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re: drum wall thermal storage questions.......................
13 apr 2002
offgridman@cs.com  wrote:

>i have heard that earth tubes have problems in the south with algae and 
>odors from growths within the tubes. we are on the gulf coast and i was 
>considering using them. we live in a moisture laden soil area on a 
>river. i think that i may still use them but use a air to air exchanger 
>to provide a barrier from the living area to the earth tube air flow.
>what do you think?

a heat exchanger could isolate growths, but this raises the cost, and the
benefit seems low to begin with. consider tallahassee, with a 67.2 f yearly
average (ground) temp and average 81.3 f air temp and w = 0.0171 in aug...
67.2 f air at 100% rh has pa = exp(17.863-9621/(460+67.2)) = 0.680 "hg and
humidity ratio w = 0.62198/(29.921/pa -1) = 0.0145, so earth tubes could
dehumidify, but the air in the house would still be very damp, 100% rh at
67.2, 91% at 70 f, and 100xexp(17.863-9621/(460+80)) = 65% at 80 f. and the
heat of dehumidification could rapidly warm the soil around the tubes in
an open system. 

sounds like you need less fresh air flow and more dehumidification.

>i have  a 24x24 living space with 10 ft walls and 6/12 pitch roof of 
>galv metal. (no attic) i thought of using a air channel from the eaves 
>to a ridge vent box that had screened openings on the gable ends to 
>provide a natural draft vent from the eaves to the gables.  the walls 
>are stained rbb pine 5/8inch, 3.5 inch insul (r11) in a 3.5inch cavity 
>finished with 1x6 tg pine.

you might remove all this and replace it with 7 8'x24'x12" r48 sips and
install an efficient ac or a solar-powered licl system that also makes hot
water. with no fresh air and no windows or doors or electrical energy use
inside the house, and a thermal conductance of 7x8'x24'/r48 = 28 btu/h-f,
you could keep it 70 f indoors for 24 hours per day with 24h(81.3-70)28
= 7594 btu/day, eg 7594/3142/3 = 0.74 kwh/day of air-conditioning with 
a cop of 3, ie 22 kwh/month worth $2.20/month at 10 cents/kwh.

nick




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