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.

 

[LD1]

Do those blow-up pools have a pump and filtration system like a full-sized pool?

IF so, you already have a pump.

We (at my parents) tee'd into the pressure line coming out of the sand filter with a ball valve for a solar heater similar to yours. Dont expect instant results.

We were flowing ~5gpm through the solar heater and the result was about 4 degrees F warmer. On a 10000 gallon swimming pool, and only circulating on the 12 sunniest hours of the day, it takes 3 days to circulate all the volume and gain 4 degrees. But in theory, 10 degrees warmer in a week isnt bad.

But aside from the solar heater, do you have a solar cover? If not..GET ONE. The benefits are two-fold. It helps warm it during the day, but the biggest benefit is keeping the heat in at night.

 

[Egon]

Will the coil be flat or vertical.

Consider a vertical stack with vertical tubing inside with the exhaust having to travel down the exterior of the vertical stack with more coils on the outside of the stack. Might have to add some air to the top to get more vapour burning. Water pump and PSV also required. Consider forced draft fan controlled by water temp.

This should qualify as a water tube boiler rather than a firetube boiler. Might have to watch temperature with the copper tubing. HP STEEL tubing may be an option?

 

[NS Gearhead]

The coil will be laying flat/ horizontal. The combustion gases will be directed in the center of the coil. I'm considering putting a diffuser plate between the coil's center and the chimney. That way the gases have to travel across the top of the coil as well.



Steel pipe would rust and the water that sits in it would brown, then get pumped into the pool. SS would be ideal, but obviously $$$. As long as the water's flowing I'm not worried about the copper.

Yes the pool has a pump and fitler. 1.5" in/ out. The sump pump I got is 3/4" slower flow... and takes the water off the bottom of the pool where it's coldest compared to the pool's pump that takes it 3/4 of the way up the water level.

 

[NS Gearhead]

Yeah, we really need to get a solar cover. When I looked at it, it was $45 I didn't want to spend at that time...but if it's going to make a difference it'll be worth it.

 

[NS Gearhead]

Just looked it up; copper has a melting point of 1085C. Chimney temp gages show 500C as being the in the danger zone... although this is 18" up the chimney and not direct flames. The water going through is cooling the copper, and won't get passed 100C, so I'm confident it'll be fine.

 

[Fiziksgeek]

True...the rate of heating is directly proportional to the contact area and the temperature difference. The best way to extra heat from anything is lots of area and lots of flow (to maximize the temp difference). Can't beat physics...I've been trying for a while now...

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.

 

[Raspy]

^^^^ You guys are right. I agree. And it works for solar or house heating or any other application where maximum heat transfer or efficiency is desired. Solar is a perfect example. The best efficiency comes from designing the system to "cool" the collectors, not "heat" the water. A very important distinction in heat transfer and efficiency.

I love backyard projects! They end up making us think about physics and efficiency and cost and practicality and on and on. Especially when everyone gets involved.

 

[Loadstar]

Just switch the condenser off your ac from air cooled to water cooled. Then at least your using wasted rejected heat.

 

[rasorbackq]

Gearhead I'm in Springfield NS I use a black poly pipe from 1/2" to 2" with several Tees Must have close to 400 ' I can get the pool (above ground 15' x48 deep) up to around 30c but its a losing battle when the temp at night drops to 18c. That little pool filter you have our lasted about 2 days and was pretty slow to do anything. We bought a a real pump and sand filter and use the poly pipe to move a lot of water . I turn the pump on a sunny day and its only a few degrees from scalding hot. . I have more spent on accessories for the pool then the $250 for the pool. Our pool is going on 10 years now.

 

[NS Gearhead]

Made the front draft




I kind of screwed up measuring and allowing enough plate to cover the last hole... oh well. It should never be fully closed anyway.

Chimney with damper




She ain't pretty... but like we used to say back home; I'm not building a piano.