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Model dynamic electrochromic glazing in EnergyPlus

asked 2015-09-11 09:19:03 -0500

updated 2017-06-04 10:28:13 -0500

EnergyPlus has an object called WindowProperty:ShadingControl that accepts a "Switchable Glazing" option, and then you define a switch point, such as solar radiation: below it's fully clear, above it's fully tinted.

This is fine and easy to setup for a binary case (fully clear/dark). As stated in the documentation: "When a shading device is present it is either retracted or activated. When it is retracted it covers none of the window. When it is activated it covers the entire glazed part of the window (but not the frame)".

How do you go about modeling a dynamic electrochromic glazing, when the glazing can take any given state in between fully clear and fully dark?

1.Is it possible to have some interpolation in between? Something along the line of this (which is from eQuest's help file):

image description

2.If not, which is what I think, I'm ok defining 4 or 5 intermediate steps (should approximate good enough). I think I'll use an EMS program to do that (would love to be proven wrong/have just missed a built-in function), but I'm unclear what variable would be equivalent to the "solar radiation". I'm guessing "Surface Outside Face Incident Solar Radiation Rate per Area". Is that correct?

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answered 2015-09-11 10:25:09 -0500

SwitchableGlazing can be modulated for daylighting control to meet an illuminance setpoint. But if your control variable is not illuminance, then you would need to use EMS with the Surface Construction State actuator.

From the Input Output Reference, WindowProperty:ShadingControl.

Somewhat hidden at the end of the introductory paragraphs

For Shading Type = SwitchableGlazing the state of the window is either clear (unswitched) or dark (fully switched) for all Shading Control Types except MeetDaylightIlluminanceSetpoint. In this case, the transmittance of the glazing is adjusted to just meet the daylight illuminance set point at the first daylighting reference point (see Daylighting). This type of control assures that there is just enough solar gain to meet the daylighting requirements in a zone, and no more, thus reducing the cooling load.

Under field Shading Control Type

MeetDaylightIlluminanceSetpoint: Used only with ShadingType = SwitchableGlazing in zones with daylighting controls. In this case the transmittance of the glazing is adjusted to just meet the daylight illuminance set point at the first daylighting reference point. Note that the daylight illuminance set point is specified in the Daylighting:Controls object for the Zone; it is not specified as a WindowProperty:ShadingControl SetPoint. When the glare control is active, if meeting the daylight illuminance set point at the first daylighting reference point results in higher discomfort glare index (DGI) than the specified zone’s maximum allowable DGI for either of the daylight reference points, the glazing will be further dimmed until the DGI equals the specified maximum allowable value.

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This seems a little black-blox-y. For this, how does it adjust the visible transmittance? Do you need to input a construction with shading or a shading device material?

Julien Marrec's avatar Julien Marrec  ( 2015-09-11 10:46:40 -0500 )edit

Yes, you still need a construction with shading. The Engineering Reference indicates that the properties are linearly interpolated between the light and dark state.

MJWitte's avatar MJWitte  ( 2015-09-14 11:20:59 -0500 )edit

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Asked: 2015-09-11 09:19:03 -0500

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Last updated: Sep 11 '15