Re: [EnergyPlus_Support] Negative Cooling Load - New file uploaded to EnergyPlus_Support

["Michael J. Witte" <mjwitte@xxxxxxxx>]

The original question was:  

> I calculated cooling load for one zone in Summer Design day
> condition. I found some strange facts when calculated cooling load
> using purchased air. When I checked "Opaque Surface Inside Face
> Conduction" I found negative cooling load through all walls at day
> time(14:00-18:00) except roof and floor. (floor is insulated.) At
> day time, "Surface Outside Temperature" is higher than "Surface
> Inside Temperature".    So, I don¡¯t know why negative cooling load
> occurred at day time. ??  

In this run the walls are 12 inches (0.3m) of heavy concrete.  Due to 
the thermal storage capacity of this construction, the inside and 
outside surface heat fluxes can be very different from each other and 
can be several hours out of phase.  The roof also gets very hot which 
can cause the inside surfaces of the walls to become warmer than the 
middle layers of the wall, causing heat to flow out from the inside 
surface even at the same time that heat is flowing in from the 
outside.   

One must be careful to understand what "Opaque Surface Inside Face 
Conduction" truly means.  It indicates the heat flow from the inside 
face of the surface into or out of the surface itself.  It does not 
indicate the heat flow from the surface to the zone air.  The cooling 
load impact of a surface is governed by the inside surface convection 
coefficient and the difference in temperature between the inside 
surface and the zone air.  In this case, the hot roof is radiantly 
heating the inside surface of the wall, and heat is flowing into the 
wall and heat is also flowing into the zone air, because the zone air 
is cooler than the wall surface.  So, it is not a "negative cooling 
load".  

Mike  



On 10 Dec 2002, at 11:54, EnergyPlus_Support@yahoogroup wrote:

> 
> Hello,
> 
> This email message is a notification to let you know that
> a file has been uploaded to the Files area of the EnergyPlus_Support
> group.
> 
>   File        : /Problem_Submittals/NegativeCoolingLoad.zip 
>   Uploaded by : hojong74 <hojong74@xxxxxxxxxxx> 
>   Description : Negative Cooling Load Occured at Day Time 
> 
> You can access this file at the URL
> 
> http://groups.yahoo.com/group/EnergyPlus_Support/files/Problem_Submitt
> als/NegativeCoolingLoad.zip 
> 
> To learn more about file sharing for your group, please visit
> 
> http://help.yahoo.com/help/us/groups/files
> 
> Regards,
> 
> hojong74 <hojong74@xxxxxxxxxxx>
> 
> 
> 
> 
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