[BLDG-SIM] natural ventilation analysis tools

[Pueltz, Gunter]

Brian,
 
as far as I know does TAS use transfer-functions for the energy transport
through components like walls and glazings; thus the internal surface
temperatures of glazings arenot modelled in a correct way. As these internal
surface temperatures are dominating the vertical near surface air flow (the
development of boundary layers), a more reliable simulation tool should be
used. I am using ESP-r from ESRU, Joe Clark, which is based on
1-D-heatconduction modelled via finite differences algorithm; thus the
absorption of solar radiation within the single panes can be calculated as
well as the resulting heat fluxes to external and internal surfaces. This
yield more correct internal surface temperatures.
 
But you have asked for detailled CFD-studies about natural ventilation: This
is currently a challenging task !
 
The basic problem is that the well known high resolving CFD simulation tools
like CFX-5 or Fluent are not able to simulate a longer period of time (due
to the high resolution this would require a huge amount of computer power),
i.e. currently simulation time is maximal a complete day; on the other hand
the storage of heat in building's mass (floors, walls, ceilings, etc.) shows
a strong effect onto the temperatures, but to get a stable solution it will
take a longer period of time (simulation time of at least 14 days ore more,
depending on the amount of storage mass). This is the reason, why you have
to use a zonal based simulation tool - like ESP-r - for the starting period
of the simulation (i.e. the first 2..3 weeks) and then you have to couple it
with a CFD simulation tool. This coupling can be done either via internal
surface temperatures (as boundary conditions for the CFD simulation) or -
even more better - with wall heat fluxes (which provides a temperature
distribution on the internal surfaces).
Currently ESP-r has the facility to couple the zonal based simulation with
an internal CFD-capability; but there are restrictions due to the number of
windows (only two openings are allowed); also the analyses of the
CFD-results shows some problems. 
These were the reasons why we coupled ESP-r with the well known
CFD-simulation tool CFX-5; we used the output from ESP-r (wall heat fluxes
and surface absorptions, air flow rates towards outside (ambient air)
calculated via an air-flow-network model) as input values for the CFD-model
and we got some nice results. If you are interested in I could send you some
examples.
 
Hope these informations help you. If you have further questions, don´t
hesitate to contact me.
 
-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: Brian Thornton [mailto:bthornton at glumac.com]
Sent: Wednesday, October 22, 2003 1:06 AM
To: BLDG-SIM at gard.com
Subject: [BLDG-SIM] natural ventilation analysis tools



Does anyone have experience with CFD, and non-CFD analysis tools for design
and energy analysis of natural ventilation? 

Tas is one I have heard a lot about lately. 

Can anyone describe their experience in learning, using, providing usable
and correct results, and extrapolating results to annual energy
usage/savings?

Any other software that provides at least some 2-D or 3-D CFD, and hourly
thermal calculations for natural ventilation? 

Thanks, 

Brian  

Brian Thornton, P.E. 
Lead Engineer, Energy Services 
GLUMAC 
I N T E R N A T I O N A L 
320 SW Washington, Suite 200 
Portland, Oregon 97204 

503.227.5280  Phone 
503.274.7674  Fax 

www.Glumac.com 

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