[Greenbuilding] Slab heat loss calculation

[Alan Abrams]

makes me wonder how Prof. Kissock's formula compares with PHPP's formula.
 FWIW, PHPP offers some options for different thermal conductivity values
according to soil types.

On a current project, I had changed the PHPP default (.07 hr ft^2/BTU in)
to .52, a median value for clay-loam--the condition indicated on my soil
map.  that simple change dropped the annual heat demand from 4.75
kBtu's/SF/year down to 4.24 -- a dramatic reduction which would have
otherwise permitted thinner subslab insulation (or some other similar
modification).

but the PHIUS certifier did not accept the change, and insisted on using
the default value.

AA


On Sat, Aug 24, 2013 at 5:44 AM, nick pine <nick at early.com> 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 ) ]? "
>>
>
> How do you estimate slab heat loss?
>
> After lots of finite difference network ground loss calculations Professor
> Kelly Kissock at U Dayton http://academic.udayton.edu/**
> kissock/http/EEB/Energy%**20Efficient%20Buildings_1.htm<http://academic.udayton.edu/kissock/http/EEB/Energy%20Efficient%20Buildings_1.htm>says an A ft^2 slab on US Rf foamboard with Rp vertical perimeter
> insulation down "to the footer" would have an approximate
> A(0.1140/(4+Rf+Rp)+0.8768/(16+**Rp)) Btu/h-F conductance from the room
> air temp to the 4 meter deep ground temp.
>
> For example, a 900 ft^2 slab on R10 foamboard with R15 perimeter
> insulation would have a 900(0.1140/(4+10+15)+0.8768/(**16+15)) = 29
> Btu/h-F conductance from a 65 F room air temp to a 58 F deep ground temp,
> so the room would lose (65-58)29 = 203 Btu/h to the slab.
>
> How much would this change with different perimeter insulation depths?
>
> Nick
>
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-- 
Alan Abrams*
**certified professional building designer, AIBD
certified passive house consultant, PHIUS*
*certified passive house builder, PHIUS**
*Abrams Design Build LLC
*sustainable design for intentional living*
cell     202-437-8583
alan at abramsdesignbuild.com
www.abramsdesignbuild.com
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