Jim,
I have simulated a number of radiant systems for other reasons, usually condensation control. My radiant systems always use more energy than air systems, but
not 200+%. I believe the radiant systems heat the air, but they also exchange more energy with walls and windows. It makes sense that for comfort, a radiant system should operate at a lower air temperature since it will be the radiant energy that creates
comfort and not the air temperature. You can probably check this in you model by looking at surface energy transfers. I’ll try to make time later this week to look at your models.
Ned Lyon, P.E. (MA, WV)
Staff Consultant
SIMPSON GUMPERTZ & HEGER
781.907.9000 main
781.907.9350 direct
617.285.2162 mobile
781.907.9009 fax
www.sgh.com
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From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
Sent: Sunday, December 10, 2017 7:09 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Radiant Floor vs Forced Air [2 Attachments]
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".
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I have confirmed that geometry, materials, setpoints and schedules are identical.
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The forced air system uses a gas-fired 92% efficient heating coil and a fixed minimum outdoor airflow for ventilation.
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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.
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The heated floor system has 2" (~50mm) EPS insulation under a concrete slab, while the forced air system has no underfloor insulation
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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.
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Unmet load hours are ~300 for both models
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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@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.
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