Heating water outdoors

mawk

hey guys, I have a project that i want to do in time for our annual christmas swim and I could do with some ideas.

after freezing our nads off for the last few years I decided this year that I'd LOVE an out door hot tub to jump into after the swim. I gave it a trial run a while back and it failed pretty bad. I could just not get it to heat.. and that was in the comfortable conditions of my back garden in fine weather.

I built a heat exchanger by coiling copper tubing, bolting that to a kettle bbq and getting a good coal fire going then pumping the water from the pool around the copper and back to the pool. but the scale was just too small. major problem is that the pool is about 12 feet in diameter. so... about 4-5 tonnes of water, depending how full.

anyone got any ideas? preferably cost effective, and not to take 4 days to heat.

lets say

• powerful
• not mains powered
• relatively affordable (I might splurge for a fun project)
• portable (has to work on a pier or beach)

gas? friction? 12v? submerged stove with a snorkle?

anyone got any ideas?

Cheeble

You might look for something like this.....

http://www.zumrocanada.com/products.php?12

Cheeble-eers

DublinDilbert

I would probably go with lighting a fire under a large copper cylinder and a small pump to drive the water around the circuit.

Your looking at 4 to 5 cubic meters of water, it should be possible to calculate the amount of energy required to raise it from say 5C -> 25C, using specific heat capacity.
5 metric tons = 5 000 000 grams
25-5 = 20
q = 4.18 x 5 000 000 x 20 = 418000000 = 418Mj

Say hypothetically you were to use a 3Kw immersion element and there was no losses, which of course there will be massive, you'd be looking at:-
3Kw = 3KJ/s

T = 418M/3K = 139333 Seconds = 38 hours :eek:

spadder

An industrial diesel fired hot pressure washer will produce plenty of hot water for you, just recircualte back into your tank, you will need a good bit of diesel / Kero though!
You can always pressure wash any manky friends before you let them it;)

mawk

DublinDilbert wrote: »

I would probably go with lighting a fire under a large copper cylinder and a small pump to drive the water around the circuit.

Your looking at 4 to 5 cubic meters of water, it should be possible to calculate the amount of energy required to raise it from say 5C -> 25C, using specific heat capacity.
5 metric tons = 5 000 000 grams
25-5 = 20
q = 4.18 x 5 000 000 x 20 = 418000000 = 418Mj

Say hypothetically you were to use a 3Kw immersion element and there was no losses, which of course there will be massive, you'd be looking at:-
3Kw = 3KJ/s

T = 418M/3K = 139333 Seconds = 38 hours :eek:

Aye, i did the same maths. And we both chose to ignore the environmental and conductive heat losses once the water goes over ambient.. Its an awful lot of water.. But the problem doesnt get a whole lot easier if i get a smaller pool.

If i hire a diesel pressure washer, will i kill it by using salt water? How tough are they?

spadder

It will be grand for a while on salt water,you won't be going too hot, so scaling wont be an issue. Just flush it afterwards with fresh water, you will need a big 20hp or 3 phase machine to get the volumes your looking for.

biblio

Maybe something along the lines of these:
http://woodentubs.com/htheating.html
http://www.islandhottub.com/
http://www.motherearthnews.com/Do-It-Yourself/2005-12-01/Country-Lore-Wood-Fired-Hot-Tub.aspx
http://www.green-trust.org/2003/hottub/default.htm
or
http://www.boundlessbathing.com/

mawk

awesome, the one in the green trust link (to cowboy-hotubs) is an idea I was thinking about in work today. sucks that i got beaten to it but its nice to know its an idea with merit. their one is a bit better thought out than mine had gotten to yet.. but I like it.