How stupid of me!

[jaskiainen]

Hi!

I had some spare time last weekend and raised my solar air heater up again

for some more testing.

So I put it up and it looked like this.

This photo is taken last time so it is not facing directly in to the sun.

My new calculations are listed below:

Tinlet = 80.6 ºF

Toutlet = 161.6 ºF or 131 ºF (I used two different blowers)

Vair = 24.3671 ft³ or 63.5663 ft³

Dair = 0.075 lb/ft^3 at sea level and 60F, but the air density decreases as it is heated, so for normal collector temperatures, 0.065 lb/ft^3 is pretty good.

Cair  is 0.24 BTU/lb-F

This fitted in Gary's formula (www.builtitsolar.com) looks like this

Qout = (Vair)(Dair)(Toutlet - Tinlet)(Cair)

Qout = 24.37 * 0.065 *(161.6ºF - 80.6ºF) * 0.24 gives me 30.8 BTU/min or 1847 BTU/hr.

This gives me about 540 watts (using two solar powered computer blowers)

And the second one is calculated with 230V/40W ductblower

Qout = 63.57 * 0.065 * (131ºF - 80.6ºF) * 0.24 gives me 49.98 BTU/min or 2998.8 BTU/hr.

This is about 880 watts.

My collector area is 34.5 ft².

So the efficiency of my collector with these figures comes out like this:

Solar In = (300 BTU/ft² - hr)(34.5 ft²) = 10350 BTU/hr

Efficiency = (Heat out)(Solar in) = (1847 BTU/hr)(10350 BTU/hr) = 0.178 (17.8%)

or

Efficiency = (Heat out)(Solar in) = (2999 BTU/hr)(10350 BTU/hr) = 0.289 (28.9%)

Not as good as i hoped for but still it makes nice amount of heat.

I left my heater up to make the global warming come true and left to help

a neighbour at his building project. It was a nice, warm, calm sunny day...

What I did find when I came back?

There was one small breeze and my collector was lying face down on the ground!

One of the small solar chargers crasher under it. (Sorry G)

The top layer of glazing was cracked many places.

What the heck was I thinking about leaving the collector up untied unsecured?

I felt quite bad and I needed something else to do for a while so we went for

a little boat trip on the lake.

Next morning my mind was settled and all seemed OK again.

I can get new glazing from work for reasonable price.

And now few selected pictures of how I made this one.

Inner layer is 2mm polycarbonate sheet and outer is/was 3mm acryl sheet.

Two layers for better winter performance. 340 beercans.

20 pipes. 17 cans in one pipe.

Insulation is somekind of acoustic insulation. It's only 30mm thick but I

hope it will be enough.

This have been a fun project for me (plenty of beer drinking).

And like my girlfriend always says:

"I need to help my boyfriend with his hobbies!"

Best regards Jaskiainen

[bob g]

i know about how you feel

my partner came in a while back with 7 solar panel 280watt jobs with attached

inverters, pretty cool

he unstrapped the stack to show me, and then took the ratchet strap and started

to crank the stack down tight like it was a sling of lumber,, and kaboom

one panel shattered under the extreme stress

that was a very expensive lesson in strapping

bob g

[TheCasualTraveler]

     With a girl by your side, drinking beer in support of your hobby, then in response to your subject line, not so stupid at all.

and I like that machine thing that cuts the holes.

[valterra]

I'm not an expert, so feel free to correct me here.

When I saw the plexiglass broken under the screws, I was reminded of similar problems I've had with plexiglass.  Plexi is flexible, the frame and screws are not.  So as soon as any pressure is put on the pane, it WANTS to break.  

I've always heard tha glass is weakest at its edges, which means the pressure from the screw is exactly at the perfect location for the plexi to crack.

Would this be a good solution?  Say you're putting a plexi pane on a wooden frame.  Pre-drill the screw holes larger than the screw itself.  Then use a rubber washer ("seal", "grommet") and tighten the screw so the head squeezes the grommet and seals the hole?

Or if your frame was thin enough, you could use bolts and rubber washers.

The point is not screwing into the plexi material at all.  That way, when the plexi flexes (and the frame doesn't) there isn't that direct pressure trying to break your plexi.  

This is probably "no duh" stuff to you guys.  But I just thought of it!

[jaskiainen]

Hi valterra!

That was my original goal, only the rubber washers were missing.

Thats why the screws are not too tight. And I did drilled the holes for

screws a little bit bigger in plexi.

The main reason why the plexi cracked was the weight of my collector.

(and couple of stones that were on the groung below it)

There is always stuff what some people here just don't think before it's

too late. Thats why everything should be written down exactly like one

makes them. Thats why there is no "no duh" stuff in here

Oh BTW. I just looked Gary's website a bit closer and find that there is

that 300BTUft/-hr wrong in my calculations. I should have used 201BTUft-hr

instead because I'm livin in lattitude 61 and it was may...

That gave me a little better performance for my panel, but only little.

New calculations are 26.6% and 43.2% efficient unit.

Regards Jaskiainen

[g reif]

nice looking colector

[g reif]

jaskiainen,

you should submit this to builditsolar.com, it would be a good addition to the alreay good ideas of others

[jaskiainen]

Hi g reif

This one is just like the one in gary's website already

http://www.builditsolar.com/Projects/SpaceHeating/BeerCanCollector.htm

Propably the only difference is my solar powered computer fans.

Thats why I see no need to add this one there.

You can see a house reflecting one of those "cracked" pictures.

Thats where i'm gonna put this baby up. The house itself is a project of

me and my friend. It's gonna use only green energy. No bills from power company.

Well actually it is just a cabin for weekends and holidays.

My goal is to make new windgenny for it and maybe buy one 50-120W solar panel.

Nice little project using almost only surplus and recycled stuff.

We try to build it without using money much. (So far used about 200€)

It is movable so it don't require building permission.

We can toe it almost anywhere we want.

Maybe I share it with you if and when it will be finished.

Regards jaskiainen

[Airstream]

I've probably helped replace $2,000,000-plus worth of Lexan and other polycarbonate glazing and I want to share: To get the longest life from a sheet of acrylic - polycarbonate - lexan..

 1) Make radiused corners on every edge, even rounding the whole outside edges to some degree AND rounding the flat-side corners to minimize the chances of a fracture point evolving from a sharp edge where the thickness across the square corner gets infinitely thin. If you really want to get perfectionist use the appropriate glue-weld solvent for the sheet material and treat those edges where you've cut, filed, sanded to remove any stress-points from the surface pores.

 2) Slot any through-bolt drillings to accommodate heave and shrinkage, get in the man'f specs and know what the dimensions will change between 0°C and 90°C! Also: use a  slider gasket (thin/hard like sheet plastic from office document protector covers) sandwiched under metal ferrules - topping backside standoffs: and/or silicone lube on rubber washers, frames etc. that might bind over the next X years.

Anyhow thats how to get a million miles rough service from plastic glazing on moving vehicles, I'm sure it applies to solar collectors too.