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re: freeze proofing -was-re: straw bale construction
29 sep 1998
andygroz   wrote:
>jeff ganaposki wrote:

>> they had 5 foot dia. kalwall tubes filled with water & fish...
>> their water filled tubes never dipped lower than 40's even
>> though the ambient air was below freezing. they did apply
>> insulating covers at night...

automatic systems can be nice...

>> they also placed water filled kalwall tubes inside their greenhouse...
>> the thermal mass did prevent large swings in temperature.

adding lots of thermal mass to a sunspace makes it a fairly constant 
cool to lukewarmish temperature in the winter, which may be fine for
plants, but doesn't make good living space or a good heat source for
an attached house. low thermal mass in a greenhouse means it can heat
up and provide useful heat for an attached house during the day, and
then it can get cold quickly at night, losing little heat from the
sunspace to the outdoors through its low thermal resistance glazing. 

> large swings in temps is exactly what i want to avoid...

in a living space, yes, but maybe that's not so important in a sunspace
or greenhouse with hardy plants.

a plastic film greenhouse might help make a "frost-protected warm
foundation" for an attached house by raising the temperature of the soil
near the inboard house foundation to the point where it never freezes.
the greenhouse might be 8' deep, so frost has to travel 8' through the
ground horizontally from south to north in order to reach the house
foundation, even though the ground freezes where the greenhouse glazing
touches the ground... that edge of the greenhouse might frost-heave
a few inches with no damage. suppose the lower horizontal member is
bolted through the treads of some inboard used tires full of dirt that
rest on the ground on 4' centers, as a "soft foundation..."

this might also be done with the non-south house walls. suppose the
house were cantilevered with a foundation 4' or 8' inside hanging walls
with soft lower edges. something like a 6" epdm rubber u with some sand
in the bottom, or plastic film walls held to the ground with tires full
of dirt, with a few feet of plastic film lying flat on the outdoor ground
with some gravel on top of that to make an air seal and keep that ground
warmer and dryer. i guess this needs some rodent protection as well, 
some hardware cloth, or a few holes to welcome rodents and cats, or cows. 
the space between the film and the house might be a nice place to store
lawn mowers or bags of leaves.

>thermal mass will most likely be water-filled 55 gal barrels,
>as they are cheap and easy to deal with...

i like smaller containers like milk jugs or 4-gallon hard plastic tubs
with higher surface to volume ratios for thermal mass heated by solar-
warmed air, vs thermal mass in the sun. thermal mass exposed to the sun
during the day can lose lots of heat through the solar glazing at night. 

>anyone know of a good inexpensive source for temperature controlled
>shutter openers/closers that don't use power?

leslie-locke makes an 8x8x16" automatic foundation vent with a spiral
bimetallic spring that opens aluminum louvers when the air temp rises.
you can adjust the (soft) temperature threshold where this occurs by
adjusting the spring with a screwdriver, or take the spring out and
turn it around to make them open when air temp falls. home depot sells
them for about $12 each.

jade mountain (jade-mtn@indra.com) sells "heat motors" to open greenhouse
sashes on temperature rise. they are filled with some sort of wax.

solar collectors used an older simpler product to prevent stagnation
damage: a bimetallic strip about 2" wide x 6" long with a rubber disk 
on the end that lifted up to open a hole. are these still being made?

nick




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