Modelling Floors with Different Interior Configurations

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Dear All,

We are encountering this problem all too often and would like to know if
anybody has a satisfactory solution. For example, in a two storey
building, the interior space configurations in each floor are
considerably different, forcing us to create two separate shells that
sit on top of each other in eQuest schematic wizard. However, when this
is the case, eQuest treats each shell as a separate building and place
exterior surfaces (ie. Roofs) between floors (instead of ceilings). The
times it takes to manually convert these into interior surfaces with the
right intra-space relationships is way out of reasonable limits.

Is there a way to create a shell with floors that each have different
interior layouts (even different exterior footprints for that matter)?

Thanks,

Omer Moltay, LEED AP

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There is an option when assigning your roof construction in the wizard to
make the space be below a conditioned space, and therefore ambient. I have
used this option before and it works beautifully. if you need more
information or a screenshot of what i am talking about let me know.

Rob

2011/2/1 ?mer Moltay

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Rob Hudson

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I think what Rob meant is "adiabatic", which means that there is no heat
transfer across the surface. This is usually an acceptable option for
buildings where each space is maintained at the same, or similar
temperatures.

--
Karen

2011/2/1 Rob Hudson

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yes, thanks for the correction.
and its only tuesday....

Rob

2011/2/1 Karen Walkerman

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Rob Hudson

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It's my feeling that it is within reason to make the assumption that hourly heat transfer between conditioned floors is not necessary to model to achieve an acceptable level of accuracy, in most cases.

Building on this assumption, I generally select "no exterior exposure" adiabatic roof and floor constructions for custom "per-floor" shells with a shell immediately above or below. Adiabatic surfaces retain the inter-floor thermal mass properties (they store heat on an hourly basis without transferring heat to/from the associated plenum/space) while slashing the required model inputs quite a bit.

The only times I would do otherwise are if:

- a space or level is unconditioned or will be conditioned to very different setpoints (invalidating the above assumption) - in this case I might model adiabatically initially but would edit/assign to be a properly-associated internal partition in detailed edit, for those spaces only.

- a shell of a multi-story building has a mixture of exterior roof surfaces and internal floor constructions on the same plane, in which case I will specify the roof construction for the whole shell, then delete the "sandwiched" roof surfaces between the floors in detailed edit.

Keep in mind: You should not feel unequivocally 'forced' to create separate shells for each differently zoned floor. While I also do this most of the time, we should keep in mind that a repeating floor pattern (using a multi-story shell) is potentially a MAJOR time saver and can justified from an accuracy standpoint in many cases: Not every energy model is created with the intent to accurately model historical consumptions to a tight degree, and if the end-goal is to inform the design process and/or achieve LEED credits (90.1 models), a reasonably "averaged" floor zoning pattern is fine where that can be achieved. The 90.1-2007 User's manual encourages such geometrical simplification and floor multipliers where it makes sense, and gives guidelines for judiciously translating HVAC zones into larger, combined thermal blocks.

NICK CATON, E.I.T.

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I am working on a dual duct simulation and I am having trouble getting
vav control to work correctly. The system is defined as a 100% OA Dual
Duct Single Fan system and I have tried everything I can think of to
get the fans to vary. When the sim runs, the fans are pegged in the
90-100% range all year. When I change to a dual fan dual duct system,
the fans will act as a vav fan is expected with a range of operating
hours throughout the year. I have tried Fan Control of "Variable Speed"
and "Fan EIR FPLR" without success. Any ideas?

Thanks,

Bryce

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Bryce:

Forgive my systems ignorance. But if you have a single fan dual duct system,
don't the hot and cold deck dampers just swing from heating to cooling? How will
the airflow vary unless you have two fans?

I can learn as well from our well versed members.

John R. Aulbach, PE, CEM

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Sorry, I should have explained further. I am trying to simulate a sequence of measures, one of which is adding variable speed control to the ahu fan for the dual duct system. That is the measure with the problem. A dual fan dual duct system with VAV control on the system fans works fine and the SS-L report shows the fan power varying while the single duct system won?t vary unless I take the 100% OA requirement out and add occupancy OA control at the zone level. Why can?t I make a single fan dual duct system have a VFD on the main ahu fan?

Bryce

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