Why are U value high in winter and less in summer ?

[Sawant Vinita]

Hi, 

I hope you are doing well.

I wanted to know why does UValue comes lesser in summer conditions than for winter conditions 

I have taken a system for which same glass is being used with same boundary conditions just the inner and outer temperature are been changed. 

So what I found was my Uvalue is higher in winter and summer it’s less. What is the reason behind it, That it’s U value high in winter and less in summer .

Thank you,

Best Regards,

Vinita Sawant 

[Reichard, Georg]

It comes from the different surface coefficients/resistances that are applied for the different seasons (which mostly relates to differences in convection, i.e. wind speed differences between the seasons).

You find the standardized values for this in documents such as ISO 6946 or the ASHRAE Handbook – Fundamentals.

 

Best,

Georg

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[Robin Mitchell]

Thanks Georg !!

Robin

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Robin Mitchell

Building Technology and Urban Systems Division
Energy Technologies Area
Lawrence Berkeley National Laboratory