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

["Jean marais" <jeannieboef@xxxxxxxxx>]

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...â??opposingâ?? 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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