MODELLING THERMAL BRDIGES IN e-quest or DOE2

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Dear building simulation colleagues,
I would very much appreciate any insights or work around to simulate
envelope thermal bridges in e-quest.
Sincerely,
LPL
-------------------------------------------------------------
Luis P?rez-Lombard
Dr. Ingeniero Industrial
Profesor Contratado Doctor
Departamento de Ingenier?a Energ?tica
Escuela Superior de Ingenieros
Universidad de Sevilla
Camino de los Descubrimientos s/n
41092 SEVILLA
Tfno.: 95.448.72.56
Fax: 95.446.31.53
e-mail: lpl at us.es
-------------------------------------------------------------

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lpl
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Hello Sir,
eQuest does not have the capability to directly model thermal bridges. The typical methodology is to calculate the effective U-value of the insulation/thermal bridge layer when building your layers for the construction. BC Hydro has published significant research on building envelope thermal bridging. See the lower portion of the webpage:
https://www.bchydro.com/powersmart/business/programs/new-construction.html#thermal

Christopher Jones, P.Eng.
Senior Engineer

WSP Canada Inc.
2300 Yonge Street, Suite 2300
Toronto, ON M4P 1E4
T +1 416-644-4226
F +1 416-487-9766
C +1 416-697-0056

www.wspgroup.com

Jones, Christopher's picture
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Follow the guidance in ASHRAE 90.1 Appendix A to determine the whole assembly values.

Marcus Sheffer
7group

Marcus Sheffer's picture
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There is also a landmark study by Morrison Hershfield in Canada which I
don't have access to at the moment that should provide guidance.

James V Dirkes II, PE's picture
Joined: 2011-10-02
Reputation: 203

One in the same.

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Christopher Jones, P.Eng.
Senior Engineer

WSP Canada Inc.
2300 Yonge Street, Suite 2300
Toronto, ON M4P 1E4
T +1 416-644-4226
F +1 416-487-9766
C +1 416-697-0056

www.wspgroup.com

Jones, Christopher's picture
Joined: 2015-06-11
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I actually helped to develop a method to model thermal bridges in DOE-2
back in 1986 that has never been widely disseminated, although I still
find it the most practical way to model 2-D heat flows in whole-building
simulations.

This method uses a two-dimensional finite-element program (WALFERFN)
that calculates one-dimensional equivalent response factors which are
written directly into the DOE-2 layers library (BDLLIB.DAT), which can
then be called by DOE-2 just like any other response factor in the library.

I've always used this technique in my residential modeling, with the
added benefit of not needing to input duplicate sets of wall layers for
the stud and non-stud portions, which measurably simplifies the models
and makes them easier to read. The last time I did significant work on
this subject was in 2000-2002, when I created for the California Energy
Commission a library of over 100 wall layers with metal framing and thus
considerable thermal
bridging. I compared the wall assembly U-values to that calculated by
ORNL's Heating-7 program, and they were
right on. Unfortunately, a few years after the project was completed,
the Commission decided to move to EnergyPlus as their reference program,
and so this work was effectively abandoned.

For more information on this technique, i.e., creating 2-D response
factors, please see this report:
http://www.whiteboxtechnologies.com/PAPERS/96_12_YJH_2Drespfacs_CEC_rpt.pdf

If there's anyone who's still running DOE-2 in batch, rather than just
the eQUEST interface, this procedure should be quite understandable.
Just e-mail me and I'll be happy to give you a copy of the WALFERFN
program and some sample input files.

Joe

Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 205A
Moraga CA 94556
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"

Joe Huang's picture
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The work I did for the CEC was done in 1996 (as indicated in the report
title), not 2000-2002, which was a follow-on effort to do 2-D foundation
heat flows.

Joe

Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 205A
Moraga CA 94556
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"

Joe Huang's picture
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Joe,
It would be very interesting to compare the methodologies in your paper with the results of the Morrison Herschfield research. BC Hydro published that detailed research.

https://www.bchydro.com/powersmart/business/programs/new-construction.html?WT.mc_id=rd_thermalguide#thermal

[cid:image003.png at 01D09C46.E75BA0D0]
Christopher Jones, P.Eng.
Senior Engineer

WSP Canada Inc.
2300 Yonge Street, Suite 2300
Toronto, ON M4P 1E4
T +1 416-644-4226
F +1 416-487-9766
C +1 416-697-0056

www.wspgroup.com

Jones, Christopher's picture
Joined: 2015-06-11
Reputation: 0

Christopher,

I took a brief scroll through the link that you provided, and yes,
there's a lot of information there. I haven't yet found a technical
description of the methodology, but I did get to the tables with pretty
colored pictures of wall sections and their computed U-values. I hope
there's more information on the dynamic characteristics of these wall
sections, i.e., thermal mass, diffusivity, etc., since those would be
needed to model them correctly in a simulation program.

In terms of comparing the methodologies, as you've suggested, one place
to start would be simply comparing the steady-state U-values derived for
the same wall constructions. I've done some digging on my end and found
an old 1997 User News newsletter with a brief description of the 2-D
response factor work I did with Fred Winkelmann and Vladimir Bazjanac
and a table listing the R-values for the 76 steel-frame wall sections
modeled. Since the whole newsletter is only 657K, I've attached it with
this e-mail. The newsletter is interesting in other ways, as well,
including the announcement of the 5th IBPSA conference to be held in the
Czech Republic :-) .

Joe

Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 205A
Moraga CA 94556
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"

Joe Huang's picture
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(modified from previous post but replacing the attachment with a link to
reduce file size)

Joe Huang's picture
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Joe,
I admit I haven?t read all the appendices. I use mainly appendix B which contains the steady-state U-values of dozens of constructions. Appendix C may provide some insights as to whether or not dynamic characteristics of the constructions were examined in their energy modeling.

From this work, BC Hydro has decided that all thermal bridging in buildings are to be accounted for when performing modeling for BC Hydro incentives. But BC Hydro also now includes blanket factors for de-rating the baseline case energy model to account for typical thermal bridging not accounted for in 90.1. It is a bit baffling to me as one has to go through a lot of work, fill in a bunch of forms to come up with almost no significant difference in relative results:

The same web page, just below ?Resources? includes this Accounting for Thermal Bridging at Interface Details along with the spreadsheets:
https://www.bchydro.com/powersmart/business/programs/new-construction.html#thermal

[cid:image003.png at 01D09C46.E75BA0D0]
Christopher Jones, P.Eng.
Senior Engineer

WSP Canada Inc.
2300 Yonge Street, Suite 2300
Toronto, ON M4P 1E4
T +1 416-644-4226
F +1 416-487-9766
C +1 416-697-0056

www.wspgroup.com

Jones, Christopher's picture
Joined: 2015-06-11
Reputation: 0

Chris, Joe,

Refer to ASHRAE 1365-RP for detailed methodology on the modeling. The same methodology was used in the BETB Guide. Sensitivity of transient analysis for the thermal modeling was addressed in 1365-RP. In terms of thermal mass impacts on energy modeling, this is dealt with in Appendix C of the report. Analysis was done using EnergyPlus? Finite Difference method for conduction.

Chris ? the point of derating the reference building in the BC Hydro incentive is to encourage design teams to understand the actual performance of their envelope (and buildings). If you just force people to include all thermal bridging when the codes were clearly developed to ignore most of this thermal bridging, then nobody will ever account for the full effects of thermal bridging.

By not being realistic, designers end up adding (and paying) for more insulation with no real added value. And the relative savings are not the same ? The differences in energy at high R-values are not the same differences in energy at low R-values.

Paperwork is quite straightforward too. It requires a few take-offs and looking up U-values/Psi Values, which an energy modeler is mostly already doing. We?ll be releasing some how-to videos in the near future to help folks along. I?ll post to this group when available.

Cheers,

Christian Cianfrone, M.A.Sc., P.Eng., LEED? AP BD+C
Principal, Building Energy Practice Lead
ccianfrone at morrisonhershfield.com

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Suite 310, 4321 Still Creek Drive | Burnaby, BC V5C 6S7
Dir: 604 454 2006 | Cell: 604 376 1315 | Fax: 604 454 0403
morrisonhershfield.com/sustainability

Christian Cianfrone's picture
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Christian,

Pardon me if my understanding is faulty, but skimming through the web pages on the
Morrison-Hershfield web site, the analysis
seems to have been done under steady-state conditions, similar to using HEATING-7 or
THERM, and is returning the effective U-value of the layer. You wrote that "...transient
analysis was done using EnergyPlus' Finite Difference method", but that's yet another
method which is time-consuming and not practical for standard simulations.

It appears the tables from 1365-RP provide only the U-value, which means that the wall
could only be modeled as a "quick" surface, and not as a delayed surface, or else one can
create a monolithic layer with an average specific-heat and density. This is not a big
issue for steel-frame walls that have little thermal mass, but could give misleading
results when modeling heavy concrete blocks or masonry walls.

The approach used in the 1986 LBNL work was somewhat different. There, a 2-D
finite-element program was used to model the wall section in 2-D (not 3-D) under dynamic
conditions by putting triangular pulses of heat on each surface, and then tracking the
thermal response of the surfaces over time (this is the standard way for calculating a
response factor time series). Once that response factor has been derived, it can be used
in the DOE-2 simulations just like any other response factor, which is a very quick and
efficient way to simulate conduction under dynamic conditions, with the only time burden
that needed to set up and generate the 2-D response factors.

Several decades ago, Oak Ridge took another approach where they used another program to
analyze the heat flows (response factors?) of the 2-D layer and replace it by a fictitious
3-layer 1-D wall having the same thermal characteristics and response, but I wasn't sure
whether that made things any more understandable. However, what I liked about both the
LBNL and ORNL approaches are that they were able to model 2-D heat flows in walls
dynamically without slowing down the simulations.

Joe

Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 205A
Moraga CA 94556
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's picture
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Joe,

I think there is some misunderstanding. The point of the research was to more accurately assess heat loss through assemblies that have heat flow paths in 3D as well as heat flow through complex details that are often ignored in typical North American practice of energy modeling for code compliance. The research did not develop accompanying transfer functions for each 3D assembly and/or detail.

The research showed that common practice was to ignore substantial amounts of heat loss ? this is where most of the inaccuracy in energy modeling is when dealing with the envelope. Refining transfer functions, as you say, has been studied in other work ? there was no need to recreate it in 1365-RP or the follow up BETB Guide.

I was also pointing out that for the climate zones for which energy modeling was done to support the 3D thermal modeling, it was shown that thermal mass has negligible energy impact, which further supports the notion that the U-value is of utmost important, and transfer functions can continue to be used as they always have been in energy models.

Hope that helps.

Christian

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