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 Gowri, Ph.D.
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:
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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
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 Huang
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 CATON, P.E.