Re: [EnergyPlus_Support] Chilled Ceilings

Good question...

1) E+ really can't model hanged hydronic ceiling panels.

2) E+ can model embedded hydronics.

3) There is a research project underway that is looking at modelling hanged hydronic ceilings and we hope it gets incorporated into e+. As e+ are doing the Fortran-->C++ transition this year, I don't expect much developement in the way of new models until next year. You'll have to ask the team for more details...bottom line is, that it is on the list.

4) You can use the embedded pipe model restrictively to approximate the hanged ceiling hydronic panel.

My best practice guide to do that is

a) split off the active areas either by splitting the base surface or using sub-surfaces (you can also embed the hydronics internal source in sub-surfaces).

b) You are restricted in that the thermal diffusivity minimum of all the layers must be met, so fast reaction times of the system are impossible. Don't use fast changing schedules, because this system has a large thermal inertia.

c) To make the layers as thin as possible, use an as small as possible timestep.

d) Yes this means you will be using thick metal plates and not thin ones.

c) To cover convection heat exchange below AND above the panel, it is best to model the panel in the floor of a plenum zone...remember to add adiquate air exchange possibilities between the plenum zone and the zone proper below. Modelling large building models this way may not be "right" for you. Alternatively, lump them together.

d) absolutely critical is to control the surface temperature of the active area. Most likely, you may need to artificially drop the supply water temperature to achieve this, but the dT will be the same, so you will still be using the correct energy.

e) normally I have a waterheater:mixed or the new water-water plate heatexchanger model between chiller and end user. DB does not yet support either by themselves yet, so try use the commonpipe model it has with the right setpoint management.

f) I have found that auto sizing works pretty well if you have split off the active area, but for best results manual sizing is best (unfortunately requires some experties). Also, setting up the auto sizing has been tricky for some users (including myself).

Mit freundlichen GrÃ¼Ã?en- Sent from my iPhone (excuse the brevity)

i. A.

Jean Marais

b.i.g. bechtold

Tel. +49 30 6706662-23

On 18.09.2014, at 19:49, "Geert Bellens geert.bellens@xxxxxxxxxxxxxxxxxxxxxx [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:

Jean,

did you ever had reactions on this thread ?
I also see the difficulty on simulating a metal chilled ceiling. Energyplus propose to use much higher metal thickness as is used in practice (+- 0.7 mm).
Which way is the best way to model a chilled ceiling like that?
Where do you out your internal source ? As there is no medium between the metal and the insulation.

--

Best regards,

Geert Bellens

Bestbuildingconcept BVBA

Jean marais schreef op 26/10/2012 7:34:

Dear Group,
As we know there are many ways to model this typical chilled ceiling (http://www.stylepark.com/db-images/cms/durlum/img/p303157_488_336-1.jpg) using the LowTempRad object associated with a construction...by that I mean the definition of the construction containing the InternalSource and where that construction's parent surface is.

1) a combined floor/ceiling is defined for the zone (inside to outside)
- perforated metal plate
- (internal source)
- Air Gap 0.5 m
- Insulation (if any)
- Slab
...reverse order is used for the floor construction used in the floor for the zone above it

2) a zone internal surface is defined, i.e. the surface verticies are defined to fall within the zone. The internal source construction is assigned to this surface...specifying the "outside face object" is a bit tricky...Ã¢??opposingÃ¢?Â? sÂ? surface name (in the current zone)...the floor of the current zone is probably best. Interzone Surface (inside to outside)
- Air Gap 0.5 m
- (internal source)
- perforated metal plate

Issues that I raise:
a) the perforated metal plate thickness must be thick enough to contain at least half the pipe diameter + the default minimum extra for the lowrad model...this means a better construction for 1) would be (inside to outside)
- perforated metal plate
- CustomMetalFinRappedAroundtheCopperPipePlusAir 0.03 m
- (internal source)
- Air Gap 0.5 m
- Insulation (if any)
- Slab
...where CustomMetalFinRappedAroundtheCopperPipePlusAir Material takes into account the contacts area of the copper pipe against the contact metal plate or fin that is against the pipe and the air fraction of air in contact with the pipe for about half it's diameter.
b) how does the interzone surface in option 2) interact with the zone interms of radiation exchange and convection? And what about internal beam calculations for internal reflections?
c) The sizing of the the lowtemprad object presents a problem...the mass flow of these units is critical as too much velocity means the pressure drop is too high, yet too little and the performance will crash due to laminar flow developing (V > 3 m/s is typical). If the velocity is very high, because I specify a long length of pipe to cover the whole ceiling area in e+, the velocity will skyrocket. Does this cause unrealistically good heattransfer rates?

My gut tells me that this should be built out onto a set model that is different from the current imbedded pipe model.

Any thoughts?

Regards,

Jean.

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Posted by: "jeannieboef@xxxxxxxxx" <jeannieboef@xxxxxxxxx>

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Re: [EnergyPlus_Support] Chilled Ceilings - Many ways to skin a cat