Re: U-value window

["Hilde Breesch" <Hilde.Breesch@xxxxxxxx>]

Michaël,

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
given:

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

best regards,

Hilde Breesch
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
e-mail: Hilde.Breesch@xxxxxxxx
http://allserv.ugent.be/~hbreesch/research

----- Original Message -----
From: Michaël Kummert <kummert@xxxxxxxxxxxxx>
To: <trnsys@xxxxxxxxxxxxxxxxxxx>
Sent: Monday, January 12, 2004 6:33 PM
Subject: Re: U-value window


> Hilde,
>
> >
> > 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,
>
> Michaël