -1 and 1.

SLAT-TRIGG-SCH
Takes the U-name of a schedule of solar intensity values (if SLAT-ADJ-TYPE = SOLAR-INTENSITY) or room temperature values (if SLAT-ADJ-TYPE = ROOM-TEMP) that are used to adjust the slat angle. For solar intensity, the schedule should have TYPE = RADIATION and the schedule value should be the sum of direct plus diffuse solar radiation incident on the window (after shading by overhangs and other obstructions) per unit window area (Btuh/h-ft2 or W/m2). For room temperature, the schedule should have TYPE = TEMPERATURE and the schedule value should be a temperature (°F or °C).

WINDOW-LAYER COMMAND
This command, and the associated WINDOW-LAYERS keyword in the WINDOW command, are used when you want to build up a window from layers, much as a wall can be built up from layers. Three types of window layer are allowed: glass, gap and blind. For example, a single-glazed window with no covering would have only a glass layer. A double-glazed window would have three layers: two glass layers separated by a gap of air or other gas. A single-glazed window with a blind would also have three layers: a glass layer and a blind layer separated by a gap. The WINDOW-LAYER command allows you to specify the type and properties of a layer.

U-name is required. To specify the set of one or more layers that comprise a window, you assign a list of WINDOW-LAYER U-names to the WINDOW-LAYERS keyword in the WINDOW command.

The program calculates the overall thermal and solar-optical properties of a window from the individual layer properties and the order of the layers in the window. Accounted for are the layer-to-layer interreflection of solar, visible and IR radiation and the dependence of transmittance, absorptance, and reflectance on the angle of incidence of solar and visible radiation on the window. For blind layers, the program accounts for the effect on transmittance of slat angle and other slat properties.

Table 37 shows all of the WINDOW-LAYER keywords and their default values by layer type. 

In the following:

 For a glass or gap layer, "front" means the outside of the layer (the side facing outdoors). For a horizontal blind in a vertical window, "front" means the side of the slat that faces up when the blind is fully open. For vertical blinds in a vertical window, "front" means the side of the slat that faces to the right when you look at the blind from the outside of the window and the blind is fully open.

For a glass or gap layer, "back" means the inside of a layer (the side facing the room). For a blind layer, "back" means the side of the slat that faces indoors when the slat points downwards (SLAT-ANGLE > 0).

 "Solar" means the full spectrum of radiation from the sun

"Visible" means the visible part of radiation from the sun

"Beam" means direct radiation

"Hemispherical" means diffuse radiation

TYPE
Takes a code-word indicating the type of layer.

GLASS                              is a layer of glass, plastic or other transparent material. 

GAP                                  is a layer of gas, usually air, but possibly argon or other gas, that separates two glass layers or a glass layer and a blind layer.

BLIND                              is a slatted shading device such as a venetian blind. The slats may be fixed or movable. A blind can be on the outside of the window, on the inside, or between glass layers.

Solar radiation keywords
TRANS-SOL-BB
For glass or blind layer: Beam-beam transmittance at normal incidence of solar radiation striking the front or back of a glass layer or slat in a blind layer. Although TRANS-SOL-BB can be defined for a blind (in the rare case that the slats are transparent or perforated), the program will calculate the transmitted radiation as diffuse.

TRANS-SOL-BH
For blind layer only: Beam-hemispherical transmittance of solar radiation striking the front or back of a slat at normal incidence. 

REFL-SOL-BH
For blind layer only: Beam-hemispherical reflectance of solar radiation striking the front of a slat at normal incidence.

BACKREFL-SOL-BH
For blind layer only: Beam-hemispherical reflectance of solar radiation striking the back of a slat at normal incidence.

TRANS-SOL-HH
For blind layer only: Hemispherical-hemispherical transmittance of solar radiation striking the front or back of a slat.

REFL-SOL-HH
For blind layer only: Hemispherical-hemispherical reflectance of solar radiation striking the front of a slat.

BACKREFL-SOL-HH
For blind layer only: Hemispherical-hemispherical reflectance of solar radiation striking the back of a slat.

Visible radiation keywords (blinds)
TRANS-VIS-BH
For blind layer only: Beam-hemispherical transmittance of visible radiation striking the front or back of a slat at normal incidence.

REFL-VIS-BH
For blind layer only: Beam-hemispherical reflectance of visible radiation striking the front of a slat at normal incidence.

BACKREFL-VIS-BH
For blind layer only: Beam-hemispherical reflectance of visible radiation striking the back of a slat at normal incidence.

TRANS-VIS-HH
For blind layer only: Hemispherical-hemispherical transmittance of visible radiation striking the front or back of a slat.

REFL-VIS-HH
For blind layer only: Hemispherical-hemispherical reflectance for visible radiation striking the front of a slat.

BACKREFL-VIS-HH
For blind layer only: Hemispherical-hemispherical reflectance for visible radiation striking the back of a slat.

Infrared radiation keywords (apply only to glass or blind layers)
TRANS-IR
The infrared transmittance of a glass layer or slat in a blind layer. Assumed independent of angle of incidence.

EMIS-IR
The hemispherical infrared emissivity of the front of a glass layer or the front of a slat in a blind layer.

BACKEMIS-IR
The hemispherical infrared emissivity of the back of a glass layer or the back of a slat in a blind layer.

Slat and blind keywords (apply only to blind layers)
SLAT-ORIENTATION
Takes a code-word that indicates the orientation of the slats in a blind layer.

HORIZONTAL                 indicates that the slats are parallel to the X-axis of the window. For a vertical window, the slats are horizontal (parallel to the ground).

VERTICAL                        indicates that the slats are parallel to the Y-axis of the window. For a vertical window, the slats are vertical (perpendicular to the ground).

SLAT-ANGLE
The angle between the plane of the slat and the window outward normal (see Figure 29). For horizontal slats in a vertical window, this is the angle between the slat and a horizontal plane; in this case SLAT-ANGLE is positive when the front of the slat points down and negative when the front of the slat points up. For vertical slats in a vertical window, this is the angle between the front of the slat and vertical plane normal to the window; in this case SLAT-ANGLE is positive when the front of the slat points to the right and negative when the front of the slat points to the left when you are facing the outside of the window.

SLAT-ANGLE-MIN
The minimum slat angle for angle-adjustable slats (due to limitations in the blind construction or control).

SLAT-ANGLE-MAX
The maximum slat angle for angle-adjustable slats (due to limitations in the blind construction or control). SLAT-ANGLE-MAX should be greater than SLAT-ANGLE-MIN.

SLAT-WIDTH
The width of the slat, as shown in Figure 29. The default value corresponds to slats that are 1.0 in wide.

SLAT-SEPARATION
The distance between slats. See Figure 29. The default value corresponds to slats that are 0.75 in apart.

BLIND-COVER
Fraction of the glazed area covered by the blind. Used only when the blind coverage is fixed (i.e., blinds cannot move up and down). It is assumed that a blind,if present, covers all or part of the glazed area of the window. It does not cover any of the framed portion of the window if the window has a frame.

BLIND-COVER-MIN
Minimum fraction of glazed area covered by blind (used when blind coverage is variable). If all of the retracted slats remain over the glazed opening (e.g., there is no recess above the window to accept retracted slats), then BLIND-COVER-MIN should be greater than

            (THICKNESS + δ) / (THICKNESS + [SLAT-SEPARATION]),

which is the fraction of the window covered by the blind when the blind is fully retracted. (Here, δ is the separation between adjacent slat faces when the blinds are fully retracted.)

BLIND-COVER-MAX
Maximum fraction of window area covered by blind (used when blind coverage is variable). BLIND-COVER-MAX should be greater than BLIND-COVER-MIN.

Keywords for a glass, blind, or gap layer
THICKNESS
The thickness of a glass layer, a gap layer, or the slats in a blind layer. For a glass layer, THICKNESS is the surface-to-surface thickness. 

For a gap between two glass layers, THICKNESS is the distance between the inside surface of one glass layer and the outside surface of the other glass layer. 

For a gap between a glass layer and a blind layer, THICKNESS is the distance between the center plane of the blinds and the glass surface. In this case, the gap THICKNESS should be greater than SLAT-WIDTH/2 to allow room for the slats when fully open. 

For a blind layer, THICKNESS is the surface-to-surface thickness of the slats. 

The default thickness for glass and gap corresponds to 1/4 in (6.3 mm) and for blinds corresponds to 0.04 in (1.0 mm).

CONDUCTIVITY
For a glass or gap layer, the conductance of the layer times its THICKNESS. For a blind layer, the conductance of the slat times its THICKNESS.

How to Model Pull-Down Shades

You can model a translucent pull-down shade by entering it as a blind with closed slats in the WINDOW-LAYERS list. In this case, you should not specify SLAT-ADJ-TYPE, SLAT-SCHEDULE, or SLAT-TRIGG-SCH. Shades that are input this way will give a more accurate calculation of solar gain than if modeled using SHADING-SCHEDULE and VIS-TRANS-SCH because inter-reflections between the shade and glass layers are properly taken into account in the calculation. 

Table 33 shows the pull-down shade layers that are in the Library. To describe your own pull-down shade layer, your input might look like the following for a shade with a solar and visible transmittance of 20% and a solar and visible reflectance of 70%:

Shade-T20-R70 = WINDOW-LAYER
TYPE               = BLIND
THICKNESS          = 0.00066
CONDUCTIVITY       = 0.0667
SLAT-ANGLE         = 89.95
SLAT-ORIENTATION   = HORIZONTAL
SLAT-WIDTH         = 0.0840
SLAT-SEPARATION    = 0.0833
TRANS-SOL-BH       = 0.20
TRANS-SOL-HH       = 0.20
REFL-SOL-BH        = 0.70
REFL-SOL-HH        = 0.70
BACKREFL-SOL-BH    = 0.70
BACKREFL-SOL-HH    = 0.70
TRANS-VIS-BH       = 0.20
TRANS-VIS-HH       = 0.20
REFL-VIS-BH        = 0.70
REFL-VIS-HH        = 0.70 
BACKREFL-VIS-BH    = 0.70
BACKREFL-VIS-HH    = 0.70 ..




----- Original Message ----- 
From: "Victor Hanby" <vhanby at dmu.ac.uk>
To: <BLDG-SIM at gard.com>
Sent: Friday, November 19, 2004 3:46 AM
Subject: [BLDG-SIM] external louvres


> Are there any simulation programs that handle external louvres by 
> calculating multiple reflections, or is it normal to e.g. factor down 
> the exposed area of glass?
> 
> Vic Hanby
> -- 
> -------------------------------------------------
> Professor V I Hanby
> Institute of Energy and Sustainable Development
> De Montfort University
> The Gateway
> Leicester LE1 9BH, UK
> +44 (0)116 257 7980,  7977 (fax)
> -------------------------------------------------
> 
> 
> ======================================================
> You received this e-mail because you are subscribed 
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