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Re: U-value window
- Date: Tue, 27 Jan 2004 13:30:18 +0100
- From: "Hilde Breesch" <Hilde.Breesch@xxxxxxxx>
- Subject: Re: U-value window
Thanks for your answer.
I've solved the problem of the variation of the U-value of a window. It was
caused by a bug in Window 5.0 and is solved in later versions (5.1 and 5.2).
In the DOE-2 report - which is used by Type 56 - wrong gass properties are
Gap Thick Cond dCond Vis dVis Dens dDens Pr dPr
1 Krypton 16.4 0.00094 0.000 0.000 0.000 248.09 0.00000 83.800 0.00000
in stead of:
1 Krypton 16.4 0.00860 2.800 2.280 7.500 3.740 -0.0137 0.660 0.00002
PhD student Buildings & Climatic Control
Ghent University, Department of Architecture & Urban Planning
Plateaustraat 22, B-9000 GENT
tel. +32 9 264 78 61 fax. +32 9 264 41 85
----- Original Message -----
From: Michaël Kummert <kummert@xxxxxxxxxxxxx>
Sent: Monday, January 12, 2004 6:33 PM
Subject: Re: U-value window
> > I'm working on a sensitivity analysis of natural night ventilation.
> > Therefore I have to vary all the input parameters in my Prebid-Trnsys
> > simulations.
> > For a window, I started to vary the U-value (from 1.07 to 1.13) only by
> > changing the thickness of the cavity filled with Krypton from 10mm to
> > 15mm in the WINDOW 5.0 program and exported the results to the window
> > library in Prebid. When I use these two windows in my simulations, I got
> > exactly the same indoor temperatures in every time step, although the
> > U-values of the 2 windows differ a little bit in the w4-lib.dat file.
> > Is there an explanation? And how can I solve this problem.
> I think the explanation to your problem might be that you are trying to
> see a too small difference. I don't have the details of your windows and
> glazing systems, but I tried to reproduce your problem as follows:
> - I created the following glazing systems:
> 1. CEN center U-Value of 1.13 (Double low-E, Krypton 7.3mm)
> 2. CEN center U-Value of 1.03 (Double low-E, Krypton 9mm)
> - First, the NFRC U values are much closer (1.17 and 1.19), so depending
> on the conditions your U-values will be much closer (Difference = 2%
> instead of 10%)
> - I included those glazing systems in "reasonably large" windows so the
> edge effect is small (2000x1500mm, Alu with break)
> - The global U value for the window (glazing + frame) are 1.925 and
> 1.944 (less than 1% difference)
> So if you have stronger edge effects, or particular ambient conditions
> that minimize the difference between the thermal performance of your
> windows, you will not notice any difference between the two of them.
> I would recommend that you test both windows with a highly insulated
> frame and steady-state ambient conditions (e.g. 20°C inside, -10°C
> outside) to check that Type 56 is reading their properties correctly.
> Kind regards,