Re: [EnergyPlus_Support] Zone Air Balance Surface Convection Rate VS Surface Inside Face Convection Heat Gain Rate

[Yan Xue <yxue2011@xxxxxxxxx>]

That makes sense to me. Thank you so much, Brent.

Yan

----- Original Message -----
From: "Brent Griffith" <brent.griffith@xxxxxxxx>
To: "EnergyPlus Support" <EnergyPlus_Support@xxxxxxxxxxxxxxx>
Sent: Wednesday, October 31, 2012 1:59:22 PM
Subject: RE: [EnergyPlus_Support] Zone Air Balance Surface Convection Rate VS Surface Inside Face Convection Heat Gain Rate









Yes they are similar and essentially represent the same thing. The sign convention is opposite of each other because one describes heat flow toward the “inside face” and the other toward the “zone air”. The values do differ slightly because of how the numerical solution works out. The Zone Air Balance version is somewhat more exact as it is based on the solution’s result for zone air temperature and is calculated only for reporting. The Surface version is used to feed into the calculation of the zone air temperature and for numerical reasons it ends up using a lagged value for the zone air temperature (from the previous timestep). 





From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Yan Xue 
Sent: Wednesday, October 31, 2012 11:51 AM 
To: EnergyPlus Support 
Subject: Re: [EnergyPlus_Support] Zone Air Balance Surface Convection Rate VS Surface Inside Face Convection Heat Gain Rate 








Dr. Li 

Thanks for your explanation. By the way, did you compare "Zone Air Balance Surface Convection Rate" with sum of "Surface Inside Face Convection Heat Gain Rate"? If so, are the two numbers similar? I mean both signs and absolute value? Thanks 

Yan 

----- Original Message ----- 
From: "YuanLu Li" < yli006@xxxxxxxxxxx > 
To: "EnergyPlus_Support" < energyplus_support@xxxxxxxxxxxxxxx > 
Sent: Wednesday, October 31, 2012 1:00:52 PM 
Subject: RE: [EnergyPlus_Support] Zone Air Balance Surface Convection Rate VS Surface Inside Face Convection Heat Gain Rate 

My last guess was not quite correct. The result from running the simulation is as follows: 

1) Output:Variable,*,Zone Air Balance Internal Convective Gains Rate,Hourly; 
This component reports the internal zone load which had contribution to the surface convection. The value displayed in my example using 300 watts of lighting gave a value of 60 watts. (0.3 visible.) and is the same for Winter and Summer with a positive sign. 

2) Output:Variable,*,Zone Air Balance Surface Convection Rate,hourly; 
This component is the sum of all the convection rates from the surfaces and the internal load. Negative in Winter and positive in Summer. 

3) Output:Variable,*,Surface Inside Face Convection Heat Gain Rate,Hourly; 
This component is for the individual surfaces, and do have a sign. The sign is positive for Winter dnd negative for Summer. (Floor an ceiling may have different signs.) 

Winter is colder on the other side the value was constant, because the ODT was a fixed value, and the sun was turned off. 

Summer is warmer on the other side and the value changes with ODT and sun radiation. I expect that the partition will follow the temperature difference rule.. 
Dr. Li 

To: energyplus_support@xxxxxxxxxxxxxxx 
From: yxue2011@xxxxxxxxx 
Date: Tue, 30 Oct 2012 12:22:17 -0700 
Subject: [EnergyPlus_Support] Zone Air Balance Surface Convection Rate VS Surface Inside Face Convection Heat Gain Rate 

Dear All 

I'm struggling with the comparison results of the variables "Zone Air Balance Surface Convection Rate" and "Surface Inside Face Convection Heat Gain Rate". According to the definition of the inputoutputreference, they both mean the heat transfer from surface to zone air. I think the sum of all surface inside convection heat gain rate should be equal to zone air balance surface convection rate, especially for a steady simulation. 

Recently, I did the steady simulation for a building with 5 zones and check surface convection variables for north zone. However, the sum of "Surface Inside Face Convection Heat Gain Rate" for all North Zone surfaces equals +8125 and the "Zone Air Balance Surface Convection Rate" equals -8136. Although the absolute value of them are similar but why with different signs (one is negative and the other is positive)? Did I misunderstand something? I attached the idf file with output of the two variables, could anybody give me the answer? Thank you very much. 

Yan 








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