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Confusing results when using SimpleGlazingSystem in EnergyPlus

asked 2023-03-08 02:52:38 -0500

Souja's avatar

updated 2023-03-08 09:59:21 -0500

Hi everyone,

I'm using WindowMaterial:SimpleGlazingSystem to investigate how SHGC impacts total electricity consumption.

In each simulation, I modified only the SHGC (U = 2.67, Visible Transmittance = 0.4).

I expect to see a decrease in electricity consumption with a lower SHGC.

However, the results below is really confusing.

image description

I have read the InputOutputReference and EngineeringReference, but I still struggle to figure out how to explain the results.

Is there anything I misunderstand?

Thank you.

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A few suggestions:

  • Maybe isolate the investigation to 1x zone (with 1x window) in your model, e.g. plot solar transmission vs zone cooling vs heating vs (variable) ventilation, even looking at autosizing of HVAC equipment. Further isolate the tests to summer vs winter design days vs off-season (less than 1% difference in results).
  • I work in a cold climate, with significant peak cooling. I do expect increased kWh with lower SHGC in many circumstances.
  • Many variables may be at play, e.g. dominant facade orientations, %FWR, internal loads/scheduling, etc.
Denis Bourgeois's avatar Denis Bourgeois  ( 2023-03-08 08:36:23 -0500 )edit

First guess is that E+'s Simple Window Model may not be the issue here. Based on the stated glazing properties, the windows should fall right in the middle of option 13 (curves FGHI). Sharp changes may occur when the model switches between curve sets, but not in this case IMHO.

Denis Bourgeois's avatar Denis Bourgeois  ( 2023-03-08 08:43:55 -0500 )edit

For what it's worth, I ran the same window types in E+ 22.2 for a residential home in Denver, and the results were smooth and as expected. So it might be unique to your model. Are you using the latest E+ release? Can you provide IDF files?

shorowit's avatar shorowit  ( 2023-03-08 09:46:29 -0500 )edit

@Denis Bourgeois thanks for your suggestions. I agree with you that the SimpleGlazingSystem may not be the issue in this case. I will examine the model following your suggestions.

Souja's avatar Souja  ( 2023-03-09 03:27:59 -0500 )edit

@shorowit I am still using E+ 9.3 but I can get reasonable results in the other models. Maybe it might be unique to this model. Thank you for your help.

Souja's avatar Souja  ( 2023-03-09 03:35:48 -0500 )edit

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answered 2023-03-09 11:08:11 -0500

Joshua Bohnert's avatar

Just some thoughts: the SGHC input to the energy use output has numerous factors between: sizing, airflows, equipment efficiency curves, solar heat gains to offset heating loads, 62.1 outdoor air calculations, etc. It is best to understand how the room itself was affected first, then chase those differences downstream. The main elephant in the room is the ASHRAE Heat Balance method, and how the change in SGHC impacted a room's ability to absorb radiation.

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Asked: 2023-03-08 02:52:38 -0500

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Last updated: Mar 08 '23