[Greenbuilding] Slab heat loss calculation

Sun Aug 25 21:57:09 CDT 2013

It sounds like you¹re describing DriCore panels.

On 8/25/13 10:39 PM, "Clarke Olsen" <colsen at fairpoint.net> wrote:

> It sounds like putting 6" of course gravel under the insulation under the slab
> is the most cost effective move, both for reducing the heat transfer, and, if
> nicely leveled and tamped, reducing the thickness of the slab. There is a
> product for basement floors which is a plastic spacer of 1/2" bonded to 1/2"
> of OSB in 2' square pieces, giving a thermal break with the floor.
> Clarke Olsen
> clarkeolsendesign.com <http://clarkeolsendesign.com>
> 373 route 203
> Spencertown, NY 12165
> USA
> 518-392-4640
> colsen at taconic.net
> 
> 
> 
> 
> On Aug 25, 2013, at 3:31 PM, John Salmen wrote:
> 
>> In the same post you are discussing cost but also talking about net zero as a
>> goal.  I think that illustrates the dilemma  how do you establish a
>> Œrational¹ system that covers 2 paradigms (jane Jacobs has an excellent book
>> Œsystems of survival¹ that explores this problem).  Jane argues you can¹t 
>> and when you try you compromise both objectives by bending over backwards it
>> goes sideways (my experiences)
>>  
>> That said I think passivehaus is a good attempt at a standard and it raises
>> challenges that get us thinking. For example 9² of foam is no longer just a
>> thermal insulating material but is a structural material  at that point its
>> thickness is related less to insulation value than structural value.  4 and
>> 6² lends itself easily to eliminating concrete slabs from buildings. Greater
>> thickness and/or density can easily allow us to eliminate concrete footings
>> and retaining walls and we have the technical data and infield applications
>> (geofoam)  to support this usage  eliminating concrete is a huge achievement
>> in reducing energy costs from a building.
>>  
>> Can I do this for a client? I don¹t know  my relationship with a client is
>> in the realm of commerce and the concept and designwork required for such
>> initiatives is in the realm of the environment  two different worlds, two
>> different areas of faith, understanding and codes of conduct.
>>  
>>  
>>  
>>  
>>  
>>  
>> 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.
>> 
>> doubling down to 4" of foam drops the SSHD to 5.28 Btus/SF/year, saving about
>> 10 therms.  
>> 
>> in summary, PHPP tends to validate Norbert's vivid example.
>> 
>> 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.  
>>  
>> 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.
>>  
>> AA
>>  
>> 
>> 
>> AA
>>  
>>  
>> 
>> On Sat, Aug 24, 2013 at 7:42 AM, Norbert Senf <mheat at mha-net.org> wrote:
>> 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.
>> 
>> -------------previous message-------------------------
>> 
>> 
>> 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.
>> 
>> 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
>> 
>> 
>> At 05:44 AM 8/24/2013 -0400, you wrote:
>>> RT <archilogic at yahoo.ca> writes:
>>> ... In putting our pants back on frontwards, someone noticed that we had all
>>> received tattoos onto our backsides:
>>> 
>>> ? ? ? ? ? "? q? =? A [ dT ( K/s + hc ) +? ( ? * T^4 ) ]? "
>>> (snip)
>> 
>> -------------------------------------------
>> Norbert Senf---------- mheat(at)heatkit.com <http://heatkit.com>
>> Masonry Stove Builders
>> 25 Brouse Rd.
>> RR 5, Shawville------- www.heatkit.com <http://www.heatkit.com>
>> Québec J0X 2Y0-------- fax:-----819.647.6082
>> ---------------------- voice:---819.647.5092
>> 
>> 
>> 
>> 
>> 
>> 
>> _______________________________________________
>> Greenbuilding mailing list
>> to Send a Message to the list, use the email address
>> Greenbuilding at bioenergylists.org
>> 
>> to UNSUBSCRIBE or Change your List Settings use the web page
>> http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenerg
>> ylists.org
>> 
>> 
>>  

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/greenbuilding_lists.bioenergylists.org/attachments/20130825/c3f9f64b/attachment.html>