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Solar Heater Success!

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Posted by dpadavona on October 3, 2005, 6:22 pm
 
I credit the links and posts in this usenet group for giving me the
knowledge to design a solar heater.  I don't have any building
experience, but after a few days of trial and error I was able to
create a working heater.

The design is based somewhat on the jrwhipple thermosyphon plans, with
some of Bill Kreamer's tips thrown in.  For instance I am using black
polyester felt for the collector.

The unit was made with 1/4" treated plywood, 1" foil topped insulation,
and extra tough plexiglass.  The heater is 3 feet x 6 feet and leans at
a slight angle against the south side of my house.

The interface with the house was the most difficult design aspect for
me.  I didn't feel comfortable cutting holes in my house, and I didn't
want to take away a south facing window either.  I had a helluva time
trying to fit the unit into the window using the jrwhipple plans.
Finally I settled on using a 1/2" thick piece of treated plywood, cut 6
inches high and with a width which matched my window frame.  I made 2
4" holes in the window interface, and another 2 4" holes in the top of
the solar heater.  I connected them using foil covered flexible venting
(like you might use for a drying machine).

I considered driving it with a CFM fan, but they seemed too expensive
to be cost effective.  Instead I took a small desktop style fan
(overkill but much cheaper) and directed it into one vent toward the
heater.  This forces air from my home into the solar heater, where it
is quickly heated and returned through the other vent.  Before using
the fan I was able to tap temps around 125F.  After using the fan I
could tap temps 20F hotter.

The results - It is currently 75 degrees outside at 1:30 pm.  I measure
a temperature of 145 degrees at the vents leading into the house!  Note
this is not the temperature inside the unit (which is even hotter) but
rather the temperature actually available to heat the house with, at
the vent.  Not that I need the heat today, but I noted I raised the
downstairs temperature 2 degrees in roughly 10 minutes.

The only thing left to do is to seal the gaps with some silicon
sealant.  I also want to insulate the venting and the plywood window
interface.

A few questions have arisen post completion, as I intend to build a
couple smaller units for the 2nd floor windows:

1.  Does anyone have tips for getting the plexiglass to stay flush
against the plywood?  I used RTV but the glass buckled slightly under
the heat.  I tried small screws but it still buckled.  No big deal, but
it does create some gap inefficiencies where the glass buckles slightly
off the plywood.

2.  From a cost perspective, is it better to go with a CFM fan anyhow?
The small desktop unit is doing the job so far.

3.  I am using treated plywood.  However should I take any steps to
make it weather resistant so it lasts a long time?

Certainly others could design a much more efficient unit.  But I am
thrilled to have completed this project.  Thanks to everyone again!


Posted by Solar Flare on October 3, 2005, 11:07 pm
 
Plastic products have a hude temperature expansion coefficient!

a. Get some slotted mounting track. Maybe a trim from a vinyl siding supply
or a thin piece of wood capped with a larger piece of trim to hold the clear
piece in a slot allowing expansion. The plastic pane can only be fastened at
one corner or spot only.

b. Use a router to make a lowered ridge into your frame and place the pane
there with mirror clips or a capping wood trim on top without holding the
edges of the pane tightly.

c. Take your box apart and route a slot near the top edge, reassemnble and
slide the pane into it.

I credit the links and posts in this usenet group for giving me the
knowledge to design a solar heater.  I don't have any building
experience, but after a few days of trial and error I was able to
create a working heater.

The design is based somewhat on the jrwhipple thermosyphon plans, with
some of Bill Kreamer's tips thrown in.  For instance I am using black
polyester felt for the collector.

The unit was made with 1/4" treated plywood, 1" foil topped insulation,
and extra tough plexiglass.  The heater is 3 feet x 6 feet and leans at
a slight angle against the south side of my house.

The interface with the house was the most difficult design aspect for
me.  I didn't feel comfortable cutting holes in my house, and I didn't
want to take away a south facing window either.  I had a helluva time
trying to fit the unit into the window using the jrwhipple plans.
Finally I settled on using a 1/2" thick piece of treated plywood, cut 6
inches high and with a width which matched my window frame.  I made 2
4" holes in the window interface, and another 2 4" holes in the top of
the solar heater.  I connected them using foil covered flexible venting
(like you might use for a drying machine).

I considered driving it with a CFM fan, but they seemed too expensive
to be cost effective.  Instead I took a small desktop style fan
(overkill but much cheaper) and directed it into one vent toward the
heater.  This forces air from my home into the solar heater, where it
is quickly heated and returned through the other vent.  Before using
the fan I was able to tap temps around 125F.  After using the fan I
could tap temps 20F hotter.

The results - It is currently 75 degrees outside at 1:30 pm.  I measure
a temperature of 145 degrees at the vents leading into the house!  Note
this is not the temperature inside the unit (which is even hotter) but
rather the temperature actually available to heat the house with, at
the vent.  Not that I need the heat today, but I noted I raised the
downstairs temperature 2 degrees in roughly 10 minutes.

The only thing left to do is to seal the gaps with some silicon
sealant.  I also want to insulate the venting and the plywood window
interface.

A few questions have arisen post completion, as I intend to build a
couple smaller units for the 2nd floor windows:

1.  Does anyone have tips for getting the plexiglass to stay flush
against the plywood?  I used RTV but the glass buckled slightly under
the heat.  I tried small screws but it still buckled.  No big deal, but
it does create some gap inefficiencies where the glass buckles slightly
off the plywood.

2.  From a cost perspective, is it better to go with a CFM fan anyhow?
The small desktop unit is doing the job so far.

3.  I am using treated plywood.  However should I take any steps to
make it weather resistant so it lasts a long time?

Certainly others could design a much more efficient unit.  But I am
thrilled to have completed this project.  Thanks to everyone again!



Posted by Philip Lewis on October 4, 2005, 5:36 pm
 dpadavona@yahoo.com writes:

hmmm... I wouldn't have thought the thermal release from the felt
would be high enough for effective transfer.


So, I thought the good thing about glass was that it reflected the IR
back into the unit.  Will plexi do the same, or are you going under
the assumption that as long as there is *any* free heat, it's a plus?

I've been thinking on this a little (see my post from last week) and
depending on answers, I might just go with the following design:

one of the leaning window designs from
http://www.builditsolar.com/Projects/SpaceHeating/Space_Heating.htm  
with the following cross section:

    1: Clear Shrink Plastic (or mostly transparent stuff)
    2: air gap (Sealed, insulative layer)
    3: plastic
    4: air gap (warm air out)
    5: black poly cloth
    6: air gap (warm air out)
    7: insualtion (foil backed foam/fiberglass or just polystyrean?)
    8: air gap (cool air intake)
    9: Insulation (bottom and sides)

What insualtion type in layer 7 would be better?
I suppose i could eliminate layers 2-5, and use foil insualtion painted
flat black for simplicity.  Would extra layers be worth it?

For layer 1 and 3, do i want to go with "clear" poly tarp (some milkyness)
or absolutely clear?  Clear obviously has less reflective benefits, so
might get more thermal gain...and the heat shrink would make for an
attractive surface. OTOH, The tarp, I have on hand... and it would
be less expensive.

Any thoughts?

--
be safe.
flip
Ich habe keine Ahnung was das bedeutet, oder vielleicht doch?
Remove origin of the word spam from address to reply (leave "+")



Posted by nicksanspam on October 5, 2005, 12:27 pm
 

Will air thermosyphon efficiently through polyester felt?

With no fan, will it melt?
 
Nick


Posted by dpadavona on October 5, 2005, 9:54 pm
 Nick,

So far the results are encouraging.  The temperatures at the entrance
to the house are 145F on a sunny day, and the temperatures in the unit
are too high for my digital thermometer to measure apparently.  After a
week the materials look fine.

I am hooking up a muffin fan tomorrow to help boost the airflow from
the heater into the house (and vice-versa).


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