[esp-r] Re: solar chimney

[Achim.geissler]

Dear Ehsan

please see further comments below.

--------- Original-Nachricht --------
 Von: "Ehsan Baharvand" 
 An: "Achim.geissler" , "esp-r at lists.strath.ac.uk" 
 Betreff: Re: AW: [esp-r]  solar chimney
 Datum: 01/04/11 11:14

  Dear Achim,   Please see my answers below:   a) what is "massiv" (your
back wall)?  This is the back wall.
Sorry, my bad english: What I meant is, "how heavy / massive" is the
construction? It does seem to change temperature quite rapidly. What is the
solar absorption coefficient you are using on the back wall?
   b) how long is your pre-simulation period, how long is your simulation
period and what does "temperature does not change" mean? "Not at all" or
"not as much as expected"?  Pre-simulation = 12 days Simulation period = 1
day (24h) Time-step = 60 ... so, 1 minute time steps?
 Integration per hour = yes   The temperatures do not change at all. This
holds for all the surface, air node temp or thermal db node temperature.  
c) what do you mean "wind effect is not included"? An afn takes wind into
account by the cp-value table you must define for external nodes.
I excluded the wind effect by using Cp=0 for all the directions.
O.K.!
   d) do the air changes (outside air) change with changed opening sizes?
Yes, see attachtment Infiltration Load / Rate. 

 e) how large are the air changes befor / after changing the opening sizes?
See attachtment Infiltration Load / Rate.  
Infiltration rate, load: These profiles look O.K. at first glance. The air
flow rate rises significantly with larger openings, the zone-wise load also
increases for larger openings (more pronounced stack effect). Have you
looked at your temperature stack?

The load in zone 1 (the lowermost one, I assume) stays quite similar. This
zone has the large external "entry"? How large are the vertical openings
between the zones as compared to the external opening at the bottom and the
openings at each level?

 f) do you have a bypass in your stack to allow for downward air flow (night
time)? How to do this?But there is no control on the air flow inside the
chimney. The control is based on free-floating. Do I need a bypass?

I am not sure if you need one, here. Generally, to allow for downward
movement of air and upward movement of air at the same time (e.g. cold
glass, warm wall) it is a good idea to split such a stack vertically, also.

 Thanking you in advance.    Kind regards, Ehsan    From: Achim.geissler 
To: EhsanBaharvand ; esp-r at lists.strath.ac.uk
Sent: Fri, April 1, 2011 9:26:47 AM
Subject: AW: [esp-r] solar chimney

 Dear Ehsan

some questions for clarification to help understand your model:
a) what is "massiv" (your back wall)?
b) how long is your pre-simulation period, how long is your simulation
period and what does "temperature does not change" mean? "Not at all" or
"not as much as expected"?
c) what do you mean "wind effect is not included"? An afn takes wind into
account by the cp-value table you must define for external nodes.
d) do the air changes (outside air) change with changed opening sizes?
e) how large are the air changes befor / after changing the opening sizes?
f) do you have a bypass in your stack to allow for downward air flow (night
time)?

Best
Achim

 

 --------- Original-Nachricht --------
Von: "Ehsan Baharvand" 
An: "esp-r at lists.strath.ac.u! k" 
Betreff: [esp-r] solar chimney
Datum: 01/04/11 09:05

  Dear all,    Problem The free-floating of a solar chimney is simulated and
a upward stream due to the solar energy occurs.  However when increasing the
infiltration (colder ambient air) by increasing the opening area to outside
the backwall inside surface temperature doesn't change!  Other thing is
that the heat load inside the chimney is being removed by the infiltration
air exchange. Eventhough I increase the infiltration air exchange, the heat
load being removed increases, but the surface temperature of the backwall
remains the same.     Question Do I forget something? W! hat can be the
problem? I'm certain about the configurations and the Air Flow Network. 
  Model The 22 zones solar chimney uses a air flow network and has 2 wind
pressure boundary nodes at the inlet and the outlet.  Each zone has a
separate connection with the outdoors through a air flow network connection,
which simulates a opening between glazing panels meant for infiltration! The
inlet and the outlet areas are connected to the ambient air thourgh a
orifice with a Cd of 0.67.  Between the cubic thermal zones fictitious
surfaces are used.  The backwall is a massive construction with adiabatic BC
at the surface outside node.  At 1.8 meter distance from the backwall there
is a glazing surface with a G-value of 0.8 and 80% of glass and it has a
external BC.  The chimney is South oriented for a Cl! imate catagory 3A
according to Ashrae 90.l.    Not included Wind effect is not included.    
Kind regards,   E. Baharvand   

  
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