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Posted by Jim on August 21, 2007, 5:23 pm
We did a bit recently on storing energy at the phase change of Glauber's
Salt (Sodium sulfate decahydrate) which melts at 90*F and when it cools
releases a tremendous amount of energy as Heat of Fusion as it solidifies.
It is less than $1/lb, and a barrel of it (dry) in a 55 gallon drum with
water circulating around it will be a major component of my new system.
> On Aug 21, 10:31 am, nicksans...@ece.villanova.edu wrote:
>> Laren Corie writes:
>> > The ultimate performance solutions are: 1) Isolate the solar gain
>> > space,
>> > to let it go cold at night. If you eliminate all of the times that the
>> > sun
>> > does not heat the room, you eliminate 100% of the backup heating, so
>> > you
>> > don't need high Rvalue windows...
>>
>> Maybe no windows at all, just plastic film glazing.
>>
>> > 2) Nighttime window insulation. Basically the same strategy, but you
>> > are
>> > closing the insulated door on the glass, instead of the whole room.
>> > There can be problems.. some of them human.
>>
>> Historically, most people tire of moving insulation twice a day. Twice a
>> year
>> seems OK. Or automatically filling a glazing cavity with soap bubble foam
>> at night. My favorite "movable insulation" is a big fan with 2
>> thermostats
>> in an insulated wall between a sunspace and a living space.
>>
>> > 3) Reduce the glazing area considerably, and get your Solar gain, via
>> > simple, low cost wall type air panels, or a single glazed sunspace,
>> > over the south wall.
>>
>> We might rethink how we use spaces. People seldom look out windows at
>> night.
>> They cover black holes with curtains. A living space might only have 1-2%
>> of
>> the floorspace as windows for small views. Picture a core living space
>> behind
>> enclosed porches, or "viewspaces" with lots of glazing for large views.
>> During
>> the day, move into a viewspace and steal some heat or AC from the living
>> space
>> with an occupancy sensor and a thermostat and a fan.
>>
>> A 32x32x8' tall living space with 16'-deep SE and SW viewspaces and
>> a 48'x48' footprint might have 24ft^2 of R4 windows with 6 Btu/h-F. An
>> R40
>> ceiling and R30 walls would add 32x32/40 = 26 and 33, with 30 more for
>> 30 cfm of air leaks, if it's tight, for a total conductance of 95
>> Btu/h-F.
>>
>> With 4 American Craftsman 6068-2 6'x80" U0.48 sliding glass doors ($269
>> each at Home Depot) or 320 ft^2 of R4 windows, a 16'x48' SE viewspace
>> would have a 123 Btu/h-F conductance. Two more doors would give a 16'x32'
>> SW space 61 Btu/h-F. The glazing might have overhangs to reduce summer
>> sun and dark mesh curtains to reduce light levels for people, eg 80%
>> greenhouse shadecloth, which preserves views, like a dark window screen.
>>
>> If the average living space temp is 65 F and we spend 4 hours per day in
>> each 70 F viewspace (Henry Mercer built bonfires on the roof and moved
>> from
>> desk to desk as the sun moved in his 6-story concrete castle in
>> Doylestown
>> PA) on an average 30 F January day in Phila, the house needs 24h(65-30)95
>> + 4h(70-34)123 + 4h(70-34)61 = 79.8K + 17.7K + 8.8K = 106K Btu/day of
>> heat.
>> With 34.1K from 300 kWh/mo of frugal indoor electrical use, we need 72K
>> more solar heat, which might come from a solar attic.
>>
>> The solar attics of Soldiers Grove
>> (seehttp://www.ece.villanova.edu/~nick)
>> can be improved. They blow warm air down into a building during the day,
>> with a motorized damper to let the attic stay cool at night. Some have
>> rock bed or hypocaust stores, but few store heat for more than 1 day.
>>
>> A new attic might have a $1/ft^2 corrugated R1 Dynaglas polycarbonate
>> 20-year south roof with a 60 degree slope and 90% solar transmission.
>> NREL says 620 Btu/ft^2 falls on the ground and 1000 falls on a south wall
>> on an average January day in Phila, so 1 ft^2 of roof would collect
>> 0.9(1000sin(60)+620cos(60)) = 1058 Btu/day.
>>
>> Nathan Hurst's "Low-cost active heat storage" story in the July-September
>> 2007 Issue 100 of ReNew (http:www.ata.org.au) shows how to collect solar
>> heat
>> with a Mazda car radiator and its 16 watt electric fan. (I have a $35
>> 1984
>> Dodge Omni radiator below my living room floor) With an 800 Btu/h-F
>> air-water
>> thermal conductance like MagicAire's 2'x2' SHW2347 duct heat exchanger,
>> we
>> could store 0.75x72K/6h = 9K Btu in 140 F water in 6 hours on an average
>> day
>> with a 140+9K/800 = 151 F attic air temp. A radiator in a box below an
>> attic
>> floor can both store and distribute heat, like this, viewed in a fixed
>> font:
>>
>> upper g
>> attic l
>> | | a
>> | | z
>> ~ ~ i south -->
>> | | n
>> | vertical | motorized / g
>> | duct | damper /
>> | | /
>> | | day /
>> | | /
>> | | /
>> | | / night attic floor
>> ---| -------------............----------------------------------
>> | . r .
>> | . d room a d.
>> | . a air d f a. f
>> | . m out i m.
>> | ==> . p a a ==> p. a <== room air in
>> | . e t e.
>> | . r o n r. n
>> | . r .
>> -------------------------------------
>> | |
>> | duct to |
>> | room floor |
>> | |
>> | |
>> ~ ~
>>
>> To collect heat, open the motorized damper and run the radiator fan.
>> They typically last 3-4K hours at 225 F. If the fan lifetime doubles with
>> every 10 C decrease, it might last 70K hours at 150 F. To distribute
>> heat,
>> close the motorized damper and run the room fan. The passive dampers
>> could
>> be plastic film over hardware cloth, aka "the 7-cent solution" invented
>> by
>> Doug Kelbaugh (now Dean of the UMich Architecture school) in Princeton in
>> 1973. The motorized damper could be polyiso foamboard with an auto
>> windshield
>> wiper motor and limit switches or Honeywell's $50 6161B1000 damper
>> actuator,
>> which only uses 2 watts as it moves up to 45 in-lb. The room air outlet
>> would
>> also have a passive damper that opens out of the page into another
>> vertical
>> duct or closet to move warm air down into the room. The floor might have
>> more
>> motorized dampers over polycarbonate film to bounce light and heat down
>> into
>> rooms during the day.
>>
>> If 1 ft^2 of glazing gains 1058 Btu/day and loses 6h(151-34)1ft^2/R1,
>> the net gain is 356, so we might need 50.4K/356 = 142 ft^2 of glazing.
>> A 4'x48' strip would do. At 140 F, we could make hot water for showers
>> with a $60 1"x300' piece of pressurized black PE pipe in a heat storage
>> tank and a simple graywater heat exchanger (eg 2 uninsulated 55 gallon
>> plastic drums) to add heat to the house.
>>
>> On an average day, with an 800 Btu/h-F radiator conductance, we can heat
>> the living space with 70 + (70-30)95/800 = 75 F water. If the viewspace
>> use patterns don't change on cloudy days, we can store 5x72K = 360K Btu
>> for 5 cloudy days in a row in 360K/(140-75) = 5538 pounds of water, ie
>> 665 gallons, in an STSS tank or a 4'x8'x3'-tall plywood box lined with
>> a single folded 10'x16' piece of EPDM rubber.
>>
>> Nick
>
> Wow, thank you for the posting. Really enjoyed it.
>
> Ken
>
>
> Opportunities are never lost. The other fellow takes those you miss.
>
>
> | Torrey Hills Technologies, LLC |
> | www.threerollmill.com |
> | www.torreyhillstech.com |
>
>
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