Posted by nicksanspam on March 14, 2007, 6:09 pm
John M writes:
> I am in the process of planning an energy efficient home
> to be built near Kalispell, Montana...
That's a difficult solar climate. NREL says 310 Btu/ft^2 falls
on the ground and 490 falls on a south wall on an average 22.7 F
December day with a 29.9 max. The average yearly (deep ground
and water) temp is 44.9 F. The WBAN No. 24146 TMY2 hourly weather
data file is useful for simple Kalispell solar house simulations.
>typically featuring super insulation and passive solar orientation...
A square foot of R2 window with 80% solar transmission on an isolated
low-mass sunspace might gain 392 and lose 6h(70-26)1ft^2/R2 = 132 Btu/day,
for a net gain of 260. A more expensive R4 window with 50% transmission
on a living space might gain 245 and lose 24h(65-17.9)1ft^2/R4 = 283, for
a 38 net loss, aka "passive solar gain" :-)
>I am inclined to try an active hot water system that would provide domestic
>hot water during the sunny season
An evacuated tube system could work all year.
>plus would charge an insulated mass under my on grade slab portion
>(60%of the house footprint) after passing through the hot water heat
>exchanger tank. I would pre-temper the cold water supply to the water
>heater/tank by coiling tubing in this warmed foundation mass (sand fill?).
Sand is a poor heat conductor. Adding water helps.
>Windows would be focused primarily to the south, to gain passive
>solar heat in the winter when the sun is out.
They are likely to lose vs gain heat on an average December day.
>I might have about 2000 squ ft on main level, (about 1300 ft slab @grade/
>mass storage area, plus 700+ ft of utility basement area), with 700+ ft
>on second level.
How about a 32' cube with 1 story below grade? :-) With US R-32 walls
and ceiling (eg 8" SIPs), it would have a thermal conductance of about
110 Btu/h-F and need about 24h(65-17.9)110 = 124K Btu/day of heat.
If 68K comes from 600 kWh/mo of indoor electrical use, it needs
an additional 56K.
On an average day, the sunspace could make 56K with T (F) air if 56K
= 768(392-6h(T-26)0.5), ie T = 132 F. Bare collectors in the sunspace
could keep a basement water tank hot, with one or two $0 300'x1"
13-gallon pressurized PE pipe coils in the tank for DHW.
A tank to store heat for 5 cloudy days in a row might have 5x56K
= (130-80)62.33 = 90 ft^3. It might be a 4'x8'x3' tall plywood box
lined with a single folded 10'x14' piece of EPDM rubber.
>The shallow roof area might be worth considering, if we assume most of
>the solar energy will be collected when the sun is higher in the warmer
>seasons.
That requires a much larger tank. November only has 580 Btu of sun
on a south wall on a 31 F average day. October is OK, with 1050 Btu
on a 41.9 F day.
Nick
Posted by Michelle P on March 14, 2007, 6:34 pm
Check with Sunelco they are in Victor, MT.
www.sunelco.com
They will give you an honest answer.
Michelle
nicksanspam@ece.villanova.edu wrote:
> John M writes:
>
>
>>I am in the process of planning an energy efficient home
>>to be built near Kalispell, Montana...
>
>
> That's a difficult solar climate. NREL says 310 Btu/ft^2 falls
> on the ground and 490 falls on a south wall on an average 22.7 F
> December day with a 29.9 max. The average yearly (deep ground
> and water) temp is 44.9 F. The WBAN No. 24146 TMY2 hourly weather
> data file is useful for simple Kalispell solar house simulations.
>
>
>>typically featuring super insulation and passive solar orientation...
>
>
> A square foot of R2 window with 80% solar transmission on an isolated
> low-mass sunspace might gain 392 and lose 6h(70-26)1ft^2/R2 = 132 Btu/day,
> for a net gain of 260. A more expensive R4 window with 50% transmission
> on a living space might gain 245 and lose 24h(65-17.9)1ft^2/R4 = 283, for
> a 38 net loss, aka "passive solar gain" :-)
>
>
>>I am inclined to try an active hot water system that would provide domestic
>>hot water during the sunny season
>
>
> An evacuated tube system could work all year.
>
>
>>plus would charge an insulated mass under my on grade slab portion
>>(60%of the house footprint) after passing through the hot water heat
>>exchanger tank. I would pre-temper the cold water supply to the water
>>heater/tank by coiling tubing in this warmed foundation mass (sand fill?).
>
>
> Sand is a poor heat conductor. Adding water helps.
>
>
>>Windows would be focused primarily to the south, to gain passive
>>solar heat in the winter when the sun is out.
>
>
> They are likely to lose vs gain heat on an average December day.
>
>
>>I might have about 2000 squ ft on main level, (about 1300 ft slab @grade/
>>mass storage area, plus 700+ ft of utility basement area), with 700+ ft
>>on second level.
>
>
> How about a 32' cube with 1 story below grade? :-) With US R-32 walls
> and ceiling (eg 8" SIPs), it would have a thermal conductance of about
> 110 Btu/h-F and need about 24h(65-17.9)110 = 124K Btu/day of heat.
> If 68K comes from 600 kWh/mo of indoor electrical use, it needs
> an additional 56K.
>
> On an average day, the sunspace could make 56K with T (F) air if 56K
> = 768(392-6h(T-26)0.5), ie T = 132 F. Bare collectors in the sunspace
> could keep a basement water tank hot, with one or two $0 300'x1"
> 13-gallon pressurized PE pipe coils in the tank for DHW.
>
> A tank to store heat for 5 cloudy days in a row might have 5x56K
> = (130-80)62.33 = 90 ft^3. It might be a 4'x8'x3' tall plywood box
> lined with a single folded 10'x14' piece of EPDM rubber.
>
>
>>The shallow roof area might be worth considering, if we assume most of
>>the solar energy will be collected when the sun is higher in the warmer
>>seasons.
>
>
> That requires a much larger tank. November only has 580 Btu of sun
> on a south wall on a 31 F average day. October is OK, with 1050 Btu
> on a 41.9 F day.
>
> Nick
>
Posted by Jeff on March 14, 2007, 6:38 pm
nicksanspam@ece.villanova.edu wrote:
> John M writes:
>
>
>>I am in the process of planning an energy efficient home
>>to be built near Kalispell, Montana...
I don't know what happened to the threading on this, or if this is
just originated by Nick.
Doesn't Gary live in Montana? Certainly a visit to
<URL: http://builditsolar.com />, Gary's site, would be in order. In
other words, he's been there and done that!
Jeff
>
>
> That's a difficult solar climate. NREL says 310 Btu/ft^2 falls
> on the ground and 490 falls on a south wall on an average 22.7 F
> December day with a 29.9 max. The average yearly (deep ground
> and water) temp is 44.9 F. The WBAN No. 24146 TMY2 hourly weather
> data file is useful for simple Kalispell solar house simulations.
>
>
>>typically featuring super insulation and passive solar orientation...
>
>
> A square foot of R2 window with 80% solar transmission on an isolated
> low-mass sunspace might gain 392 and lose 6h(70-26)1ft^2/R2 = 132 Btu/day,
> for a net gain of 260. A more expensive R4 window with 50% transmission
> on a living space might gain 245 and lose 24h(65-17.9)1ft^2/R4 = 283, for
> a 38 net loss, aka "passive solar gain" :-)
>
>
>>I am inclined to try an active hot water system that would provide domestic
>>hot water during the sunny season
>
>
> An evacuated tube system could work all year.
>
>
>>plus would charge an insulated mass under my on grade slab portion
>>(60%of the house footprint) after passing through the hot water heat
>>exchanger tank. I would pre-temper the cold water supply to the water
>>heater/tank by coiling tubing in this warmed foundation mass (sand fill?).
>
>
> Sand is a poor heat conductor. Adding water helps.
>
>
>>Windows would be focused primarily to the south, to gain passive
>>solar heat in the winter when the sun is out.
>
>
> They are likely to lose vs gain heat on an average December day.
>
>
>>I might have about 2000 squ ft on main level, (about 1300 ft slab @grade/
>>mass storage area, plus 700+ ft of utility basement area), with 700+ ft
>>on second level.
>
>
> How about a 32' cube with 1 story below grade? :-) With US R-32 walls
> and ceiling (eg 8" SIPs), it would have a thermal conductance of about
> 110 Btu/h-F and need about 24h(65-17.9)110 = 124K Btu/day of heat.
> If 68K comes from 600 kWh/mo of indoor electrical use, it needs
> an additional 56K.
>
> On an average day, the sunspace could make 56K with T (F) air if 56K
> = 768(392-6h(T-26)0.5), ie T = 132 F. Bare collectors in the sunspace
> could keep a basement water tank hot, with one or two $0 300'x1"
> 13-gallon pressurized PE pipe coils in the tank for DHW.
>
> A tank to store heat for 5 cloudy days in a row might have 5x56K
> = (130-80)62.33 = 90 ft^3. It might be a 4'x8'x3' tall plywood box
> lined with a single folded 10'x14' piece of EPDM rubber.
>
>
>>The shallow roof area might be worth considering, if we assume most of
>>the solar energy will be collected when the sun is higher in the warmer
>>seasons.
>
>
> That requires a much larger tank. November only has 580 Btu of sun
> on a south wall on a 31 F average day. October is OK, with 1050 Btu
> on a 41.9 F day.
>
> Nick
>
Posted by Solar Flare on March 15, 2007, 3:31 am
How does an R4 lose twice as many BTU per day as an R2 window? You
used 24 hours for one and 6 hours for the other.
Not sleeping well Nick?...LOL
> A square foot of R2 window with 80% solar transmission on an
> isolated
> low-mass sunspace might gain 392 and lose 6h(70-26)1ft^2/R2 = 132
> Btu/day,
> for a net gain of 260. A more expensive R4 window with 50%
> transmission
> on a living space might gain 245 and lose 24h(65-17.9)1ft^2/R4 =
> 283, for
> a 38 net loss, aka "passive solar gain" :-)
> Nick
>
Posted by nicksanspam on March 15, 2007, 11:08 am
>How does an R4 lose twice as many BTU per day as an R2 window? You
>used 24 hours for one and 6 hours for the other.
Exactly.
>> A square foot of R2 window with 80% solar transmission on an isolated
>> low-mass sunspace might gain 392 and lose 6h(70-26)1ft^2/R2 = 132 Btu/day
>> for a net gain of 260. A more expensive R4 window with 50% transmission
>> on a living space might gain 245 and lose 24h(65-17.9)1ft^2/R4 = 283,
>> for a 38 net loss, aka "passive solar gain" :-)
US DOE passive solar guidelines suggest using windows with
a min 60% solar transmission and max U0.35. How well would
they work on a Kalispell sunspace and living space?
Nick
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> to be built near Kalispell, Montana...