Water heating, in a vehicle

[Short_Shot]

So if you reduce the engine heat by much you will affect the mpg. Using a alternator requires horsepower. Like running A/C cost mpg. Or is it redundant you want? I once built a heat exchanger to heat water entering water heater. It captured heat from the shower drain. My self built RV I used tankless Lp and cook with it as wall. Last year we used it for 9 days in March plus 5 three day weekends plus I lived in it for 10 days cooking and showered all on half a 20 lb LP tank. I have never spent the money on hydronic vacuum tubes,but as good as they are said to be thrown a few on the roof 3 pumps, 2 plate exchangers and valves and you could have engine waste or solar.

Most people are not worried about that. The efficiency is turned into useful energy

 

[eXodus]

Engine temperature has a small affect on fuel efficiency. The bigger issue from the tree huggers point of view is that if you run coolant through the hot water tank it will take longer after a cold start for the engine to reach operating temperature and will take longer for the catalyst to light off and emissions to improve.

If using this approach you would want to have a system in place that monitors engine temperature and does not start pumping coolant to the water holding tank until operating temperature was reached. Then, a pump would kick on and only a small amount of coolant would be circulated to prevent the temperature of the engine from dropping. If it were to drop a couple of degrees, the pump would turn off and wait for operating temperature to be reached again.

Nothing a small mechanic thermostat can not solve.

I've been using engine coolant heat exchangers for a long time and as long you are not standing and idling it doesn't makes a difference. At partial load an engine heats up within the first mile for all emissions systems to come fully functional.

There are two coolant circuits on an engine, the small one with the cabin heater and the large one with the radiator.

 

[eXodus]

If you are driving and ‘wasting’ fuel at part throttle there are periods when the horsepower (watts) produced by the motor cannot be less and have the motor still run… so there is ‘free’ power available

Remember the Caddy in the 80s with the cylinders that would drop out to boost mileage?
Remember Bruce Crower experimenting with half-cycle V8s?
Remember Smokey Yunick?

There are several vehicles today that drop cylinders in no-load situations, to avoid burning fuel without a purpose.

I am not incorrect. It’s not the alternator isn’t a load that uses gasoline, it’s that sometimes it doesn’t take more gasoline to run an alternator depending on the driving conditions.

A gasoline vehicle only uses maximum 30% of the energy contained in fuel to rotate the crank.

The other 70% are heat. One gallon of gas are 33 kWh of energy. For every gallon you burn, you are producing 23kwh of heat. About 30% of that heat goes out the exhaust.

So for every gallon, your coolant gets about 14kwh of pure waste energy.

So do some math figure how many gallons you burn per hour and you get an idea how much heat you got available.

My RV for instance gets 10 mpg when driving 60mph. So I'm burning 6 gallons per hour.

6 gallon x 14kwh equals 84kwh of free waste energy to heat water.

 

[Short_Shot]

A gasoline vehicle only uses maximum 30% of the energy contained in fuel to rotate the crank.

The other 70% are heat. One gallon of gas are 33 kWh of energy. For every gallon you burn, you are producing 23kwh of heat. About 30% of that heat goes out the exhaust.

So for every gallon, your coolant gets about 14kwh of pure waste energy.

So do some math figure how many gallons you burn per hour and you get an idea how much heat you got available.

My RV for instance gets 10 mpg when driving 60mph. So I'm burning 6 gallons per hour.

6 gallon x 14kwh equals 84kwh of free waste energy to heat water.

Steam turbine. Send it.

 

[12VoltInstalls]

but this has nothing to do with an alternator using any kind of "free power". The whole concept you are presenting defies logic. If there was extra power available to drive an alternator using the same amount of fuel, is in contradiction to the law of conservation of energy. It does not happen.

I am not talking about defying the law of conservation of energy LOL

The little quotes: “ “ I used or italics are there on purpose.

When you run your car heater you are using “waste” as any heat or energy- alternator or heater- not applied to the work is ‘waste.’ An inefficiency.

Correct. The ‘free’ is not necessarily free. But the percentage load is - or can be- minuscule. In some conditions essentially not measurable by the gas gauge.

Argue if you want to but between Smokey Yunick and GM and I think even Toyota Tundras with variable valves and some other current vehicles utilize methods to fractionally decrease fuel use by shutting down use when not deemed necessary.

This does not defy thermal or energy science. It points out that with trucks especially older or large RVs there is no apparent consequences to running other equipment. This is due to either low percentage of losses or the power production of the motor in some flat or particularly downhill driving isn’t fully utilized or not at all. This is why ‘mileage’ races use coasting to gain sometimes HUGE fuel savings.

The second alternator isn’t doing some magic thing or defying the law of conservation of energy in any way- it just is a high likelihood of not visibly or noticeably altering fuel mileage.

Nothing defies the laws of science. He wasn’t talking about laboratory conditions but was looking at possible ways of creating practical methods of creating hot water for several options of use.

Your diatribe above goes down rabbit holes of stuff I never suggested. Cylinder deactivation for example: how on earth did you think that was a free energy reference?? It was a reference to the fact that at times during driving a distance in a vehicle all the possible power is not required. Tesla uses this concept, basically all e-cars use regen, and my 2021 nissan rogue company car has an incredible coast functionality.

Way, way back to Crower and Yunick and many others they knew about excess power. Yunick explored several things including high heat operations which virtually all vehicles today use.

There are no suggestions of energy science laws being broken in anything I wrote. Just the fact that you can run a second alternator potentially with no apparent consequences. Ymmv lol- pun intended
Thank you.

 

[noenegdod]

The shower water heat reclamation concept? I was not aware of its use in residential systems.

Yup, been done since late 90s early 2000s The typical heat exchanger is put in the main stack but is quite expensive (Canadian link in CAD): https://www.homedepot.ca/en/home/ca.../water-heaters/drain-water-heat-recovery.html

Smaller units that install right under the shower can be had or easily made

I have heard of similar concepts with air intake/exhaust though.

Yup, HRV (heat recovery ventilators) have been around even longer.

 

[noenegdod]

An alternative (that I have not found a diagram for, but would like to) is to use a heat exchanger between the engine cooling system and the water heater heating loop, rather than tying directly into the engine cooling loop. I think this would be preferable in some regards (leaving your engine cooling system as untouched and unmodified as possible).

That would be added complexity. The system you linked to simply cuts into and increases the length of the heater hoses and sticks the heat exchanger in the blue tank. Same thing you are talking about but simpler installation. Down side of what they did is it will take longer for the engine to warm up to operating temperature. In my opinion a better approach as described in another post I made is to put Ts into the supply and return heater hoses and install a small pump that is turned on when engine operating temperature is reached.

 

[noenegdod]

Nothing a small mechanic thermostat can not solve.

That is certainly one way to solve the problem

I've been using engine coolant heat exchangers for a long time and as long you are not standing and idling it doesn't makes a difference. At partial load an engine heats up within the first mile for all emissions systems to come fully functional.

This will depend entirely on how much water you are heating up and how much fuel you are putting on the engine in that mile

There are two coolant circuits on an engine, the small one with the cabin heater and the large one with the radiator.

Yes, the "small one" has no thermostat located anywhere in it and it is isolated from the "big one" by a thermostat. Making the water heater loop part of the "small one" with out any control built in will increase the time it takes the engine to reach operating temperature. It is just a fact about mass you can not deny. The amount of time is dictated by how much water you are trying to heat.

 

[noenegdod]

A gasoline vehicle only uses maximum 30% of the energy contained in fuel to rotate the crank.

The other 70% are heat. One gallon of gas are 33 kWh of energy. For every gallon you burn, you are producing 23kwh of heat. About 30% of that heat goes out the exhaust.

So for every gallon, your coolant gets about 14kwh of pure waste energy.

So do some math figure how many gallons you burn per hour and you get an idea how much heat you got available.

My RV for instance gets 10 mpg when driving 60mph. So I'm burning 6 gallons per hour.

6 gallon x 14kwh equals 84kwh of free waste energy to heat water.

That is the rule of 3rds. 1/3 into mechanical, 1/3 into the coolant and the last third out the tail pipe.

 

[noenegdod]

I am not talking about defying the law of conservation of energy LOL

The little quotes: “ “ I used or italics are there on purpose.

When you run your car heater you are using “waste” as any heat or energy- alternator or heater- not applied to the work is ‘waste.’ An inefficiency.

Correct. The ‘free’ is not necessarily free. But the percentage load is - or can be- minuscule. In some conditions essentially not measurable by the gas gauge.

Argue if you want to but between Smokey Yunick and GM and I think even Toyota Tundras with variable valves and some other current vehicles utilize methods to fractionally decrease fuel use by shutting down use when not deemed necessary.

This does not defy thermal or energy science. It points out that with trucks especially older or large RVs there is no apparent consequences to running other equipment. This is due to either low percentage of losses or the power production of the motor in some flat or particularly downhill driving isn’t fully utilized or not at all. This is why ‘mileage’ races use coasting to gain sometimes HUGE fuel savings.

The second alternator isn’t doing some magic thing or defying the law of conservation of energy in any way- it just is a high likelihood of not visibly or noticeably altering fuel mileage.

Nothing defies the laws of science. He wasn’t talking about laboratory conditions but was looking at possible ways of creating practical methods of creating hot water for several options of use.

Your diatribe above goes down rabbit holes of stuff I never suggested. Cylinder deactivation for example: how on earth did you think that was a free energy reference?? It was a reference to the fact that at times during driving a distance in a vehicle all the possible power is not required. Tesla uses this concept, basically all e-cars use regen, and my 2021 nissan rogue company car has an incredible coast functionality.

Way, way back to Crower and Yunick and many others they knew about excess power. Yunick explored several things including high heat operations which virtually all vehicles today use.

There are no suggestions of energy science laws being broken in anything I wrote. Just the fact that you can run a second alternator potentially with no apparent consequences. Ymmv lol- pun intended
Thank you.

The argument is completely asinine. What you have just said is that since the engine is consuming so much fuel, you will never notice adding a little bit more load so go ahead and do it and you will never notice it, like it has no consequence. It has consequence for the entire duration the engine is operating.

This is a failure of logic. You would never suggest that someone would buy and use a generator to accomplish the same task. Everyone would simply call you stupid. The act of pouring a small amount of fuel into generator and watching it being consumed highlights exactly what is being used to accomplish the task. However, instead you are suggesting that someone go out and buy an alternator, brackets, belts, wiring and hardware, Pay or take the time to install and then add that fuel you were putting into the generator instead into the tank of your vehicle and because it is just a tiny percentage of what you are putting in any way it doesn't matter.

Do what ever makes you feel good but facts dont care about you feelings.

 

[Short_Shot]

It will definitely add a bit of load if you're adding circuits to pump coolant through.

However the increase in consumed heat will be effectively irrelevant. All it will do is run a fraction of a degree cooler overall, probably not a detectable amount. The engine already needs to get rid of that heat. Either you pump it to atmosphere or you take a shower with it. Your pick, but it's not going to be an appreciable extra load.


The alternator on the other hand. The topic of your debate here, I assume....

That's a great way to burn up a lot of fuel fast lol

 

[12VoltInstalls]

The argument is completely asinine. What you have just said is that since the engine is consuming so much fuel, you will never notice adding a little bit more load so go ahead and do it and you will never notice it, like it has no consequence. It has consequence for the entire duration the engine is operating

You don’t really have to be a jack wagon

Some of us don’t mind spending to get energy. Like I don’t turn my stereo and sub amp off when I drive to save the environment. It’s ok to have a different opinion about using fuels than me or anyone else but you don’t have to call people asinine to keep your own perspectives.

I had this 1969 westfalia VW bus with an inverter, accessory battery with isolator, vcr, color TV, and refrigerator. On trips in flat areas (Ohio etc) I got about 23mpg with or without the inverter running. I wouldn’t have cared if it were measurable. It doesn’t bother me now, didn’t bother me then. Sorry if that offends you.

Other people have their own opinions, sometimes they parallel mine:

the increase in consumed heat will be effectively irrelevant. All it will do is run a fraction of a degree cooler overall, probably not a detectable amount. The engine already needs to get rid of that heat. Either you pump it to atmosphere or you take a shower with it. Your pick, but it's not going to be an appreciable extra load

And sometimes they don’t:

That's a great way to burn up a lot of fuel fast lol

And depending on the situation he could be right. Probably is in many cases.

you are suggesting that someone go out and buy an alternator, brackets, belts, wiring and hardware, Pay or take the time to install and then add … because it is just a tiny percentage of what you are putting in any way it doesn't matter.

Yup, I’m saying there’s a good chance it won’t matter.
At the very least it would work.

It was merely an idea to consider; who knows? it might stimulate thought on something creative in another area.

It was an idea and you think I’m killing your bunnies I guess.

Cheerio and thumbs up.

 

[Short_Shot]

Alternator load is significant on fuel.

Whatever wattage you pull out of it adds that plus losses to the engine and ~768w = 1 hp.

Standard alts are 50 to 60% efficiency. So loading up an alt with an extra 600w is going to be some 1.5hp more.

When you consider most vehicles only need 10 to 20 hp to maintain 60mph, depending on aerodynamics of course, suddenly that 1.5hp extra is as much as 15% increased fuel requirement while cruising along.


Figuring out an exact result is much more complex and requires the aerodynamic factor be accounted for as well as terrain, and how much percentage of average fuel economy it is will be less because obviously there are times when you're using much more engine output and that 1.5hp is nothing next to 300 hp but the point stands.

Its significantly extra fuel relative to what's used at highway speeds.

 

[12VoltInstalls]

obviously there are times when you're using much more engine output and that 1.5hp is nothing next to 300 hp but the point stands.

Its significantly extra fuel relative to what's used at highway speeds.

Yes exactly.

I have no debate with that. It’s facts.

An RV as OP was inquiring about would be less noticeable than the wattage in a minivan.

And even that would be less so if you didn’t use a 25000W heating element LOL

 

[noenegdod]

You don’t really have to be a jack wagon

Some of us don’t mind spending to get energy. Like I don’t turn my stereo and sub amp off when I drive to save the environment. It’s ok to have a different opinion about using fuels than me or anyone else but you don’t have to call people asinine to keep your own perspectives.

I had this 1969 westfalia VW bus with an inverter, accessory battery with isolator, vcr, color TV, and refrigerator. On trips in flat areas (Ohio etc) I got about 23mpg with or without the inverter running. I wouldn’t have cared if it were measurable. It doesn’t bother me now, didn’t bother me then. Sorry if that offends you.

Other people have their own opinions, sometimes they parallel mine:

And sometimes they don’t:


And depending on the situation he could be right. Probably is in many cases.


Yup, I’m saying there’s a good chance it won’t matter.
At the very least it would work.

It was merely an idea to consider; who knows? it might stimulate thought on something creative in another area.

It was an idea and you think I’m killing your bunnies I guess.

Cheerio and thumbs up.

If you think I am offended by what you are suggesting you are absolutely wrong, again. Just pointing out you are in fact wrong and supporting my argument.

 

[12VoltInstalls]

If you think I am offended by what you are suggesting you are absolutely wrong, again. Just pointing out you are in fact wrong and supporting my argument.

If you weren’t offended why did you call me asinine? Just because you don’t understand the difference between practical applications, empirical references and literal science? Because you like to argue? Or just angry at life and take it out on people by splitting hairs or other acerbic plume?

This topic was a good read, an interesting thread.
I’m rather annoyed with myself to have participated in derailing it.

“Water heating, in a vehicle”

 

[Short_Shot]

Yes exactly.

I have no debate with that. It’s facts.

An RV as OP was inquiring about would be less noticeable than the wattage in a minivan.

And even that would be less so if you didn’t use a 25000W heating element LOL

An RV likely has a much larger alt and load though.

Likely proportional with the crappy aerodynamics involved to still produce a significant hit.

 

[noenegdod]

If you weren’t offended why did you call me asinine? Just because you don’t understand the difference between practical applications, empirical references and literal science? Because you like to argue? Or just angry at life and take it out on people by splitting hairs or other acerbic plume?

This topic was a good read, an interesting thread.
I’m rather annoyed with myself to have participated in derailing it.

“Water heating, in a vehicle”

Yet you continue.....

Everyone does and says stupid things at times. It does not make you inherently stupid or asinine. Myself included.

Edit: When you are wrong, the people around you have an obligation to point it out so you can stop making stupid mistakes.
Jordan Peterson

 

[Dzl]

That would be added complexity.

To the system overall, yes. But to the engine cooling system I think it might introduce less change/complexity (still thinking it through). With a heat exchanger you aren't substantially increasing hose lengths, coolant volume, etc. Just adding a heat exchanger in the existing circuit. The downside is more complexity overall though. So idk..

The system you linked to simply cuts into and increases the length of the heater hoses and sticks the heat exchanger in the blue tank. Same thing you are talking about but simpler installation. Down side of what they did is it will take longer for the engine to warm up to operating temperature. In my opinion a better approach as described in another post I made is to put Ts into the supply and return heater hoses and install a small pump that is turned on when engine operating temperature is reached.

I'll look into your idea more. What is the advantage of plumbing into the heater lines as opposed to the main coolant lines?

 

[noenegdod]

To the system overall, yes. But to the engine cooling system I think it might introduce less change/complexity (still thinking it through). With a heat exchanger you aren't substantially increasing hose lengths, coolant volume, etc. Just adding a heat exchanger in the existing circuit. The downside is more complexity overall though. So idk..

I have rethought saying that using an external heat exchange would add complexity. That is probably wrong and it would also make it easier to ensure you are only extracting heat from the cooling system when you are at operating temperatures.

If you cut in a bar and plate or a tube in tube style (both have their advantages and disadvantages) into the heater circuit, and just pump water to the heat exchanger from your storage tank you can easily integrate a thermostat so it only pumps water when the engine is hot and as you say coolant volume remains basically the same which is desirable.

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Being that you may travel to freezing temperatures it would be good if the return line to the tank was above the waterline in the tank so that the fresh water traveling to the heat exchanger siphoned back to the tank and no fresh water remained in the lines. You would also want to ensure the heat exchanger could drain as well.

I'll look into your idea more. What is the advantage of plumbing into the heater lines as opposed to the main coolant lines?

The main issue is line size. Ting into a 1.5 or 1.75" hose is a lot harder to find parts for than it is for regular 5/8" hose. The other thing is the coolant in the heater circuit is always full engine temp. The rad circuit will vary in temp and volume flowing through it.