How IES calculates Window U value at glazed construction?

[saimmemon1234]

Please reply
Dear IES support team,
I am a PhD Researcher and in the middle of journal paper write-up. I'd appreciate your help in understanding my following query please.
In spite of knowing the IES guidance notes, CIBSE guidelines and BS standards. I am trying to understand how IES calculated the U value of window at the building template manager>Construction details>glazed constructions section. As the U values of the windows are different for different sizes of the windows used in the modelled building in the IES. There must be the authenticate method, calculation, assumption or standard behind this calculation.
Normally according to CIBSE Guide A and BS standard the window U value need to be calculated by considering the window area and glazing area. But in the Building Template Manager>Construction>Glazed Construction> window U value can easily be assumed without knowing whether it considers the window sizes or not. If so then each window has different window U values so then why IES calculates window U value as one as constant?
In buildings or houses, we normally have different window sizes now if the software ignores the window sizes and assumed a constant window fraction or assumption then please let me know with proves from guidelines or any authenticate proof.
I understand the glazing U value is the centre of pane U value which can be calculated by using BS En ISO standard 673 and which applies to IES software, so issue with glazing U value.

Could you please clarify this problem as I am in the middle of my journal paper write-up. I would really appreciate your help of understanding the U window calculations approach used by IES.

Your earliest reply will highly be appreciated
Yours Truly

Saim Memon MIET MIEEE, MSc, BEng, Student Member CIBSE
PhD Researcher, Distance Learning Tutor (Part Time)

Centre for Renewable Energy Systems Technology(CREST)
School of Electronic, Electrical and Systems Engineering,
Loughborough University, Loughborough,
Leicestershire, LE11 3TU
United Kingdom

Mob: +44 (0) 7735518528
Tel (off): +44 (0) 1509635357
Fax (off): +44 (0) 1509635341
E-mail: S.Memon@lboro.ac.uk

[Terence]

The displayed U-values are calculated according to the selected U-value method, which determines the surface resistances used in the calculation.

During simulation the U-value and the solar transmittance calculations are superseded by calculations which take account of the particular conditions applying at each time step: direct and diffuse solar irradiance, solar incidence angle and convection coefficient on both surfaces. See the ApacheSim Calculation Methods user guide for more information.