Heat recovery from car radiator.

[questionsarewis]

Trying to see if it is viable to capture waste heat from radiator of cars(s) to pre-heat water heater and or radiant floor. Off grid homeowner here and every little bit of energy counts!

Enclosed garage. R-50 SIP panel "house" to pull nose of car into, Solar-powered fan to draw air over a metal fin system filled with glycol alcohol. Heated fluid is drawn towards water heater and or radiant storage tank. Simple system, am I as dumb as I think I am?

 

[marcusl]

I don't know what a Sip paneled house is. My thought is that the radiator doesn't store enough heat to make it worthwhile (only a large van or suv has a radiator with even 1 gallon capacity, you can figure out the stored heat). What you want is to suck the heat out of your engine block, that's a big hot mass especially if it's a V8. You could install an aftermarket electric water pump to circulate coolant through the block after you turn the vehicle off.

Is it worthwhile? Calculate the heat stored in the block, subtract the energy spent in fans and pumps, and then you'll know.

 

[Danger]

Welcome to PF, questionsarewis.
While what you want is certainly possible, Marcus has made the main point. Is it worth it?
I have an idea of how to achieve it fairly easily and cheaply, but I don't know how effective it will be. And keep in mind that it will only work for a very short time, and only when the car has been driven recently. Here goes:
Build a heat exchanger, perhaps from a water heater tank or similar, and fill it with the same water/antifreeze mix that you use in your vehicle (in the same quantity that the vehicle holds EDIT: no, there should be more than the vehicle holds). There should be 2 hoses from it long enough to reach the car, with a thermometer mounted in one of them. Put shut-off valves near the ends, to prevent draining.
Insert a diverter valve to a tap on your lower radiator hose, and another shut-off-valved tap just after it (between it and the rad).
When you park the vehicle after a drive leave it running. Immediately connect the hose with the thermometer to the first tap, and the other hose to the second. Open the shut-off valves in the hoses and switch the diverter valve to the 'flush' position. Let the engine water pump force the coolant into the heat exchanger. It should force the cool stuff that was already in the exchanger into the second tap. When the thermometer drops to room temperature, you've completed the transfer. Shut the motor off, switch the diverter valve back to the 'drive' position, close the shut-off valves, and disconnect your hoses.
I don't know how much you can get in the way of recycled heat, but there might be enough to do something useful like fill a dishwasher.
Put some filtration in the system to prevent contaminating your coolant, and make very sure that your diverter valve hook-up doesn't leak.
It's still up to you to figure out whether or not it's worthwhile.

 

[marcusl]

Hi Danger,
Good to cross paths with you again!
questionsarewis, I like to calculate things. I assume you live in a cold climate, otherwise you wouldn't be so energy-hungry in the first place. It's snowing here today, so I'll use my numbers as an example.

Imagine you have a 4500 lb SUV with a V8 since anything smaller probably doesn't have enough heat to bother with. The engine block and heads (which are accessable to the coolant) probably weigh around 400 lbs and reach a temp, we'll say, of 250F. The frame, chassis, body, suspension, etc. maybe weigh 3000 lbs and when I drive home from work they are 20F. I pull into my 50F garage. The ratio of heat lost from the garage over heat given to the garage is
3000*(50-20) / 400*(250-50) = 1.12
and when you add the heat lost by opening up the garage door to pull in, your vehicle is an overall drain on the household heating budget. You do even worse by inefficiently draining the heat from the radiator.

Conclusion: in the winter, you gain more heat by leaving the SUV in the driveway!

 

[Danger]

Good to cross paths with you again!

Likewise. Good explanation of the efficiency there.
I just thought of a further complication with the system that I came up with. There's no way it will work the way I was thinking of, because I forgot to account for the vehicle thermostat. It will close and shut off coolant flow through the engine, and thus through the heat exchanger, when the temperature drops below 230 or whatever. I also don't know what effect depressurizing the coolant system will have upon the temperature of the emerging fluid.
This is why I usually try to work something out properly before posting.

 

[brewnog]

As the others have pointed, the juice just isn't worth the squeeze.

However, you might be interested in looking into a micro-cogeneration unit. This could provide electricity and heat for your home, at upwards of 90% efficiency (compared with perhaps 30-40% with a traditional home).

Just a thought...

 

[Danger]

Hmmm... (this is sort of an edit to my last post)...
I suppose that you could build your connections for my system by drilling and tapping into opposite sides of the thermostat housing to bypass it.
But, again, it's not worth it.

 

[wxrocks]

There have been some cars (Cadillac I think) that have experimented with this (sorta). Some have a "thermos" in them so that you don't have to run the car to have heat right away. There has also been some experiments with storage devices in the drive train for mechanical energy as you brake to gain more acceleration (a lot like a hybrid, except mechanical energy is stored as such).

So if anything, I would maybe add a thermos type device so that you don't have to warm up your car and will have instant heat!

 

[brewnog]

wxrocks, I don't think this was the OP's idea; the idea was to use energy from a warm parked car to heat a house.

Developing the idea and my suggestion of micro-cogen, I wonder whether a system using your car's engine as a source of electricty and heat for your home could be made to work. Some kind of docking station would obviously be required with the necessary fuel, water and power connections, but my first impressions would be that the power and heat outputs are probably not that far off what's required for the average home.

Russ, any basic general figures on power and heat consumptions for average domestic households in western countries?

 

[wxrocks]

I understand that -- but a problem we all face is thinking globally with energy savings. It is nice to at least think a few steps farther down the line in energy savings. The gas you save by not running the car to warm up could then be used to heat the house.

If the car is not running -- I just can't see any gain in taking the heat from a car -- there are much better ways to save energy.

 

[brewnog]

I think global issues with energy savings should be going a bit further than not warming up a Cadillac before you take it out...!

wxrocks, my proposal was not for a car which isn't running. My idea was to have the car actually run, in the garage, to power and heat your home.

 

[Danger]

Not sure about efficient heat transfer, but at least if it's running you can also use the exhaust as a source. As for electricity, just build a roller rig like a chassis dyno with a generator hooked up.

 

[brewnog]

I was thinking about this as a serious proposal. Not just exhaust heat, why not jacket water and any intercooler water heat too? And why have a chassis dyno where it could be feasible to incorporate a PTO or alternator into new vehicles designed to be used as a CHP installation?

I'd really like to see this as a proposal. Who was asking about final year uni projects?

 

[marcusl]

Won't a reciprocating IC engine be inefficient compared to burning natural gas? I'm not just waving hands. The gas furnace has been optimized over 150 years to solve your this problem, and is 90 to 92% efficient (modern two stage furnace) in heating your house. The car does badly because it solves a different problem, namely producing mechanical power while minimizing heat production. Better would be connecting the driveshaft to a heat pump and extracting heat from the (cold) outside to warm the interior, in addition to capturing the engine's waste heat. However, a) it would suck to switch the driveshaft each morning and evening and b) heat pumps operating in this mode are inefficient so I bet even this approach loses fairly significantly.

Unless you are making free solar or wind energy (both good ideas), I find it hard to believe you can improve on the utility industry's century or more of optimization.

 

[Q_Goest]

Hi Question. I wonder if you're still lurking? Anyway, welcome to the board.

If you were to have a storage tank of water inside your car such that you could essentially eliminate the radiator and store all the heat inside this tank you might get enough energy to make it worth while, but as you'll see, there's not a tremendous amount of energy here.

Let's say we have a tank with 100 lbm of water (about 12 gallons, give or take). Let's say you heat that water using your engine to 210 F, and then you're able to use that heat down to 90 F. The dU for this is 120 Btu/lbm. So for 100 lbm, you get 12,000 Btu. This equates to roughly 3.5 kW hrs. Where I live, electricity costs roughly $0.07, so you can save the equivalent of 24.5 cents worth of electricity with a 100 lbm tank. You'd need 400 pounds to save $1. That might actually be worth it if you can save that much energy every day, or if you spend significantly more for energy.

Now ask, "Can the vehicle produce that much heat?" Think about how much power it takes to drive your car, and then estimate the heat loss through the radiator. That's how much you'll be able to capture given 100% efficiency in capturing that heat. I'll come back to this question if you'd like, or perhaps someone else would like to dig into it.

 

[brewnog]

Won't a reciprocating IC engine be inefficient compared to burning natural gas? I'm not just waving hands. The gas furnace has been optimized over 150 years to solve your this problem, and is 90 to 92% efficient (modern two stage furnace) in heating your house. The car does badly because it solves a different problem, namely producing mechanical power while minimizing heat production. Better would be connecting the driveshaft to a heat pump and extracting heat from the (cold) outside to warm the interior, in addition to capturing the engine's waste heat. However, a) it would suck to switch the driveshaft each morning and evening and b) heat pumps operating in this mode are inefficient so I bet even this approach loses fairly significantly.

As far as heat recovery goes, yes, the efficiency will be less than a modern gas boiler. However, if you treat the electricity generated as a byproduct (ostensibly 35% of the fuel input), and offset this against the cost, then I reckon you'd definitely be in with a fair scheme by which to offset the heat and electricity costs required for the average home, particularly if you use the same natural gas that your boiler would. I suppose the heat pump would work in certain climates, but I still like the idea of cogeneration, or trigeneration for warmer climates.

 

[Danger]

I was thinking about this as a serious proposal. Not just exhaust heat, why not jacket water and any intercooler water heat too? And why have a chassis dyno where it could be feasible to incorporate a PTO or alternator into new vehicles designed to be used as a CHP installation?

Oh, I was just thinking if someone wanted to cobble something together at home rather than a commercial product. And I actually meant the exhaust heat in addition to that of the water jacket. If it were a commercial unit, I'd also consider using a turbocharger as the water pump to avoid parasitic losses on the fan belt.

 

[russ_watters]

As far as heat recovery goes, yes, the efficiency will be less than a modern gas boiler. However, if you treat the electricity generated as a byproduct (ostensibly 35% of the fuel input), and offset this against the cost, then I reckon you'd definitely be in with a fair scheme by which to offset the heat and electricity costs required for the average home, particularly if you use the same natural gas that your boiler would. I suppose the heat pump would work in certain climates, but I still like the idea of cogeneration, or trigeneration for warmer climates.

Generally, cogen is looked at from the other way around: the heat is a biproduct of the electricity generation. You don't lose much electricity by adding cogen, but if you want to use a heating boiler to generate electricity, you lose a lot of heat.

An electric generator on an IC engine with little in the way of extra goodies to increase its efficiency may be 35% efficient at making electricity, by a decent stock residential boiler or gas furnace is upwards of 95% efficient at heating your house.

So to answer marcus's question: If your primary goal is generating power and you have 65% of your energy going up a stack, it may make sense to throw an aft-end boiler on it to recover the heat. If your primary goal is generating heat, it never makes sense to throw a generator onto your boiler.

Regardless...

I was thinking about this as a serious proposal. Not just exhaust heat, why not jacket water and any intercooler water heat too? And why have a chassis dyno where it could be feasible to incorporate a PTO or alternator into new vehicles designed to be used as a CHP installation?

I'd really like to see this as a proposal.

So would I. I'm not convinced it would be worthwhile, but it could be. At the very least, it could make for a nice emergency backup system. I'm too lazy to do any calculations, but I'm reasonably certain a car engine could easily provide both the heat and electricity for the decent sized house at barely above idle power.

More generally, cogen is something that larger commercial buildings tried in the '80s and somewhat surprisingly, it has turned out to not be economically viable. One client of mine, a 750 unit condo building in Philly, is getting rid of their cogen plant, which at one time was a highly regarded test-case in Philly. It is maintenance intensive and needs a well-trained engineering staff to run it, but worse than that, deciding when to run it is not a simple economic decision.

 

[B. Elliott]

This is almost funny. Over the past couple of weeks I've been thinking about the exact same thing. What sparked the idea was that I have an extra Chevrolet 350 sitting in my shop collecting dust. One day i thought to myself, what would keep me from mounting the engine on a stand, inside or outside the shop, (most likely outside because of the nose) and somehow route lines from the engine to a radiator inside, while a fan mounted to it blows the hot air throughout the shop?

This also sparked a few other goofy ideas. For instance, add an additional alternator (or two) to the engine and use it as a possible power supply for equipment or, to provide light for the shop its self.

How much power does just one typical auto alternator put out anyway? I'm thinking somewhere around 1000w if memory serves me right (usually doesn't). I then thought hey, why not also route the air conditioning lines inside and then have it blow cold air for the summer?'

To get the maximum amount of heat from the engine i also imagined mounting it outside in a small enclosed... to capture as much heat as possible and then also use the hot air in the enclosure to further aid the heating. Quite a bit of heat is lost and radiated away just from the engine block its self.

 

[marcusl]

As far as heat recovery goes, yes, the efficiency will be less than a modern gas boiler. However, if you treat the electricity generated as a byproduct (ostensibly 35% of the fuel input), and offset this against the cost, then I reckon you'd definitely be in with a fair scheme by which to offset the heat and electricity costs required for the average home, particularly if you use the same natural gas that your boiler would. I suppose the heat pump would work in certain climates, but I still like the idea of cogeneration, or trigeneration for warmer climates.

Are you sure you can get 35% of the fuel energy out as electricity? The EPA says mechanical efficiency of a gasoline auto engine is about 30% (the EPA would like to see it increase to 40% by 2012), and I'm thinking an alternator is probably around 90%.

 

[brewnog]

Generally, cogen is looked at from the other way around: the heat is a biproduct of the electricity generation. You don't lose much electricity by adding cogen, but if you want to use a heating boiler to generate electricity, you lose a lot of heat.

Increasingly, this isn't the case. Several installations I'm working on at the moment cost the same to fuel as their original gas boilers did. The electricity is the byproduct; it goes straight onto the grid, and the payback is something silly like 18 months.

Are you sure you can get 35% of the fuel energy out as electricity? The EPA says mechanical efficiency of a gasoline auto engine is about 30% (the EPA would like to see it increase to 40% by 2012), and I'm thinking an alternator is probably around 90%.

Well I was only throwing figures around, but a Diesel will easily give upwards 35% mechanical efficiency, and I reckon if you operated a gasoline engine at optimum conditions (peak bsfc, rather than over a typical drive cycle) on an optimum fuel you'll easily exceed that, once it's been modified for thermal efficiency (as with any other cogen unit).

This is almost funny. Over the past couple of weeks I've been thinking about the exact same thing. What sparked the idea was that I have an extra Chevrolet 350 sitting in my shop collecting dust. One day i thought to myself, what would keep me from mounting the engine on a stand, inside or outside the shop, (most likely outside because of the nose) and somehow route lines from the engine to a radiator inside, while a fan mounted to it blows the hot air throughout the shop?

Ooh, yay, we have a volunteer!

Why not give it a go? Rather than just using automotive alternators, why not make the most out of all that mechanical power and get a proper 240V alternator to bolt onto the flywheel housing?!

 

[Danger]

Ooh, yay, we have a volunteer!

Why not give it a go? Rather than just using automotive alternators, why not make the most out of all that mechanical power and get a proper 240V alternator to bolt onto the flywheel housing?!

Might I make one additional suggestion? Throw on a set of heavily insulated 8-into-1 headers terminating in either a large turbocharger (just the turbine side) geared to another alternator, or a secondary heat exchanger.

 

[B. Elliott]

Ooh, yay, we have a volunteer!

Why not give it a go? Rather than just using automotive alternators, why not make the most out of all that mechanical power and get a proper 240V alternator to bolt onto the flywheel housing?!

Lol. I'm really thinking about it! I'm having a friend of mine who's handy with a welder come over and take a look at what I have to work with. The 240v alternator is a very good idea. I completely overlooked that as an option.


Danger;

The only problem I can think of (off the top of my head) with using the exhaust to turn another alternator would be a matter of required load, as there's not a lot of exhaust pressure when the engine isn't under load. You can switch a turbo car into neutral and rev to the moon and it won't build much boost (if any at all). But, put it in drive, hold the brake and floor the gas and you have a completely different beast. I have noticed that on turbocharged cars, while at idle, the turbine barely moves. A lot like blowing on a pinwheel. It freespins very easily but if you tried to drive something off that pinwheel, there'd be no movement. Then again that is with the compressor side fighting to compress air, so it may act differently with the compressor removed and an alternator attached.

The heat exchanger is another good idea though. Yet another I overlooked! I like where you're you're going with the turbocharger though.

I love this forum!:!)

 

[Danger]

I didn't know about that aspect of turbos. I'm a firm believer in positive-displacement Roots blowers for cars, so I haven't looked into turbos much. Thanks for the tip.
And one of the main reasons that I love this forum is guys like you. I'm pretty useless about most scientific stuff because of no education, but someone with an interesting project gives me a chance to exercise my brain. And, as in this example, I usually end up learning something while I'm at it.

 

[brewnog]

The other thing about using a proper alternator is that you'll be applying enough load to the engine to actually get some heat into (and out of) it. An engine idling with no load wouldn't be much use as a heater, but load it up, get some fuel into it, and you'll get loads of heat back out of the thing. And the bonus is all that electricity you can then power your lights with.

I wouldn't even dream about taking any drive off any turbos, just use them for the boost and use the heat from the exhaust to heat water.

 

[DarrenUK]

I was involved in the construction of a CHP unit using a 1970's diesel Mercedes light van engine that was connected by v belts to an 1950's slip ring industial motor (run as an alternator) and used for heat and power.

If anyone is interested in following this up I could post a few links to sites I've run across.

Best

Darren

 

[Koonism]

wouldn't the weight of the extra tank and the weight of the water contribute to lower fuel milage in terms of fuel consumption. Depending on the weight of water in the U.S. or Britain. The added weight & cost to transport would negate the positive returns on heat recovery unless you took out the seats to compensate for the added weight. Not practical in my opinion. I'm not a math guru..just an engineer.

 

[brewnog]

Darren, I'd very much like to see those links!

 

[DarrenUK]

Hello brewnog,

Quite a long discussion (26 pages!) about diy CHP, most made from vehicle engines, biofuel slant (Its a thread on a biofuels forum)
http://biodiesel.infopop.cc/eve/forums/a/tpc/f/249605551/m/189605261

This is a good place to get started on a long web trawl
http://www.green-trust.org/cogen.htm
(from which http://www.green-trust.org/autogen.htm relates to 'hooking' u your car)

I also saved a couple of posts from a forum (no longer online) by a bloke here in the UK who was using a small fiat IDI diesel car engine in a home made CHP unit. He was powering and heating his house and a stable block using chip fat for fuel. I had some email correspondance with him at that time. I could post all that here (there is a fair bit) if that would be of interest.

Personally I think for CHP it is better to start with a fixed speed stationary engine of some type. Preferably some thing which is designed to give good power at low rpm. I know of a few companies offering this sort of system and/or selling components if that is also of interest. I could post some of this information if it would be of use.

Best

Darren

 

[Artman]

Just insulate the garage. If the garage is attached to the house the heat lost from the car goes into the garage and slows the heat loss from the house to the garage. No heat exchanger is necessary.