Redneck pool heater 3.0

[NS Gearhead]

So I've got a 16'x42" inflatable pool. The problem is; it's freakin' cold.

My first version of a pool heater had a little 120V pony pump running water through 10' of copper tubing through my fire bowl. We were gaining 6deg C. Got the pool up to 29 C from 26 in a day. There were three big drawbacks; 1. The pump was very loud 2. I had to constantly stoke the fire, and went through alot of wood. and 3. I think the sparks ruined the pool

After replacing the pool with another, I upgraded to a sump pump, and built a solar panel


Roughly 175' of 1/2" plastic pipe. So far... less then impressive. It'll gain a constant 2deg when it's sunny... but man, we've had alot of cloud on our "nice" august days. I thought to myself I can either add another panel (more money that may not work), slow the water down (don't want to hurt the pump), or somehow stop and start the pump. I got myself a digital timer... and set it to 5 min on and 10 min off. The problem with this is that I can only set it for 20 on/ off cycles. 5 hours. Neither the constant 2deg or on/ off have produced much results. So I started thinking about how I could improve the wood burning method.

My three problems could be solved. The sump was nice and quiet. A "wood stove" of sorts would burn much longer and use less wood, and simply setting it farther from the pool would solve the spark issue. Not to mention I could get way more out of it with more copper loops in it. This is quickly costing me way, way too much for the amount it's been used... but I'm in too deep now to leave it be and not use it much. So I'm doing this as cheap as I can.

Here's the start of my "wood boiler" LOL


At first I was going to cut the bottom 1/3 off and set it on the fire bowl... but thought what the heck I'll try using it this way... if I don't like it I can always go back and cut it up.





So far this hasn't cost me anything yet. Tomorrow I'll stop in and get 4' of stove pipe which is around $40, then I plan to put as much 1/2" copper tubing as I can up to a max of 100' ($120) either on the underside of the lid, or on a shelf just under it.

The handle I used is actually off of the old bunker gun on the boiler at work. (we switched to natural gas) Kind of nice to find a use for it.

 

[NS Gearhead]

Here's the pool

 

[Piston]

I've often thought of using something like an old woodstove to try to heat the pool on the cheap. But...with 30k gallons in a 20x40 inground pool, I doubt I'll make much of a difference. I'll be interested to see how you make out.


Did you weld a solid piece between the wood burning portion and the upper portion of the drum? Are you going to fill the 55gallon drum with water, then have all the coil tubing inside it?

 

[NS Gearhead]

I actually do have a normal wood stove that I thought of setting up for this...then realized it would need a little "dog house" built around it to keep it sheltered... so that would be a couple $100s... this can be brought in the shed between uses.

The only water will be in a coil of tubing like this...

... set inside the drum. Everything else is wood/ fire. I'd like to have some temp gages on the inlet and discharge lines to see the difference... but they can be pricey. We'll see.

 

[Piston]

I would think that if you could separate the firebox and the drum, and fill the drum with water to get it really hot (as hot as possible) then use the cool tubing, it would be a whole lot more efficient.

 

[Raspy]

NS,

You'll get the maximum efficiency out of your solar system if you let the water run faster through the coil, rather than slower. Faster means the coil is cooler and therefore losing less heat to the surrounding air, so more to the water in the coil.

Design it to cool the transfer water rather than heat the pool. The result will be more energy to the pool.

If you put a piece of clear plastic over the coil, you might get more heat out on marginal days. But that tube can melt if you leave the plastic on in direct sun with no water in the tube.

Some old boilers were designed like your barrel. They have a coil running around the outside, like a spring, then a bunch of passes over the top. You could lay the coil on top of the barrel with some space between the coils for smoke to pass. Or two layers. A rebar grid over the barrel to hold the lower coil and a rebar grid between the two layers. Very efficient. LOL.

Or set a 30 gallon barrel inside the 55. Put them where the pool gravity feeds the 30 gallon and you pump the heated water back to the pool. Top of 30 gallon equals pool water level. The fire goes up between the barrels in a very efficient heat exchange. Set the bottom of the 30 on fire bricks to make a fire box in the 55.

What do you think?

 

[KennyG]

I've been looking into this for a while and haven't found a good solution. Solar should work well but you need a much larger area. The former owner had a solar system on the pole barn roof that apparently did a decent job of heating the in-ground pool. Unfortunately, the attachment caused the roof to rust out and I had to put on a new roof and I don't want to repeat that expense. I don't have another good location for the collector. The wood stove with copper tubing can work well but apparently the copper can result in staining the pool liner unless you control the pH carefully. The best solution would probably be a wood stove with a stainless water jacket, but that would be pretty expensive.

 

[forgeblast]

Solar Water Heating Projects and Plans has some great ideas.

 

[NS Gearhead]

I should mention I'm a boiler operator. Heat transfer and efficiency is what I do for a living... although you wouldn't know if from my first two attempts. LOL I guess cheap and easy aren't always the way to go. In my line of work their's two types of boilers; water tube where water filled tubes surround the furnace or "fire box" and fire tube boilers where the fire tube travels through a shell filled with water, then turns around and the combustion gases pass through several "fire tubes" back through the body of water and out the stack. What I'm making is more like a water tube boiler. Of course for it to be more accurate I'd have to line the entire inside of the barrel with copper tubing. This would probably be the most efficient design. The more surface area and the longer the water stays in contact with combustion gases the better. On our types of boilers there are multiple passes of combustion gases before exiting the stack, but with mine being natural draft and not forced it's not really an option... unless I did a double horizontal barrel setup... but then I'd need way, way more copper tubing and end up with steam out the other end.

I don't have any experience with boilers that use a water jacket around the fire box... but from what I've read they can remove too much heat from the fire and make it difficult to maintain proper combustion, as well as produce dangerous amounts of creosote. Not to mention it would be much more difficult to build something water tight... especially considering how thin barrels are.

Anyway, with my coil over the fire I'll get radiant and convection heat. 10' of copper tubing in an open fire produced a 6deg differential, so I'm confident that this setup will produce the results I'm looking for. In fact, I'm thinking of what type of draft control I'm going to use to slow the fire down as it may produce water hot enough to cause some damage.

Yes copper can be a problem if the ph is allowed to go out of range... so don't let it go out of range.

 

[mikehaugen]

The more surface area and the longer the water stays in contact with combustion gases the better.

I would have to disagree. The longer the water stays in the tubes will make the water hotter, yes, but overall btu's will increase with more flow. The temperature difference will be greater and heat will transfer faster. Raising 100 gallons of water 1 degree is better than raising 10 gallons of water 9 degrees.

The surface area part is correct.