# Big difference between glazing conduction by HB and in steady-state

**URL:** <https://discourse.ladybug.tools/t/big-difference-between-glazing-conduction-by-hb-and-in-steady-state/4700>\
**Category:** honeybee-legacy\
**Tags:** energyplus, energy\
**Created:** [December 14, 2018, 10:40am UTC](https://discourse.ladybug.tools/t/big-difference-between-glazing-conduction-by-hb-and-in-steady-state/4700 "2018-12-14T10:40:34Z")\
**Posts on this page:** 1\
**Showing post:** 4

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**Author:** ![SaeranVasanthakumar](https://discourse.ladybug.tools/user_avatar/discourse.ladybug.tools/saeranvasanthakumar/32/5079_2.png) [@SaeranVasanthakumar](https://discourse.ladybug.tools/u/SaeranVasanthakumar)\
**Post date:** [December 17, 2018, 5:28pm UTC](https://discourse.ladybug.tools/t/big-difference-between-glazing-conduction-by-hb-and-in-steady-state/4700/4 "2018-12-17T17:28:31Z")

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> [@chris](#):
>
> As for the reason why you might have more heat loss through the window at night than your steady state calculation, this might be the result of the fact that E+ dynamically calculates the resistance of air films on either side of the window construction and these air films can contribute a lot to the U-values (especially when the glass isn’t well insulated).

Agreed, and another contributing factor to underestimating conduction loss here may be the radiation loss from the window to the clear sky. That is, clear (as opposed to overcast) skies have a high absorptance to emittance ratio and thus your windows will experience net radiation loss to the sky; as a function of your emittance-weighted view factor to your surroundings.

@Tiantian, I think the easiest way to account for these surface convection, and radiation exchanges without tracking all energy interactions through your glass, is simply to substitute the surface temperatures of your glazing assembly in your Fourier’s Law calculation, in place of the interior room and exterior wetbulb temperatures.

I attempted a similar experiment a while ago here: [Eplus Conduction Rate and Uvalue of the wall check](https://discourse.ladybug.tools/t/eplus-conduction-rate-and-uvalue-of-the-wall-check/3929), albeit for opaque constructions during night time conditions. Since glazing should have negligible thermal mass, this same strategy should work fine for glass during the daytime.

S

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