Author Topic: Creating a solar heating unit on the cheap (Read 3608 times)

freeEnergy4me · « **on:** April 03, 2008, 11:06:55 PM »

Ok, here's the general idea:

Let the oustide air come through a long series of black painted aluminum cans (thin aluminum) and have a hose to go inside the house with a fan at the end to suck the air thru.

So far, where I am at:

Painted cans

I am using epoxy to connect the cans with an air tight seal. I avoided using silicon because its messy and bulky....and it blocks additional surface area from sun exposure. With epoxy it's as if the cans are one long unit with out really having a connection point(s) so it's all sun-exposed aluminum.

I drilled holes in the bottoms of the cans to allow the air to pass. I doubt it will affect air flow since it's just air.

For the ends I will just use the bottom ends of the cans to terminate them, i.e. to seal them. For connections I bought a roll of flexi-aluminum which is very easy to cut and work with...on $5 for this roll.

Two cans connected:

Very quick and easy building so far! I will keep you updated!

freeEnergy4me · « **Reply #1 on:** April 03, 2008, 05:15:10 PM »

Here is the $5 roll of flexi-aluminum

richhagen · « **Reply #2 on:** April 03, 2008, 06:16:08 PM »

It reminds me of the one that FrankG poste about here, which is listed on his site at:

http://www.theworkshop.ca/energy/collector/collector.htm

If it's different, it is probably worth a read. Rich

freeEnergy4me · « **Reply #3 on:** April 03, 2008, 06:42:25 PM »

Another guy also did it recently. I am definately imitating them....with some wrinkles.

The black cans are the same, I am just using a longer air path that will heat the air considerably more. I am using a zig-zag connection of cans so that instead of just going top to bottom, the air goes thru every can. Also, I am not using silicone, but epoxy which is easier to work with, imho. And it is very durable and less bulky than a caulk would be.

If you don't use epoxy, start! It is a great adhesive.

I'm also using some aluminum flex to conjoin the cans.

My unit is not going to occupy a window, as windows help direct sunlight heat the house. It will sit on my roof and have heat enter through a hose with a fan at the end to pull air in.

All in all, the same concept. I just thought I'd do a diary for the heck of it. Since I've brought my electric bill down, I'm going to focus on my outrageous heating bills.

TheCasualTraveler · « **Reply #4 on:** April 03, 2008, 06:46:38 PM »

Mmmmmm, Mountain dew!

spinningmagnets · « **Reply #5 on:** April 03, 2008, 06:52:13 PM »

Since you are using a fan, it will still work even though some of the columns flow down. That being said, I would recommend having all the vertical columns flowing UP to take advantage of a small amount of thermosiphon effect (heat rises).

Thermosiphon hot air collectors have been built that do not require a fan because the effect is so useful if done right. In a properly configured collector, the size of fan needed is greatly reduced.

High air flow is very desireable for hot air collectors. If the flow is so slow that the temperature coming out the top of the collector is very hot, it will provide a very impressive demonstration of heat collection, but a fast flow will actually transfer MORE heat to the room being warmed.

You probably already know, but, "builditsolar.com" has a lot of info on projects like this. Best of luck, and have fun!

freeEnergy4me · « **Reply #6 on:** April 03, 2008, 09:53:54 PM »

Thanx!

I almost guarantee this will kill my winter heating bills. I just wanted to thank the other people for posting it in the first place.

As for the heat rising effect, the cans will be at nearly a 45 degree angle. They are going to sit on my roof next to my solar panels facing south. So the effect will be somewhat negated.

I figure if the air has to traverse a long path of hot cans, it will be very hot as opposed to just warm. I'll just have to increase the throughput of air.

Now, how do you warm your house at night?? Any suggestions? I'll check out buidit and see what they say.

I put a black can filled with engine oil in the sun and it retained the heat for awhile. I wonder how long a big array of black cans with oil in them would radiate heat after the sun went down?

ZooT · « **Reply #7 on:** April 03, 2008, 11:41:03 PM »

I wonder how long a few painted flat black plastic 5 gallon pails full of water would stay warm after the sun went down?

Bruce S · « **Reply #8 on:** April 04, 2008, 07:52:56 AM »

freeEnergy4me;

For oil, instead of engine oil, you might try using transmission oil. Its built to be much more stable at both cold and hot temp swings, along with working well in pumps.

Bruce S

tecker · « **Reply #9 on:** April 04, 2008, 10:15:42 AM »

Bladders made of EPDM rubber roofing is good they can be glued togeter to any size .

freeEnergy4me · « **Reply #10 on:** April 04, 2008, 10:35:06 AM »

Do you have an idea of how long heated oil/transmission fluid will stay warm?

I figure it will keep heat longer than water.

freeEnergy4me · « **Reply #11 on:** April 04, 2008, 10:38:59 AM »

I thought about this as well. I figure that most plastics that hold liquids have some decent thermal transfer conductivity. You'd think?

But aluminum is by far one of the best options. It is a great conductor.

I've seen those indoor columns of water that heat up thru direct sunlight then radiate heat at night.

ghurd · « **Reply #12 on:** April 04, 2008, 10:41:17 AM »

I keep getting the feeling you are confusing how fast something absorbs heat, with extra BTUs.

If it stays warm longer, it takes longer to heat up.

Just because it stays warm longer doesn't mean it has more heat from the BTUs that were available.

If it needs to stay warm longer, insulate it.

G-

scottsAI · « **Reply #13 on:** April 04, 2008, 10:45:18 AM »

Hello freeEnergy4me,

Great to see your projects, keep it up!

Water will store as much if not more BTU/gal then oil, plus if it leaks not much mess.

Phase change materials store more BTU/lb than water, not much else can.

Water is cheaper than oil in most places.

Sorry to burst your bubble, this will not Kill your heating bill!-) unless you're using several dozen of them.

Air flow is best with less restrictions, holes between the cans looks small?

Restrictions will require more fan power to get a desired air flow.

The hotter the air the less efficient the solar collector will be. The hotter the collector the more heat it radiates out without heating the air (black body radiation).

Air flow and fan power are conflicting requirements, a balance is needed to be effective.

Due to black body radiation water stored in the collector will re-radiate its heat back out at night. Considering a black tank behind a single glass pane has an R value just above 1.

Storing the water in an insulated container R20+ will be MUCH better. Place the tank above the collector using the thermosiphon effect to move the water, no pump required.

As mentioned www.builditsolar.com has many inexpensive solar heating ideas.

Have fun,

Scott.

Bruce S · « **Reply #14 on:** April 04, 2008, 11:10:49 AM »

What ghurd says is true.

Tranny Fluid will be easier to handle than water to do its properties of being able to stay within a set viscosity over a wide range of temps. Its pretty much self cleaning too, so you might think about getting some for free from a local flush/fill type shops. Try getting a small amount and soaking a couple cans with your epoxy on them that are stuck together just to make sure it won't turn the epoxy stuff into goo.

You could also use a more complex system that stores the warmed fluid in a highly insolated container that would then be used to transport that heat in the evening to a heat distribution item.

However, more complex can also mean possible less eff% due to losses.

The one main gain from using the oil is that unless your located in -20F weather for days on end, it's not likely to freeze, so a drain back system shouldn't be needed.

BUT there's the possible need for a pump to move the stored/heated oil to place needing heat etc...

Tranny Fluid can be a mess to work with too, it likes to find leaks and make messy puddles.

Hope this helps and doesn't stop you from trying.

Any use of even a little bit of the solar heating gains will go a long way to helping keeping the bills down along with that way cool feeling of saying "I did this"

Bruce S

PS, Don't do like I did, and get the idea that mineral oil and a small submersible water pump will work. Worked, but mineral oil gooped up the pump. wan't a good thing thing. Pump cost me $5, oil for 20fl.oz was $5. mess was all day. And the Tranny oil would destroy the cheap plastic they're made of.

richhagen · « **Reply #15 on:** April 04, 2008, 03:02:13 PM »

Use more epoxy huh. . . and cut down on the use of hot glue???

coldspot · « **Reply #16 on:** April 04, 2008, 03:56:52 PM »

Solar air heating-

I'd never try running any fluid in a system made from cans.

I'm building a system like that using cans also. Larger cans 24oz, black in color stock, so less painting, with larger openings stock, and larger holes in the bottoms with a hole saw.

no zig-zag, just combining the air at the top of each row.

The intake will be from the floor in the winter and the outlet will be into a insulated box/bench filled with plastic bottles of water. This I hope to be able to hold the heat from the day to also be able to get some from it in the evenings.

This system I'm also thinking I could be able to reverse in the summer, sucking the inlet from the ceiling and the outlet just blowing outside as a sort of get the hot air out. But at night I'm thinking that I could run some fans to have it cool the water bottles and then be able to draw cool air from inside the box to replace the hot air being sucked out during the day.

Most of this is still just in my head and a bunch of box's of parts saved,(two years worth of cans only about half have been washed out, was planning a 10'x10' wall but now only 5' high windows with 3' overhang eves and starting down 1.8' from the top of the wall for this 44` lat.).

The plan is for using this in my next shed/shop.

also a liquid system and floor heating.

$0.02

Chagrin · « **Reply #17 on:** April 04, 2008, 07:58:41 PM »

The specific heat of oil is less than half that of water. It's not a good choice.

You just can't beat the heat capacity of water. You'd have to go to liquid helium, hydrogen, or ammonia for a better specific heat.

freeEnergy4me · « **Reply #18 on:** April 04, 2008, 10:33:29 PM »

The reason for using something else is find a substance that holds the heat. Insulation I guess would be a good idea. But if you had a substance that took long to heat, it would take longer to cool as well.

So even tho water is easy to heat, it also cools just as quickly.

The concentrators they use in Nevada use oil as do...cars to cool engines. Because they absorb more heat and don't change state like water.

I guess I'm thinking out loud. How do you capture heat? If you've taken a hot bath, you know how short heated water stays warm. Just thoughts. After all, if you can simply re-design your house to take in direct sunlight then you don't need any additioinal help warming your home. It's after the sun goes down...

freeEnergy4me · « **Reply #19 on:** April 04, 2008, 10:38:30 PM »

No, I just want something to "keep the heat". Water is awesome as long as you keep heating it. But it takes many gallons of water to "keep the heat" where I'm guessing oil would stay warming longer, not more BTUs, just less BTUs right away. In other words, the water would be warm for a short period and give off it's heat right away when oil would stay warmer longer, distributing the same BTUs over a longer period.

If only I could buy those blocks they use to coat the Space Shuttle, lol. They absorb the heat incredibly well!

What is the best capacitor of solar heat? That is my quest!

jonas302 · « **Reply #20 on:** April 05, 2008, 09:29:51 AM »

Maybe if you had some black bricks behind your cans they would store some heat to

I had thought about checking into the 3or 4 inch aluminum pipe they use to exaust from the water heater for solar collecter

Chagrin · « **Reply #21 on:** April 05, 2008, 11:40:34 AM »

Concentrators in Nevada use oil because they're not storing the heat - they're transferring it. They also don't have to worry about steam. Engines don't use oil for cooling. They might cool the oil, sure, but the primary cooling system is the (water/glycol) radiator.

spinningmagnets · « **Reply #22 on:** April 05, 2008, 12:08:11 PM »

Exercise caution when designing a "night air" thermal store for cooling warm summer air during the day. Great care must be taken to avoid condensation inside the system and mold formation. There must be an answer for this but I don't know it yet.

For storing warm air in the winter, I have read about a hybrid material storage from the Delaney house postings at builditsolar.com

Masonry block will absorb whatever solar heat is available much quicker than buckets/drums of water, but water will hold 5 times the BTU's than masonry by volume.

Heat comes out of the top of the collectors and is directed to the top of the insulated heat store containment. Whether pumped by fan or thermosiphon, the warm air sinks while shedding heat. The top half is water, and the bottom half is masonry. The masonry absorbs most of the available heat.

After the sun goes down, one-way flappers stop any reverse-flow heat shedding out the collectors. Heat from the masonry slowly migrates to the water drums above it. This is important, because if the sun only comes out for a couple hours the next day, you will want to absorb as much of it as possible. The higher temperature difference from the cooler blocks in the lower half will cause more total heat absorbtion.

If you used only water, its heat uptake is slower and some of the available sun won't get absorbed. You could just use all masonry, but the heat store would need to be 4 times bigger to hold the same amount of BTU's as the hybrid store.

I haven't built one, but it is part of my future plans.

coldspot · « **Reply #23 on:** July 26, 2008, 02:26:36 AM »

"Masonry block"

Sounds like bottles of water sitting on bricks.

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Author Topic: Creating a solar heating unit on the cheap (Read 3608 times)