Recycled engine heat as you drive

[bretco]

Hi,

Just wondering if anyone has tried putting an insulated tank (maybe about 100 gallons) in the back of their pickup truck and bypassing the radiator to allow the engine to heat the tank full of water. It could be valved to turn the radiator back on if the tank gets too hot. A friend & I were discussing the feasibility of salvaging this heat and using an internal tank heat exchanger to claim it back as domestic hot water. Maybe some type of quick connect system to the house water supply. I'm already doing a similar process with my woodstove boiler with heat exchanger.Thinking of the wasted heat an internal combustion engine wastes, this would have to be better than dumping the heat to the atmosphere without first using it. Just thought I'd throw this out to the forum for feedback.

Bretco

[kell]

Sounds great in principle.  The devil is often in the details.  You may need baffles to keep the water from sloshing and destabilizing the vehicle.  You'll be hauling hundreds of pounds of water (and using up more gasoline). You'll have to pump that water into the house somehow every time you get back from a car trip...  and when you go somewhere and park overnight while the water cools off all the extra gas you burned will have gone to waste, along with the wear on your suspension.  That, or you leave with an empty water tank and have to find somewhere to fill it up for the trip back... but once the water is warmed up the extra gas expended to haul the added weight of the hot water will have been wasted.

An appealing concept perhaps, but I have to say I can't think of a way to make it work in the real world.

[zmoz]

Also, it would probably take quite a drive to warm up all that water. Before that happens, your engine is going to be running much cooler than usual, which is NOT good for it in the least and causes even less gas mileage. (in addition to the extra weight you are carrying) Your engine is designed to run with ~200 degree water circulating in it, not cold water.

[bretco]

I was thinking of retaining the thermostat to maintain engine temp so it still runs normally and 100 gallons of water (800 lbs) would definitely drop the mileage somewhat, but with an engine that is probably already only 20% efficient, with the rest wasted heat, capturing that heat has to have potential benefit. I think I'll try an experiment with my F150 and an old oil tank in the back and see if there's possibly any value to this idea. I'll post results if anyone is interested.

Bretco

[Adrian L]

What would be better would be a heat exchanger around the motor coupled to some sort of steam turbine to run a generator, which charges a couple of deep cycle batteries in the back, batteries are heavy, but a couple of 30kg batteries wouldn't effect the milaeage much and store a good 2-4kw max.....

With all these hybrid cars around im surprised they haven't bothered to make a prototype that does this, we all know how much a car engine wastes energy in heat!

Adrian L

[wooferhound]

It's been pointed out several times here, that it is better to reclaim the heat from the exhaust system, than from the water system.

[zmoz]

Thermostat isn't really going to help you. As soon as it opens a flood of cold water will come through and make it cold again...then the thermostat will close again, heat up the water, open, get cold, close, ect. Sounds pretty bad for the engine to me....

[Demetri]

If I was going to build such a system, I would leave the original cooling system essentially intact. Run the engine coolant through a heat exhanger to heat extra water, do not let the two systems come into contact. I absolutely would not drink or bath in water that has run through the cooling system of a car, propylene glycol(antifreeze) is a fairly nasty poison. If the engine's thermostat controlled when coolant flowed through the heat exhanger, there would be no more temperature swings than there are when the coolant flows through the radiator. Valves could be used to select whether coolant goes to the heat exchanger or the radiator. Hth.

Demetri

[dualsporter]

Sounds very interesting. Definitely want to hear about your results. Major downer, as I'm thinking, is related to where you are located. If you are in a cold climate where freezing temp.s must be delt with, and you use... say a 250 gallon oil tank... with a 50/50 mix of antifreeze, you're looking at investing in 125 gallons of antifreeze at $4.00 / gallon (wholesale), you've got a $500 experiment going. Maybe put a copper heat exchanger loop inside the tank and only fill the tank about 2/3 full of plain water. Reduces your cooling system volume (as compared to other method) and will probably survive being frozen. You'd just have to drive a little (ahem) farther to melt it before good heat rise could occur. Keep us updated.

Dualsporter

[bretco]

Hi Zmoz,

But isn't that what really happens anyway when the thermostat opens, a flood of cold water (from the radiator, instead of the tank) constantly makes the thermostat cycle from closed to sort of open until equilibrium  sort of lets the thermostat "modulate" the water to the engine core.

I'm thinking that the engine won't really see the difference if I use a tank in conjunction with the radiator and the original engine thermostat.

By the way, I'm still working on my PMG wind generator that I've been gathering info from the otherpower board for some time. I just need to move myself where the zoning rules for my town don't go so far as to look in your underwear drawer to see if you can put up a winmdill!

Bretco

[bretco]

Hey Demetri,

I would'nt dream of interchanging the glycol coolant from my truck to the house domestic water system. I'm already running an isolated system from my wood boiler that heats my domestic water via homemade heat exchangers ( my last gas bill showed about $2.00 usage for Oct-Nov in Vermont.) I totally isolate the "dirty" woodsove water from the "clean" city water with lots of copper tubing heat exchangers. Anyhow, I think maybe the experiment in itself might be worthwhile in establishing how much "waste" heat can be reclaimed from a vehicle, and I think it won't be all that difficult to rig up a way to "suck" the heat from my truck tank to the house tank, after all, my wood boiler is sort of doing the same thing, but now I will have to "download" the hot water to my house system, quick release valves etc.

[zmoz]

The problem is the small amount of coolant in your engine heats up in just a few minutes. With 100 or more gallons of water...you would have to go on a REALLY long drive just to get it to heat up, and all along the way you'd be running cold water through your engine. Did I mention that was bad for it yet?

[Old F]

Bretco

Here is something that I use with my wood boiler that could all so be used with engin exhaust.

For a heat exchanger for domestic hot water I used a old propane water heater with the burner

that had gone bad removed.

I welded 3/4 inch fittings to the flu and pumped water from the

stove thru it works like a charm.

Seeing how they are designed for high temp combustion gases

in the first place they should be a good fit for engin exhaust.

And they can be had free for the hauling.

Old F

[wooferhound]

The question about engine heat has been asked here before, with 17 comments...

http://www.fieldlines.com/story/2003/10/10/111948/27

[monte350c]

Hi All,

An automotive thermostat will open basically as needed - it doesn't have to be all the way open or shut. It will open only as much as the temperature of the water passing over the expansion capsule. A good example of this is an automotive engine installed in a marine application (Mercruiser stern drives for example) where lake or sea water is used directly for cooling. If you have a 190 stat in it, it will run at 190, taking in only enough cold water to maintain that temp.

Ted.

[bretco]

Thanks for pointing me to the other postings about recycling engine heat. The exhaust heat exchanger really has me thinking! I can hear my pickup out in the driveway getting nervous!!

Thanks all

Bretco