Self recerculating hot water?

[woodduck]

Hi Guys,

Here's one for you science gurus. I'm whacking together a temporary spa/hot tub for my mates birthday on the weekend out of an old trough, a pump and some poly. Not sure how it's gonna go but I'll give it a crack. It's not going to be real warm here saterday (first day under 35 here in months :laughing-rolling: ) so I wanted to heat the water up a bit. It will hold around 1500 ltrs so it would drain my hot water heater in no time and cost me a mint. I was thinking of using this deisel heater here...

IMG_20180222_160820.jpg

I then want to wrap copper tube around it and circulate water through it to heat the spa.

My question is...... will the water recerculate itself from the hotter water expanding and running out the top of the coil and pull more water in from the bottom of the spa? Or will it need to be pumped? I remember doing a project with a boat powered by a coil and a flame at school like this but am unsure if it was recirculating the water or just boiling making the boat move. I wasn't a great student 8-} :laughing-rolling:

Thanks guys. If I get it working you'll all have to come try it one day :handgestures-thumbupleft:

[bluc]

My money is on needing a pump :-B dont think you could siphon above the water level in the trough..

[RuddyCrazy]

only way to know is suck it and see :))

If the trough height is slightly lower than the copper coils and the output pipe comes from the base of the trough it may just work

[wynnum1]

What about burning wood to heat the water.

[hillzabilly]

Firstly I think without a pump someone may get scorched with very hot water and steam,I made that metho powered boat at skool too!,my brother got a small inflatable pool with small pump very cheap and for heating he ran the water thru some copper coils set up over the gas burners in the BBQ with the hood down,worked ok but took a fair while and cost a bottle of gas.May be you could use one of ya boilers and circulate the water with a pump,like a RIMS or HERMS set up.Hot things and drunk people are not always a good mix.cheers hillzabilly :handgestures-thumbupleft:

[Professor Green]

I think it will work. It's basically the same principal as a camp hot water service where you run a coiled pipe from bottom of the tank into a fire and back again and the main body of water is moved through the coil by natural convection.

I don't know that it will be terribly efficient though.

Cheers,
Prof. Green.

[woodduck]

I here ya there hillz, I won't have it on once people are there way too dangerous. I was going to get it going early in the day just to get the chill off the water really. My other option is a gas instantaneous hot water system.

Thanks guys :handgestures-thumbupleft:

[Sam.]

Still like a demon tomorrow and run all your RC water to the spa :D

[db1979]

Still like a demon tomorrow and run all your RC water to the spa :D

Do you recon he's got the still for the job? 8-}

[db1979]

It could work without a pump. Convection currents take hot fluids up and cold fluids down. So you'd need your heater positioned lower than your spa. If that's not possible then you'd need a pump. Houses in cold climates with boilers for central heating have them in their basement for this reason, as opposed to the attic.

Hot fluids are lower in density than cold fluids. Hot rises, cold sinks.

[woodduck]

Thanks db, I've been waiting in anticipation for your response, I knew it'd be right up your ally :handgestures-thumbupleft: I thought that might be the case with needing the heater lower than the tub. What about if the heater is lower than the high water level say inline with the middle of the tub, would that be enough to get it to work? It would have some head pressure then.

[db1979]

Glad to help mate :handgestures-thumbupleft:

I think a bigger height difference will make it work better, but also the diameter and length of tubing will affect it too, as will the temperature differential. But I'm getting out of my depth beyond that.

[db1979]

Thought a bit more about this. Heating the top of the spa won't efficiently heat the bottom of the spa. You'd need your heating tubes to get to the bottom of the spa so convection within the spa can take the heat all the way through it. I think you'd end up with cold water on the bottom and warm water on the top otherwise. So I think you'd definitely need to have the heater below the bottom of the spa.

[woodduck]

Thanks mate, I'll see what I can come up with :handgestures-thumbupleft:

[Doubleuj]

KISS. That’s all that really needs to be said.
As Sam said, do a bunch of runs or boil a heap of water in your boiler. By the time it’s cold you should all be too pissed to care :laughing-rolling:

[Aussiedownunder01]

Stop rooting around pump it

[Lowie]

Don't forget to chuck some cholorine (for hygeine - body fats floating on the top are not nice, and Hydroclauric acid (to balance the ph) in it a few hours before you pile in mate. And, make sure you put some of that coloured dye in it to stop people pissing in your spa! :handgestures-thumbupleft:

[woodduck]

:laughing-rolling: :laughing-rolling: :laughing-rolling: definitely need some of that dye.
Would I need chlorine etc if it's only for one night? Guess it couldn't hurt.

She's all done. The spa pump I had here was buggered so had to go for second option and just used a pressure pump, won't be as good but will give the idea that we are in a spa :laughing-rolling: . I ended up using my little magnetic pump that I use for transfering wash to recerculate the water through the coil. I'll start her up in the morning and see how she goes. I'll post picks of the redneck spa tomorrow :handgestures-thumbupleft:

[warramungas]

Hi Guys,

Here's one for you science gurus. I'm whacking together a temporary spa/hot tub for my mates birthday on the weekend out of an old trough, a pump and some poly. Not sure how it's gonna go but I'll give it a crack. It's not going to be real warm here saterday (first day under 35 here in months :laughing-rolling: ) so I wanted to heat the water up a bit. It will hold around 1500 ltrs so it would drain my hot water heater in no time and cost me a mint. I was thinking of using this deisel heater here...

IMG_20180222_160820.jpg

I then want to wrap copper tube around it and circulate water through it to heat the spa.

My question is...... will the water recerculate itself from the hotter water expanding and running out the top of the coil and pull more water in from the bottom of the spa? Or will it need to be pumped? I remember doing a project with a boat powered by a coil and a flame at school like this but am unsure if it was recirculating the water or just boiling making the boat move. I wasn't a great student 8-} :laughing-rolling:

Thanks guys. If I get it working you'll all have to come try it one day :handgestures-thumbupleft:

For any sort of efficiency you'll need a pump mate. You'll have an open loop of copper at both ends, I assume, one in the bottom and one in the top just below the top of the water. The pressure diff will stay the same and you'll only heat the water in the loop with any efficiency.
We call those demon heater cause they're hot as hell and the ones I've seen running would melt copper piece of piss if the tube is allowed to get too hot like in the water vaporising before it can get any distance into the tube and you have a tube of steam.
Get some water flow and you'll heat the pool up in no time. Stainless tube would be safer if you've got it. Those things glow red hot.

[woodduck]

Thanks warra :handgestures-thumbupleft: yep these heaters work a treat. I'll give it a trial run tomorrow morning before anyone is around, we don't need an accident :handgestures-thumbupleft: