Michelle writes from Traverse City, MI:
>... The frame of the structure is an old metal corn crib. It has
>a metal roof and steel mesh walls. There is a rubble foundation
>with a 2 foot rock wall on top, outside the steel mesh, to put
>the straw bales on to keep them out of the snow. The bales can be
>tied to the steel mesh on the inside and with bamboo on the outside...
What protects the bales from rain? You might put Typar between the bales
and the bamboo and polyethylene film between the bales and the mesh.
NREL says 490 Btu/ft^2 of sun (not much) falls on a south wall on
an average 25.4 F December day with a 31.2 max temp and
an average 28.3 daytime temp in Traverse City.
>One idea was to put a deck-like thing at the top, above
>the top bales. This deck would go all the way around and
>would be water-proofed much like a roof...
Good insulation... US R50 or so.
>There will be a frame on the inside and it will be divided into
>two levels w/ 6 foot cielings and a small loft in the top...
... 6' seems low. Would this be a 12' diam x 12' high cylinder
with 339 ft^2 of exterior 2nd floor surface and a 339ft^2/R50
= 6.8 Btu/h-F thermal conductance to outdoors?
>The floor of the second level will be steel mesh to allow airflow.
>It will be used for hanging and drying herbs.
With 96 ft^2 of $2/ft^2 U0.58 Therma Glas Plus twinwall polycarbonate
thermosyphoning solar siding (eg 2 4x12' vertical sheets) with 80% solar
transmission over the south wall and 3/4" of water under the ceiling,
the second level could average about 100 F over an average December day.
It might cool to 38 F after 5 cloudy days in a row:
10 PI=4*ATN(1)
20 TA%.4'24-hour average Dec temp (F)
30 TM1.2'average daily max temp (F)
40 TDAY=(TA+TM)/2'average daytime temp (F)
50 SSUNI0'sun on south wall (Btu/ft^2-day)
60 LDAY=6'solar collection time (hours per day)
70 ASID–'solar siding area (ft^2)
80 TSID=.8'siding solar transmission fraction
90 USID=.58'siding U-value
100 TSUN=TDAY+SSUN*TSID/LDAY/USID'Thevenin sun temp (F)
110 GSUN=ASID*USID'siding conductance (Btu/h-F)
120 GCRIB=6.8'2nd floor crib conductance (Btu/h-F)
130 AC=PI*(12/2)^2'ceiling area (ft^2)
140 GC=1.5*AC'ceiling air-water conductance
150 DW=.75'ceiling water depth (inches)
160 CC=DW/12*62.33*AC'ceiling capacitance (Btu/F)
170 TC=TDAY+(TSUN-TDAY)/(1/GSUN+1/GCRIB)/GCRIB'ceiling charging temp (F)
180 RC=1/GC+1/(GSUN+GCRIB)'ceiling charging resistance (Btu/h-F)
190 RCC=RC*CC'charge time constant (hours)
200 RCD=(1/GC+1/GCRIB)*CC'discharge time constant (hours)
210 NUM=TC+(TA-TC)*EXP(-6/RCC)-TA*EXP(-6/RCC)*EXP(-18/RCD)
220 DEN=1-EXP(-6/RCC)*EXP(-18/RCD)
230 TDC=NUM/DEN'day ceiling temp (F)
240 TDA=TDC+(TC-TDC)/RC/GC'day air temp (F)
250 TNC=TA+(TDC-TA)*EXP(-18/RCD)'night ceiling temp (F)
260 GNC=4*1.714E-09*(TNC+460)^3*AC'night radiation conductance
270 TNA=TA+(TNC-TA)/(1/GNC+1/GCRIB)/GCRIB'night air temp (F)
280 PRINT TDC,TDA,TNC,TNA
290 T5C=TA+(TDC-TA)*EXP(-5*24/RCD)'5-day ceiling temp (F)
300 G5C=4*1.714E-09*(T5C+460)^3*AC'5-day radiation conductance
310 T5A=TA+(T5C-TA)/(1/G5C+1/GCRIB)/GCRIB'5-day air temp (F)
320 PRINT T5C,T5A
average December day
dusk dawn
ceiling air ceiling air
106.6096 112.5513 87.57344 84.42088 F
after 5 cloudy 12.8 F days...
ceiling air
39.08537 38.18356 F
>We'll be building two larger buildings over the next couple
>of summers as well. The first of the larger buildings will be
>a bioshelter for all-season growing, small animal housing, and
>composting. We'd like to try to build it in two sections.
>The first will be the rear shed/animal keeping/composting area
>which will be at the ground level. The side facing the south
>will be part rock for solar gain because it will eventually become
>the back wall of the front greenhouse section. We'd like to set
>the greenhouse section about 4 feet into the ground to increase
>winter insulation and height.
You might heat this building with animals and compost,
using a condensing air-air heat exchanger...
>We'd like to build the third building with strawbale and tires or
>some other natural or recycled materials. It will be set into a hill.
>The lower level will have four small dorm-type units to house
>future interns and volunteers. The second level will have
>a common area/library/kitchen.
... and heat this from below, as in the corn crib. You might cover
an icosahedron made from 25 20' steel pipes with chicken wire, then
newspaper, then welded-wire fence, then an inch or two or concrete,
then a hairnet of old tires tied together with dacron rope and filled
with peat moss, then whitewashed polyethyelene film, then more tires.
How big would it be? How many tires?
> All of this will be off-the-grid with solar and wind and will be
>heated using passive solar techniques and radiant heat using
>a wood boiler or combination of wood and solar hot water.
Wood is work, with particulate pollution. Better to bury the wood
in plastic bags, for less atmospheric CO2.
Nick
>>... We'd like to build the third building with strawbale and tires or
>>some other natural or recycled materials. It will be set into a hill.
>>The lower level will have four small dorm-type units to house
>>future interns and volunteers. The second level will have
>>a common area/library/kitchen.
>... and heat this from below, as in the corn crib. You might cover
>an icosahedron made from 25 20' steel pipes with chicken wire, then
>newspaper, then welded-wire fence, then an inch or two or concrete,
>then a hairnet of old tires tied together with dacron rope and filled
>with peat moss, then whitewashed polyethyelene film, then more tires.
>How big would it be? How many tires?
10 PI=4*ATN(1)'icoscalc
20 L 'strut length (feet)
30 HWALL=L*COS(PI/6)'wall height (feet)
40 ATRI=HWALL*L/2'triangle area (ft^2)
50 ACOVER*ATRI'cover area (ft^2)
60 OD=2*L/2/SIN(2*PI/10)'OD on ground (feet)
70 ID=2*OD/2*COS(2*PI/10)'ID on ground
80 PRINT L,ID,OD
90 HATTIC=SQR(L^2-(OD/2)^2)'attic height (feet)
100 HEIGHT=HWALL+HATTIC'total height (feet)
110 PRINT HWALL,HATTIC,HEIGHT
120 AFLOOR=5*ID/2*L/2'floor area (ft^2)
130 ATOTAL=3*AFLOOR'total floor area (ft^2)
140 PRINT AFLOOR,ATOTAL,ATRI
150 DTIRE=2'tire diam (feet)
160 ATIRE=PI*(DTIRE/2)^2'tire area (ft^2)
170 NTIRES=2*ACOVER/ATIRE/1.09'number of tires
180 PRINT ACOVER,DTIRE,NTIRES
20 27.52764 34.02603
17.32051 10.51463 27.83513
688.191 2064.573 173.2051
2598.076 2 1517.419
PA taxes tires destined for landfills, so tire stores
give $1/tire to people who take them away :-)
Nick
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>a metal roof and steel mesh walls. There is a rubble foundation
>with a 2 foot rock wall on top, outside the steel mesh, to put
>the straw bales on to keep them out of the snow. The bales can be
>tied to the steel mesh on the inside and with bamboo on the outside...