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aboard_epsilon
01-01-2012, 04:30 PM
Something thats not been discussed here ..well i don'tdon't think it has.

http://www.youtube.com/watch?v=n7SGzlnDscg&feature=related

plenty more info and designs on youtube

cheap project ..maybe

and will help to heat workshops ...will add to what you already have, or stand alone to take the chill off.

i have a huge pile of double glazing units

i have the fan .. fan is 6 inch from brand new faulty power supply

i have the wood
all i need now is the aluminium and a thermostat

don't quite know how it would perform in the British cloud coverd winter ..but i have noticed that the coldest days are usually cloud free ..

and my workshop always retains the night temperatures in it ..and is slow to warm up, even in summer its mostly cold in there....i would imagine it would make working in the shop a lot more pleasant.

will have a go at it this summer.

unless you guys talk me out of it ..but for the outlay ..ive nothing to loose but a bit of time....and a few watts to power the fan.

btw these glazing panels are coated on the inside to ratain heat ..im really not sure which way around to use them in this project ..or if they would be benificial or a hinderance

all the best...markj

TGTool
01-01-2012, 04:43 PM
Seems like a good proposition. Air to air heaters are simple. Leaks don't cause major headaches. I saw one years ago using steel shavings for the heat collection in place of the tubes in the video, which would fit right in with this forum. Another modification used beer cans with one end cut off and set (swaged maybe) into a flat plate and painted completely black to try to minimize reflectance from the surfaces. Air was passed along the back for the heat transfer. Since automobile radiators were once made by stacking short tubes side by side and soldering the ends (again probably slightly flared on the ends) I wondered whether cans couldn't be stretched on the open end into a hex to stack together without the plate. Had some cans saved up once to try but never quite got to it.

lugnut
01-01-2012, 05:15 PM
Way back in the 70's I made a small collector like the one TGTool mentions using cut off beer cans. I used a small wood box and an old double pane window I had for the cover, a small fan with a stack switch out of an old furnace. The darn thing got so hot that if cracked the inner pane of glass. I also had to redo the beer cans and paint them with high temperature paint. Even with 10° outside temperatures, it would produce 110° discharge air. I never followed up on perfecting it. I think I got the idea from a Mother Earth Magazine. I know they work.

Gazz
01-01-2012, 05:19 PM
As already mentioned, beer or soda cans can be used for the tubing. One plan I saw the maker was cutting the ends in kind of pie shaped sections and then turning and twisting the cut sections to provide"swirl" of the air as it move up the tube. I don't know how much that would improve the efficiency. I f you search youtube for beer can solar heaters I think you will get some hits. I do wonder what you do with those sort of things in the summer though. Even with fans shut off and vents/ports closed off, there would still a lot heat made that would have to go somewhere.

aboard_epsilon
01-01-2012, 05:26 PM
As already mentioned, beer or soda cans can be used for the tubing. One plan I saw the maker was cutting the ends in kind of pie shaped sections and then turning and twisting the cut sections to provide"swirl" of the air as it move up the tube. I don't know how much that would improve the efficiency. I f you search youtube for beer can solar heaters I think you will get some hits. I do wonder what you do with those sort of things in the summer though. Even with fans shut off and vents/ports closed off, there would still a lot heat made that would have to go somewhere.

i suppose you could just Chuck a blanket over it ..when it gets so hot that it may damage itself

Evan
01-01-2012, 06:57 PM
I am just finishing up my design for an air to air heat exchanger for an electric dryer. It uses pop cans and I figured out a slick way to cut off the ends so they snap together. I will explain when I post the project.

vpt
01-01-2012, 07:03 PM
Does it have to be metal? Why not black plastic piping? I know when you lay it down in the sun it gets hot, already black, cheap, and stuff.

Evan
01-01-2012, 07:08 PM
In warm weather it will get got enough to melt PVC or ABS.

darryl
01-01-2012, 08:03 PM
I saw a version of that long ago that used aluminum flashing folded up into an accordian shape, painted flat black, and placed inside the box in similar fashion. That gives a very large surface area to exchange heat with the air. There were designs that would track the sun, while others were passive.

lugnut
01-01-2012, 09:45 PM
I done a little searching for the Solar heater that I posted about earlier and Found it! it wasn't a Mother Earth thing, but Popular Mechanics. Google Books have all the old PM Magazines from the beginning. Here is a link to it if your interested.
http://books.google.com/books?id=OOIDAAAAMBAJ&pg=PA103&lpg=PA103&dq=rock+filled+A+frame+solar+collector&source=bl&ots=uAevMEl45b&sig=kSGF38Lu4w41jfAWA9nZ-UZYCyE&hl=en&sa=X&ei=NhIBT9eQGYmoiALts9yjDg&ved=0CGUQ6AEwBw#v=onepage&q=rock%20filled%20A%20frame%20solar%20collector&f=false

flylo
01-01-2012, 10:05 PM
Great idea,Thank you!

JoeLee
01-02-2012, 12:18 AM
Many years ago I made a solar heater for my pool that worked on the same idea only instead of air flowing through the tubes it was recirculated pool water. It was a 4' x 8' box mounted on my garage roof made out of 2 x 10's, inside the frame were several copper alum. coils that were originally air conditioner coils and I painted them black. The top of the box was covered with that wavy translucent fiberglass panel stuff (can't remember what it's called) When the sun was shining the water temp was around 120 degrees but I had to really throttle down the flow rate of the water or it would just come out luke warm and in a 35 k gallon pool it didn't make much difference. I later scrapped the idea. I cool rain would drop the water temp 10 times faster than a hot sunny day would warm it.

JL..................

Evan
01-02-2012, 12:48 AM
When you are heating something like a pool with direct heating of the pool water the temperature differential of the water going out of the heater and into the pool is irrelevant. You want the water to flow as fast as possible consistent with not wasting too much energy pumping it.

Even if the water going back to the pool doesn't feel warmed at all, it is. The larger the the differential between the incoming water and the entire length of the solar heater the more energy it absorbs. Slowing it down so the water in the heater becomes warm reduces the heat differential and therefor the heat transfer. The solar heater should feel cold, not warm. If it is warm it is rejecting and re-radiating incoming heat with subsequent lower efficiency.

Sophiedoc
01-02-2012, 09:26 AM
I used flexible dryer duct coiled and sprayed black coiled in my collector box with a bathroom fan to move the air from shop and back.

mitsue
01-02-2012, 10:25 AM
I built a solar air heater similar to www.cansolair.com style. I had my doughts at first untill I saw one running at -20c outside putting out 35c temp. Due to short hours and low angle of sun during winter the performance goes down. Edmonton's mean average temperature/year is 3c. winter to spring and spring to summer, (also summer to fall and fall to winter) it cuts about 30% of heating my single car garage. Output when running is about 10000 to 12000 btu average. I used the solar pop can style, mounted at 70deg to catch the winter sun angle. that makes it a little self regulating spring/summer/fall as output falls off as the sun goes higher. If I did it again I would set them at 50degrees to improve spring/fall performance. The biggest issue was getting enough cfm airflow thru the cans. I tried 6"/8" duct fans but the restriction was too much for the fans to overcome. I ended up using a furnace squirrel cage, variable speed fan assembly with a fan motor speed controler. (like a dimmer but made for cieling fans). Yesterday the unit ran for about 3 hours steady pumping 38c air into the garage. By itself it won't keep the temp up but it holds back the chill. I can come in after a sunny day with -20c temps and it is around 10c at bench level. It helps keep the air statified by lifting the cold air off the floor. I would run it with my propane tanktop heater and the temp at the floor would closely match the rest of the garage.
I like them and they do work.
Darcy

aboard_epsilon
01-02-2012, 12:58 PM
hmm

i have a lot to find out .

like why are coke cans any better than a flat panel

as the way i see it, they can curve around ..and a percentage of the can will be in the shade when the sun isn't directly overhead ..

same with corrugated or convoluted or castellated.

the panel has an inlet and an outlet ....inlet takes the cold air out of the building ..outlet puts the heated air into the building.

wonder if a few mirrors capturing light elsewhere and bouncing it onto the panel will help ..

are there any sun tracking gizmo's ideas that will turn it into the sun and not require any external power source.

all the best..markj

darryl
01-02-2012, 02:05 PM
The exchange of heat from a collector surface to the surrounding air is greater when the area of contact is largest- hence the desire to have a large surface area where the sunlight can deliver its energy, and the most air can touch the surface to absorb that energy. A folded or corrugated surface has more surface area than a flat plate in the same width and height, and in addition it presents more area 'flat on' to the sun when the sun is to one side or the other of the collector- in other words not directly facing it. Even a flat black surface will reflect much of the light hitting it if it's coming from an angle. With the tubes or cans, there's always some area directly facing the sun, so that again would mostly be better than just a flat surface. Some of the properties change if you make it track the sun, but you still would want to maximize the surface area which in in contact with the air that's eventually absorbing the heat.

It comes to mind that if you cover a collector with a flat acrylic sheet, that will also reflect much of the light hitting it if it's coming in at an angle. If you track the sun, that effect is gone, but that makes what could be a very simple system more complicated. I've only just thought of this, but perhaps making the acrylic cover corrugated as well would lessen the amount of energy reflected away. Of course, at the same time it would increase the surface area facing the outside air, and that might lose more heat to the atmosphere than you would gain by making the cover corrugated. I tend to think that the gains would be more than the losses, particularly if you are blowing the air through the collector at a decent rate. After all, the surface that's really absorbing the heat in the first place is the interior structure.

Now if you corrugate the cover panel, it can make for a stronger structure that would easily be capable of withstanding passive water pressure. You could then use a pumped water system to carry the heat out of the collector, although heat to air is still simpler and much less trouble-prone.

Just adding a few more thoughts on the matter.

mitsue
01-02-2012, 04:01 PM
I believe with cans the whole can heats up quickly because it is aluminum and the air passing thru can scrub heat off the whole surface. Some designs use a baffle to swirl the air as it passes by. I spaced my cans 1/8" apart and used reflective poly foil underneath to reflect a little sun to the backside. Also the rounded top surface provides more surface area than a flat panel. Next I want to try the type with black screen that the air passes thru.

Evan
01-02-2012, 05:16 PM
It is always better to cover the collector with something transparent. The reflection losses are more than made up by preventing convection losses to the surrounding air.

A single layer of ordinary glass is worth 10% reflection loss per surface with the radiation normal to the surface. As the angle becomes oblique losses mount dramatically once past certain angles.

This is a wildly non linear effect as it depends on the index of refraction and the point at which Total Internal Reflection (TIR) kicks in. For light entering glass the curve is approximately a second power law curve with little change in admittance until past about 60 to 70 degrees. However, for light exiting glass the difference is dramatic. For regular window float glass or tempered glass the critical angle is 42 degrees. Fortunately, window glass isn't optically flat so total internal reflection doesn't trap all the light. If it did you wouldn't be able to see through a window past 42 degrees angle of incidence.

Prisms are optically flat (meaning flat to better than 1/4 wavelength green light). Once the TIR angle is exceeded the glass surface acts as a perfect mirror.

Bottom line though is that once the incidence angle exceeds about 45 degrees losses become rapidly greater to the point that little energy is gained. That means glass covered panels have about a 90 degree effective energy collecting angle. That also works out to a maximum of 6 hours per day with good efficiency if they are in fixed position.

Most plastics have a lower index of refraction which varies with the type. They can give a wider admittance angle but suffer from rapid degradation of transmittance properties.

aboard_epsilon
01-02-2012, 05:56 PM
So, maybe put a 2 inch high glass fence around the cover-glass to stop the wind taking more heat from it .

a clear matt coating on the glass may help too...never seen clear matt though .would probably make it opaque.

wonder if a computer program could generate the ideal cross section for all conditions and angles of the sun.

will start collecting pop cans .

all the best....markj

mitsue
01-02-2012, 05:59 PM
It is always better to cover the collector with something transparent. The reflection losses are more than made up by preventing convection losses to the surrounding air.

A single layer of ordinary glass is worth 10% reflection loss per surface with the radiation normal to the surface. As the angle becomes oblique losses mount dramatically once past certain angles.

This is a wildly non linear effect as it depends on the index of refraction and the point at which Total Internal Reflection (TIR) kicks in. For light entering glass the curve is approximately a second power law curve with little change in admittance until past about 60 to 70 degrees. However, for light exiting glass the difference is dramatic. For regular window float glass or tempered glass the critical angle is 42 degrees. Fortunately, window glass isn't optically flat so total internal reflection doesn't trap all the light. If it did you wouldn't be able to see through a window past 42 degrees angle of incidence.

Prisms are optically flat (meaning flat to better than 1/4 wavelength green light). Once the TIR angle is exceeded the glass surface acts as a perfect mirror.

Bottom line though is that once the incidence angle exceeds about 45 degrees losses become rapidly greater to the point that little energy is gained. That means glass covered panels have about a 90 degree effective energy collecting angle. That also works out to a maximum of 6 hours per day with good efficiency if they are in fixed position.

Most plastics have a lower index of refraction which varies with the type. They can give a wider admittance angle but suffer from rapid degradation of transmittance properties.


Great info Evan. Your info is proven out by my panels output decreases late spring into summer as the sun's angle is higher in the sky.

SteveF
01-02-2012, 06:05 PM
Out of curiosity, does anyone know of somewhere on the Internet where someone has built one of these things and actually done a proper, valid engineering study of how well they work?

Do they heat air when the sun is bright, of course they do. But at night, they radiate heat OUT of the building. Plus energy is consumed by the fans that move the air. So, its entirely possible that the energy lost at night plus the energy to run the fan is more than the energy gained during the day, or that even if the collector gains energy it would be cheaper to just run an electric baseboard heater.

Any links?
Steve

aboard_epsilon
01-02-2012, 06:10 PM
i would imagine you would put some sort of automatic shutter on it that closes the ducts when the temperature falls below a certain point ..

eg a green house window opener has such a thing.

http://www.ebay.co.uk/itm/Bayliss-XL-Autovent-Automatic-Greenhouse-Window-Opener-/300627780473?pt=UK_Home_Garden_Garden_Structures_F encing_CV&hash=item45fecfe379

and the fans are thermastatically controlled ..they would be off.

all the best.markj

darryl
01-02-2012, 06:42 PM
I'm sure you would include some method of closing off the piping at the point where the temperature inside the collector reaches the inside temperature. If you're using round tubing as air ducting, you can easily create a gate valve which will close up to the point where it could almost prevent pressurized air from passing. Of course there wouldn't be what you'd call pressurized air in the system- the most it would be is that from a circulating fan.

The gates themselves could be covered on one side with a layer of styrofoam, so there wouldn't be much in the way of heat loss through the closed gates.

Considering the angle of the sun, you could pretty much manually set the vertical angle of the collector every so often. This would be more or less a seasonal thing- if the sun is low in the sky, set the collector pretty much vertical. If the sun is high you'd be setting it closer to horizontal.

Sun up to sun down is a different story, since you have up to 180 degrees of change in the direction the sun shines from. I'm not a solar energy expert by any means, so I can only guess at how much of an improvement in energy gain you can get by tracking the sun- you might be able to double your daily influx. Whatever the tracking system is, it should be simple and virtually foolproof- otherwise you'll be fooling with it more often that you might like to. You can't rely on flexible ducting to last through seasons of flexing, and 'wrist' joints are going to be subject to leaking, weather conditions, and contaminants. Not to say that a reasonable job of this can't be done though- there probably is a decent method of creating this part of the structure.

Evan
01-02-2012, 06:43 PM
Out of curiosity, does anyone know of somewhere on the Internet where someone has built one of these things and actually done a proper, valid engineering study of how well they work?

My dirt simple solar water heater gathers around 2 to 3 kilowatt hours per sunny day to preheat my well water. The only cost is the circulating pump which is 1/5 hp for about 6 hours when it is sunny. That costs about 0.8 kilowatts hours for the day. I haven't put an automatic temperature differential switch on it yet. That would save even more power as it would shut off when clouds move over. This was well worth doing as our well water is only 43F all year.

It dropped my electric bill by around 25 to 30 percent. I determined the amount of power collected by measuring the temperature rise of the heat exchanger barrel water using a USB thermometer connected to a computer.

This is the collector, an old 4' satellite dish with a 100ft coil of pvc tube. Water is circulated to a tank in the basement made from a 55 gallon food grade poly drum. That tank has an exchanger loop of 100 ft PEX which is plumbed in to the cold water pipe before it goes into the electric water heater.

The only modification to the household plumbing is a pair of regular faucets in the cold line with a ball valve between them so that the exchanger can be disconnected and bypassed. If code doesn't like it I close the faucets, take off the lines and open the ball valve. Now there is nothing he can say. I keep the exchanger tank sterile with monthly shots of chlorine.

http://ixian.ca/pics9/solar4.jpg

This is an example of the performance during average spring weather around here. You can see by the rising trace that it is only on about 6 hrs per day. Furnace activity also show because it has another loop to collect waste heat from the furnace flue via a heat exchanger collar on the flue pipe and a loop by the wood burner.

http://ixian.ca/pics9/solargain.gif

vpt
01-02-2012, 07:52 PM
Well anyone could draw up a graph in paint.

JoeLee
01-02-2012, 09:54 PM
My dirt simple solar water heater gathers around 2 to 3 kilowatt hours per sunny day to preheat my well water. The only cost is the circulating pump which is 1/5 hp for about 6 hours when it is sunny. That costs about 0.8 kilowatts hours for the day. I haven't put an automatic temperature differential switch on it yet. That would save even more power as it would shut off when clouds move over. This was well worth doing as our well water is only 43F all year.

It dropped my electric bill by around 25 to 30 percent. I determined the amount of power collected by measuring the temperature rise of the heat exchanger barrel water using a USB thermometer connected to a computer.

This is the collector, an old 4' satellite dish with a 100ft coil of pvc tube. Water is circulated to a tank in the basement made from a 55 gallon food grade poly drum. That tank has an exchanger loop of 100 ft PEX which is plumbed in to the cold water pipe before it goes into the electric water heater.

The only modification to the household plumbing is a pair of regular faucets in the cold line with a ball valve between them so that the exchanger can be disconnected and bypassed. If code doesn't like it I close the faucets, take off the lines and open the ball valve. Now there is nothing he can say. I keep the exchanger tank sterile with monthly shots of chlorine.

http://ixian.ca/pics9/solar4.jpg

This is an example of the performance during average spring weather around here. You can see by the rising trace that it is only on about 6 hrs per day. Furnace activity also show because it has another loop to collect waste heat from the furnace flue via a heat exchanger collar on the flue pipe and a loop by the wood burner.

http://ixian.ca/pics9/solargain.gif

Evan, what is the temperature drop from your heat dishes to the poly drums in your basement??? I would think you have either insulated and buried the lines depending on distance. Also if this is a closed system and you have freezing temperatures do you have anti freeze in the lines??

JL....................

Evan
01-03-2012, 01:34 AM
Well anyone could draw up a graph in paint.

Paint?? Maybe you can but I find that program utterly useless.

The hot hose is insulated most of the length both outside and inside with urethane foam. I found a perfect product that is a lot cheaper than the regular slit flexible foam pipe insulation. It is a urethane foam hollow tube "beater stick" made for water and pool play. They go on sale at the end of summer for a dollar or so for a 5 foot piece and are thicker than regular pipe insulation. I'm not that concerned about efficiency. It already pays well enough and has long since paid back the minor investment.

I drain the system before it freezes hard and switch to the furnace heat capture loop. That one uses a tiny pond fountain pump that only draws maybe 25 watts. This time of year it is on all the time.

Incidentally, I have seen up to a 5 kilowatt hour gain on some days. That is around 80% efficiency. Those are days when there are big fluffy white clouds in the sky but they aren't over me. The extra reflected light increases the insolation. The same applies to solar electric panels. The usual 2 to 3 KWh is about 40 to 50% efficiency which still isn't bad for such a simple rig.

Incidentally, when it comes to painting things black, not all flat black paints are equal. About half the insolation is in the IR wavelengths and not all black paints are "black" in the IR band. To be effective in IR the paint must be formulated with carbon black pigment rather than dyes. Most flat black paints are but all high temperature flat black paints are, such as barbecue paint and stove paint.

SteveF
01-03-2012, 04:14 AM
It dropped my electric bill by around 25 to 30 percent. I determined the amount of power collected by measuring the temperature rise of the heat exchanger barrel water using a USB thermometer connected to a computer.



There you go, now that is a proper analysis! As opposed to sticking a thermometer once into the incoming air flow. Nice graph also.

Solar heating of water is pretty much accepted to be efficient, which is why there are a fair number of companies selling the hardware and even available tax credits. I'm looking for something to support the solar air exchangers that were shown in the original video.

Steve

Black_Moons
01-03-2012, 04:45 AM
So, its entirely possible that the energy lost at night plus the energy to run the fan is more than the energy gained during the day, or that even if the collector gains energy it would be cheaper to just run an electric baseboard heater.

Any links?
Steve

I promise you the fan will be nearly 100% efficent at producing heat, Just like the baseboard heater :) Any additional heat you manage to gain while the fan is running is 'free'

hitnmiss
01-03-2012, 10:31 AM
Evan, what clear plastic did you cover your dish with?

monkers
01-03-2012, 01:10 PM
How big of an area could you heat like this and how big of panels would be needed to heat a 2 car garage? Interesting idea

hojpoj
01-03-2012, 02:16 PM
Out of curiosity, does anyone know of somewhere on the Internet where someone has built one of these things and actually done a proper, valid engineering study of how well they work?

Do they heat air when the sun is bright, of course they do. But at night, they radiate heat OUT of the building. Plus energy is consumed by the fans that move the air. So, its entirely possible that the energy lost at night plus the energy to run the fan is more than the energy gained during the day, or that even if the collector gains energy it would be cheaper to just run an electric baseboard heater.

Any links?
Steve

http://builditsolar.com/

Check near the bottom of the 'Experimental' section.

It's a good hub with a lot of great ideas. I've dickered around with the can-collector, and in a completely un-optimized, unglazed prototype (can stacks sitting in my patio sunroom), I was still seeing a 30-degree F rise in temperature. I still leave it in there starting in the fall, as it brings the temp up to a pleasant level even in the winter. That's only with 120 cans, about 12 cans high in each stack.

Apparently 3 separate layers of window screen (black aluminum) is actually one of the most efficient capture/exchange mediums for a DIY hot air collector.

The reason the water-based systems are more prevalent is because you have the opportunity to store the heat for later demand. One of my co-workers is about ready to throw the switch on his solar hot-water heating system that he just installed. It's like a retrofit hydronic floor heating setup.
He's projected that it will save him a couple hundred bucks a year on his energy bill due to heating, with a calculated payoff period of about 7 years. Looking at how he's calculating things, it all looks reasonable.

Hot air collectors when properly designed will pump a lot of heat in, but their purpose is not to replace heating, only to offset the heat demand during production hours. This is true for most systems, as converting solar radiation to heat is the most efficient way to get 'Free Energy'. To get enough to cover all your demands and storage needs would require a ridiculously oversized system. So just remember- it's just a supplement, not a replacement

Evan
01-03-2012, 07:57 PM
The dish is covered with regular vapour barrier poly, maybe 6 mil or so. It gets raggedy after a summer so I replace it for a cost of a couple of bucks.

Calculate the amount of heat gained as about 500 watts per sq metre of collector area per hour of clear direct sun within 45 degrees of any side of straight on. Ad to that any heat produced by electric motors used to circulate the air but subtract that from your cost saving. It's a very good way to leverage the electric energy spent on circulating the air. At 100% efficiency you can gain about 1000 watts per sq metre.

With my system I also have heat storage in the exchanger tank so it helps heat the house after the sun goes down. That's obvious since the temperature on the graph is dropping the entire time until it is turned on the next day.

Assume 4 sq metres of collector, air only, with good sun 100 days per heating season for 6 hours per day. If the heat was electric that would produce about $120 worth of heat per year. More importantly it will produce it where you might not otherwise be willing to spend the money, like my cold garage shop.

It will be one of my projects for next year and I will instrument it to see just how effective it is.

Abner
01-04-2012, 08:49 AM
Documentation/study- I had similar questions about an actual instrumented study being done on solar. I found this. http://www.nofossil.org/ The graphs match Evan's with the draw down on temp with water use, which, obviously, these are not 1,000 hp boilers we are talking about here. I have cold water to (38 deg F all year) so thank you Evan for the inspiration. Looking up temp sensors was mind opening, many built for USB ports - wow, what an interesting time to be alive in.

Evan- I was thinking if it is poly of just letting the thing freeze, any comments? How about leaks when it gets hot?

Popcan solar There are several you tube's where people have gone to to great lengths, and with much craftsmanship, build one of these only to completely f'up the inlet/outlet location. The proper way to get uniform flow is first in /last out. ie- the inlet should be in the lower right hand corner and the outlet in the upper left hand corner. Like a car radiator.

aboard_epsilon
01-04-2012, 10:10 AM
Popcan solar There are several you tube's where people have gone to to great lengths, and with much craftsmanship, build one of these only to completely f'up the inlet/outlet location. The proper way to get uniform flow is first in /last out. ie- the inlet should be in the lower right hand corner and the outlet in the upper left hand corner. Like a car radiator.

yup ..there's a few there with the inlet/outlet confused ..some with just an outlet ..and the inlet is the outside air.

some with fans pushing air into them ..some sucking.

some at about 10 degrees off verticle

some lieing flat.

so what's this can cutting idea of yours Evan.

all the best.markj

madwilliamflint
01-14-2012, 04:10 PM
I've just gotten back from Home Despot where I picked up a 36x48 piece of plastic, 10' of 4" black tubing and a couple joint thingies, some high-heat flat black krylon, foam insulation panels (more like "tiny compressed ball" packing material than the foam sheets) and some assorted furnace type caulking (and a caulk gun because I'm a home n00b too.)

So we'll see. I have 6 cases of soda cans I've accumulated so far, but I'm going to focus on building the frame tonight.

elf
01-14-2012, 04:26 PM
A gentle touch of the top of a pop can to a belt sander will remove the top quickly assuming the belt sander is running:D

madwilliamflint
01-14-2012, 04:33 PM
A gentle touch of the top of a pop can to a belt sander will remove the top quickly assuming the belt sander is running:D

I like the idea, but wouldn't a belt sander then grab the can and squnch it?

I'm gonna go downstairs and give it a try.

Forrest Addy
01-14-2012, 09:32 PM
Isn't steel, specifically, hot rolled black scaled steel, a good absorber of solar heat?

An old pipefitter I knew built his own solar heating plant. His house has a good south exposure and his roof ridge ran east and west. He built a box of plywood faced with glass and had sheets of plain ol' body steel as an absorbing surface. He insulated sides and back with pink Dow insulation and ran insulated ducts to his furnace plenum. He set the whole rig up to the winter sun angle. I got into the picture because he asked me what that angle was: at 48 degrees North - its roughly 25 degrees above the horizon. I think Bonner used 30 degrees as optimum for the heating season.

He was uncertain of the numbers so he built it plenty big: 8 ft x 52 ft. In freezing weather around here we often get clear blue skys.

The solar heat plant put out so much heat it would drive you out of the 2000 sq ft house on all but the coldest days. Bonner solved this problem with a half dozen old water heaters in the basement, a bunch of plumbing, a pump, and a car radiator in the plenum. There were flappers to direct heat etc. It made a pretty good "Kansas farmer" heat plant if you didn't mind the constant fiddling. In time refinements brought timers and thermostats etc so it was almost automatic. It worked slick for nearly 30 years but it was ugly. When old Bonner died and the house was sold. The new owners ripped it off the roof and hauled it to the dump. Stupid them. Bonner liked to brag he used less than fifty gallons of fuel oil a year.

So if your home is sited right, you don't mind ugly, over building, and a couple of years to refine it, a home brew solar heat plant makes a lot of sense. Your wife will hate it because it aint orthdox and no matter how clever you are it will stick out of the roof making unharmonious lines.

madwilliamflint
01-14-2012, 09:44 PM
Well I've got an awful location, way up in bumbleberry new york. But the way I figure it it can't do "nothing." And it's well worth my project time.

I'm a bit through the first attempt since my previous post, built a 3x4' box and started on a 4" hole in the bottom for the duct.

Had to stop on account of my hands and wrists.

Why couldn't I have been all mad scientisty when I was in my 20s?

steve45
01-14-2012, 10:40 PM
This is an interesting idea, but I wonder about the guy in the video. Who owns a pink rifle?

As far as heating a swimming pool, it doesn't matter how fast you pump the water. Pump it slow, and you get a small quantity of hot water. Pump faster, and you get a larger quantity of warm water. What matters is the surface area of the heater relative to the pool area.

I built a solar heater from poly pipe years ago for my in-ground hot tub. I came home from work the first day and discovered that the 130 degree rated thermometer had blown out! I just used black poly pipe. I expanded the system in an effort to heat the pool, but had endless problems with the barb fittings on the poly pipe coming loose. They've got better fittings now.

My pool is pleasant in the daytime during the summer, but it cools off quickly. Someday, I'm going to install a storage tank of about 2000 gallons that I can heat during the daytime, then circulate through the pool when I use it in the evening.

aboard_epsilon
01-16-2012, 07:14 AM
Back to solar-air

Ive been looking into this a bit more

i think it needs a differential thermostat

only one i could find ..im sure there are others ..its just that they will be under other names ..what names ./..i need suggestions

http://www.ebay.co.uk/itm/Differential-Thermostat-solar-heating-hot-water-/300451133492?pt=LH_DefaultDomain_0&hash=item45f4487834

above not much good without the probes / thermocouples or power supply...you need two thermocouples one inside the building and one in the solar box ...or inside the exhaust and inlet

without one of these you will be constantly adjusting things, and you manually turning the fan on and off ..

if a fixed temperature stat is put in ..for instance a cold building like a workshop ...there is such a variation in temperature that you never have it set at the right optimum temperature.

BTW ..no links to anything expensive ..to keep this project economical ..would suggest top price of £20 or $30

all the best..markj

ptjw7uk
01-16-2012, 07:43 AM
Why do you need a differential thermostat, just buy 2 room stats one inside and one outside(in the heater unit) you then have a differential unit.
I think a SPST will do , just switch live on one and neutral on the other.
Peter

aboard_epsilon
01-16-2012, 07:55 AM
when i thought about that peter ..it didnt compute in my head ...

you satill have the problem of what to set each one to

for instance one day it may be so cold that its below the settings that youve turned the two on at

the temperatrure in the winter can be anything like -5 to plus 10c

imn the summer it can be plus 2 to 25 degrees c

these are the temps of the ambient air ..not the box temperature...

i dont know how the box is going to perform ..no idea at all ..so cannot even guess .

all the best.markj

aboard_epsilon
01-16-2012, 08:42 AM
this looks ok

http://www.ebay.co.uk/itm/Temperature-Controller-Thermostat-Water-Heater-Solar-System-Panel-Water-Tank-/120832587109?pt=LH_DefaultDomain_0&hash=item1c222ef565 (http://www.ebay.co.uk/itm/Temperature-Controller-Thermostat-Water-Heater-Solar-System-Panel-Water-Tank-/120832587109?pt=LH_DefaultDomain_0&hash=item1c222ef565)

says

Control temperature difference: 1 - 15 °C

but says it has only one probe ..i dont get it ..if it neads to work out a difference you need two .

i will email him ...but i wont expect much as a reply ,...as looking at the listing, he isnt english .

got reply ...its not suitable

same thing basically in the uk ..a lot cheaper ..but still the same configeration..one probe !

http://www.ebay.co.uk/itm/Digital-Temperature-Control-Thermostat-Controller-New-/260935092415?pt=UK_AudioElectronicsVideo_Video_Tel evisionSetTopBoxes&hash=item3cc0f188bf

all the best.markj

aboard_epsilon
01-16-2012, 09:24 AM
OK Ive found the right device, it has more than two probes..bunus ! ..i will assume that it works for air as it works for water ..just need some copper plates to mount the probes on to make it more sensitive ..

http://www.ebay.co.uk/itm/Solar-System-Panel-Different-Temperature-Controller-/110412847156?pt=UK_Gadgets&hash=item19b51e5834

need to find it cheaper than this though

all the best.markj

mitsue
01-16-2012, 09:39 AM
The thermostat goes in the box to monitor the inside box temps. The thermostat is differential in say it turns on at 110f and off at 90f or what you set it at. When I went looking for a "snap disc" type, I had to order them in because they are being phased out. I ended up using one from a regular furnace that I could adjust and has a 6" long, 5/8 dia. probe. I also mounted a cheap indoor/outdoor thermometer in the box so I could see the actual temp inside and can tell if my fan speed is overpowering the box.

madwilliamflint
01-16-2012, 09:47 AM
Only thing I have left in mine is more cans. I figure I can wait three weeks until I drink 12 cases of diet dew or I can stand outside a recycling center and pay a couple people for their bags of cans.

As I see it, having looked at a bunch of these videos (and in practical terms, having gotten no further) the real quandary is how to store the excess heat for when the panel isn't in operation (i.e. when the sun goes down.)

I saw some mentions of the heat retention properties of salt, so I envisioned some daisy-chaining of barrels of salt, but I've no idea if that makes any sense or if I'm just getting all crazysauce again.

Lew Hartswick
01-16-2012, 09:59 AM
I saw some mentions of the heat retention properties of salt, so I envisioned some daisy-chaining of barrels of salt, but I've no idea if that makes any sense or if I'm just getting all crazysauce again.
That is called Glauber Salt and it stores the heat by phase change but
it does "wear out" over the years. It will be a lot more expensive to
implement than just plain old water. So that will be a big help but you
want lots of surface area so the transfer will be faster. ie. not a 55
gal drum lots of smaller containers.
On the subject of differential thermostats it would be a fairly simple
matter to do it with a bit of electronics. The difference between "on"
and "off" is NOT a differential thermostat, it's just the hysteresis of
the device. But a true differential is what is needed so that anytime the collector is warmer than the "shop" it runs BUT then you do need
the ability to "store" the excess when it get too warm in the shop.
OR shade the collector to reduce the input.
...Lew...

Mad Scientist
01-16-2012, 02:23 PM
If you want to build your own differential thermostat try this. I built it to turn on an attic fan but only when it was hotter inside then outside.
http://i68.photobucket.com/albums/i17/mscientist/FANCONTROL.jpg
I got 90-140 degree air out of this, unfortunately it wasn’t enough to heat up the backyard.

http://i68.photobucket.com/albums/i17/mscientist/solarpanel.jpg

aboard_epsilon
01-16-2012, 02:53 PM
If you want to build your own differential thermostat try this. I built it to turn on an attic fan but only when it was hotter inside then outside.
http://i68.photobucket.com/albums/i17/mscientist/FANCONTROL.jpg
I got 90-140 degree air out of this, unfortunately it wasn’t enough to heat up the backyard.

http://i68.photobucket.com/albums/i17/mscientist/solarpanel.jpg

know zilch about electronics..so not going there ...unless you want to exp-lain the whole diagram what the symbols mean ..pointing out what each componant is ..and how to wire it for 12 volt only. :D...dont understand how the 12 volt comes out of the wrong side of the transformer for a start.

Evan
01-16-2012, 03:01 PM
This seems to be an ideal application for SMA (Shape Memory Alloy, aka Nitinol). Use a SMA spring to open the flap that admits warm air into the heated space. A small hole in the flap would admit air over the spring. As the temperature goes down through the SMA transition temperature the flap would be drawn closed by it's own weight, stretching the spring. In doing so it would slow the airflow causing it to slow through the collector and recover more heat in marginal conditions. When the temperature goes fully below the SMA transition temperature the flap would close completely. The fan could be switched on and off by a another small bit of SMA coupled to a microswitch mounted in the collector.

This is about a simple as it gets with no electronics involved and relatively cheap too. SMA is available from a number of sources in a variety of temperature grades including around room temperature. Cost for the amounts required would be less than $15.

Lew Hartswick
01-16-2012, 03:24 PM
If you want to build your own differential thermostat try this. I built it to turn on an attic fan but only when it was hotter inside then outside.
http://i68.photobucket.com/albums/i17/mscientist/FANCONTROL.jpg
I got 90-140 degree air out of this, unfortunately it wasn’t enough to heat up the backyard.

http://i68.photobucket.com/albums/i17/mscientist/solarpanel.jpgYep That is what I was referring to. I would have added an
adjust to allow for a required amount of diff before turning on and
how much hysteresis does that make (the positive feedback around
the op amp?
...lew...

Black_Moons
01-16-2012, 03:33 PM
Better idea: Power the fan with a heat engine using the collector temp verus inside temp :)

Mad Scientist
01-16-2012, 06:05 PM
how much hysteresis does that make (the positive feedback around
the op amp?
...lew...
Don't recall as I made this a number of years ago, however was quite sensitive to temperature change. But replacing R4 with a trimpot would make it adjustable.

danlb
01-16-2012, 06:36 PM
Years ago solar was a big thing. For heat storage, one design had insulated, baffled bins of river rock that the hot air flowed through once the house was hot enough. The coarse rock (an inch or two across) allowed airflow but heated up well. At night a diverter shut off the solar panel. When heat was needed at night, a louver in the ducts circulated air though the rocks as long as they were significantly hotter than the inside temperature.

Dan

datsun280zxt
01-21-2012, 03:18 PM
So, I realize pop cans are cheap to free, but if a guy had access to thin wall Aluminum tubing for cheap, wouldn't it work the same? Or is there an issue with air speed being slowed down by the constant change in size of the pop can. I saw a few videos of guys using guttering, but they were still packing it with pop cans. I was kind of thinking about getting some smaller tuning around 1.5-2" and using it instead. Any thoughts on this? I recently quit drinking pop almost entirely, and it would take me a very long time to gather enough cans to do this project....and its cold and sunny out right now! I can get the tubing in just about any size for $2.50lb.

darryl
01-21-2012, 04:00 PM
My feeling is that using a corrugated aluminum structure is going to be more efficient at both gathering heat and exchanging that heat with the air. If you're going to buy the material to begin with, why not buy thin sheet aluminum to begin with and fold it up yourself, or buy expanded metal screen. I haven't had experience with expanded metal myself, but I can see that it would be a pretty good heat absorbing thing. Someone mentioned this earlier-

Using pop cans doesn't seem like a very efficient collector medium, but it sure seems cheap. Remember, you do pay for those cans when you buy the drink they contain.

Just doing my duty here, adding more confusion to the mix :)

aboard_epsilon
01-21-2012, 04:38 PM
corrigated would be ok on a steerable panel ..some parts would be in the shade a lot of the time on a non steerable panel.

same with the coke cans really.

we cant even copy nature cause every living thing avoids intence sunlight

you also have a problem eith the reflection from the glass ...must be some materiall out there that you could coat the glass with that still lets through as much light/heat

all the best.markj

Lew Hartswick
01-21-2012, 11:12 PM
Or is there an issue with air speed being slowed down by the constant change in size of the pop can. I saw a few videos of guys using guttering, but they were still packing it with pop cans. I was kind of thinking about getting some smaller tuning around 1.5-2" and using it instead.. It's not "slowing it down" that you want, it's making the flow turbulent
through the tubing. To aid in heat transfer between the tubing and the
air.
Remember it's NOT high temperature you are after is HEAT .
They AREN'T the same thing.
If you have an electrical background it's like the difference between , power and energy, or watts and watt-hours.
...lew...

datsun280zxt
01-22-2012, 11:06 AM
It's not "slowing it down" that you want, it's making the flow turbulent
through the tubing. To aid in heat transfer between the tubing and the
air.
Remember it's NOT high temperature you are after is HEAT .
They AREN'T the same thing.
If you have an electrical background it's like the difference between , power and energy, or watts and watt-hours.
...lew...
I found some sights showing and testing the screen method
http://www.n3fjp.com/solar/solarhotair.htm

http://www.builditsolar.com/index.htm

Both sights seem to come to the conclusion that the screen type collectors seem to work the best for money, and even debate that they simply work the best.

As for making the air turbulent in a tube design I saw some pretty unique fin/swirl designs done with the pop cans that would potentially help with that. Something like that could still be easily done with the tubing as well, but maybe it wouldn't be as effective.

My next question in regards to fan position, will it be better to set it up as a pusher or puller? My thoughts go towards a puller. I've always been told that when regarding fans, they tend to be more efficient pulling air through a restriction versus pushing it through one.

My plans are to build a rather large collector (or possibly multiple smaller ones). I want to have something that will span the south side of my shop which is 24' and could potentially go 8' tall. I have very good sun coverage there with little to block it in the winter time. My thought for a fan was to use a squirrel cage fan from a smaller furnace. My garage is insulated with fiberglass to R11. I am currently using a kerosine forced air heater to heat my shop, but I'd like to minimize the use of it as it does get costly to run. My biggest concern is that I haven't seen anyone do a big "screen type collector" to see what kind of results they got with it. I don't really like being the guinea pig with a project of that magnitude. I've also seen both fiberglass mesh screen used as well as aluminum screen mesh. I'd be leaning towards the aluminum screen for its ability to absorb and transfer heat well.

I have seen some really large guttering based collectors that seem to work pretty well. Obviously the cost of those would be significantly more so I'm leaning towards the screen collector after doing some more online research based on results others have done in the links I posted above. So who has any input based on the screen type collectors?

Evan
01-22-2012, 04:28 PM
My next question in regards to fan position, will it be better to set it up as a pusher or puller? My thoughts go towards a puller. I've always been told that when regarding fans, they tend to be more efficient pulling air through a restriction versus pushing it through one.

Pull. A single row fan with ordinary blades like a computer fan is a crappy compressor. It can't even develop an inch of water column pressure. The blades stall and that is the end of all pumping action. Given zero back pressure they will always develop a low pressure area behind the blades and that will result in flow no matter what the flow resistance may be (barring no opening :D ).

As for a swirl device in a stack of pop cans, there isn't any chance of laminar flow through such a stack. Through a constant diameter smooth pipe, yes.

Velocity does matter. When you are heating a swimming pool you want maximum heat, temperature doesn't matter because the pool will be considerably colder and you aren't looking for a lot of temperature rise. You are heating a fluid with very high heat capacity and good conduction properties. Also, water is opaque to most wavelengths of infrared radiation.

When you are heating a living space the quality of the heat is much more important. "Quality" refers to the amount of heat per unit volume of fluid. In a living space you are heating a fluid (air) that has a very low heat capacity and poor heat transfer properties. Air is a very good insulator via conduction.

To gain best heat transfer you need maximum temperature differential. Because of the conduction insulating properties of air you also need maximum exposure time to the heat source. That means high volume and low velocity for most efficient heat transfer. You want to maximize the transfer surface area and also maximize the time in contact. Air is transparent to radiation and can only be efficiently heated via conduction, meaning direct contact to the heated surface.

Evan
01-22-2012, 05:21 PM
I'd be leaning towards the aluminum screen for its ability to absorb and transfer heat well.

Aluminum is terrible at transferring heat via radiation. That really doesn't matter though when heating air. The surface acts as a total internal reflector which is why it doesn't glow red hot even when above the Draper point of 977F which is when nearly all materials begin to emit light. Even at the melting point of 1220F it doesn't glow except in near darkness. To make aluminum into a reasonable radiator it must be coated with something that is, such as black paint which is basically a plastic with carbon black. Even then aluminum still acts as an internal reflector at the metal/paint interface. That will tend to reduce the heat transfer to the coating.

When dealing with heat mirrors it doesn't matter what is in contact with the mirror or which side of the material appears to be the mirror. With anything that looks like a mirror that surface acts as a mirror equally on both sides, external and internal. It is the actual surface itself that is the mirror. Aluminum has a very wide range of wavelengths at which it reflects very well. Not all materials do. Silicon for instance can be polished to a very effective mirror at visible wavelengths but not far below the visible band it is highly transparent. Stainless Steel only reflects about 50% of visible light.

Aluminimum does have a much higher heat capacity than plastics but that is only important if the heat isn't being removed quickly enough. If the amount of air moving through a collector is matched to the heat capacity of the collector material such that the temperature of the collector is kept somewhat below the maximum attainable then it should make no negative difference whether the collector material is aluminum or plastic. It may even work somewhat better with plastic.

aboard_epsilon
01-22-2012, 05:39 PM
Aluminum is terrible at transferring heat via radiation. That really doesn't matter though when heating air. The surface acts as a total internal reflector which is why it doesn't glow red hot even when above the Draper point of 977F which is when nearly all materials begin to emit light. Even at the melting point of 1220F it doesn't glow except in near darkness. To make aluminum into a reasonable radiator it must be coated with something that is, such as black paint which is basically a plastic with carbon black. Even then aluminum still acts as an internal reflector at the metal/paint interface. That will tend to reduce the heat transfer to the coating.

When dealing with heat mirrors it doesn't matter what is in contact with the mirror or which side of the material appears to be the mirror. With anything that looks like a mirror that surface acts as a mirror equally on both sides, external and internal. It is the actual surface itself that is the mirror. Aluminum has a very wide range of wavelengths at which it reflects very well. Not all materials do. Silicon for instance can be polished to a very effective mirror at visible wavelengths but not far below the visible band it is highly transparent. Stainless Steel only reflects about 50% of visible light.

Aluminimum does have a much higher heat capacity than plastics but that is only important if the heat isn't being removed quickly enough. If the amount of air moving through a collector is matched to the heat capacity of the collector material such that the temperature of the collector is kept somewhat below the maximum attainable then it should make no negative difference whether the collector material is aluminum or plastic. It may even work somewhat better with plastic.

plastic is insulating ..the air going through the inside of a plastic pipe would not pick up heat convected from the outside of the pipe ..as readily the coke can idea.

all the best.markj

Evan
01-22-2012, 05:54 PM
We aren't talking about coke cans. In the case of using window screen as a collector material it is the surface that will be heated and the surface that will transfer the heat to the air. In that instance the thermal conductivity is not relevant nor is the heat capacity. As long as the air can remove the heat as fast as it is collected it will work very well, perhaps better than Aluminium.

aboard_epsilon
01-22-2012, 06:07 PM
what's a window screen ..dont think those things are available in this country ..so wouldn't be relevant to me .

all the best.markj