Thanks, Javed.
As you know, one can become blind to the obvious if you've stared at it for hours, so I love and appreciate the fact that people are willing to offer insights. Thank you!
- The comparison, in this case, is between a forced air system which introduces outdoor air and a radiant system which needs a supplementary DOAS to provide outdoor air. As a result, the DOAS has no economizer - it's 100% OA
- The burner for the radiant systems' DOAS is irrelevant because I've forced its capacity to 0w. This is an odd approach sometimes used in the US. The OA is introduced at the roof line with no heat, anticipating that it will mix reasonably with the room air before affecting people comfort.
- I think operative temperature control is proper for a radiant system and thus will use it.
- The blow-through vs draw-through was not intentional :(Â Since the heating coil has zero capacity, however, it won't affect results.
On Mon, Dec 11, 2017 at 7:43 AM, Javed Iqbal eee.javed@xxxxxxxxx [EnergyPlus_Support] <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:
Dear Jim,Here are the potential reasons for this discrepancy. It worth looking into following sections.
- Economizer is missing in radiant file
- Burner efficiency is 80% in Coil:Heating:Fuel Radiant AHU supplyÂ
- Temperature is still controlled at Operative temperature - - ZoneControl:Thermostat:
Operativetemperature - by just deleting it effects heating energy - Forced file has draw through arrangement whereas Radiant file has blow through arrangement - heat addition through fan
Hope this helps to some extent.--On Mon, Dec 11, 2017 at 1:09 AM, Jim Dirkes jim@buildingperformanceteam.com [EnergyPlus_Support] <EnergyPlus_Support@yahoogroups.com > wrote:ÂDear 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".Â
- 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
Website l  LinkedIn
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, CEASr. Energy AnalystÂ--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@xxxxxxxxxxxxxxxxxxxxxxxxxxx
Website l  LinkedIn
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.
__._,_.___
Posted by: Jim Dirkes <jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
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