<div dir="ltr">to confirm or confound Norbert's calculations, I ran some hypothetical changes through PHPP. <div><br></div><div>the Current Project calls for 9" of subslab geofoam rated at R-4.2 per inch, and clocks in with a specific space heat demand of 4.75 Btus/SF/year. The house contains 1735 SF of *treated* floor area (which is the actual interior floor area, not including partitions and other unusable areas).</div>
<div><br></div><div>changing to 2" of foam increases the SSHD to 5.90 Btus/SF/year, requiring about 20 additional therms of natural gas to make up the difference. Local cost for the first 45 therms per month runs $0.3853/therm.<br>
<br>doubling down to 4" of foam drops the SSHD to 5.28 Btus/SF/year, saving about 10 therms. <br><br>in summary, PHPP tends to validate Norbert's vivid example.<br><br>the bigger question is of course, does this exercise in itself invalidate the PH requirement to hit the magic 4.75 target? It's worth noting, and perhaps no surprise that the cooling load is higher with the thicker subslab insulation. </div>
<div><br></div><div>This all goes back to my original point, which seems to have gotten lost under some slab, that rules of thumb-- such as, that two, or four, or however many inches of subslab foam is "enough"--only gets us so far, and that if we are to achieve a performance standard, or a means of achieving net zero, or carbon neutral, or whatever measure--some rational system of putting this all in a greater context is necessary.</div>
<div><br></div><div>AA</div><div><br></div><div><br><br>AA</div><div><br></div></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Sat, Aug 24, 2013 at 7:42 AM, Norbert Senf <span dir="ltr"><<a href="mailto:mheat@mha-net.org" target="_blank">mheat@mha-net.org</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Or, you could invest that $1350 in a US 30 yr bond @3.8% instead of styrofoam and get $51.00 per year instead of $4.00.<br>
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-------------previous message-----------------------<u></u>--<div class="im"><br>
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A 5 lb piece of wood burned at 70% efficiency gives about 32,000 BTU. That would cover the slab heat loss for 7 days. For a 5 month heating season, it would need 100 lbs of wood. Doubling the foam thickness to R20 would save about 50 lbs of wood per year. At $240 per cord, that's a saving of about $4.00 per year.<br>
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At $1.50/sq ft for the extra foam (not counting labour), 900 sq ft would cost $1350, for a simple payback of 337 years..........N<br>
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At 05:44 AM 8/24/2013 -0400, you wrote:<br>
</div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="im">
RT <<a href="mailto:archilogic@yahoo.ca" target="_blank">archilogic@yahoo.ca</a>> writes:<br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
... In putting our pants back on frontwards, someone noticed that we had all received tattoos onto our backsides:<br>
<br>
? ? ? ? ? "? q? =? A [ dT ( K/s + hc ) +? ( ? * T^4 ) ]? "<br>
</blockquote></div>
(snip)<br>
</blockquote><div class="HOEnZb"><div class="h5">
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