Re: [EnergyPlus_Support] Does U-value change with temperature?

["Jean Marais jeannieboef@xxxxxxxxx [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx>]

Joe and Edd have good points, however for most estimates we assume the effect is negligable for the "surface to surface" U-value. What does change are the film resistances which are convection dependant...and e+ calculates those dynamically. So the overall u-values are changing all the time. This is not to be confused with RATED u-values, which are the manufacturer specs at given rating test conditions.

2017-01-18 15:56 GMT+01:00 'Edward G. Lyon' eglyon@xxxxxxx [EnergyPlus_Support] <EnergyPlus_Support@xxxxxxxxxxxxxxx>:

 

A lot of that work is now part of the WUFI program.  WUFI materials can have variable R-Values with temperature and moisture content and WUFI will calculate instantaneous total assembly R-Values.  This is a likely coming standard that will need to be integrated into E+.

 

Ned Lyon, P.E. (MA, WV)
Staff Consultant

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From: EnergyPlus_Support@yahoogroups.com [mailto:EnergyPlus_Support@yahoogroups.com]
Sent: Wednesday, January 18, 2017 12:05 AM
To: EnergyPlus_Support@yahoogroups.com
Subject: Re: [EnergyPlus_Support] Does U-value change with temperature?

 

 

I remember seeing a report by Jeff Christian of ORNL decades ago that looked into the change in conductivity for insulation products as a function of temperature.  I recall he found something like a 10% change over the range of ambient temperatures.  If you're interested, you should do a Google Search of the technical literature (or ORNL reports) and see if you find something.

Joe

Joe Huang

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On 1/11/2017 10:42 PM, Amrita Ghosh amritaghosh1986@xxxxxxxxx [EnergyPlus_Support] wrote:

 

Hi,

 

Can anyone tell me if U-value of a material changes with temperature? 

 

While evaluating the U-value, if the convective heat transfer coefficients (h) change, the U-value changes. But does it also change when the temperature, indoor or outdoor, changes? Since the equation states: U=Q/(A. deltaT)

where deltaT= temperature difference between indoor and outdoor.

 

Thank you,

Amrita

 

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Posted by: Jean Marais <jeannieboef@xxxxxxxxx>

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