Exhaust heat for a water heater?

[chasespeed]

For pressure relief, I would go with a T&P relief valve for a hot water heater Pops off at 150psig, or 200*...then will close. You can also manually open it.

And yes, I can see steam flash by allowing the water to rush back into the heat exchanger. Same thing can happen with steam boilers... let water back in too fast, and you crack the casting. You would have to TRICKLE it down into the exchanger.

I think its a great idea... really, BUT, if I were you, I would look at adding a "cut-out" to the exhaust, thats operated with a cable or electrical...

THAT way, you can re-route the exhaust, and control things MUCH more safely, and easier....

I think the cable operated one is a better option, cheaper, and with a locking cable, you can modulate how much heat you want going to the heat exchanger.

Hope that helps some... might take up a little space, but, might also increase life span, reliability, and reduce issues with the heat exchanger going dry, or too hot all the time...

 

[R_Lefebvre]

Interesting idea here. I won't bother questioning why, it's obvious we've already moved past that.

The exhaust system also cools down rapidly as you move away from the engine - the manifold is the best place to draw off heat, but the pipes are relatively cool.

First of all, that's not really true. Well, at idle, the exhaust is barely warm, but when moving, it is quite hot. The rear foglight/reverse light fixture on my Discovery fell out of the bumper, and was hanging from the wire in front of my tail pipe for an hour or 2 while I was on a highway. The exhaust gas melted the lamp, so I figure at least 300F, and that's with being mixed with atmospheric air somewhat at the back. And the rear bumper valance on my trackday car melted around where the tailpipe exits, but that's exceptional.

I think the most reliable and easiest thing to do here would be to wrap a copper tube around an exhaust pipe, and simply solder the tube to the pipe. That will give you your structure you need to prevent the tube failing, and also increase the heat transfer.

I remember playing with one of the EGR coolers from a diesel on another engineer's desk at Dana. IIRC, Dana makes them, so there's a starting point. In fact, it is probably Long Manufacturing in Mount Forest Ontario that makes them. Long is or was a division of Dana. They make a lot of heat exchangers of various types, mostly coolant or fluid coolers for the OEM automotive and ATV markets.

The one I remember playing with was about the size of a beer bottle with flanges on the ends, the exhaust flows through the bottle end to end, and inside there were tubes so the exhaust could flow through cooling water jacket, all brazed SS.

When you shut the pump off, the water in the Hx will boil off, so you need to let it escape, don't pressurize the system. When you turn the pump back on, the water will flash off the over-hot metal. Over time, this thermal shock may cause your system to fail. Probably your biggest problem.

 

[Metal Twister]

Very good points guys... Well guess I had better start collecting parts :jumping: As mentioned earlier I will take a lots of pics of how the build goes. and will keep you up to date on the project. Thanks for all the input and suggestions. Hope your not out crazying the crazy here. :wings:

 

[corax]

I saw this over on another forum and thought I'd post it here to give you a few ideas for the shower-head mounting - slick job

guy used the extenal shower head door from an RV

 

[Metal Twister]

Very nice... Im thinking a shower head of some type, a couple 12 volt receptacles, Maybe even a small sink and mirror of some type? At least a long enough hose on the shower that I can wash some dishes off . I like that allot. Thanks for the post!

 

[5Runner]

I had this same idea, and have been researching it and finding my parts. Did you ever do this, how did it turn out. I thought I would try using annealed copper tubing. It is soft enough to wrap around the exhaust. I already found the right size 5 gallon water tank that is long and skinny and will fit in front of my gas tank.

I have the whole system design ready to go (hot and cold water tanks and pump/filter for creekside fill-ups), but the heat exchanger is the big question. I would love to hear your experiences with this before I do my own tests.

Here is a video with an internal coil design. At about 4.5 minutes into the video he tests the design and produces steam in about 10 or 15 seconds of the engine running. If your still thinking of this concept, its worth watching. I think with an external coil it will take longer to heat up a whole circulating 5 gallons, but we're not trying to produce steam either...
http://www.youtube.com/watch?v=UxXPKRTFoNM

 

[5Runner]

I'm still working on this...just taking some time.

Here is a good link with some information about making a heat exchanger with a copper coil like I have been thinking. They fill the tube with sand/salt so that when then bend it around the main pipe (exhaust) it keeps its shape. Great idea!

http://www.bio-power.co.uk/exchanger.htm

 

[djacidjac]

exhaust is too hot. makes steam. you'll break something or boil away your water. Design an exhaust-heat water distiller instead. use tried and true coolant exchanger for domestic hot water. stainless steel on ebay for 40$ USD.

 

[PPCLI_Jim]

here is what i did using the coolant.it was a while ago though . i used a piece of copper that was the size of the coolant tube and wrapped it with smaller copper tubing so it was in contact with it then soldered it to the coolant tube . from there i took a tube of larger tubing and wrapped it in fiberglass to insulate it and hold the heat in i then plumbed my water though it . as i only had a small tank i used the waters own power to circulate it hot vs cold water thermodynamics etc... . you could easily put a pump on the system .:chef:

 

[Grayjay]

Good write up of a home fabricated unit here:

http://www.drivenachodrive.com/about-nacho/water3/

 

[NIVEK_TURK]

I've been pondering the idea of running water through the A/T cooler portion of the radiator on my 4runner after I do the external tranny cooler. This would of course be with a new never used radiator. I just wonder how that would work..

 

[danfromsyr]

it would possibly bring the water above the boiling point which would create steam at the sprayhead.

 

[danfromsyr]

just be cautious and researched when dealing with a potential of steam, esp steam under pressure
you don't just go opening your radiator cap once hot, temperatures can be the same.
we may have different ideas on your heated water containment and circulating system. so either a clear design or pics will help best.
the oem use of a radiator cooler for the ATF is that ATF is hotter than the coolant.. but your water will be gaining heat from the ~100*c coolant

 

[NIVEK_TURK]

It would be a fun experiment to do I think with the size of the cooler and flow rate it may keep the temp comfortable. I was thinking of just a one time flow through and not circulating it. It just maybe a trial and error thing.