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Old 08-10-2022, 02:06 PM   #1
Mini-Skoolie
 
Join Date: Nov 2021
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Using exhaust heat for water heater

Hi, I know many have thought about this, and I'd like to see some updated ideas.
I have a short 16 passenger shuttle bus with a Trtiton V10 and the whole floor gets very hot due to the exhaust. It's an incredible amount of energy I just cannot bear to let go to waste.
I'm imagining copper tubing wrapped around the exhaust pipe, similar to this:
I found a product that uses some of these ideas: https://polarpower.com/products/gene...eat-exchanger/

Their brochure has more details and raises some relevant safety concerns, such as introducing water to an empty, hot system (boom) https://www.polarpower.com/wp-conten...anger_0115.pdf

I am aware of using the coolant for this, and I even have one of those rear heaters that draw from the coolant system, but I just can't believe that it would be as efficient.

I imagine a cold water tank that maintains to the coil system, which thermosiphons to an insulated hot tank. The hot tank would have a protected pressure release valve.

Curious if the hot and cold tanks would naturally balance?

There is one serious con to this plan, now that I think about it. Drawing heat away from the exhaust might slow exhaust gases, putting more resistance on the exhaust stroke of the cylinders, leading to more engine inefficiency, more emissions, more gas.

Let me know your thoughts!

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Old 08-10-2022, 02:38 PM   #2
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the copper would need something to seperate it from dissimilar metals or it will corrode.
other than that i would want a pump controlled by an aquastat directly in to the hot tank and feed the hot tank with the cold tied into the hot line with a check valve into the return port. as well as the cold in.
a pressure relief valve piped out to a same location is a must.
solar hot water systems us ethylene glycol/antifreeze.
also look up shower drain heat exchangers?
i have installed those in multi story buildings as well.
glad that wasnt my spent on them.
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Old 08-10-2022, 03:18 PM   #3
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something like that might heat up some water while driving but wont do much while you are parked and the tank you heated runs out.. also your exhaust can get much hotter than boiling which means you are creating pressure (or making steam).. if you are driving all day long and climbing mountains where your exhaust is quite hot how do you plan to limit the heating.. the water in the exhaust loop is going to super heat (and potentially super-pressurize if you got it hot enough)....
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Old 08-10-2022, 03:22 PM   #4
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if you want, you can purchase a product that does this. An EGR cooler is an exhaust pipe with a water jacket. You could also pipe your coolant lines from your engine to a liquid to liquid heat exchanger. The question is.. how often do you want hot water while your engine is running (or ran within the last hour). You still need other systems to heat the water which will cost way less and likely be used more often than the exhaust heater.
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Old 08-11-2022, 12:20 PM   #5
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Quote:
Originally Posted by cadillackid View Post
something like that might heat up some water while driving but wont do much while you are parked and the tank you heated runs out.. also your exhaust can get much hotter than boiling which means you are creating pressure (or making steam).. if you are driving all day long and climbing mountains where your exhaust is quite hot how do you plan to limit the heating.. the water in the exhaust loop is going to super heat (and potentially super-pressurize if you got it hot enough)....
thats why i brought up a pump with aquastat and mixing cold water with it into the return porn.
and could also add a solenoid valve on the cold mix line to help control the setpoint temperature.
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