[Greenbuilding] Slab heat loss calculation

[Norbert Senf]

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 ) ]? "
>
>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 
>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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-------------------------------------------
Norbert Senf---------- mheat(at)heatkit.com
Masonry Stove Builders
25 Brouse Rd.
RR 5, Shawville------- www.heatkit.com
Québec J0X 2Y0-------- fax:-----819.647.6082
---------------------- voice:---819.647.5092