[Virtual-sim] Hydronic radiant cooled slab systems in IES Virtual Environment

Fri Mar 6 01:04:44 PST 2009

For anyone interested in modeling hydronic radiant cooled floor and/or ceiling slabs with IES Virtual Environment, the following paper available from the Center for the Built Environment (CBE) at http://www.cbe.berkeley.edu/research/pdf_files/Moore2008-RadCoolSimulations.pdf <http://www.cbe.berkeley.edu/research/pdf_files/Moore2008-RadCoolSimulations.pdf>  provides a detailed explanation of methods and documentation of 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> 
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________________________________

From: Timothy Moore
Sent: Fri 3/6/2009 12:07 AM
To: bldg-sim at lists.onebuilding.org
Cc: Rebecca.Leigh.Butler at gmail.com
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 modeler within the VE will need to run whenever natural ventilation is to be accounted for, but not if there were no operable windows and the hollow-core was to be cooled by mechanically driven supply airflow. 

In the case of natural ventilation, you may also wish to use the MicroFlo CFD tool within the VE to determine the performance of specific openings, cavities, or occupied spaces under specific conditions. 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 <https://mail.iesve.com/exchweb/bin/redir.asp?URL=http://www.iesve.com/> 

**Design, Simulate + Innovate with the <Virtual Environment>**
<https://mail.iesve.com/exchweb/bin/redir.asp?URL=http://www.iesve.com/disclaimer.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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