[Bldg-sim] IES VE: Radiant, hollow core ceiling

[Matutinovic, Luka]

Timothy,
 
Thanks for the great summary.  Do you know if it's possible to model
Thermodeck in eQuest by tricking the system somehow?  I've bumped up the
thermal mass of the floors, but it's obviously not having as big an
impact as correctly modelling the CFD component.  I had a thought about
modelling a pre-coil to simulate the damping effects of the slab in
reducing peaks and then manually removing that energy, but I'm not sure
if this is correct.  Any thoughts?
 
Cheers,
 

Luka Matutinovic, B.A.Sc., LEED(r) AP

Green Building Consultant
 
T. 416.487.5257 ext. 317  
F. 416.487.9766  
Toll Free 1.888.425.7255
www.halsall.com 

HALSALL ASSOCIATES LTD. 
Toronto  Richmond Hill  Ottawa  Sudbury 
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2008 Globe and Mail

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________________________________

From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Timothy
Moore
Sent: Friday, March 06, 2009 3:59 AM
To: bldg-sim at lists.onebuilding.org; virtual-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] IES VE: Radiant, hollow core ceiling


Rebecca and others, 

 

Modeling air-cooled (or heated), hollow-core radiant slabs (such as
TermoDeck) within IES Virtual Environment is a relatively
straightforward matter:

 

1) Include the hollow-core geometry in your model. This must be
segmented to properly capture the changing delta-T over distance as the
supply air gains heat while passing through any sections of the floor
cavity that are going to be in series rather than parallel
configurations. 

 

2) If the hollow core is cooled via natural ventilation, then the volume
of the core spaces needs to be coupled to the plenums or zones that
include the operable openings. Like windows or other operable openings
in the occupied spaces, these openings can be controlled via schedules,
interior conditions, climate variables, or formulae including any of
these. The coupled MacroFlo dynamic bulk airflow modler within the VE
will need to run whenever natural ventialtion is to be acconted for, but
not if there were no operable windows and the hollow-coore was to be
cooled by mechanically driven supply airflow. 

 

In the case of natural ventialtion, you may also wish to use the
MicroFlo CFD tool within the VE to determine the performacne of specific
openings, cavities, or occupied spaces under specific conditons. The
bulk airflow model and thermal simulation are used to set up initial
boundary conditions for the CFD model, and then the results from the CFD
run can then inform revision of the operable openings in the dynamic
bulk-airflow + thermal modeling. While the CFD work can be valuable in
determining performance and refining the model, it is not required to
run the dynamic bulk-airflow + thermal modeling of the naturally
ventilated spaces, nor is it required for modeling the hollow-core
floor.

 

3) Apply convective heat transfer coefficients to the interior surfaces
of the hollow-core material constructions appropriate to the use of this
core space as a duct (see ASHRAE Fundamentals for determining
appropriate coefficients). You will need to calculate the equivalent
air-film resistance, as this is the value you will change, replacing the
air-film resistance associated with the default variable coefficient for
natural convection in the Constructions dialog. Then open the Derived
Parameters dialog from there to confirm that the convective heat
transfer coefficient calculated by the VE is what you intended (and thus
that you have entered the correct air-film resistance value). Note also
that the bottom surface construction of the hollow-core ceiling will be
applied as the Ceiling construction for the occupied space below, and
therefore the "Outside" surface air-film resistance for this element
will be the one facing the interior of the hollow core.

 

4) If air-cooling or heating of the hollow core is mechanically driven,
set up the system in ApacheHVAC with the supply air running through the
hollow core geometry as would be done in the actual building. If it is a
mixed-mode system, wherein the cavity is alternately cooled by
mechanical supply air and natural ventilation, then set up the controls
such that these modes hand-off appropriately-i.e., if no overlap is
desired, ensure that controllers for both system include common sensed
variable and thresholds, and non-overlapping responses at these
thresholds.

 

IES VE is in fact exceptionally well suited to doing this and provides
appropriate means of controlling such systems and of accounting for the
full range of radiant and convective heat transfer paths involved. 

 

As with any tool, taking the time to first understand how to use the
tool properly is important to getting appropriate results. 

 
Timothy Moore 
Senior Consultant - Special Projects 

Mobile: 415 810 2495 
Office: 415 983-0603
timothy.moore at iesve.com <mailto:timothy.moore at iesve.com> 
www.iesve.com
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________________________________


From: Rebecca Butler [mailto:Rebecca.Leigh.Butler at gmail.com] 
Sent: Thursday, March 05, 2009 8:50 AM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] IES VE: Radiant, hollow core ceiling

 

I have a question regarding the capabilities of IES VE and its CFD
package and I was hoping someone might have some experience or insight
to help get me started on the following problem.  We have a concept
cooling design which includes a radiant hollow core concrete ceiling
through which evaporatively cooled air is routed.  The air which is
routed through the radiant ceiling comes from a central evaporative
cooler and is then exhausted at the exterior of each room after it has
passed through the airflow passages in the ceiling.  Just to be clear,
this is not a typical radiant system in that electricity is being used
to cool the slab but instead evaporatively cooled outdoor air is being
used in its place.  We also want to couple these effects with natural
ventilation which occurs because of the use of operable windows.  

We are trying to analyze the effects of these techniques in a cooling
season in Colorado (hence the benefit of the evaporative cooler).  We
have conducted rough calculations of the benefits of using such a system
using standard ASHRAE energy transfer techniques and we want to verify
our results.  Have you ever heard of this type of system being modeled
in IES VE and/or is it capable of modeling such a system?  Is there a
way to modify the "radiant ceiling" option in IES to take into account
the saving which would occur by using evaporatively cooled air in the
place of electricity?  If not, is there a way to manually create such a
system from the ground up?

Any help would be greatly appreciated.  Thank you.

Rebecca Butler
LEED AP
Enermodal Engineering
(303) 861-2070 

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