[esp-r] Re: g-value analysis

[Pueltz, Gunter]

Gulsu,
 
the problem in ESP-r is that the g-value is not calculated (and used)
explecitly.
A more sophisticated model is used: 1-D-finite differences together with
heat sources
in the glaz panes; the heat source is the absorption of solar radiation
within the
glaz panes. But nevertheless you could get a g-value from the results
library
(varying with time) in the following way:
 
In common the g-value shows two parts: The transmission of solar radiation
and
the so called secondary heat gain, which represents the heatflux from the
inner
surface of the glazing into the room. The sum of solar radiation
transmission and
secondary heat flux is the g-value.
 
In ESP-r the solar radiation transmission is calculated depending on the
angle of 
incidence of the sun (based on the values given in the optics-lib). The
problem is 
that ESP only calculates the entering solar radiation as the sum over all
glazing 
(see toggle solar process in the res-modul). So you can use this value for 
solar radiation transmission for the first part of the g-value only if you
have one
single window - otherwise you have to splitt this value in several parts and
assign
them to the different glazings. And be aware that this value varies with
time - as
the sun is changing it´s incidence angle during day .....
 
The second part of the g-value - the secondary heat gain - must also be
extracted
a little bit elaborately: You have to look at the surface balance of the
glazing
(inner surface towards the room) and the sum of convective and longwave
radiative 
heatflux is the secondary heat flux of the g-value. 
But be aware that this heat fluxes also vary with time, as the
absorption of solar radiation within the glaz panes varies with time (again 
corresponding to the incident angle of the sun) and also the convective and
radiative heat fluxes into the room vary with time, corresponding to
cooling,
internal heat gains, etc.
 
Overall you can get a variable g-value for your glazing, which is a little
bit elaborately
to calculate. Thus you might ask the ESP development team to include an
additional
output - the g-value - for each glazing in future versions of ESP-r.
 
-Gunter
 
--------------------------------------------
Dr.-Ing. Gunter Pültz
Müller-BBM GmbH
Robert-Koch-Str. 11
82152 Planegg bei München
Telefon +49 (89) 85602-336
Telefax +49 (89) 85602-111
http://www.mbbm.de <http://www.mbbm.de/> 
email:plz at mbbm.de 

  
 
 

-----Original Message-----
From: esp-r-bounces at lists.strath.ac.uk
[mailto:esp-r-bounces at lists.strath.ac.uk]On Behalf Of Gulsu Ulukavak
Harputlugil
Sent: Wednesday, January 31, 2007 8:52 PM
To: esp-r at lists.strath.ac.uk
Subject: [esp-r] g-value analysis


hi,
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?)

 
Thanks in advance.
 
Gulsu

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.strath.ac.uk/archives/esp-r/attachments/20070201/4f59e483/attachment.html