[Equest-users] Question regarding "U-EFFECTIVE" value

Chris Baker CBaker at cci-alliance.com
Mon Jul 21 16:11:22 PDT 2014


Thanks Joe!

One of my shells is just being problematic because it is slab with ground contact rather than above unconditioned space.

I was trying to make the gold flag with "UND" go away from detailed edit but it appears that the way the program models a slab with ground contact is very specific and cannot easily be changed (because of the layering).  I thought this was an error or something wrong that I did.

These days the program will create a special layer in the floor system that has an R-value directly corresponding to any exterior insulation you have on the slab.  The layer has no thickness or other properties, only r-value.  It is automatically created in detail edit if you specify any kind of ground contact slab in the DD wizard.

The program also will automatically specify a 1 foot layer of soil under the slab which is great (I think you used to have to do this manually).

I experimented with deleting and remodeling shell 5 from scratch in DD wizard.  The gold flags persisted!  The confusing part is the flags denote an underground wall (where there is none).  But I think the reason is because of how the program recognizes the floor layer buildup (or at least that's a theory).

I'm going to go back to my original model, input the missing "U-EFFECTIVE" values and try to run the compliance analysis again based on the info you provided.

-Chris

From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Joe Huang
Sent: Sunday, July 20, 2014 5:20 PM
To: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Question regarding "U-EFFECTIVE" value

Chris,

Your intuition is correct, but your equation is incorrect.  The idea of an "U-EFFECTIVE" is to modify (generally reduce) the conductivity of an underground surface from what it would be based on the input material properties. Since the compliance requirements for foundations are given in F-factors, which are conductivities per foot of exposed perimeter, you should set the U-EFFECTIVE to produce the same total conductance, i.e.,

     U-EFFECTIVE x (Area of Underground Surface) = F-Factor x (Length of exposed perimeter)

Thus, in your example, the total conductance is 21.97/h-F, and the U-EFFECTIVE will be 21.97/(Area of the underground surface).

There is another technical detail that I need to mention, though. Back in the early 1990's, FSEC pointed out that using the U-EFFECTIVE produced an inconsistency in the Weighting Factor, so that a significant amount of the heat flow into the space was being lost.  In response, Fred Winklemann and I (we were both at LBNL at that time) have recommended against using U-EFFECTIVE, but rather to add a fictitious resistance layer to the outside of the underground surface so that its conductivity equals the U-EFFECTIVE. This was all written up in an old DOE-2 User News article, but I don't have the link handy.  I also don't know whether the U-EFFECTIVE in eQUEST is the same as in DOE-2.1E, or has automated the procedure described in the Winklemann article.

Joe

Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 108D
Moraga CA 94556
yjhuang at whiteboxtechnologies.com<mailto:yjhuang at whiteboxtechnologies.com>
http://weather.whiteboxtechnologies.com for simulation-ready weather data
http://www.whiteboxtechnologies.com
(o) (925)388-0265
(c) (510)928-2683
"building energy simulations at your fingertips"

On 7/20/2014 1:29 PM, Chris Baker wrote:
I am having some trouble running my compliance anlaysis.  The cause is apparently a floor system modeled with an underground wall.

When I went back and looked at the properties of the affected floors, "U-EFFECTIVE" value has been left blank.

My question is, wouldn't you be able to figure "U-Effective" by multiplying the two compliance inputs together.

In this instance ...  42.25 (ft) X 0.52 (Btu/h-ft-F) = 21.97 (Btu/h-ft2-F)

Thus U-effective should show "21.97" instead of being blank.  Is this a correct assumption?

I'm not sure if this is the cause for the compliance analysis error but if I try to manually change "U-Effective" to zero, it sais
Range Checking Violation for Underground Wall 'EL5 Flr (G.SSW1.U1)' U-EFFECTIVE: Error: Input must be > 0.0001

Thus being blank would be causing the compliance errors, would it not?
(Because there is no value for the DOE2 engine to factor into the calculations when you run the analysis.)

[cid:image001.jpg at 01CFA4F6.084196E0]


Chris Baker
CCI CAD Drafter


________________________________
CCI-Alliance Confidentiality notice: This message is intended only for the person to whom addressed in the text above and may contain privileged or confidential information. If you are not that person, any use of this message is prohibited. We request that you notify us by reply to this message, and then delete all copies of this message including any contained in your reply. Thank you.




_______________________________________________

Equest-users mailing list

http://lists.onebuilding.org/listinfo.cgi/equest-users-onebuilding.org

To unsubscribe from this mailing list send  a blank message to EQUEST-USERS-UNSUBSCRIBE at ONEBUILDING.ORG<mailto:EQUEST-USERS-UNSUBSCRIBE at ONEBUILDING.ORG>


________________________________
CCI-Alliance Confidentiality notice: This message is intended only for the person to whom addressed in the text above and may contain privileged or confidential information. If you are not that person, any use of this message is prohibited. We request that you notify us by reply to this message, and then delete all copies of this message including any contained in your reply. Thank you.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20140721/8f1cacb2/attachment.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image001.jpg
Type: image/jpeg
Size: 32139 bytes
Desc: image001.jpg
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20140721/8f1cacb2/attachment.jpg>


More information about the Equest-users mailing list