[Bldg-sim] Looking for a slab F-factor paper

Nick Caton ncaton at smithboucher.com
Wed Sep 25 12:45:35 PDT 2013


Joe - on this topic:

I was involved with a string of large footprint facilities in cavern spaces, where the floors and ceilings were effectively un-insulated limestone, far underground.  For the purpose of determining building loads to size equipment, we were able to make a set of comfortable assumptions with respect to the surrounding air conditions and perimeter losses, but the challenge of determining an appropriate constant heat loss through the substantial rock floor/ceiling surfaces proved an uncertain venture.

Deciding the extent to which those losses should slow (or not) over time as the conditioned facility warms up the surrounding earth further complicated some comparative ROI assessments for conditioning equipment options.

In hindsight (and having not yet absorbed the linked literature), this more nuanced 2000 era approach which separately addresses the perimeter and core losses seems like a great stride towards addressing such concerns.  In advance of familiarizing myself with this approach, are you aware of any publicly available tools/software packages utilizing this method that could be leveraged for load calculations in a similar scenario?  Would you suggest a different approach?

I've said this before but not nearly as often as it crossed my mind:  thank you for your ever-helpful contributions!

~Nick


[cid:489575314 at 22072009-0ABB]

NICK CATON, P.E.
SENIOR ENGINEER

Smith & Boucher Engineers
25501 west valley parkway, suite 200
olathe, ks 66061
direct 913.344.0036
fax 913.345.0617
www.smithboucher.com

From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Joe Huang
Sent: Wednesday, September 25, 2013 1:15 PM
To: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Looking for a slab F-factor paper

The 1988 paper is available at   http://www.whiteboxtechnologies.com/PAPERS/88_YJH_etal_Fdn_Model.pdf

There was a discussion a few months back on the EnergyPlus_Support bulletin board on F-factors that you might be interested to read (go back to April 24-25).  Here is what I had posted at that time:

-----
Jean, others,

It was quite a surprise to read your e-mail and find that the old F-Factors that I calculated back in 1988 are still being referred to in Standard 90.1.  If you're interested in more details of that effort, there's an ASHRAE Transaction paper

Huang, Y.J., L.S. Shen, J.C. Bull, and L.F. Goldberg 1988. "Whole-house simulation of foundation heat-flows using the DOE-2 program", ASHRAE Transactions, Vol. 94-2.

and a 1998 User News article written by Fred Winkelmann on its implementation in DOE-2 ( http://www.whiteboxtechnologies.com/PAPERS/Fdn_modeling_user_news_articles02-2.pdf )

The F-Factors are per lineal feet of perimeter from Tout to Tin of the space containing the foundation. There are actually several ways to implement this model: (1) model a monolithic foundation as an exterior wall and adjust the R-value of the layer so that  U*A = F*PL (Perimeter length) -- this is the method shown in the Winkelmann article,  (2) decompose the foundation into two regions - a perimeter strip 1-2 ft wide and a core for the remainder; model the perimeter as an exterior wall, adjusting its R-value accordingly, but model the core as an adiabatic layer.  When I was working with DOE-2, there was a practical problem that layers can't be too thick or the response factor would fail, so I could only add at most 2.5 ft of soil. I don't know if EnergyPlus has similar limitations.  Ideally, you would want to model as much soil as possible to get the thermal dampening effect.

The main deficiencies with this technique are (1) Tout is the outside air temperature, (2) the foundation is treated as a single layer.  I know there's a temptation to model the foundation as a underground layer tied to the soil temperature, but that would be wrong since the F-Factors were calculated air-to-air.

In the late 90's (1998-2000), I worked with Fred Winkelmann and Vladimir Bazjanac for the Calif. Energy Commission to develop what I think is a much better model that is now the approved method for Title-24. This model uses a similar approach as before,  except instead of a single F-Factor, there are six Foundation Conductances for two domains (perimeter and core) and three heat flow paths ("quick" to the outdoor air temperature the past 3 weeks, "slow" to the  monthly ground temperature, and "constant" to the deep ground temperature). The model is not only more accurate, but  more flexible for different building conditions. If anyone's interested in the report, it's available at  www.whiteboxtechnologies.com/downloads/00_02.YJH.CEC_Fdn_Model.pdf<http://www.whiteboxtechnologies.com/downloads/00_02.YJH.CEC_Fdn_Model.pdf>

If I have it in my power, I would urge everyone to stop using the 1988 model and switch to the 2000 model, but since the F-Factors seem to have been institutionalized by now, that would be irresponsible. So, I'll be happy to answer questions about the use of either model.

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

(o) (925)388-0265

(c) (510)928-2683

"building energy simulations at your fingertips"

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

(o) (925)388-0265

(c) (510)928-2683

"building energy simulations at your fingertips"

On 25/09/2013 9:56 AM, Gowri, Krishnan wrote:

I am in the process of reconstructing slab F-factor calculation method and would like to get a copy of the paper cited below (used in REScheck):

Y.J.Huang, L.S.Shen, J.C.Bull and L.F.Goldberg, "Whole-House Simulation of Foundation Heat Flows Using the DOE-2.1C Program,"  ASHRAE Trans. 94 (2), 1988



If any of you can help, that would be great.  Thanks,



-krishnan______________________
Krishnan Gowri, Ph.D.
Senior Research Engineer

Pacific Northwest National Laboratory
1100 Dexter Ave.,  BSRC-510

Seattle, WA 98109
Tel:  206-528-3216







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