Improvised root cellar? Any ideas?

[Nick Pine]

We could go a long way further with food-self sufficiency if
we had a root cellar...

Right. First estimate the number of freezing and melting degree days.
NREL says Allentown's average temp is 26.6 in January, with an average
daily low of 18.8, so T(t) = 26.6+(26.6-18.8)sin(2Pit/24), which hits
32 F when t = 12/Pisin^-1((32-26.6)/(26.6-18.8)) = 2.92 hours, so the
number of melting degree hours in an average day is 2X the integral of
T-32 from 2.92 to 6 (peak temp time), ie 2(-7.8x12/Picos(Pit/12)-5.4t)
= 9.74 MDh/d or 12.6 MDD in January. Here's a complete list:

10 PI=3D4*ATN(1)
20 DATA 18.8,26.6,31,20.9,29.3,28,29.9,39.4,31,38.8,49.7,30
30 DATA 49.3,60.3,31,58.8,69.4,30,63.6,74.1,31,62.0,72.2,31
40 DATA 54.2,64.7,30,42.5,53.2,31,34.2,43.1,31,24.4,31.8,31
50 FOR M=3D1 TO 12'months of year
60 READ TMIN,TAVG,NDM'min temp, avg temp (F), days/month
70 IF TMIN>32 THEN FDH=3D0:MDH=3D24*(TAVG-32):GOTO 140'no freezing
80 ARG=3D(32-TAVG)/(TAVG-TMIN)
90 T32=3D12/PI*ATN(ARG/SQR(-ARG*ARG+1))'time temp reaches 32 F
100 FDH=3D(32-TAVG)*(6+T32)
110 FDH=3D2*(FDH+(TAVG-TMIN)*12/PI*COS(PI*T32/12))
120 MDH=3D(TAVG-32)*(6-T32)'melting degree hours per day
130 MDH=3D2*(MDH+(TAVG-TMIN)*12/PI*COS(PI*T32/12))
140 FDDM=3DNDM*FDH/24'freezing degree days per month
150 MDDM=3DNDM*MDH/24'melting degree days per month
160 PRINT M,FDDM,MDDM
170 FDD=3DFDD+FDDM'freezing degree days per year
180 MDD=3DMDD+MDDM'melting degree days per year
190 NEXT M
210 PRINT "Yearly F/MDD",FDD,MDD

month freezing DD melting DD

1 179.986 12.58596
2 116.5683 40.96831
3 9.290816 238.6909
4 0 531
5 0 877.3
6 0 1122
7 0 1305.1
8 0 1246.2
9 0 980.9999
10 0 657.2
11 0 344.1
12 76.14696 69.94694

Yearly F/MDD 381.9921 7426.092

The garage contains LOTS of storage space, but food in
it would freeze too. We had two nights of -26F temperature
last winter, and many many nights of -0F temperature.

You may be colder than Allentown, with a -12 F 30-year record min...

The money we can spend is EXTREMELY limited. We could
probably manage a couple of hundred dollars, but that's all.
A couple of hundred dollars would buy a couple of hours of
back-hoe plus operator work, but water runs through the
ground (our neighbors are building an extension to their
house, and they've been pumping and pumping and pumping).

Above-ground sounds better. You might make an 8' cube with R50 strawbale
walls and ceiling or a larger domed structure like a celtic burial mound
with lots of bags of leaves under plastic film under a hex tire "hair net."
Building with tires is nice in PA, since people will pay you about $1 each
to take them away.

Part of the inside space might be an "ice closet" that's open above to
make a "cold trap" for outdoor air. The 8' strawbale cube has about
6x8'x8'/R50 = 7.7 Btu/h-F of thermal conductance, and 144 Btu will melt
a pound of ice, so we need P pounds of ice, where 144P = 24hx7426x7.7,
so P = 9530 pounds or 149 ft^3. With 382 FDD and A ft^2 of air-water heat
transfer surface, 24x382x1.5A = 9530x144, so A = 100 ft^2 (not much.)

The ice closet might be 4' wide x 8' long x 8' tall, with 2x4 posts on
2'x4' centers like this (viewed from one end in a fixed font):

up
2' 2'
---------------
|. .| | The water/ice might live in 30" poly film ducts on
|. duct.| duct | 5' wide droopy-trough welded-wire fencing shelves
| . . | | with an approximate 4/3x2x1 = 2.67 ft^2 cross section
----------------- (approximating the catenary with a parabola.) This
| | | would hold 8x2.67x8x64 = 10920 pounds of ice with
| duct | duct | about 8x6.65x8 = 426 ft^2 of surface, leaving
| | | 4x8x8' of space for food storage at about
----------------- 8' 32 F, all year.
| | |
| duct | duct | We need some insulation between the ice closet and
| | | the food to avoid freezing. With an R2 8'x8' wall,
----------------- we have something like this at noon in July:
| | | Tf
| duct | duct | 32 F ---www---*---www--- 84.5 F
| | | 1/32 1/7.7
-----------------------------------
I = (84.5-32)/(1/32+1/7.7) = 326 Btu/h, so

Tf = 32+326/32 = 42 F.

In very cold times, some water containers under (wood pallets?) under
the food might freeze before the food does, or we might put enough extra
water in the closet to avoid freezing it all during the coldest winters.

Nick

 

[Pat Meadows]

Right. First estimate the number of freezing and melting degree days.
NREL says Allentown's average temp is 26.6 in January, ..

You may be colder than Allentown, with a -12 F 30-year record min...

Right, our climate is nothing whatsoever like Allentown's.
We had -26 F twice last winter, and many nights of -20 F or
thereabouts. Average temperature for January here is
something like 16F (I forget exactly).

If you're trying to picture our climate, you'd do better to
think 'Buffalo, NY with less snow' than to think
'Allentown'. Or think: Adirondacks. Or Rochester, NY.

In very cold times, some water containers under (wood pallets?) under
the food might freeze before the food does, or we might put enough extra
water in the closet to avoid freezing it all during the coldest winters.

Thanks, Nick. I've 'locked' your posting so it won't delete
and will give it some thought.

Pat