[esp-r] Re: g-value analysis

[Pueltz, Gunter]

Jon,

you are right that the g-value is defined in EN 410 - but only
for GLAZINGS and NORMAL incidence of solar radiation !!!!!!
This restricted definition is not valid for a complete facade
and different incident angles.

The g-value can also be defined more commonly for the complete
facade (which means for the combination of glazing AND shading) 
as the ratio from external incident solar radiation to internal
solar heat gain in the room. You can take a look on these 
definitions in EN 13363-2 or - most accurate - in ISO 15099.
As the sun azimut and elevation varies during day, the g-value
varies also of course. 
As I mailed to ESRU some years ago I think it would be helpfull,
if ESP-r would have an additional output parameter: The time row
for the variable g-value (commonly defined as ratio of incident
solar radiation to internal heat gain (= sum of solar radiation
transmission and convective and radiative heat flux into the room))
for each glazing in the simulation model. 

-Gunter 
 
> -----Original Message-----
> From: esp-r-bounces at lists.strath.ac.uk
> [mailto:esp-r-bounces at lists.strath.ac.uk]On Behalf Of Jon 
> Hand (clcv10)
> Sent: Thursday, February 01, 2007 11:29 AM
> To: Gulsu Ulukavak Harputlugil
> Cc: esp-r at lists.strath.ac.uk
> Subject: [esp-r] Re: g-value analysis
> 
> 
> 
> A recent question about the 'g' value of a transparent construction.
> 
> > for a sensitivity analysis, one of my parameter is g-value of  
> > glazing. But I could not modify "only" g-value to check its effect  
> > on energy consumption in Esp-r v.11.2.I could be able to make  
> > visible transmittance modification and u-value modification of  
> > glazing separately. If I am not wrong there was a discussion held  
> > about g-value before here in this list. Will you remind me if this  
> > subject is explained before?
> > Moreover will someone explain me calculation procedure of 
> heat gain  
> > from glazings in Esp-r? (specific question is: how is g-value   
> > calculated for a particular glazing in Esp-r and when/where is g- 
> > value used in calculations?)
> >
> 
> In ESP-r a 'g' value is a "derived value" which is partly based on  
> information
> held in the databases and some information specified by the user. The
> user is asked for data that is not yet held in our databases but  
> which is
> required for the g-value report calculation.
> 
> The calculations for the 'g' value reported are based on the  
> specifications of
> EN 410:1998. And it does not have any part within an ESP-r simulation
> (those who have read the EN 410 document might notice that it 
> takes a  
> number
> of interesting liberties with the physics).
> 
> To do a sensitivity study you need to alter the thermophysical and  
> optical parameters
> actually used by ESP-r and then re-generate the g value report.
> 
> -ESRU
> 
> _______________________________________________
> esp-r mailing list
> esp-r at lists.strath.ac.uk
> http://lists.strath.ac.uk/mailman/listinfo/esp-r
>