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re: store cold from winter for summers and visa-versa?
22 may 1997
john willoughby wrote:
>could you store the cold from winter (some large underground insulated tank)
>and use it to cool in the summer, while at the same time using another
>resovoir to do just the opposite; store summer heat to heat in the winter.
there's a book by (john?) hait, called _passive annual heat storage_...
why store solar heat for 6 months, outside of arctic zones, when the sun
shines a lot more often than that?
your question is fascinating. it sounds like such a nice simple system. no
solar collectors, fireplaces, heat pumps, air conditioners, etc. just store
temperature peaks and valleys over a year, using something analogous to an
electronic diode peak picker. or maybe offset and "attenuate the weather,"
using something like a 2 pole integrator with a 180 degree phase shift at
a frequency of one year :-) an rcrc sandwich wall?
recall those two brothers who built a house with 13 million pounds of rocks,
as described in mother earth news. it would have had an rc time constant of
over a year if covered outside with 3" of foam. it would not have had
_perfect_ temperature control, with no way to lose heat from the inside
when it's warmer outdoors, but it would have been quite comfortable, with
very small temperature swings. making two heat reservoirs is more complicated
than making one, but it allows making hot water all year, and perhaps
refrigeration, and maybe some kind of skutterite thermoelectric or stirling
engine to make the miniscule electrical power needed in tomorrow's energy-
efficient house.
electronic circuits work better in "push-pull" configurations like cmos. the
solar houses of norman saunders have very accurate temperature control because
they have a "cool store" as well the "warm store" found in most solar houses.
the cool store (some rocks in the basement) is cooler than the living space,
and the warm store (some sealed containers of water in the attic) is warmer,
so the house temperature can be controlled exactly by bringing cool air up
from the basement or warm air down from the attic, using 2 fans and a 2'x2'
airshaft, regardless of weather. two stiff heat sources, norman might say.
(his pe is in electrical engineering.) he says a properly-designed solar house
is as likely to need cooling as heating in any season.
the cool store only needs to be a bit cooler than 70 f for house cooling.
norman uses the earth for a cool store, with some rocks for an air-earth heat
exchanger. dampening the earth under the rocks, with a vapor barrier, might
increase the downward heat conduction of very dry ground. year round ice is
more trouble to make, and not needed for house cooling in most parts of the
us. it might make an expensive refrigerator. a good freezer is 0 f, hard to
make with outdoor air and ice. sun on a surface can raise its temperature
a lot more than night sky radiation can lower it.
a warm store might be combined with an on-site sewage treatment system, and
a cold store might also be a fridge or rainwater cistern. it might have
a freezer inside.
>what would be a suitable storage medium? rocks? water?
water stores about 3 times more heat than rock by volume...
>how big a storage volume would be needed?
big, for ice, especially if it's does more than keep itself cool. (what would
you do about condensation in ice house insulation, especially underground?
seems like the tiniest pinhole would relentlessly make insulation soggy.
hot water may need a smaller volume, if sunshine happens more often than
freezing air, or if heat is stored as the absence of water, at about 1,000
btu/lb, in an uninsulated mostly empty tank of lithium chloride solution,
concentrated in summer, and diluted by absorbing water which evaporates from
a dampened basement floor in the winter, with a vapor barrier to avoid radon.
some people might build combination warmstore/icehouses, say outdoor 16x16x8'
tall structures near houses, with shallow roofponds covered with 2 layers of
greenhouse poly film with the upper one inflated. they might have r40 walls.
here's a phila tmy2 simulation for a box containing 11 tons of hot water and
21 tons of ice:
10 apond=256'pond area (ft^2)
20 lwt=14'length of water tank (ft)
30 wwt=4'width of water tank (ft)
40 dwt=6'depth of water tank (ft)
50 awt=2*(lit+wit)*dit+2*lit*wit'water tank sides, top and bottom area (ft^2)
60 rwat=40'us r-value of water tank sides, top and bottom
70 watcond=awt/40'thermal conductance of water tank (btu/h-f)
80 vwat=lwt*wwt*dwt'volume of water tank
90 wwat=64*vwat'approx weight of water tank
100 tw=50'initial water temperature (f)
110 lit=14'length of ice tank (ft)
120 wit=8'width of ice tank (ft)
130 dit=6'depth of ice tank (ft)
140 ait=2*(lit+wit)*dit+2*lit*wit'area of ice tank sides, top and bottom (ft^2)
150 rice=40'us r-value of ice tank sides, top and bottom
160 icecond=ait/40'thermal conductance of ice tank (btu/h-f)
170 vice=lit*wit*dit'volume of ice tank
180 wice=64*vice'approx weight of ice tank
190 pice=.8*wice'initial ice weight
200 boltz=1.74e-09'stefan-boltzman constant
210 ftemp4=(460+32)^4'abs. freezing temp (r) to the 4th power
220 open "tmycool" for input as #1
240 for h=1 to 8760'one line of weather data per hour, for a typical year
250 line input#1, s$'input a line from tmy2 file
260 day=val(mid$(s$,1,4))'day of year (1-365)
270 globm=val(mid$(s$,10,4))'global horizontal radiation (wh/m^2)
280 globe=globm*3.41/10.76'global horizontal radiation (btu/hr-ft^2)
290 temp=val(mid$(s$,27,4))'ambient temp (f)
300 atemp4=(temp+460-10)^4'abs sky temp? (r) to the 4th power
310 if temp > 32 goto 350
320 'make ice
330 heatflow=apond*boltz*(ftemp4-atemp4)'heat removed from water
340 if pice < wice, then pice=pice+heatflow/144'total pounds of ice
350 'heat water?
360 sunin=apond*globe*.9'amount of sun that falls on pond
370 heatflow = sunin - apond*boltz*((tw+460)^4-atemp4)'net heatflow into pond
380 if heatflow > 0 and tw < 212 then tw = tw + heatflow/wwat'heat water
390 heatflow = (tw-temp)*watcond'heatflow from water tank to ambient
400 tw=tw-heatflow/wwat'cool water
410 if temp < 32 goto 440
420 heatflow = (temp-32)*icecond'heatflow from ambient to ice tank
430 if pice > 0 then pice = pice - heatflow/144'melt ice
440 if h mod 672 <>0 goto 480'report about once a month
450 pcice=int(100*pice/wice+.5)
460 twr=int(tw+.5)
470 print day,temp,twr,pcice
480 next h
490 close 1
day of midnight hot water per cent
year temp (f) temp (f) ice
28 24 107 100
56 36 142 100
84 49 174 99
112 58 201 98
140 60 212 94
168 61 212 90
196 68 212 84
224 68 212 78
252 69 212 73
280 66 212 68
308 63 212 66
336 45 212 69
364 26 212 80
nick
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