Building a DIY solar heater for the garage

[D.M. Procida]

There's no heating in the garage, but there is damp.

On the other hand, it does have a nice large south-facing roof, so I
want to have a go a building a solar heater.

I have in mind a wooden frame, containing a long folded tube behind a
double-glazing panel and backed with a reflective surface.

The tube would be a long series of aluminium drinks cans, painted matt
black.

The will have ducts to the garage; one to draw cold air out of it, and
the other to bring warm air from the heater back in.

A small solar-powered fan would draw air through the tube.

I've found several descriptions of such projects, and their success.

Using air rather than water seems much simpler than trying to make a
system that uses water to transfer the heat, while using empty drinks
cans for the tube would help keep weight down.

Daniele

[NT]

On Nov 19, 10:15 am, real-not-anti-spam-addr...@apple-juice.co.uk

I think the gold standard for air heaters is 3 layers of black
shadecloth fixed in its frame at an angle like so:

air in at bottom, out at top. Glazing is on the right. Unheated income
air touches the glazing, heated air never does.
: = shadecloth

. ______
. :||
. || : ||
. || : ||
. || : ||
. _:____||


NT

[David WE Roberts]

"D.M. Procida" <real-not-anti...@apple-juice.co.uk> wrote in
message
news:1kaz59f.1a03sgkic99fkN%real-not-anti...@apple-juice.co.uk...

I assume that, given that hot air rises, you will have a strong enough fan
to drive the hot air down to floor level before exiting the ducts?
I would be interesed to know which bits you use to achieve this, as I have a
south facing roof on the shed and could use some 'free 'heating in the
winter.

Cheers

Dave R
--
No plan survives contact with the enemy.
[Not even bunny]

Helmuth von Moltke the Elder

(\__/)
(='.'=)
(")_(")

[D.M. Procida]

NT <meow...@care2.com> wrote:

> I think the gold standard for air heaters is 3 layers of black
> shadecloth fixed in its frame at an angle like so:
>
> air in at bottom, out at top. Glazing is on the right. Unheated income
> air touches the glazing, heated air never does.
> : = shadecloth
>
> . ______
> . :||
> . || : ||
> . || : ||
> . || : ||
> . _:____||

That - also:

<http://wiki.diyfaq.org.uk/index.php?title=Solar_Thermal#Space_heating>

looks a lot simpler than the kind of thing I was looking at (e.g.:

<http://hackedgadgets.com/2011/11/16/solar-pop-can-heater-system-build-r
oundup/>

It's not clear to me what advantage one system would have over the other
in terms of effectiveness.

Daniele

[D.M. Procida]

David WE Roberts <nos...@btinternet.com> wrote:

> > I have in mind a wooden frame, containing a long folded tube behind a
> > double-glazing panel and backed with a reflective surface.
> >
> > The tube would be a long series of aluminium drinks cans, painted matt
> > black.
> >
> > The will have ducts to the garage; one to draw cold air out of it, and
> > the other to bring warm air from the heater back in.
> >
> > A small solar-powered fan would draw air through the tube.
>

> I assume that, given that hot air rises, you will have a strong enough fan
> to drive the hot air down to floor level before exiting the ducts?

How powerful would a fan need to be?

Daniele

[Frederick Williams]

"D.M. Procida" wrote:
>
> There's no heating in the garage, but there is damp.
>
> On the other hand, it does have a nice large south-facing roof, so I
> want to have a go a building a solar heater.
>

> [...]

I know nothing about these things, so this may be a silly suggestion,
but why not make a big double glazed window in your south-facing roof so
that the sun comes in and does all the work in situ, so to speak?

--
When a true genius appears in the world, you may know him by
this sign, that the dunces are all in confederacy against him.
Jonathan Swift: Thoughts on Various Subjects, Moral and Diverting

[NT]

On Nov 19, 12:28 pm, real-not-anti-spam-addr...@apple-juice.co.uk
(D.M. Procida) wrote:

With the shadecloth collector, heated air never comes in contact with
the glazing. This much reduces glazing heat loss. With cans, heated
air is generated on both sides of the can. The hot air outside the can
meets the glazing, and heat loss occurs.

Hot surfaces radiate heat away. Black drink cans simply radiate this
back out (their silver interior doesnt). Shadecloth reradiates in both
directions, and the multiple layers mean that a lot of the reradiation
is blocked from existing the collector.

The shade cloth collector allows free flow of air, so if mounted on a
wall, no fan is needed. Parallel strings of cans arent quite as good
in this respect, and a bit more fan power is needed when roof
mounting.

Finally the cloth collector is far lses work to make.


NT

[NT]

On Nov 19, 12:39 pm, Frederick Williams

<freddywilli...@btinternet.com> wrote:
> "D.M. Procida" wrote:
>
> > There's no heating in the garage, but there is damp.
>
> > On the other hand, it does have a nice large south-facing roof, so I
> > want to have a go a building a solar heater.
>
> > [...]
>
> I know nothing about these things, so this may be a silly suggestion,
> but why not make a big double glazed window in your south-facing roof so
> that the sun comes in and does all the work in situ, so to speak?

That would work as well if you added a good insulating shutter and
could control it automatically.


NT

[D.M. Procida]

I'd need some kind of fan anyway, as this thing will be mounted on the
roof of the garage.

What exactly is shade cloth? I have some dark blue blackout blind
material hanging round - would that do?

How does the air filter through the shade cloth? There's a version here:

<http://www.builditsolar.com/Experimental/AirColTesting/ScreenCollector/
Building.htm>

that uses aluminium mesh rather than cloth.

> Finally the cloth collector is far lses work to make.

Yes, certainly.

Many designs seen to use nothing more than corrugated PVC rather than
double-glazing, which seems like an odd choice when large double-glazed
panels can be had for nothing if you look in the right skip.

Daniele

[NT]

On Nov 19, 4:38 pm, real-not-anti-spam-addr...@apple-juice.co.uk (D.M.

not at all, shade cloth is like netting

> How does the air filter through the shade cloth? There's a version here:
>
> <http://www.builditsolar.com/Experimental/AirColTesting/ScreenCollector/
> Building.htm>
>
> that uses aluminium mesh rather than cloth.
>
> > Finally the cloth collector is far lses work to make.
>
> Yes, certainly.
>
> Many designs seen to use nothing more than corrugated PVC rather than
> double-glazing, which seems like an odd choice when large double-glazed
> panels can be had for nothing if you look in the right skip.
>
> Daniele

True in Britain, not true in saner countries.


NT

[NT]

On Nov 19, 12:34 pm, real-not-anti-spam-addr...@apple-juice.co.uk

I dont know. If I had to guess it would be around 10w as a starting
point. Underrunning a more powerful fan reduces noise and prolongs
bearing life.


NT

[NT]

On Nov 19, 10:15 am, real-not-anti-spam-addr...@apple-juice.co.uk
(D.M. Procida) wrote:

You can increase both output and efficiency with an external
reflector. If its a single storey garage attached to a 2+ storey
house, putting the collector as near to the house as possible means
you can add a reflector on the house wall, and capture more light &
heat in the collector.


NT

[David WE Roberts]

"D.M. Procida" <real-not-anti...@apple-juice.co.uk> wrote in
message

news:1kazc6q.1m2t2xv10uwk9bN%real-not-anti...@apple-juice.co.uk...

I was hoping you could tell me ;-)

Firstly it would depend on the volume of your garage.

{Someone throw me a mathematician and/or engineer quickly}

If your garage is at 5C and the air in your heating array is at 35C then you
have a 30C temperature difference.
If you want your garage to be a nice pleasant 20C then you have to replace
half the volume of your garage with warmed air to achieve this - but quickly
enough to compensate for the heat loss through the structure.
Hmmm.....half the volume of your garage every 30 minutes to allow you to get
up to temperature in 30 minutes (which does not seem an unreasonable taget)?
So work the volume of your garage out in cubic feet, halve it, divide by 30
and you know how many cubic feet per minute you have to shift.
This specifies your fan(s).
These specify your solar panel.
You would have to allow a bit more push because you are having to push warm
air downwards whereas I think most extractor fans expect to be pushing air
horizontally.
The hotter your heat exchanger gets, the less volume you should have to
exchange.
e.g. get your heat exchanger to 65C and you only need to exchange 25% of the
garage volume of air.

Someone who has already done this or at least the calculations should be
along shortly (I hope).

[fred]

In article
<1kaz59f.1a03sgkic99fkN%real-not-anti...@apple-juice.co.uk>,
D.M. Procida <real-not-anti...@apple-juice.co.uk> writes

It might be nice to add some thermal mass to the system so that heat
collected during the day could released at night when condensation is
more likely. Using water as a medium with an insulated cylinder for
thermal storage might provide that for you. Circulation by convection.
--
fred
it's a ba-na-na . . . .

[NT]

On Nov 19, 6:21 pm, "David WE Roberts" <nos...@btinternet.com> wrote:
> "D.M. Procida" <real-not-anti-spam-addr...@apple-juice.co.uk> wrote in
> messagenews:1kazc6q.1m2t2xv10uwk9bN%real-not-anti...@apple-juice.co.uk...

If you pick a higher power than strictly needed, then the system will
be more useful on days where less temp rise is achieved


NT

[NT]

On Nov 19, 6:25 pm, fred <n...@for.mail> wrote:
> In article
> <1kaz59f.1a03sgkic99fkN%real-not-anti-spam-addr...@apple-juice.co.uk>,
> D.M. Procida <real-not-anti-spam-addr...@apple-juice.co.uk> writes

>
> >There's no heating in the garage, but there is damp.
>
> >On the other hand, it does have a nice large south-facing roof, so I
> >want to have a go a building a solar heater.
>
> >I have in mind a wooden frame, containing a long folded tube behind a
> >double-glazing panel and backed with a reflective surface.
>
> >The tube would be a long series of aluminium drinks cans, painted matt
> >black.
>
> >The will have ducts to the garage; one to draw cold air out of it, and
> >the other to bring warm air from the heater back in.
>
> >A small solar-powered fan would draw air through the tube.
>
> >I've found several descriptions of such projects, and their success.
>
> >Using air rather than water seems much simpler than trying to make a
> >system that uses water to transfer the heat, while using empty drinks
> >cans for the tube would help keep weight down.
>
> It might be nice to add some thermal mass to the system so that heat
> collected during the day could released at night when condensation is
> more likely. Using water as a medium with an insulated cylinder for
> thermal storage might provide that for you. Circulation by convection.

Yes. But thats a costly way to do it.
You also cant have circulation by convection when the heat source is
on the roof.


NT

[D.M. Procida]

NT <meow...@care2.com> wrote:

> > > > > I think the gold standard for air heaters is 3 layers of black
> > > > > shadecloth fixed in its frame at an angle like so:
> >
> > > > > air in at bottom, out at top. Glazing is on the right. Unheated income
> > > > > air touches the glazing, heated air never does.
> > > > > : = shadecloth
> >
> > > > > . ______
> > > > > . :||
> > > > > . || : ||
> > > > > . || : ||
> > > > > . || : ||
> > > > > . _:____||
> >

> > What exactly is shade cloth? I have some dark blue blackout blind
> > material hanging round - would that do?
>
> not at all, shade cloth is like netting

OK, I think I understand this better now. As air rises through the
system, it has less opportunity to lose heat by conduction with the
cooler glazing at the front.

I don't think this is going to work for me though, because the only
place I can mount it is on a sloping garage roof - I haven't a suitable
vertical south-facing surface to mount it on.

I think something like this might work though (you have to imagine this
rotated 30 degrees anti-clockwise, because it's on a sloping roof):

Sunlight
| | | |
| | | |
| | | |
| | | |

|==============================| <-- double-glazing panel
| | <-- air space
|------------------------------| <-- clear plastic sheet
===: > :: > :: air flow > :: > ::=== <-- layers of wire mesh
|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~| <-- reflective layer
|''''''''''''''''''''''''''''''| <-- insulation


The air enters at the lower (left) end, passing over the layers of wire
mesh. There shouldn't be too much loss by conduction, because the
double-glazing panel, the air space and the plastic sheet should create
a decent insulation system.

The wire mesh will inevitably radiate some of the heat it collects back
into space, but less will be lost because it's in layers.

Daniele

[David WE Roberts]

"NT" <meow...@care2.com> wrote in message
news:676f9a31-2198-42c2...@p5g2000vbm.googlegroups.com...

*Yes. But thats a costly way to do it.
*You also cant have circulation by convection when the heat source is
*on the roof.


For some values of can't - if the heat exchanger is on the lower 2/3 of the
roof and the water tank is in the top 1/3 then there will be limited gravity
circulation.
However you are then potentially looking at a strange hot water tank - a
long thin cyclinder?
Not the easiest and simplest way of doing things, and you also have to worry
about freezing during long periods of no sunshine.
However an electric water pump driven by a solar panel could be an
alternative to the electric air pump to give a pumped hot water system with
all the components more or less level with each other.
I think this is how some solar water heating systems work.
Of course you would also need a pump to circulate the stored heat - and what
is going to power that?

[Nick Odell]

On Sun, 20 Nov 2011 10:55:30 -0000, "David WE Roberts"
<nos...@btinternet.com> wrote:

<snip>

>Of course you would also need a pump to circulate the stored heat - and what
>is going to power that?

Stirling engine?

Nick

[David WE Roberts]

"D.M. Procida" <real-not-anti...@apple-juice.co.uk> wrote in
message

news:1kazbva.1yup81u1drj7a8N%real-not-anti...@apple-juice.co.uk...

Just realised that I might have 90% of the components of a heating system
lying around.
My shed (uk.d-i-y passim) faces north, and the rear south facing wall is
close to a fence.
Just checked, and the top third of the wall is in sunlight at the moment,
and we are quite near the winter solstice (a month?).
So it looks as though I have potential sunlight throughout the winter.
Now I have two sheets of corrugated plastic lying around and lots of bits of
potentially useful wood.
So perhaps I could construct a frame out of battens and run the two sheets
of plastic horizontally along the wall.
Paint the wall black, drill some holes through the wall top and bottom, and
I have a heat exchanger which will heat the top of my shed under the
insulation and hopefully circulate the air by drawing in colder air at
shoulder height and pushing it out at head height.

First cut gives warm head and cold feet, but does increase the overall
temperature of the inside of the shed.
Main issue - long and thin heat exchanger so a lot of holes at bottom and
top to ensure good air flow.
Would fewer larger holes be better, perhaps offset to get a diagonal flow?

Main question - how deep should the wood frame be?
Less volume of air should heat quicker and flow faster, I would think.

Second cut could include a deeper frame and shadecloth.

Third cut could include a solar powered fan.
[I do have a lot of small panels of garden solar lights - wonder if these
could be recovered?]
Better to push cold air up, or pull warm air through or down?

If I wasn't overloaded with 101 things to do I might rush out and experiment
:-)

Other issue - how to stop it overheating in the summer when the last thing
you want is hot air circulating in your nice cool shed.

Cheers

Dave R

[Nick Odell]

On Sun, 20 Nov 2011 12:36:59 -0000, "David WE Roberts"
<nos...@btinternet.com> wrote:

<snip>

>Other issue - how to stop it overheating in the summer when the last thing
>you want is hot air circulating in your nice cool shed.
>

I'd been thinking about a water-based garage solar heating system and
come to the conclusion that overheating in the summer was the big
problem. But this circulating air idea looks as if it has legs. Surely
all you need to do to stop overheating in summer is to close the vents
into the garage whilst opening vents into the unit so all the unwanted
heat can escape. What would be really k3wl though would be to use all
that waste heat to drive a refrigerator/air conditioner.

Nick

[NT]

On Nov 20, 12:15 am, real-not-anti-spam-addr...@apple-juice.co.uk
(D.M. Procida) wrote:

> NT <meow2...@care2.com> wrote:
> > > > > > I think the gold standard for air heaters is 3 layers of black
> > > > > > shadecloth fixed in its frame at an angle like so:
>
> > > > > > air in at bottom, out at top. Glazing is on the right. Unheated income
> > > > > > air touches the glazing, heated air never does.
> > > > > > : = shadecloth
>
> > > > > > .  ______
> > > > > > .       :||
> > > > > > . ||   : ||
> > > > > > . ||  :  ||
> > > > > > . || :   ||
> > > > > > .  _:____||
>
> > > What exactly is shade cloth? I have some dark blue blackout blind
> > > material hanging round - would that do?
>
> > not at all, shade cloth is like netting
>
> OK, I think I understand this better now. As air rises through the
> system, it has less opportunity to lose heat by conduction with the
> cooler glazing at the front.
>
> I don't think this is going to work for me though, because the only
> place I can mount it is on a sloping garage roof - I haven't a suitable
> vertical south-facing surface to mount it on.

I dont see that causing any problem, it just means you'll need a fan,
plus a thermostat, or better a garage thermostat plus a diffrential
stat.

> I think something like this might work though (you have to imagine this
> rotated 30 degrees anti-clockwise, because it's on a sloping roof):
>
>                  Sunlight
>         |       |       |       |
>         |       |       |       |
>         |       |       |       |
>         |       |       |       |
>
>      |==============================| <-- double-glazing panel
>      |                               | <-- air space
>      |------------------------------| <-- clear plastic sheet
>    ===: > :: > :: air flow > :: > ::=== <-- layers of wire mesh
>      |~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~| <-- reflective layer
>      |''''''''''''''''''''''''''''''| <-- insulation

So you've added a 3rd layer of glazing - good in winter if it can cope
with stagnation temp in summer, which with triple glazing will be
punishingly high. And that means more expensive insulation & frame.

You've added a reflector, but I think a black surface would be better
there

And if I understand correctly, you've decided to not angle the cloth,
or in this case metal mesh. That means you dont get the benefit of
keeping the hotter air off the glazing.

> The air enters at the lower (left) end, passing over the layers of wire
> mesh. There shouldn't be too much loss by conduction, because the
> double-glazing panel, the air space and the plastic sheet should create
> a decent insulation system.
>
> The wire mesh will inevitably radiate some of the heat it collects back
> into space, but less will be lost because it's in layers.
>
> Daniele

NT

[NT]

On Nov 20, 4:13 pm, Nick Odell

I wonder how well it would work to simplify it further. Simply replace
some of the siding with the plastic sheet, matt the inside face of it,
and hang a silvered plastic film curtain inside. Open curtain for
heat, close it for cool.


NT

[harry]

On Nov 19, 12:39 pm, Frederick Williams
<freddywilli...@btinternet.com> wrote:

There is a net heat loss through all roof mounted windows. ie it lets
more out than it gains. Unless ther is a shutter, closed at night and
on bad days.

[harry]

On Nov 19, 12:22 pm, "David WE Roberts" <nos...@btinternet.com> wrote:
> "D.M. Procida" <real-not-anti-spam-addr...@apple-juice.co.uk> wrote in

> messagenews:1kaz59f.1a03sgkic99fkN%real-not-anti...@apple-juice.co.uk...

> (")_(")- Hide quoted text -
>
> - Show quoted text -

I have several solar devices.
They all work very well in Summer but poorly in Winter when you need
space heating.
The further problem is that heat stores don't work well enough to be
useful.

[D.M. Procida]

NT <meow...@care2.com> wrote:

> > I don't think this is going to work for me though, because the only
> > place I can mount it is on a sloping garage roof - I haven't a suitable
> > vertical south-facing surface to mount it on.
>
> I dont see that causing any problem, it just means you'll need a fan,
> plus a thermostat, or better a garage thermostat plus a diffrential
> stat.

I meant, it's why I think the angled cloth won't work for me. Because
this box is more horizontal, as soon as any air warms up it will rise -
towards the glazing above it. I don't see how a wire or cloth mesh will
prevent that.

Basically, as soon as the angled mesh layer is the wrong side of
vertical, any warm air will be rising through it towards the glazing.

> > I think something like this might work though (you have to imagine this
> > rotated 30 degrees anti-clockwise, because it's on a sloping roof):
> >
> > Sunlight
> > | | | |
> > | | | |
> > | | | |
> > | | | |
> >
> > |==============================| <-- double-glazing panel
> > | | <-- air space
> > |------------------------------| <-- clear plastic sheet
> > ===: > :: > :: air flow > :: > ::=== <-- layers of wire mesh
> > |~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~| <-- reflective layer
> > |''''''''''''''''''''''''''''''| <-- insulation
>
>
> So you've added a 3rd layer of glazing - good in winter if it can cope
> with stagnation temp in summer, which with triple glazing will be
> punishingly high. And that means more expensive insulation & frame.

What's the significance of a stagnation temperature?

> You've added a reflector, but I think a black surface would be better
> there

I want to bounce heat back into the mesh/air flow.

Daniele

[NT]

On Nov 20, 9:51 pm, real-not-anti-spam-addr...@apple-juice.co.uk (D.M.
Procida) wrote:

> NT <meow2...@care2.com> wrote:
> > > I don't think this is going to work for me though, because the only
> > > place I can mount it is on a sloping garage roof - I haven't a suitable
> > > vertical south-facing surface to mount it on.
>
> > I dont see that causing any problem, it just means you'll need a fan,
> > plus a thermostat, or better a garage thermostat plus a diffrential
> > stat.
>
> I meant, it's why I think the angled cloth won't work for me. Because
> this box is more horizontal, as soon as any air warms up it will rise -
> towards the glazing above it. I don't see how a wire or cloth mesh will
> prevent that.
>
> Basically, as soon as the angled mesh layer is the wrong side of
> vertical, any warm air will be rising through it towards the glazing.

The fan means air will be blown through the collector 100x as fast as
it could ever rise, so not a problem.

> > > I think something like this might work though (you have to imagine this
> > > rotated 30 degrees anti-clockwise, because it's on a sloping roof):
>
> > >                  Sunlight
> > >         |       |       |       |
> > >         |       |       |       |
> > >         |       |       |       |
> > >         |       |       |       |
>
> > >      |==============================| <-- double-glazing panel
> > >      |                               | <-- air space
> > >      |------------------------------| <-- clear plastic sheet
> > >    ===: > :: > :: air flow > :: > ::=== <-- layers of wire mesh
> > >      |~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~| <-- reflective layer
> > >      |''''''''''''''''''''''''''''''| <-- insulation
>
> > So you've added a 3rd layer of glazing - good in winter if it can cope
> > with stagnation temp in summer, which with triple glazing will be
> > punishingly high. And that means more expensive insulation & frame.
>
> What's the significance of a stagnation temperature?

The collector has to survive the stagntion temp on a hot 95F day when
youre not running the fan. With triple glazing thats going to be
wickedly high, and probably rules out the use of wood or polystyrene.

> > You've added a reflector, but I think a black surface would be better
> > there
>
> I want to bounce heat back into the mesh/air flow.

Well, you'd be better off not doing so.

> Daniele


NT

[The Other Mike]

On Sat, 19 Nov 2011 10:15:20 +0000,
real-not-anti...@apple-juice.co.uk (D.M. Procida) wrote:

>There's no heating in the garage, but there is damp.
>
>On the other hand, it does have a nice large south-facing roof, so I
>want to have a go a building a solar heater.
>
>I have in mind a wooden frame, containing a long folded tube behind a
>double-glazing panel and backed with a reflective surface.
>
>The tube would be a long series of aluminium drinks cans, painted matt
>black.
>
>The will have ducts to the garage; one to draw cold air out of it, and
>the other to bring warm air from the heater back in.
>
>A small solar-powered fan would draw air through the tube.
>
>I've found several descriptions of such projects, and their success.
>
>Using air rather than water seems much simpler than trying to make a
>system that uses water to transfer the heat, while using empty drinks
>cans for the tube would help keep weight down.

http://www.iedu.com/Solar/Panels/

No connection etc


--

[D.M. Procida]

NT <meow...@care2.com> wrote:

> > Basically, as soon as the angled mesh layer is the wrong side of
> > vertical, any warm air will be rising through it towards the glazing.
>
> The fan means air will be blown through the collector 100x as fast as
> it could ever rise, so not a problem.

I haven't understood how, in my scheme, mounting the mesh at an angle
will make any difference.

> > > > I think something like this might work though (you have to imagine this
> > > > rotated 30 degrees anti-clockwise, because it's on a sloping roof):
> >
> > > > Sunlight
> > > > | | | |
> > > > | | | |
> > > > | | | |
> > > > | | | |
> >
> > > > |==============================| <-- double-glazing panel
> > > > | | <-- air space
> > > > |------------------------------| <-- clear plastic sheet
> > > > ===: > :: > :: air flow > :: > ::=== <-- layers of wire mesh
> > > > |~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~| <-- reflective layer
> > > > |''''''''''''''''''''''''''''''| <-- insulation
> >
> > > So you've added a 3rd layer of glazing - good in winter if it can cope
> > > with stagnation temp in summer, which with triple glazing will be
> > > punishingly high. And that means more expensive insulation & frame.
> >
> > What's the significance of a stagnation temperature?
>
> The collector has to survive the stagntion temp on a hot 95F day when
> youre not running the fan. With triple glazing thats going to be
> wickedly high, and probably rules out the use of wood or polystyrene.

I think it needs some of those expanding-wax-controlled louvres that
up-market greenhouses have.

> > > You've added a reflector, but I think a black surface would be better
> > > there
> >
> > I want to bounce heat back into the mesh/air flow.
>
> Well, you'd be better off not doing so.

Because?

Daniele

[harry]

On Nov 21, 12:13 pm, The Other Mike

> --- Hide quoted text -

>
> - Show quoted text -

Or even.
http://www.designbuilder.co.uk/programhelp/trombe_walls.htm

[js.b1]

On Nov 20, 4:13 pm, Nick Odell
<gurzhfvp.jbexf...@ntlworld.com.invalid> wrote:

> What would be really k3wl though would be to use all
> that waste heat to drive a refrigerator/air conditioner.

Wickes have a combo heat pump / air con / dehumidifier 830x450x450 on
offer at £189 currently. It is a mobile unit, needs an 'ole in a wall
etc. Just a benchmark costs against.

You may need quite a bit of insulation - Dec-2010 whilst exceptional
was a long period of crystal clear nights allowing temperatures to
drop away severely. Anything with water in will need protecting
against such scenarios and insulation to keep inside what solar energy
did fall. There was a lot of daytime solar energy in that period to
harvest too.

[NT]

On Nov 21, 5:23 pm, real-not-anti-spam-addr...@apple-juice.co.uk (D.M.
Procida) wrote:

> NT <meow2...@care2.com> wrote:
> > > Basically, as soon as the angled mesh layer is the wrong side of
> > > vertical, any warm air will be rising through it towards the glazing.
>
> > The fan means air will be blown through the collector 100x as fast as
> > it could ever rise, so not a problem.
>
> I haven't understood how, in my scheme, mounting the mesh at an angle
> will make any difference.

Ah. I'll try and ascii it clearly.

. _______
. :|
. | : |
. | : |
. | : |
. | : |
. |: |
. _______|

Notice how the cloth goes from corner to corner. All the air goes
through the cloth, not just past it. And the slight pressure
differential across teh cloth keeps t he 2 volumes of air separate,
unheated and heated.

If the air merely goes past the cloth, its less effective at cooling
the cloth, which then radiates more heat out. Also the hot air reaches
the glazing, and more is conducted out.

> > > > > I think something like this might work though (you have to imagine this
> > > > > rotated 30 degrees anti-clockwise, because it's on a sloping roof):
>
> > > > >                  Sunlight
> > > > >         |       |       |       |
> > > > >         |       |       |       |
> > > > >         |       |       |       |
> > > > >         |       |       |       |
>
> > > > >      |==============================| <-- double-glazing panel
> > > > >      |                               | <-- air space
> > > > >      |------------------------------| <-- clear plastic sheet
> > > > >    ===: > :: > :: air flow > :: > ::=== <-- layers of wire mesh
> > > > >      |~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~| <-- reflective layer
> > > > >      |''''''''''''''''''''''''''''''| <-- insulation
>
> > > > So you've added a 3rd layer of glazing - good in winter if it can cope
> > > > with stagnation temp in summer, which with triple glazing will be
> > > > punishingly high. And that means more expensive insulation & frame.
>
> > > What's the significance of a stagnation temperature?
>
> > The collector has to survive the stagntion temp on a hot 95F day when
> > youre not running the fan. With triple glazing thats going to be
> > wickedly high, and probably rules out the use of wood or polystyrene.
>
> I think it needs some of those expanding-wax-controlled louvres that
> up-market greenhouses have.

I presume there are cheaper temp control options

> > > > You've added a reflector, but I think a black surface would be better
> > > > there
>
> > > I want to bounce heat back into the mesh/air flow.
>
> > Well, you'd be better off not doing so.
>
> Because?
>
> Daniele

its better to keep the heat on the hot side of the cloth, where it
wont lose heat. If you reflect the light back, some will get reflected
right out.


NT

[D.M. Procida]

NT <meow...@care2.com> wrote:

> On Nov 21, 5:23 pm, real-not-anti-spam-addr...@apple-juice.co.uk (D.M.
> Procida) wrote:
> > NT <meow2...@care2.com> wrote:
> > > > Basically, as soon as the angled mesh layer is the wrong side of
> > > > vertical, any warm air will be rising through it towards the glazing.
> >
> > > The fan means air will be blown through the collector 100x as fast as
> > > it could ever rise, so not a problem.
> >
> > I haven't understood how, in my scheme, mounting the mesh at an angle
> > will make any difference.
>
> Ah. I'll try and ascii it clearly.
>
> . _______
> . :|
> . | : |
> . | : |
> . | : |
> . | : |
> . |: |
> . _______|
>
> Notice how the cloth goes from corner to corner. All the air goes
> through the cloth, not just past it.

OK, I get it - the top layer of mesh will be hottest, so we especially
want the air to travel through this top layer in particular (but through
the others too).

A concertina folded mesh might work too to achieve some of this:

air flow ---> /\/\/\/\/\/\/\ --->

but would be hard to make.

Thanks for the explanation.

Daniele

[Martin Brown]

Before you invest too heavily in a complex solar powered winter heating
system for your garage you might want to look out of the window and
count the number of decent sunny days in a UK winter.

Since you want this to be nearly optimum for the winter months it needs
to be south facing and at 60-70 degrees to the horizontal to try and
catch as much winter sun as possible. This will also help a bit with the
summer stagnation overheating problem. On the roof at a typical pitched
roof angle it will be optimised for the summer sun track.

--
Regards,
Martin Brown

[D.M. Procida]

NT <meow...@care2.com> wrote:

> Ah. I'll try and ascii it clearly.
>
> . _______
> . :|
> . | : |
> . | : |
> . | : |
> . | : |
> . |: |
> . _______|
>
> Notice how the cloth goes from corner to corner. All the air goes
> through the cloth, not just past it. And the slight pressure
> differential across teh cloth keeps t he 2 volumes of air separate,
> unheated and heated.
>
> If the air merely goes past the cloth, its less effective at cooling
> the cloth, which then radiates more heat out. Also the hot air reaches
> the glazing, and more is conducted out.

I have obtained my double-glazing panels, so I am going to start
experimenting this weekend.

I'm wondering whether layers of shade-cloth or layers of metal mesh
would be better as the collector for the system. Metal, I feel, would do
a better job, with more thermal mass.

Also, I think that I should aim to get as much air moving through the
collector as possible - in which case, perhaps instead of a single
collector running corner to corner I'd do better with two or more in
series, each arranged so that the air must be drawn through them.

Daniele

[NT]

On Dec 3, 9:22 am, real-not-anti-spam-addr...@apple-juice.co.uk (D.M.
Procida) wrote:

Thermal mass in the collector is of no use to you. I didnt understand
the 2nd bit.


NT

[D.M. Procida]

NT <meow...@care2.com> wrote:

> > I'm wondering whether layers of shade-cloth or layers of metal mesh
> > would be better as the collector for the system. Metal, I feel, would do
> > a better job, with more thermal mass.
> >
> > Also, I think that I should aim to get as much air moving through the
> > collector as possible - in which case, perhaps instead of a single
> > collector running corner to corner I'd do better with two or more in
> > series, each arranged so that the air must be drawn through them.

> Thermal mass in the collector is of no use to you.

It will help smooth out the output from the system - by how much I don't
know.

Anyway, I got some shade cloth this morning from a hardware store, so I
will experiment with that.

> I didnt understand the 2nd bit.

Instead of a single set of three layers running corner to corner, three
sets of three layers, each one taking care of one-third of the surface
area, so that each molecule of air has to pass through nine layers.

But I won't bother; it seems unnecessarily complex and would be extra
work for the fan.

Daniele

[NT]

On Dec 3, 12:08 pm, real-not-anti-spam-addr...@apple-juice.co.uk (D.M.
Procida) wrote:

> NT <meow2...@care2.com> wrote:

> > > I'm wondering whether layers of shade-cloth or layers of metal mesh
> > > would be better as the collector for the system. Metal, I feel, would do
> > > a better job, with more thermal mass.
>
> > > Also, I think that I should aim to get as much air moving through the
> > > collector as possible - in which case, perhaps instead of a single
> > > collector running corner to corner I'd do better with two or more in
> > > series, each arranged so that the air must be drawn through them.
> > Thermal mass in the collector is of no use to you.
>
> It will help smooth out the output from the system - by how much I don't
> know.

It wont, but even if it did it wouldnt be an advantage. You get most
out and lose least out of a solar panel when thermal capacity is
minimised, and the fan or passive airflow stops and starts with the
available sun's heat. Delaying cool off by 2 or 3 seconds wont make a
noticeable difference in practice. Shadecloth collectors are already
an exceptionally good design, I dont think anyone's managed to improve
on them yet.


NT

[Martin Brown]

On 03/12/2011 09:22, D.M. Procida wrote:
> NT<meow...@care2.com> wrote:
>
>> Ah. I'll try and ascii it clearly.
>>
>> . _______
>> . :|
>> . | : |
>> . | : |
>> . | : |
>> . | : |
>> . |: |
>> . _______|
>>
>> Notice how the cloth goes from corner to corner. All the air goes
>> through the cloth, not just past it. And the slight pressure
>> differential across teh cloth keeps t he 2 volumes of air separate,
>> unheated and heated.
>>
>> If the air merely goes past the cloth, its less effective at cooling
>> the cloth, which then radiates more heat out. Also the hot air reaches
>> the glazing, and more is conducted out.
>
> I have obtained my double-glazing panels, so I am going to start
> experimenting this weekend.
>
> I'm wondering whether layers of shade-cloth or layers of metal mesh
> would be better as the collector for the system. Metal, I feel, would do
> a better job, with more thermal mass.

You don't want much thermal mass in the collector. You want something
that gets warm enough to be at least faintly useful even in the feeble
winter sun. The thing is barely going to work adequately even on the
sunniest winter days so you may as well configure it so that it does
produce some warm air out at ~20C as soon as is reasonably possible
(rather than taking forever to warm up from overnight frosts).

>
> Also, I think that I should aim to get as much air moving through the
> collector as possible - in which case, perhaps instead of a single
> collector running corner to corner I'd do better with two or more in
> series, each arranged so that the air must be drawn through them.

You have got just about everything wrong in what you plan to do. The
only thing you have right is the double glazing panel and even that is
wasted in this application. Far better to have it output a modest amount
of air at a useful temperature - then with a bit of ducting you might at
least be able to keep your feet warm. All forcing too much air through
it will do is give you a not quite so cold draft!

And you may as well take your air intake for this contraption from the
highest point in your garage which is where any warm air you blow into
it will end up (assuming here that the garage door is closed).

A 1W 12v battery top up solar panel and a cheap and nasty computer fan
will probably blow more air through it than the panel can ever heat in
winter unless it is very large indeed.

Regards,
Martin Brown

[NT]

On Dec 4, 9:58 am, Martin Brown <|||newspam...@nezumi.demon.co.uk>
wrote:

> On 03/12/2011 09:22, D.M. Procida wrote:
>
>
>

> > NT<meow2...@care2.com>  wrote:

Maximum return with minimum loss occurs when the panel's fed with the
coldest air, which is at floor level. That also minimises hot & cold
spots.

Shadecloth panels are often used passively, with plastic film dampers
to stop airflow when the panel's cold.


NT

[Martin Brown]

> Maximum return with minimum loss occurs when the panel's fed with the

> coldest air, which is at floor level. That also minimises hot& cold

> spots.
>
> Shadecloth panels are often used passively, with plastic film dampers
> to stop airflow when the panel's cold.

It really depends on whether the purpose is to extract as much thermal
efficiency as possible from the collector or to warm up the relatively
finite volume of air inside the garage to a comfortable temperature.

You could well be right that there is no advantage to recycling the warm
air that collects at the top of the garage. I was thinking that it would
give the device more chance of working in weak hazy sun. The purpose
being to move such warm air as it can produce to somewhere near where
you want it.

At our UK latitude and with our damp foggy winters I suspect it is an
exercise in futility to build a solar powered garage heater. YMMV

Regards,
Martin Brown

[D.M. Procida]

Martin Brown <|||newspam|||@nezumi.demon.co.uk> wrote:

> At our UK latitude and with our damp foggy winters I suspect it is an
> exercise in futility to build a solar powered garage heater. YMMV

^^^ fun

I may not get anything very practical out of it in the end, but it will
have cost me little and I'll have learned something by doing something.

Daniele

[NT]

On Dec 4, 1:22 pm, Martin Brown <|||newspam...@nezumi.demon.co.uk>

In any given sun conditions, the collector has a certain stagnation
temperature. The collector ceases giving any heat when the interior
air approaches that T_stagn. The colder the air intake, the more
conditions under which it outputs at least some warmth.

> The purpose
> being to move such warm air as it can produce to somewhere near where
> you want it.

Output will always go to the same level, from where the air then
stratifies a bit. When heat is needed, the worst offender comfortwise
is the coldest air near the floor.

> At our UK latitude and with our damp foggy winters I suspect it is an
> exercise in futility to build a solar powered garage heater. YMMV
>
> Regards,
> Martin Brown

Some of the time yes, and some of the time it'll make a big
difference. The proposed triple glazing willl extend its usefulness.


NT

[The Other Mike]

On Sat, 3 Dec 2011 09:22:30 +0000,
real-not-anti...@apple-juice.co.uk (D.M. Procida) wrote:

>I'm wondering whether layers of shade-cloth or layers of metal mesh
>would be better as the collector for the system. Metal, I feel, would do
>a better job, with more thermal mass.

Despite what has been posted by others thermal mass in a collector
*can* be good. There are quite a few Trombe walls around the UK that
have been in successful service for decades.

http://en.wikipedia.org/wiki/Trombe_wall


--

[NT]

On Dec 5, 7:57 pm, The Other Mike <rootpassw...@somewhereorother.com>
wrote:

> On Sat, 3 Dec 2011 09:22:30 +0000,
>

> real-not-anti-spam-addr...@apple-juice.co.uk (D.M. Procida) wrote:
> >I'm wondering whether layers of shade-cloth or layers of metal mesh
> >would be better as the collector for the system. Metal, I feel, would do
> >a better job, with more thermal mass.
>
> Despite what has been posted by others thermal mass in a collector
> *can* be good. There are quite a few Trombe walls around the UK that
> have been in successful service for decades.
>
> http://en.wikipedia.org/wiki/Trombe_wall

yes, in a different situation though


NT