Re: [EnergyPlus_Support] Weird results with a very simple model

[Niraj Poudel <nirajpdl@xxxxxxxxx>]

Ned, has a brilliant suggestion. I would delve deeper into the documentation on how exterior solar radiation is treated at the interface of the window. I was not well versed on how Energplus performs specular reflection off of glazed materials so the documetation would help you out for sure.  
Nirja

On Sun, Mar 2, 2014 at 6:00 PM, Niraj Poudel <<mailto:nirajpdl@xxxxxxxxx>nirajpdl@xxxxxxxxx> wrote:
> I agree with Jim that it is imperative that one become familiar with each variable on is asking for. I would also like to add to that and recommend for you to delve into the weather file, manipulate it, or create one yourself to have a sinusoidal or constant outdoor dry bulb temperature, custom radiation fields among others, so you can really pinpoint as to what is going on within energy plus related to your project, Because now you have a total control of your 'boundary conditions' so to speak. 
> I hope this helps.
> Niraj
> 
> 
> 
> On Sunday, March 2, 2014, Jim Dirkes <<mailto:jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx>jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>>  
>> 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: 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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