<div dir="ltr"><p class="MsoNormal">Chris,</p><p class="MsoNormal"><br></p><p class="MsoNormal">DOE2/eQuest doesn't model temperature-dependent R-Values. The technical reason is that DOE2 uses the response factor method for 1-D heat conduction. This is a Laplace Transform method which relies on the theory of residues to numerically solve the heat equation. This method greatly speeds up simulation times compared to direct finite-difference methods, but it relies on the underlying equations being time-invariant and linear. The problem with a temperature dependent R-Value is that it makes the heat equation non-linear. Almost any practical detailed simulation of a whole building is going to use some form of the response factor method for conduction, so this isn't just a limitation to DOE2/eQuest. So to add this capability to the engine would require a fundamental change to the underlying mathematics with a huge penalty in computation time. The best solution might be to aim for some annual average value based on climate data suggested by others.</p><p class="MsoNormal"><br></p><p class="MsoNormal">Aaron<br></p><p class="MsoNormal"><br></p><p class="MsoNormal"><br></p><p class="MsoNormal"><br></p><p class="MsoNormal">One thing one of our suppliers has asked about is
how the R-values get treated in equest, specifically, for foam board
insulation and it opened up some reflection and in-depth thought on how
this might be addressed in equest moving forward.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">I decided to post this more to incite discussion (my knowledge on this is limited).</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">It appears that NRCA has been publishing R-value
testing data separate from the actual NRCA roofing manual as they get
newer data and more accurate data.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">I was emailed a 2016 PDF file called “Insulation
Design Predictability in Alaska” containing testing data and R-value
variations by temperature for different foam board media. If you email
me I can forward it.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">The result - that has been the trend over the last
few years - is that rated R-values have been going down for
polyeurethane board and polyiso board.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">The example for polyisocyanurate from 2014 was
telling. At 75 degF a 2” polyiso board had an average (mean) R-value of
5.55 out of a total of 7 samples.</p>
<p class="MsoNormal">The sampling for the same 2” polyiso at 25 degF had an average R-value of 4.049 (some say the newer data is 3.9).</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">One question is how we might be able to address
this in equest in the future as we push for more accurate
representations of energy usage and energy modeling in equest.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">A published R-value on a cut sheet is not
necessarily the performing R-value of the material in an Alaskan winter
where we can get -40F or -50F for up to a week before warming up to -10
or -20 (sometimes colder). And Alaska is definitely
not alone in this.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">But it doesn’t appear that even NRCA has testing
data for any foam board under a temperature of 25 deg F (which is warm
for Alaska in winter).</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">The question some people have in Alaska is how this
will be addressed in terms of energy efficiency calculations – which,
obviously, isn’t easy to answer.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">There’s a definite bell curve associated with the
testing data that shows a steep dropoff of R-value with temperature –
particularly temps colder than 25F – for both polyeurethane board and
polyiso.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">It would appear that the only way to achieve an
accurate representation in cold climates would be to conduct independent
testing and establish an overall annual average R-value (or at least a
calculated number).</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">But even this would not necessarily be accurate. An
equest model with a single (averaged) input R-value would represent
slightly elevated cooling needed in summer and heating in winter that
would likely be reflected as “too efficient” than
what you would see in reality.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Given the lack of data we ended up going with
cutsheet standard values for our previous model in equest but I,
obviously, now know that 2” polyeurethane board is not necessarily one
R-value or another.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">When we model a wall or roof buildup in equest we
are doing so to represent the thermal performance of the unit throughout
a model year – with the foam being just one piece of the puzzle.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">What isn’t clear is how we might be able to move
forward with more accurate data. Our foam supplier that manufactured
all the material for our LEED project was asking me if there was some
way to address this moving forward. I can’t say…</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">To my knowledge, it still remains to be addressed
since we don’t have a lot of accurate testing data applying to these
materials in places like Climate Zone 8 or 8A here in Alaska.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">So without accurate testing data we really can’t
even calculate the R-value accurately other than to continue the
bell-curve of the current data into the lower temps. But then you would
be seeing a 2” polyiso foam board with R2 when you
get into your below zero temps which is – wow… Something is wrong
here.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">The manufacturer said this was due to the nature of
how the foam changes with temp – specifically, if the cells within the
foam can shrink with cold temps.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">It is even possible that this stressing of the
material over extended periods can cause it to pull in moisture and
moisture-laden air (slight amounts) which could also play a roll in cold
temps. But to what extent this can occur is unknown.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">I’m curious what others have seen or come across or how we might be able to reflect this more accurately in equest.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Thank you!</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Chris Baker<br>
CCI Alliance of Companies</p>
<p class="MsoNormal">Fort Wainwright, AK</p>
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