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RE: [EnergyPlus_Support] Weird results with a very simple model
And the short answer is that the glass reflects more solar during the summer when the sun is high in the sky and admits more solar in the winter when the sun is low in the sky (incident solar angles). The opaque wall absorbs the energy striking it with much less reflection in the summer and does not admit solar energy into the space during the winter.
Ned Lyon, P.E. (MA, WV)
Staff Consultant
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From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Jim Dirkes
Sent: Sunday, March 02, 2014 5:21 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: RE: [EnergyPlus_Support] Weird results with a very simple model
Athinodoros,
You are using perhaps the only energy analysis software that can tell you exactly why the results are occurring. IN order for it to ?tell? you, however, you must become very familiar with the Output:Variable objects. Read up on these! Practice using them!
p.s., It is also very helpful to specify Output:VariableDisciontary,IDF; in your IDF, and then review the resulting .rdd file for applicable variables
From: <mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx>EnergyPlus_Support@xxxxxxxxxxxxxxx [<mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx>mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Athinodoros Tzoulis
Sent: Sunday, March 2, 2014 4:33 PM
To: EnergyPlus Support
Subject: [EnergyPlus_Support] Weird results with a very simple model
Hi all,
I have created 2 very simple models and I wanted to make a comparison in order to study the effect of glazing.
The model is as follows:
- 5.4x3.6x2.7m room
- All surfaces apart from the facade are adiabatic
- All vertical walls including the facade have no thermal mass, the floor and ceiling have thermal mass.
- R-value of the facade= 0.94, which means approximately U-value=0.9 (if we add ri=0.13 and rout=0.04)
- No windows
- No internal heat gains
- No HVAC systems
- No infiltration
- External gains due to ambient temperature
- No radiation
- Longwave radiation due to the sky still is present. I have set the the sky temperature at 0oC constantly.
The second model is exactly the same as the first one with the difference that the facade is fully glazed (no frame, no shading). The glass is modelled with simple window model.
- U-value of the glass facade =0.9
- g-value =0.5 (this does not play a role since no surface is exposed to sun radiation)
- The rest is exactly the same
I have compared the mean air temperature of the 2 models. Attached you can find the results for the temperatures of the 2 models. The blue line is the temperature of the opaque model and the red line is the room with the fully glazed facade. In summer the temperature of the opaque room is higher and in winter vice versa. This seems like U-value or thermal mass of the opaque room is smaller, which is not the case.
I expected that the temperatures of the 2 rooms would be the same since the U-value is the same (heat flux due to external temperature is the same) and there is no radiation. Moreover, glass is opaque to longwave infrared radiation.
Does longwave radiation play a role?
Is there anything else to know about glazing modelling (simple window model) in E+ ?
Any clue?
Thanks in advance.
Best regards,
Athinodoros Tzoulis
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