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re: is it possible to make your own solar (hot water) collector?
13 jan 2002
david delaney  wrote:

>"bas bekema"  wrote in message

>> i would like to invest time (little money) to make a system that keeps my
>> garage (50 m2) at least frostfree, and perhaps even at a nice
>>temperature.
>
>i believe a hot air system would be more appropriate to warm your garage.
>simpler, cheaper, less maintenance.  a hot air system to keep the garage
>warm on sunny days could be particularly simple if you were willing to let
>your garage get as cold as outside at night.

well, it won't get that cold, given its thermal mass. it may not get
very warm either, since the netherlands have little winter sun.

>consider a cheap plastic sunspace attached to the south wall of the garage,
>with a small opening to the sunspace high in the south wall and several
>openings to the sunspace low in the wall.

sounds like a good start. the garage wall behind the sunspace might be
covered with some sort of dark insulator. 

>a small thermostatically controlled fan would move warm air
>through the small high opening from the sunspace into the garage.

that may not be worth doing. the holes at the top might amount to
5% of the wall area, with another 5% for the bottom holes... 

>if you want to keep the garage from freezing at night, it gets a little more
>complicated and expensive. you will certainly have to put some insulation in
>your garage.

or maybe outside the garage walls, as a way to include their thermal mass
and leave more indoor space.

>you might have a passive plastic-film back-draft damper on the inner
>(garage) side of the fan to interdict a night time thermosyphon
>through the sunspace.

good idea.

>you could consider hanging a ton or two of one-gallon or two-gallon
>plastic jugs of water (about 250 one-gallon jugs per ton) from the
>rafters of the garage (if it's strong enough) with some insulation above
>them.

now that is weird, but it has the advantage that you can control the garage
temp with a slow ceiling fan, and only heat it when it is occupied, saving
stored heat for useful times. i've tried storing heat in cloudy plastic milk 
jugs indoors, out of the sun. i've noticed they tend to develop leaks over
time, especially with any mechanical stress. i've also tried 10'x4" thinwall
pvc sewer pipes tucked between the rafters, replacing the usual crossed
spreaders with horizontal 1x3s under the rafters. a cap on each end and a
#3 rubber stopper in a single 3/4" hole seems to work well. you can put 3
between rafters on 16" centers, storing about 17 lb h20/ft^2. 

>arranged either on the underside of the roof, or in any case as an inverted
>cup the rim of which is below the bottom of the jugs but above the upper
>opening to the sunspace.

a clever way to avoid insulating the whole garage. the resistance to
downward heatflow in air is about r5.5 per inch, ie that kind of still
air is a good insulator...

>you should be able to see many of the jugs when standing at different
>locations in the garage, since the heat transfer from the jugs to the lower
>parts of the garage will be by radiation. the jugs will warm surfaces that
>they can "see"...

the radiation conductance is about 4x0.1714x10^-8(460+70)^3 = r1.
you might reduce this with a horizontal reflective thermal curtain
that pulls across below the pipes on a couple of wires. greenhouses
use these.

>...with appropriate insulation in the walls of the garage, and above
>the jugs, your cars should be significantly warmer in the morning of
>a night after a sunny day.

i've heard that can be bad for car corrosion, with snow and road salt.

nick




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