[Equest-users] Slab on Grade Floor Heat Loss

[Nathan Miller]

Fixed my typo in the F-factor heat loss calc (should have read 50 ft of perimeter)… See below.

Nathan Miller, PE, LEED AP BD+C – Mechanical Engineer/Senior Energy Analyst
RUSHING | O 206-285-7100 | C 207-650-3942
www.rushingco.com<http://www.rushingco.com/>

From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Nathan Miller via Equest-users
Sent: Friday, February 2, 2018 2:33 PM
To: Paul Diglio <paul.diglio at sbcglobal.net>; equest-users at onebuilding.org
Subject: Re: [Equest-users] Slab on Grade Floor Heat Loss

In the past I’ve done a conversion of F-factor (perimeter based) slab-on-grade heat loss to U-factor (area) and input that in on a zone-by-zone basis if I really wanted to nail down SOG heat loss.

Example- Space is 20’ x 30’, but the exposed perimeter is only two of the faces (20’ + 30’). Lets say it is uninsulated SOG.

F-factor from 90.1: F = 0.73 Btu/(hr*ft*F)

Perimeter based heat loss: 0.73 Btu/(hr*ft*F) * 50 ft = 36.5 BTU/(hr *F)

Then we can back-calculate the U-factor to assume for the whole floor to equate to that heat loss: 36.5 BTU/(hr *F) = 600 SF * X BTU/(hr*SF*F) -> U = 0.0608 BTU/(hr*SF*F)

You can create a custom floor construction for each space to provide the U-factor to produce equivalent heat loss that the F-factor calcs are telling you lose. For purely core zones (no exposed perimeter), I guess the F-factor calcs are telling us were not really losing heat through that slab (doesn’t’ seem right, but it probably is relatively small)

Nathan Miller, PE, LEED AP BD+C – Mechanical Engineer/Senior Energy Analyst
RUSHING | O 206-285-7100 | C 207-650-3942
www.rushingco.com<https://url.emailprotection.link/?a6X-5ry0mOOudUi-eMfQ7K9LfplwNoMV9idJhgEyf85c~>

From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Paul Diglio via Equest-users
Sent: Friday, February 2, 2018 2:19 PM
To: equest-users at onebuilding.org<mailto:equest-users at onebuilding.org>
Subject: [Equest-users] Slab on Grade Floor Heat Loss

I recently submitted a model to the local utility company for an incentive.  Part of the buildings' first floor is slab on grade.

One of the comments I received back is that this erroneously shows up as an exterior surface and I should delete all the slab on grade floors in the component tree.  Doesn't seem right to me.

I did a few and it does reduce the overall energy consumption.  In the 3D model, no floors show, just open to the interior of the zone.

So is eQuest assuming that without this floor, there is no heat loss out the bottom of the zone?  Is this reasonable?

Thank you,

Paul Diglio
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