Hybrid Car – More Fun with Less Gas

Solar Air collectors? Do they work? Buy or make?

register ::  Login Password  :: Lost Password?
Posted by Stuart Gold on October 25, 2004, 6:15 pm
 
: quoted-printable

I have converted my garage to an art studio. After insulating the walls =
and ceiling, I now have to figure out how best to heat the place in the =
winter. I'm located in the foothills of the California
Sierra Mts at about 2200 ft altitude. In the winter, it's in the =
40's-50's during the day and at night mid to high 20's. I'm right on the =
top of a ridge with a solid straight on southern exposure. In fact, I =
already have a 54. KW solar PV system in place ( =
http://www.shadowandlight.com/house/solar3.jpg  ) .

I am have been thinking about using Solar Air heating for the garage / =
Art studio (just behind the PV solar array in the above photo). I've =
researched it a bit and am pondering either buying or building a solar =
air collector. Here are the following questions:

1. Will a Solar collector supply most if not all the heat that I will =
need?

2. Will I save any money if I build versus buy a pre-built one? Looking =
mostly at the cleardome system ( http://www.cleardomesolar.com/  )

3. If I do decide to build, Is Glass or polycarbonate best for the top? =
What are the advantages /disadvantages?

4. For the adsorber plate Tin is much cheaper than copper. What =
materials off the best bang for the buck?

5. Many of the pre-built units have thermo switches that start a fan =
when the air reaches 100 degrees. Is there any place to buy this =
separately if I decide to build?

ANY other information by ANYONE who has done this kind of thing before =
would be VERY MUCH APPRECIATED. ........Thanks in advance.........Stuart

stuart@shadowandlight.com
------=_NextPart_000_002E_01C4BA83.52652920
Content-Type: text/html;
    charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META http-equiv=Content-Type content="text/html; =
charset=iso-8859-1">
<META content="MSHTML 6.00.2800.1476" name=GENERATOR>
<STYLE></STYLE>
</HEAD>
<BODY>
<DIV><FONT face=Arial size=2>I have converted my garage to an art studio. After
insulating the walls and ceiling, I now have to figure out how best to =
heat the
place in the winter. I'm located in the foothills of the California
</FONT></DIV>

<DIV><FONT face=Arial size=2>Sierra Mts at about 2200 ft altitude. In the
winter, it's in the 40's-50's during the day and at night mid to high =
20's. I'm
right on the top of a ridge with a solid straight on southern exposure. =
In fact,
I already have a 54. KW solar PV system in place ( </FONT><A

href="http://www.shadowandlight.com/house/solar3.jpg"><FONT  face=Arial
size=2>http://www.shadowandlight.com/house/solar3.jpg</FONT></A><FONT  face=Arial
size=2>&nbsp;)&nbsp;.</FONT></DIV>

<DIV><FONT face=Arial size=2></FONT>&nbsp;</DIV>
<DIV><FONT face=Arial size=2>I am have been thinking about using Solar Air
heating for the garage / Art studio (just behind the PV solar array in =
the above
photo). I've researched it a bit and am pondering either buying or =
building a
solar air collector. Here are the following questions:</FONT></DIV>

<DIV><FONT face=Arial size=2></FONT>&nbsp;</DIV>
<DIV><FONT face=Arial size=2>1. Will a Solar collector supply most if not all
the heat that I will need?</FONT></DIV>

<DIV><FONT face=Arial size=2></FONT>&nbsp;</DIV>
<DIV><FONT face=Arial size=2>2. Will I save any money if I build versus buy a
pre-built one? Looking mostly at the cleardome system ( <A
href="http://www.cleardomesolar.com/">http://www.cleardomesolar.com/</A=


<DIV><FONT face=Arial size=2></FONT>&nbsp;</DIV>
<DIV><FONT face=Arial size=2>3. If I do decide to build, Is Glass or
polycarbonate best for the top? What are the advantages
/disadvantages?</FONT></DIV>

<DIV><FONT face=Arial size=2></FONT>&nbsp;</DIV>
<DIV><FONT face=Arial size=2>4. For the adsorber plate Tin is much cheaper than
copper. What materials off the best bang for the buck?</FONT></DIV>

<DIV><FONT face=Arial size=2></FONT>&nbsp;</DIV>
<DIV><FONT face=Arial size=2>5. Many of the pre-built units have thermo switches
that start a fan when the air reaches 100 degrees. Is there any place to =
buy
this separately if I decide to build?</FONT></DIV>

<DIV><FONT face=Arial size=2></FONT>&nbsp;</DIV>
<DIV><FONT face=Arial size=2>ANY other information by ANYONE who has done this
kind of thing before would be VERY MUCH APPRECIATED. ........Thanks in

advance.........</FONT><FONT face=Arial size=2>Stuart</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT>&nbsp;</DIV>
<DIV><FONT face=Arial size=2><A
FONT></DIV></BODY></HTML>

------=
Posted by Gary on October 25, 2004, 10:38 pm
 
Stuart Gold wrote:

I have a solar air collector on my garage (see link below) -- it is
fairly large, but has no storage.  Basically on a sunny day, my garage
  starts getting comfortable about an hour after it starts getting
sun.  It is fine for the rest of the day, and a ways into the evening.
  During the nighttime, it normally cools to around 10 F over the
ambient.  On cloudy days, it just depends on how cloudy it is, but if
its pretty cloudy, it does not deliver much heat.  This meets my
requirements just fine, as I can just wait until it comfortable, but
some form of supplementary heat and/or heat storage may be needed if
you want the garage to always be comfortable.

There are some temperature graphs showing inside/outside temperatures
of my garage at the link below.

Your experience might vary from this depending on your climate, how
much collector you install, and insulation levels.

Link for garage collector info: http://users.montanadsl.net/~reysa/
The first pdf is the garage collector, and the 2nd is an idea for
another type of garage collector.


Mine cost $00 to build, or about $ per sqft (at $ per hour for
labor :-))  It took three days to build.


I used corrugated PolyCarbonate ($ per sqft).  I am quite satisfied
with it.  You do need to be careful how you support it (see the link).
I'd try to avoid glass with a high iron content (looks green from the
edge), as it does not transmit as much light.

PolyCarbonate:                   Glass:
Easy to handle, cut...           Harder to handle, cut...
20ish year life when UV treated  Lasts forever (or til broken)
High impact resistance         Low impact resistance
Transmits 90%                    Varies, but 85%(?) is typical
R value about 1                  R value about 1
Max service temp 250F            Very high
Good support reqd                Good support reqd
$ to $.5 per sqft              More


If you use a solid absorber that the air flows behind, I would think
that metal siding or roofing would be a good buy.  The conductivity of
any metal is so high compared to the air film that the heat has to be
transfered through that I doubt you would be able to tell any
difference between copper and and steel or alum (except in your wallet
:-).

For an air collector, an absorber that the air flows through might be
a good choice.  This could be 2 or 3 layers of window screen, expanded
metal lath, or (I have heard) furnace filter media.
I used black metal window screen, and it seems to work fine.


I think that this kind of thermostat is commonly used to control
electric baseboard.  Any hardware store should have them.

The one I built uses only natural convection, and (so far) I am pretty
happy with it.  If I worked in the garage a lot, I might add a ceiling
fan just to keep things stirred up.


Another option would be just to add "a lot" of South wall glazing, and
let the sun shine in and be absorbed.
Nick can probably amplify this (and define what "a lot" might mean),
but a wall of PolyCarbonate glazing would be a more efficient
collector than a wall of air collectors.  If the too much light or
glare is a problem, then shade cloth hung just North of the glazing
would cut the glare and absorb the heat.

Gary



Posted by Stuart Gold on October 26, 2004, 12:32 am
 Great information. Thanks!! I'll look over the pdf's that you linked to. I'm
sure that it'll take me a while to get through them. Regarding the
polycarbonate. Would Twin-Wall Polycarbonate be the best to use or can
single sheet be just as good. I don't want a collector that big on the side
of my building. I was thinking that 4' X 8' would be about the maximum size
that I would want. I guess that maximizing efficiency for me is the name of
the game.
For the absorber, I'll probably go with tin siding




Posted by Gary on October 26, 2004, 2:52 pm
 Stuart Gold wrote:

Hi Stuart,

I think that, other things being equal, the Twin-Wall would perform
somewhat better than single wall.  It does not transmit as much
sunlight (bad), but it cuts heat loss out the glazing from the
absorber by quite a bit (good).

Just from handling some samples of the Twin-Wall, I would guess that
it would need less support (its stiffer), and be somewhat easier to
work with.  If you look at some of the greenhouse plans on the
Internet, you can probably find some good mounting schemes.

 >I don't want a collector that big on the side

Here is a VERY ROUGH cut at what you might achieve with a 32 sqft
collector:

Garage Heat Loss:
Assume the garage is a 25 ft square, and that that overall you
insulated the roof and walls to R19, and the garage door wall to R4,
and ignore the floor loss.

    Qloss = (25*25)/R19 + 25*9*3/R19+25*9/R4)
               = 125 BTU/hr-F

So, for each degree of temperature difference between the outside
temperature and the inside temperature you lose 125 BTU per hour.
You can adjust this up or down depending on the actual size and
insulation levels you used.

Collector Heat Gain:
Assuming 60% solar collector efficiency, and that you are at 40 deg
latitude, with the panel mounted on a South facing wall, on a full sun
day in January:

   At 9am   -- say Toutside = 20F, Tinside = 70F:
    Gain = (170 BTU/hr-ft^2)(32 ft^2)(0.6 efic) = 3300 BTU/hr
         Loss = (125 BTU/hr-F)(70F - 20F) = 6300 BTU/hr

         So, the the solar heater is providing about half of the
         heat being lost by the garage.
         The rest would have to come from your backup heater.

   At 12 noon -- say Toutside = 40F, Tinside = 70F:
    Gain = (260 BTU/hr-ft^2)(32 ft^2)(0.6 efic) = 5000 BTU/hr
         Loss = (125 BTU/hr-F)(70F - 40F) = 3800 BTU/hr

         So, at noon, with more solar gain and less heat loss, the
         collector is providing all the heat loss and a bit more.

   At 3pm  -- say Toutside = 40F, Tinside = 70F:
    Gain = (170 BTU/hr-ft^2)(32 ft^2)(0.6 efic) = 3300 BTU/hr
         Loss = (125 BTU/hr-F)(70F - 40F) = 3800 BTU/hr

         So, by mid-afternoon, the heat loss starts to get larger
         than the heat gain that the solar panel is providing, and
         you would have to start supplying some heat with the
         backup heater.

Overnight, the garage temperature (if not heated) would drop down
toward ambient.  In the morning you would need a big shot of heat from
the backup heater to get the garage temperature up to 70F.  At around
9 am the solar heater would start providing a substantial part of
garage heat loss, and it gets better as the day goes on.

Cloudy days would cut this by a lot.

Obviously, a panel with an efficiency of better than 60% would do a
bit better, but this is not easy to achieve.  The panel area, and how
well you insulated are the two big factors.

So, 32 sqft would do some useful work, but twice that would
be much better.
In the picture, is the South garage wall the one above the PV panels
with the three windows?  If so, the windows will also provide some
useful solar gain.
If they are about 10 ft^2 each, then you have the equivalent of a 2nd
32 ft^2 panel.  They will work much better if you can cut the night
loss with insulating covers.

--
Just to look at this another way:
If those are 100 watt PV panels, the daily output might be about:

    (40 panels)(100 watts/panel)(5hrs peak sun) = 20kwhr/day

For two of the 32 ft^2 solar air collectors, the output might be about:

    (1730BTU/ft^2)(64ft^2)(0.6)
          = 66000 BTU/day   or 66000 BTU/3412BTU/kwhr = 19 kwhr

So, you would be getting (VERY ROUGHLY) the same energy out of a
couple 32 ft^2 solar air collectors as you get out of the PV rig --
not bad!



Once you get a collector design in mind, you might want to post a
description, and get some comments on the likely efficiency.  Getting
the details right can make a lot of difference.

Gary

Posted by Ecnerwal on October 26, 2004, 3:27 pm
 

That's shooting yourself in the foot - available heat starts with
collector area. I find this a rather strange affectation when I look at
the picture, since it's already dominated by the PV panels. A single
panel would look much weirder on that wall than 4 panels arranged so you
have panel-window-panel-window-panel-window-panel. Give them a blue
trim-paint job to match the windows, and set the head-height equal to
the tops of the windows if appearance is a major concern - consistent
window top line is a normal architectural trick. You could try using a
brownish adsorber to better match the siding, but black looks a lot like
a window, since it will be glazed over.

--
Cats, Coffee, Chocolate...vices to live by

This Thread
Bookmark this thread:
 
 
 
 
 
 
  •  
  • Subject
  • Author
  • Date
please rate this thread