[Virtual-sim] IES VE: Radiant, hollow core ceiling - TermoDeck (ventilated hollow core slabs) Simulations
Alexander Engström
alex at termodeck.com
Sat Mar 28 02:45:32 PDT 2009
Dear Timothy
We have tried to model TermoDeck together with IES in UK with the approach
you describe. Unfortunately, the results from IES simulations have differed
from the results we expect to find. There seems to be two major problems
with modelling TermoDeck in this way:
1. The actual air-to-slab heat transfer in a hollow core slab is quite
different from what you get from standard correlations for fully developed
duct flow.
2. The vertical conduction through the solid concrete “walls” between
the cores is significant, also in a situation where both the zone below and
that above have similar conditions. This is because the film coefficients at
the floor and the ceiling will be significantly different. This conduction
process is completely neglected if the core “walls” are treated as if they
were physical walls of a room. In a 1D model, and as I understand it also in
IES, a vertical wall will only conduct horizontally. As a result, the net
conduction over the TermoDeck slab is severely underestimated.
Our proprietary model of TermoDeck will treat both these phenomena with
sufficient accuracy and it has been experimentally validated (including a
test building). It has also been verified with regard to reality in more
than 380 projects world-wide.
We strongly advise consultants and clients to contact us to discuss and
correctly design projects incorporating ventilated hollow core slabs. There
are many aspects involved in these systems that must be carried out
correctly in order to perform properly: Slab customization, Slab layout
configuration, Thermal modelling and Controls. If the controls are not
properly designed the function will not be very good. Our experience tells
us that this is a big concern as our control specifications are not always
implemented correctly.
Best Regards
Alexander Engström
TermoDeck International Ltd
Box 227, 133 02 Saltsjobaden, Sweden
Phone: +46 8 717 16 71
Mobile: +46 70 643 05 95
Fax: +46 8 748 95 11
PO Box 4805, London SW1W 0XA, United Kingdom
Phone: +44 207 821 5066
Fax: +44 207 828 1871
Email: <mailto:alex at termodeck.com> alex at termodeck.com
Skype: alexander_engstrom
<http://www.termodeck.com> www.termodeck.com
-----Ursprungligt meddelande-----
Från: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] För Matutinovic, Luka
Skickat: den 6 mars 2009 14:13
Till: Timothy Moore; bldg-sim at lists.onebuilding.org;
virtual-sim at lists.onebuilding.org
Ämne: Re: [Bldg-sim] IES VE: Radiant, hollow core ceiling
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® 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
Burlington Calgary Vancouver Dubai
‘50 Best Workplaces in Canada’
2008 Globe and Mail
P Please consider the environment before printing this e-mail
_____
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
<mailto:timothy.moore at iesve.com> timothy.moore at iesve.com
<https://mail.iesve.com/exchweb/bin/redir.asp?URL=http://www.iesve.com/>
www.iesve.com
**Design, Simulate + Innovate with the <Virtual Environment>**
<https://mail.iesve.com/exchweb/bin/redir.asp?URL=http://www.iesve.com/discl
aimer.html>
_____
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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