[esp-r] Re: g-value analysis

[Jon Hand (clcv10)]

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