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Re: [EnergyPlus_Support] Radiant Floor vs Forced Air



Dear Jim,

Here are the potential reasons for this discrepancy. It worth looking into following sections.
Hope this helps to some extent.

On Mon, Dec 11, 2017 at 1:09 AM, Jim Dirkes jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx [EnergyPlus_Support] <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:
 

Dear Forum,

I'm comparing performance of a forced air heating system against a heated floor for a 100K ft2 (~10K m2) warehouse ... and I've never evaluated a heated floor energy model so I am not quite sure how it "thinks". 
  • I have confirmed that geometry, materials, setpoints and schedules are identical.
  • The forced air system uses a gas-fired 92% efficient heating coil and a fixed minimum outdoor airflow for ventilation.
  • The heated floor uses a gas-fired 94% efficient boiler, and also has a DOAS that introduces the identical outdoor airflow of UNheated air into the zone.
  • The heated floor system has 2" (~50mm) EPS insulation under a concrete slab, while the forced air system has no underfloor insulation
  • It seems that the heating energy for both systems should be moderately close - same minimum outdoor airflow, same zone heating load, very similar heating efficiency ... but my results are 240% MORE natural gas energy for the heated floor.
  • Unmet load hours are ~300 for both models
  • Both systems provide no heat in the summer months
I've compared IDFs and see no errors, yet the gas difference makes no sense to me - so I must be missing something. Can you offer any suggestions?

p.s., IDFs attached in case anyone has time to review them, but I'm mostly wondering if there's something about how the heated floor works which is substantially different than forced air and requires, for example, a different control scheme.

--

James V Dirkes II, CEO / President
The Building Performance Team Inc.
1631 Acacia Dr, Grand Rapids, MI 49504

(alphabet soup of efforts for greater understanding: PE, BEMP, BCxP, LEED AP)

Direct / Mobile: 616.450.8653
jim@xxxxxxxxxxxxxxxxxxxxxxxxxxm

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Coffee conversation:
Caring about truth means that we will look for evidence that disproves our proposition with the same diligence that we look for evidence that supports it.




--


Javed Iqbal, LEED AP, CEA
Sr. Energy Analyst 



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Posted by: Javed Iqbal <eee.javed@xxxxxxxxx>


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