Exhaust heat for a water heater?

[JeepN95YJ]

I think this is an interesting project. I love your FSJ.

A big disadvantage to an exhaust-based system where I live is RUST!

It would be a shame to go to so much trouble and then need to replace it every 5-6 years. I do applaud the creativity, though. I'm looking forward to watching your Jeep progress.

 

[Metal Twister]

Yeah your right, maybe I should go ahead and build it out of stainless. I should flange so it would be easy to replace when the rest of the exhaust rots away that way it would be easy to work into your new exhaust new system.

And thanks for the props on the old beater. Its coming along slowly. wish I had the time to just get it all done but that's just wishful thinking on my part. :ylsmoke:

 

[chet]

have you thought about just wrapping some soft copper around the exhaust close to the manifold say 5 or 6 wraps and then insulating over it with header wrap? you can leave the ends long to get away from the ehaust and then test out what kind of heat you get from it. seems like it would be quite simple to make. I would keep it external to the actual exhaust system and easy to take off if there was a problem.

 

[ntsqd]

That is about where he started with the idea. The problem is that while it may work, it won't be a good indicator of what is possible. The thermal conductivity won't be great.

On the thermal pump control, were it me I'd go looking for a 12VDC powered PID controller that uses a std thermocouple. The Tempco's (120VAC) that I just installed on a test fixture at work are easily programmable for temperature and the acceptable error band width. Much, much better control than just a temperature switch. If you find one with self-tune capability it would be a good thing.

 

[Metal Twister]

There is an adjustable fan switch that we use when we install AC units on the hotrods. It allows the cooling fans to come on at what ever water temp we want. seems to be just what the Doctor ordered, specially since I have a couple laying around here somewhere. As far as the ease of fabricating the unit up... I have a full fab shop with all the sheet metal tools needed to make it a easy project. It would be easier for me to build it and install it than try to fool around with the manifold. Heck who knows maybe Im on to our next big seller. LOL I think for the majority what is available already would work just fine. This is just my way of having fun... Pretty sick. huh.

 

[off-roader]

Additionally, how do you control the amount of heat or how hot the water is? Rev the engine?

Not to sway you towards the water coolant method but by tapping into the hoses coming from your heater core you can control the heat by adjusting the car heater's temperature knob.

 

[Metal Twister]

Additionally, how do you control the amount of heat or how hot the water is? Rev the engine?

Not to sway you towards the water coolant method but by tapping into the hoses coming from your heater core you can control the heat by adjusting the car heater's temperature knob.

I think post Number 14 answers your question?

Dont worry about swaying me away, As mentioned this is a personal venture and just to satisfy my personal curiosity. As in post #15 that might be the way for most to go. Just seeing if I can build a better mouse trap... Maybe not :ylsmoke: But I do believe Change is Opportunity...

 

[etbadger]

Most of the modern diesels have exhaust gas recirculation systems that send exhaust gas back into the intake. This contains a gas to fluid heat-exchanger so the engine coolant can cool off the exhaust heading back for a re-burn.

Many folks remove them from their engine due to issues with the thermal stresses causing the coolant passages to eventually crack and dumping coolant into the intake (sudden unregulated water injection, theorized to cause may of the Ford 6.0L head-gasket failures by some). Additionally they get plugged up with condensate and carbon from the exhaust that settles out as it is being cooled.

Few points here: First, you can probably find some of those tubes cheap on a diesel truck web-site, and they are designed for almost exactly what you want (exhaust -> fluid heat extraction). Second, you may end up with the same issues (material fatigue and failure, exhaust crud buildup), but it doesn't seem as if the consequences are all that dire if there is a rupture or blockage.

Interesting idea.
-Erik

 

[Metal Twister]

Most of the modern diesels have exhaust gas recirculation systems that send exhaust gas back into the intake. This contains a gas to fluid heat-exchanger so the engine coolant can cool off the exhaust heading back for a re-burn.

Many folks remove them from their engine due to issues with the thermal stresses causing the coolant passages to eventually crack and dumping coolant into the intake (sudden unregulated water injection, theorized to cause may of the Ford 6.0L head-gasket failures by some). Additionally they get plugged up with condensate and carbon from the exhaust that settles out as it is being cooled.

Few points here: First, you can probably find some of those tubes cheap on a diesel truck web-site, and they are designed for almost exactly what you want (exhaust -> fluid heat extraction). Second, you may end up with the same issues (material fatigue and failure, exhaust crud buildup), but it doesn't seem as if the consequences are all that dire if there is a rupture or blockage.

Interesting idea.
-Erik

No problem at all if it does rupture... Other than a mass amount of water running out the tail pipe or possibly steam. It could be alarming until you reliazed what was going on.:Wow1: Thanks for the info. on the diesels. I will check into the heat exchangers and see if they will be usable for what I am up to here.
Thanks again

 

[michaelgroves]

It seems to me you may be a victim of your own success - if the system is very effective you will soon find you have your entire tank of water at 100 deg C (or whatever you regulate it at). Won't you have a problem with the water still in the exhaust at 500 deg? Surely you'll have to actively stop more water from entering the HE (not just stop pumping it), as well as having a pressure blow-off?

 

[Metal Twister]

It seems to me you may be a victim of your own success - if the system is very effective you will soon find you have your entire tank of water at 100 deg C (or whatever you regulate it at). Won't you have a problem with the water still in the exhaust at 500 deg? Surely you'll have to actively stop more water from entering the HE (not just stop pumping it), as well as having a pressure blow-off?

HUM... Good point...As long as I can vent off the remaining water in the H.E. why couldn't I just turn it off? When the pump stops nothing is going into the H.E.? My new thought for the day. :clapsmile: Maybe a in line resettable pressure relief valve set at say 200 psi or so? Or maybe just open a 12 volt solenoid valve to vent the H.E. when not in use?

 

[Metal Twister]

I have been giving this some thought this morning and as long as the return line from the heat exchanger is open to the reservoir (holding tank) and the holding tank is vented the hot water in the H.E. would just pressure it self empty. So, I see no reason that turning off the pump wouldn't work without any extra doodads... The holding tank would have to be vented though, and maybe a check valve to keep the water from the holding tank from slopping back into the H.E.... ? Right?

 

[ntsqd]

Given the opportunity the HE will boil off any water within it. The line from the HE to the reservoir will slowly dry out. The line from the pump to the HE may present a small problem. Not too worried about it drying out, as it somewhat will, but that when still full that heat will conduct down it to the pump. I would suggest a high point in that line that is higher than the reservoir level as a simple solution.

 

[Metal Twister]

Will do thanks for the tip. That should be the last obsticle as far as I can see? :smiley_drive:

 

[michaelgroves]

When the pump comes back on, there will be a rush of steam? And quite a bit of it, I should imagine.