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re: vegetable oil fueled central heating
18 oct 2002
john beardmore wrote:
>>the licl would stay inside the box, evaporating some water on an average
>>day and absorbing water vapor on a cloudy day. the phase change stores a
>>lot more heat by volume than warm water, with no loss of heat over time.
>is the phase change evaporation and condensation or dissolving and
>crystalising ?
please read it again. licl can absorb about 10x its weight by volume.
>>glaubers salt gets tired, mechanically. after a few or a few hundred
>>cycles, it stops cycling and needs to be stirred. it also needs a high
>>surface to volume ratio because the crystals that form inwards fro
>>the container wall have a significant thermal resistance.
>
>so is stirring it so hard ? or s to a ratio for that matter ?
people have built "mechanical decoherers" with lots of soft tubes of salts
rolling on wheels, and so on. no more complicated than a sewage treatment
plant in your living room. larger s/v ratios raise packaging costs.
>>arithmetic can be helpful here. a big window with no storage might
>>provide 3 hours of heat
>
>for a south facing room...
sure.
>>if sunny days are like coin flips,
that's one simple distribution... 1/2 of the days are average, with an
average amount of sun. the probability of 2 cloudy days in a row is 1/4,
3 is 1/8, 4 is 1/16, and a 5-day heat store can give 97% solar heating.
>> adding overnight storage might raise this to 50%.
>
>only if you get enough energy in during those three hours. will you ?
yes, if you design a house to keep itself warm on an average day, with
an average amount of sun, eg 3 hours, and the well-insulated higher temp
cloudy day store with a small solar collector doesn't have to provide
any heat at all for the house on an average day.
>> two days could raise it to 75%, and so on...
>
>seems to me that experience suggests that even in spring and autumn,
>solar power won't give you the energy required for heating a typical
>house to the temperatures required by typical occupants.
we need atypical houses :-) airtight, with lots of insulation, heat
storage for 5 cloudy days, and so on.
>what you suggest above may be true if you have enough collector area and
>good enough insulation and you like the idea of vast amounts of licl
>hanging about...
not that vast. try some numbers. the "collectors" might be south windows.
the heat store might be a counter near a south window with a reflective
floor to the south and several layers of glazing on the south side of
the counter.
>is what you're doing any better than the conservatory and concrete
>(thermal mass) approach used by the likes of the hockerton housing
>project ? i think they claim to have no heating systems at all.
i don't know houghton. sounds like old-fashioned mass and glass, ie
"direct loss houses" or "trombe walls." see below. a house with enough
insulation and internal electrical energy usage may need no heating
system at all. then again, maybe they figure a small electric space
heater or gas log isn't "a heating system."
every day is sunny for george and charlotte britton of lafayette hill.
and for vivian vanstory of north philadelphia. vanstory's 1,280-square-
foot house uses 60 percent less energy than a comparably sized dwelling
built to mininum energy-code standards. the britton's 2,900-square-foot
house is blessed with energy bills 20 percent lower than one of comparable
size... the design of the house incorporates "passive" solar principles.
there are large double pane windows and sliding glass doors on the south
side. inside, tile floors and a trombe wall absorb the sun's heat during
the day and radiate it at night... a stone fireplace on the south wall
of the living area provides additional heat during colder months...
britton said... "we have a fire every day of the winter."
sounds like a department store sale, with energy bills that are "20% lower"
and fires every day of the winter. what's the annual fuel bill, including
wood? ases passive solar pioneer steve baer defines a solar house as
"one with no other form of heat..."
nick
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