Does E+ consider interior shading when calculating the operative temperature?

asked 2018-07-16 08:50:56 -0600

rafael.alonso
933 ●1 ●6 ●12 http://atmoslab.io

updated 2018-07-16 10:54:53 -0600

__AmirRoth__

4446 ●5 ●17 http://bleedinggreenna...

Hi all,

I´m working on the thermal analysis of a wintergarden, made of polycarbonate with an internal shading that deploys depending on the temperature.

Is the operative temperature calculated with the temperature of the shading material, or with the temperature of the polycarbonate roof? I don´t see many changes between both options, and I guess it should make a difference.

Thanks,

Rafael

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answered 2018-07-26 18:03:36 -0600

MJWitte

9760 ●6 ●10 http://www.gard.com/

This may get a little deep, but I want to document the details here.

Based on a quick inspection of the source code, it appears that the surface inside face temperature (TempSurfIn) for a window is the temperature of the inside face of the glazing. This variable is used for meant radiant temperature and operative temperature calculations (wrong for a shaded window).
A separate effective surface temperature is calculated for shaded windows (EffInsSurfTemp) which is defined as "Effective inside surface temperature for window with interior blind or shade; combination of shade/blind and glass temperatures." This temperature is used for interior radiant exchange (correct).
For the equivalent layer window model (Construction:WindowEquivalentLayer) EffInsSurfTemp = TempSurfIn, so you may see the impact you expect if you use the equivalent layer window model.

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Many thanks for the detailed reply - I´m picking up on this now that I have a case to test and workaround it.

Great to know, so I will discard Operative Temperature provided by E+, and calculate it separately using the air temperature and surface temperatures from point 2.
Is there any output to pull out the "Effective inside surface temperature for window with interior blind or shade; combination of shade/blind and glass temperatures" Going through the list of outputs, there is nothing that resembles it.
Wouldn´t this mean that the shading is fixed, always deployed?

rafael.alonso ( 2018-10-31 07:17:23 -0600 )edit

re 2. No. It would not be difficult to add if you want to build your own custom version.

re 3. Well, yes, but you could use EMS Surface Construction State to change the window construction as desired.

MJWitte ( 2018-10-31 15:10:22 -0600 )edit

Ah, great thanks! I'll explore option 3 through the EMS Surface Constructtion State.

rafael.alonso ( 2018-11-01 04:53:37 -0600 )edit

I finally got the EMS Surface Construction State working, really handy. However, it seems that none of the shading objects,

WindowMaterial:Shade:EquivalentLayer WindowMaterial:Drape:EquivalentLayer WindowMaterial:Blind:EquivalentLayer WindowMaterial:Screen:EquivalentLayer

has any field to specify thickness and material conductivity. How could I model something like a 5mm thick curtain, so that it adds to the thermal resistance of the whole window?

rafael.alonso ( 2018-11-07 12:00:21 -0600 )edit

WindowMaterial:Gap:EquivalentLayer is the only part of the equivalent layer model with user inputs for thermal characteristics. The thermal performance of the other layers are calculated internally. So, you could add another layer of gap+glazing to represent the drape thermal resistance.

MJWitte ( 2018-11-07 19:21:14 -0600 )edit

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answered 2023-12-13 04:48:55 -0600

MatteoMerli
51 ●1 ●4

Hi @MJWitte,

Reading this thread, I understand that the radiant temperature of a zone (and consequently the operating temperature) is calculated based on the internal surface temperature of the glass, regardless of the presence of curtains.

I simulated a shoebox in EnergyPlus 23.1 with and without curtains in front of a window. I observed that the 'Surface Inside Face Temperature' of the window differs between the two scenarios: with curtains, the temperature is higher in winter and lower in summer. Additionally, the operating and radiant temperatures of the area vary by a few degrees between the two scenarios. I would have expected to obtain the same temperature values.

Has the issue with the radiant temperature calculation been addressed in one of the latest versions, or is there another explanation for the values I obtained? Unfortunately, I cannot upload pictures due to the low karma score.

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There have been some recent changes related to MRT Calculations but this issue has not been resolved yet. The surface heat transfer does fully account for the shade, so there is a change in the glass temperature. But the operative temperature calculation is using the glass temperature and emissivity rather than the shade temperature and emissivity. So there is an impact from the shades on operative temperature, but not as much as it should be depending on the shading material.

MJWitte ( 2024-01-02 10:34:06 -0600 )edit

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