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re: sizing a heating system
15 jun 2000
news  wrote:

>i didn't understand your drawing, even when using
>courier it was unintelligible.

perhaps you are using an unusual terminal, like an asr-33?

>it appears you are promoting the solar closet.

not in my posted response to your question. the heat store in that
sunspace wasn't a solar closet. i've been favoring concentrating
solar attics lately, for some of the reasons you mention...

>i looked at your web site at: http://www.ece.vill.edu/~nick/ and
>had a half decent look at it.

perhaps you should try full-decency :-)

>some initial comments.  let me know if they are inaccurate:

ok.

>secondary heating from occupancy and loss from air changes appears to be
>ignored.

that's accurate, altho they typically don't change the picture much.
all this is capable of indefinite elaboration, but even this simpler
version often gets misunderstood.

>a lot relies on having an average u value of 0.167 and a building net
>heating requirement of 1kw.

no. that's an example, but the paper contains an algorithm to size the
heating system to any particular structure. better insulation makes a
sunspace and solar closet smaller. 

>its not stated how to get the average this low when there is a significant
>amount of glazing...

put most of the glazing on a low-thermal-mass sunspace that can stay
cool overnight and on cloudy days, with an insulated wall between the
sunspace and the living space.
 
>it seems very bright - during the 6 hours of sunlight each square metre
>contributes at an *average* of half a kilowatt! for the uk this appears
>high as a winter average.

the best uk locations are like average us locations.

>i'm not sure why the r value for the glazed part of the closet is 0.1
>(ie u=10).  it would work better with a standard dgu.

i'm not sure what you are talking about here. we suggested a single
layer of glazing over the sunspace and another single layer over the
closet, inside the sunspace, with an air gap and a dark insulated wall
behind that, to make an air heater, and some containers of water behind
that. the sun doesn't shine on the containers, and sunspace air never
enters the closet... 

>i also don't understand how the closet collector is magically transformed
>between the u10 glazing during the day and the u0.25 (ie r4) wall structure
>overnight (i can't see the diagrams - do they help?  some mechanical
>contraption?).

seeing the diagrams might help :-) the insulated closet wall behind
its glazing has a damper at the top and the bottom to let warm air
circulate between the glazing cavity, ie the air heater, and the box
containing the water containers during the day. air circulation stops
at night.
 
>its probably worth revisiting the heat loss and gain calc
>for the store with local conditions.

sure. a concentrating attic might work better where you live.
or storing heat all summer long by dehydrating a lithium chloride
solution and recovering it by hydration with groundwater vapor,
thus cooling the groundwater and warming the house with this
"chemical heat pump." 

>i wonder if there would be a benefit to using a diy solar collector
>with a selective absorber to separate the collection and force the
>hot water from the collectors to the top of the store. 

sure. the concentrating solar attic might be the diy solar collector.
make the steep south roof transparent, and line the parabolic north roof
with aluminiumized mylar (about $1/m^2) to make a solar trough that
bounces sun down into a 1 m wide x 8 m long hydronic collector on the
floor near the north wall. pump the hot water through a big plastic
agricultural tank downstairs in the house. clear sun may only happen
for a few hours a week in cloudy climates, but it can account for
a large fraction of the solar energy received.

>you'd have a lot more flexibility then about how to use it - you might
>be able to run towel rails...

why yes, towel rails...

>uunder floor heating, and heat exchange to preheat domestic hot water.

them too.

>...you need a dump in summer or your store will boil, which would be
>'unfortunate', or have a damper arrangement to close up the closet.

right. god also changes the sun angle. shading, overhangs, vines and 
ventilation can help...

nick




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