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King Friday
12-04-2006, 05:13 PM
How do hybrid vehicles produce heat for the cabin?

Stan Doubt
12-04-2006, 07:36 PM
A google search for various models and "heater core" revealed enough hits to convince me that most produce heat much like a normal vehicle, by circulating engine coolant through a small radiator inline with the ventilation system. There might be some models that use electrical resistance heating, or a combination of the two, but I did not turn up anything in my brief search that led me that way.

Xema
12-04-2006, 07:44 PM
Bear in mind that a hybrid vehicle gets the energy for any longish trip by burning fuel in a heat engine, the waste heat of which is an excellent source for cabin heat.

Cabin heat for a 100% electric vehicle is a much bigger problem; basically, it must come from diverting stored energy that otherwise would be useful for propulsion.

MrFloppy
12-04-2006, 08:34 PM
Agreed. Hybrids still have a good old internal combustion engine that is liquid cooled.

AFAIK, there is no pure electric car for sale by a major manufacturer. The method of heating such a car however would likely be a small electric water heater with a water to air heating core like a traditional vehicle.

Diceman
12-04-2006, 08:37 PM
Still, what if you want heat, and the hybrid is in battery mode? Does it start the engine just so you'll have a heat source? Or do you not get heat until whenever the engine kicks in?

Xema
12-04-2006, 08:42 PM
... likely be a small electric water heater with a water to air heating core
Why the water?

friedo
12-04-2006, 09:05 PM
Why the water?

Water can be heated much hotter than the desired air temperature, and a tank can store the heat for quite a while. That's probably a lot more efficient than exposing an electric heat element to the air directly.

Fear Itself
12-04-2006, 09:13 PM
Water can be heated much hotter than the desired air temperature, and a tank can store the heat for quite a while. That's probably a lot more efficient than exposing an electric heat element to the air directly.Yeah, but any kind of electric heat is going to severly crimp the mileage of a single charge of the batteries.

Xema
12-04-2006, 09:16 PM
... probably a lot more efficient than exposing an electric heat element to the air directly.
It seems to me that a simple heat element would be efficient, lightweight, compact and relatively inexpensive. How would a heated-water system gain efficiency?

R. P. McMurphy
12-04-2006, 09:29 PM
Still, what if you want heat, and the hybrid is in battery mode? Does it start the engine just so you'll have a heat source? Or do you not get heat until whenever the engine kicks in?

Yes, the engine kicks in for passenger comfort, just like air conditioning in a hot environment.

People misunderstand hybrids. They are not econoboxes that are trying to squeeze the last possible mpg out of the gas tank. They are cars that are designed to perform as good as, or better, than what the buying public expects while delivering better gas milage and lower emmissions.

The engineering behind the hybrids is not to force buyers to suffer and make sacrifices. It's to move the auto technology ahead. If that means keeping the passenger cabin at a comfortable temperature then the car is designed to do that. Of course, all cars are computer controlled these days. If the engineers want to program the car for nothing other than gas milage than they could adjust the software and make the passengers dress accordingly.

friedo
12-04-2006, 09:43 PM
It seems to me that a simple heat element would be efficient, lightweight, compact and relatively inexpensive. How would a heated-water system gain efficiency?

You can store heat in the tank when you're driving down-hill (generating electricity) and release it later when the cabin gets cold. With an exposed heating element, you have to draw power immediately when you need heat, regardless of how much you're already drawing from the electrical system.

InternetLegend
12-04-2006, 09:50 PM
Yes, the engine kicks in for passenger comfort, just like air conditioning in a hot environment.Our Escape hybrid gives you the choice: if you want heat (or A/C) when the gasoline engine's not running, you can turn the climate control to the appropriate setting and it'll kick the engine on. Then you have the choice of watching your little gas mileage graph get all depressing or of toughing it out until your engine comes on for power. If you set it for defrost (windshield or rear window), the gas engine will stay on.

The car stays in gasoline mode until the engine is warmed up. At that point, even if it drops into electric and stays there, I still get a decent amount of warmth from the heater for between five and ten minutes, depending on how cold it is. And I'm very rarely able to keep the car on solely electric for much longer than that anyway.

Xema
12-04-2006, 10:11 PM
You can store heat in the tank when you're driving down-hill (generating electricity) and release it later
Right, but you could also store the energy in the battery and release it later.


With an exposed heating element, you have to draw power immediately when you need heat, regardless of how much you're already drawing from the electrical system.
True. OTOH, when you start the vehicle you have to draw off a bunch of energy to heat the water, a charge of heat that is ultimately going to be wasted (when the vehicle shuts down).

friedo
12-04-2006, 10:24 PM
Right, but you could also store the energy in the battery and release it later.


:smack:

Malacandra
12-05-2006, 09:28 AM
Yeah, but any kind of electric heat is going to severly crimp the mileage of a single charge of the batteries.

How severely? I'm guessing that even a slow electric vehicle is going to have at least a 20kW engine (<30bhp), and probably wouldn't need more than 0.5kW for electric heating. That's a 2.5% hit for the heating.

Mr. Slant
12-05-2006, 11:33 AM
How severely? I'm guessing that even a slow electric vehicle is going to have at least a 20kW engine (<30bhp), and probably wouldn't need more than 0.5kW for electric heating. That's a 2.5% hit for the heating.

For the record, 30 horsepower in a compact car is enough to push you along at a good 55-65 MPH.
If you're tooling around in town at 30-40 MPH at a steady speed, you may be operating on more like 10-15 HP.
People don't realize the power reserves modern vehicles have. You can run a car the size of a Ford Taurus at Interstate Superhighway speeds on a 70 HP engine all day long as long as you're not trying to climb the Appalachian mountains with it.

iamthewalrus(:3=
12-05-2006, 01:21 PM
Everybody here seems to be assuming that you can't just use the waste heat from the engine in an electric car, just like you would in a car with an IC engine. Why not? Are electric motors really so efficient that they don't produce enough waste heat to warm the cabin?

N9IWP
12-05-2006, 02:55 PM
The 200$+ Prius airc conditioner compresser runs off an electric motor, and so the gas engine doesn't need to start to run the compressor. (earlier models the compressor did run off the gas engine).
Of course, eventually the gas engine will need to run to renew the battery.

For heating, it is a convential system, thogh I have read there is also an electric heater that helps out. http://en.wikibooks.org/wiki/Toyota_Prius_FAQ

The gas engine will run for a while in the cold, this isn't so much for passenger comfort, but to get the catalytic converter hot for emission reduction.
Hot coolant (oxymoron alert) is stored in a thermos to help speed up warming.

Brian

Balthisar
12-05-2006, 03:47 PM
Everybody here seems to be assuming that you can't just use the waste heat from the engine in an electric car, just like you would in a car with an IC engine. Why not? Are electric motors really so efficient that they don't produce enough waste heat to warm the cabin?
Well, yeah. Waste is why they're so efficient. If you removed the waste heat and exhaust from a gasoline engine, then they'd be equally efficient.

iamthewalrus(:3=
12-05-2006, 04:12 PM
Well, yeah. Waste is why they're so efficient. If you removed the waste heat and exhaust from a gasoline engine, then they'd be equally efficient.I realize that they're more efficient, but are they so much more efficient that there's not enough waste heat to heat the cabin?

Just going by the numbers mentioned in this thread, 500 W needed for heat and a 20 kW electric motor (mentioned as being near the lower limit of what you'd find in a production car), that's 97.5% efficiency. The reasonable assumption of a more powerful engine makes the ratio even higher. I find it hard to believe that electric cars are much more efficient than that. Even if the engine is, the battery's got to get pretty warm while it's discharging.

The Tesla roadster has a water cooling system for the battery, so clearly there's some serious heat being produced there. Assuming that the radiator is in the front of the car, that heat is already close to the front of the cab.

Gorsnak
12-07-2006, 12:32 AM
Even if the engine is, the battery's got to get pretty warm while it's discharging.
"Pretty warm" isn't going to cut it. I just drove home 270km through -26C weather and I had to stop halfway to block the rad with carboard because my heater was blowing "pretty warm" air and the cabin was getting colder and colder. There's pretty much zero chance my old Camry is as efficient as a hybrid. I've often wondered how a Prius does for cabin heat in serious cold (-26 doesn't count, I mean like -40, where plenty of conventional vehicles struggle).

iamthewalrus(:3=
12-11-2006, 01:18 PM
"Pretty warm" isn't going to cut it."Pretty warm" was not intended to be a quantitative analysis. I'm having trouble coming up with an actual number for the efficiency of a Li-ion battery, but I've heard numbers in the 80-90% range before.

My calculations before showed that 2.5% the power as waste heat was sufficient to heat a car for normal cold (but not extreme) temperatures. Surely 10-20% would be enough to heat it even at -40 or so. I suspect that your Camry was perfectly capable of generating the heat required, but that the climate control systems of the car are simply not designed to operate well at those temperatures.

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