[Equest-users] F-Factor to U-Value

[Ashok Vijayashree]

Hope its not too late for me to join this discussion.

If I look at 90.1 table A6.3 F = 0.73 is equal to 150mm concrete poured
directly on earth that is unheated. However, if you look at the article
"Underground Surfaces" by Fred Wilkenmann *
http://esl.tamu.edu/pub/DOE%2D2%5FOCR%5FManuals/*<http://esl.tamu.edu/pub/DOE%2D2%5FOCR%5FManuals/>
*  (DOE2 articles ground coupling models) page 10 *and look at Table 1 F
factors of an uninsulated and uncarpeted concrete slab on grade, F factor is
1.10.

Am I misinterpreting the article? Is the 0.73 of ASHRAE table A6.3 carpeted?
Because if it is then the F-factor in the table 1 will be 0.77 which is
close to ASHRAE.


Thanks,

Ashok

On Fri, Oct 15, 2010 at 1:20 AM, Kelsey VanTassel <KVanTassel at sustaineng.com
> wrote:

> Hmm, now that I am looking at it again, I am not sure I am doing it right
> either. I thought the F-factor presented in the tables was already
> correcting for the R-value of the slab and soil, but now I'm not sure. I may
> be double-counting.
>
>
> I ran into this problem too because in wizard mode, the menu of insulation
> configurations for slab-on-grade floors did not have the particular
> combination I needed. Here's what you can do in detailed edit mode instead:
>
>
> 1.       On a space-by-space basis (or for the whole floor if it is all
> heated or unheated slab) calculate the R-value of the fictitious layer of
> insulation covering the slab:
>
> Equivalent R-value = ((F-factor * Exposed Perimeter length)/Area of space
> or floor)^-1
>
> (hint for determining exposed perimeter length: just add up all the widths
> of the exterior walls for that space. Double-click on the first exterior
> wall in the component tree and then press the down arrow in the menu to page
> through the list of just exterior walls)
>
>
> 2.       Create a custom material of type Resistance with this R-value.
>
>
> 3.       Create (or modify) the underground floor construction using the
> following layers (outside to inside):
>
>
> ·         Material you just made
>
> ·         Light soil damp 12 in
>
> ·         6 in HW (140lb) concrete
>
> Kelsey Van Tassel
> Mechanical Engineer | kvantassel at sustaineng.com<mailto:
> kvantassel at sustaineng.com>
> 608.836.4488 ext. 20 | Fax: 608.836.4477
>
> Sustainable Engineering Group
> 901 Deming Way, Suite 201
> Madison, WI 53717
> www.sustaineng.com<http://www.sustaineng.com/>
>
>
> From: equest-users-bounces at lists.onebuilding.org [mailto:
> equest-users-bounces at lists.onebuilding.org] On Behalf Of Will Mak
> Sent: Thursday, October 14, 2010 10:47 AM
> To: equest-users at lists.onebuilding.org
> Subject: Re: [Equest-users] F-Factor to U-Value
>
> eQuest requires an input of a U-Value when modeling a slab on grab layer.
> Typically, you enter a F-Factor to account for the loss per perimeter
> length. I did some research but could not find any solid conclusions on what
> is suppose to be done to convert the F-Factor to a U-value or configure
> eQuest to correctly model this. Any suggestions?
>
> Thanks!
>
> William Mak, LEED Green Associate
> Mechanical Design Engineer
>
> EPSTEIN
> Architecture
> Interiors
> Engineering
> Construction
>
> 600 West Fulton Street
> Chicago, Illinois 60661-1259
>
> D (312) 429-8116
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>
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