glazing U-value

hannes · Posts: 18 Location: Gent

Hello,
I'm modelling a building with glazing I selected from the DB database (outerpane SGG Climaplus Cool-lite KN155 and innerpane SGG Planilux separated with Argon 16mm).
The calculated SGGC and light tramsmission factors correspond quite well with the data provided by SGG.
It's the calculated ASHRAE U-value (2.551 W/m²K) that is different from the provided EN673 value (1,4 W/m²K), which has an impact on the calculated heating load.
What is the explanation for this and why is the possibility left open to change this calculated U-value?
Besides, changing this U-value doesn't affect the heating design calculation.

Regards,
Hannes
Technum NV

bhandari · Posts: 86

Hannes,
The difference probably is due the different heat transfer coefficients used in the calculations of U Factor. For example, EN673 uses exterior heat transfer coefficient - ho=23 W/m2K while ASHRAE uses ho= (26 W/m2K + radiative heat transfer coefficient) which would approximately be 30W/m2K. The value reported by manufacture are generally based on ASHRAE heat transfer coefficients.

Please note that E+ will remove the heat transfer coefficients used for U factor calculation and calculate the heat transfer coefficients based on wind velocity and surface roughness. So, this is not left to open, as in both the cases (ASHRAE vs EN673), E+ will use the same glazing properties for the calculations.

regards,
Mahabir

hannes · Posts: 18 Location: Gent

Thank you,
I think the difference is due to the fact the coating on the outermost pane is modelled on the outside (side1). In Window5 there is a possibility to flip the pane to have the coating on the right side. Is this possible in DB too?
Regards, Hannes

Florent · Posts: 2

You can create a new environnemental condition in Window5 with a 15K Outside/Inside deltaT like the EN673.
I think it will be useful to have this possibility in DB.

Regards,
Florent

AJ Lester · Posts: 72 Location: Auckland

Hello Hannes,

At present I believe that DB does not have the capability to handle flipping panes of glass or demonstrating which side of the glass a coating is on - it is on the development list for a future version.

See this response from Andy to an earlier question on a similar topic:

http://www.designbuilder.co.uk/component/option,com_forum/Itemid,25/page,viewtopic/t,1127/

So hopefully it shouldn't be too long before we see this functionality in DB!

All the best,

Andrew

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