[Bldg-sim] Modelling of Ventilated Facades with Cavity Blinds - Blind Parameters

[Per Sahlin]

Hi Graham,

FYI, the new version of IDA ICE, which is currently in beta testing, has a
complete implementation of the ISO 15099 multi pane window model. This makes
it possible to model window and blind combinations from first principles as
you desire.

Best regards,

Per Sahlin

> -------- Original Message --------
> Subject: 	[Bldg-sim] Modelling of Ventilated Facades with Cavity
Blinds
> - Blind Parameters
> Date: 	Wed, 02 Apr 2008 16:15:06 +0800
> From: 	hamnmegs at ozemail.com.au <hamnmegs at ozemail.com.au>
> Reply-To: 	hamnmegs at ozemail.com.au
> To: 	bldg-sim at lists.onebuilding.org
> 
> 
> 
> Hi all,
> We are revisiting ventilated facades with cavity blinds in an attempt to
> minimise the fabric heat loads on a building.  We are looking at
> internally and externally ventilated options.  My experience in this
> area is limited to use of bulk airflow modelling (IES Apache or use of
> Arup's in house tools during the time I worked for them).
> 
> We have done some preliminary digging around to source the best software
> to determine average annual performance, bulk temperatures etc
> recognising that CFD will always have a place in understanding airflows
> and temperatures in more detail.  Our current position is:
> 1) We explored the possibilities with Energy+ and the ventilated facade
> / cavity model 2-3 years ago and were unable to generate results that we
> had confidence in.  In skimming the version updates it does not appear
> that there has been further work on this module so we don't plan to go
> back to Energy+.
> 2) We use IES Apache extensively but the blind inputs are indirect
> (unknown) rather than direct (known) properties and thus lead to
> uncertainty (see below)
> 3) We were initially encouraged by the ICE software out of Sweden, but
> now understand that the blind inputs are similar to IES.
> 
> IES / ICE take as input for the blind the a SHGC modifier (1 - SHGC =
> the overall reflected component of the blind be it SW or LW radiation)
> along with the proportion of this which ends up as shortwave versus
> longwave radiation.  There is also a U-Value / conductance modifier.
> The blind can be incident solar or time controlled like most programs.
> 
> We would prefer to input blind transmittance and absorptance (or
> reflectance) and let the software dynamically determine SHGC.  Until you
> have an understanding of the temperature of the blind which is a
> function of incident solar radiation, ambient temperatures, cavity
> ariflow etc you won't know exactly what the longwave radiation component
> is of the SHGC.  So the egg comes before the chicken ... .
> 
> In short the longwave component of the blind SHGC is a strong function
> of other dynamic or design variables and as such cannot be
> pre-determined with confidence in our professional opinion.
> 
> Does TRNSYS or other overcome this limitation?
> 
> Any suggestions? Any killer papers out there that have correlated
> longwave blind SHGC to different glazing & blind types and ventilation
> arrangements? for a variety of solar / ambient conditions ..... ?
> Anyone considering a PhD in the near future in this area :)?
> 
> Regards,
> Graham
> 
> 
> **
> 
> *Graham Carter* |* Manager Sustainable Design* | *Lend Lease design*
> 
> T 61 2 9236 6347 | F 61 2 9383 8124 | M 0407 949 193
> 
> 30 The Bond, 30 Hickson Road, Millers Point NSW 2000
> 
> graham.carter at lendlease.com.au
> 
> 
> 
> --
> 
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>    Mika Vuolle                           Equa Simulation Finland Oy
>    mika.vuolle at equa.fi                   www.equa.fi
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