Will the Chevrolet Volt be a failure or a success?

^^ Saying energy economy I mean energy/distance.
The ICE is heating the cabin with waste heat from the ICE, the EV is using energy that would otherwise be used to move the car.

 

I think it's because when you burn gasoline to power the vehicle, as well as for cabin heat, you increase its effective efficiency because you are using waste heat for the cabin. Otherwise that waste heat will exit the back end of the vehicle. Although it is not a 1:1 gain, since using waste heat will cause the ICE to run slightly less efficiently, the combined heat and power will increase the efficiency.

Whereas for battery power, you basically are taking away from range by heating the cabin using battery power.

So for gas, waste heat is a byproduct that becomes useful, in essence it is "free", while for electricity it is a straight loss.

 

*shrug* Neither of us know.

Well, I didn't intend to set you off on a rant but there is nothing about the PHV that suggests it will be immune to EV-mode range loss in the winter. It has the same electric heater problem as the Volt and, worse, no active thermal management of the battery pack. You can pre-warm the cabin on house power but not the battery.

I'm curious what detail I'm missing that will make the PHV work so well in the cold.

Is this Priuschat thread about a test showing 6 miles bogus?

 

There is a report that backs you up already.



PHEV15 spec awfully look like Prius PHV and PHEV40 like the Volt.

 

In an ICE car, as long as it can get to normal operating temperature, the only impact using the heat incurs is from the tiny bit of electricity to run the fan. It uses energy in the cooling system which would otherwise be transferred out through the main radiator - the ICE (in)efficiency bill has already been paid, so to speak - routing it to a radiator that's mounted in the cabin instead.

It's as 'free' as it gets IMHO. The Prius does it one better with the heat exchanger in the exhaust system.

 

I think in conventional vehicles, running the heat does not reduce efficiency appreciably because the ICE runs continuously.

In the Prius, running the heater steals heat from the ICE or the coolant. Since the ICE has a tendency to shut off, it actually makes it run inefficiently because once it starts up again will want to run longer in a lossy fashion to heat itself back up.

I have a very good climate and the ICE will still go back into a warmup cycle after a good ICE-off idle at a red light. Though that does generate some electricity, it's better if the ICE ran only when needed for load and demand.

 

Did you read the report?

So, sure, you only lose 20% of "EV range" with the PHEV15 car but only because it runs the ICE almost right away. The PHEV40 is burdened with pure electric heat although that's not a design constraint, while the PHEV15, which could do pure electric heat, is not. With active thermal management of the battery, the Volt could just as easily maintain nearly all its "EV" range if they chose to run the engine for one minute out of every five. They chose not to do it that way.

Yes, the clearly modeled after those two plus the Leaf but I just read that the PHV Prius has an electric heat pump. Does it behave like the model they used for the report.

I take issue with some of the data too. The document claims steady state A/C and heat loads are the same and that is, by observation, not even close.

 

This is the right idea, but let me rephrase it to make it technically correct: In conventional vehicles, cabin heat is essentially free because at least that much heat must be discarded during normal operation. Current engine designs require cooling (not adiabatic). This is generally done by circulating engine coolant through a radiator, discarding the heat into the air, or using the heat to warm the cabin. As long as the amount of discarded heat exceeds that needed for warming the cabin, the heat is essentially free.

The Prius design wastes less heat. The engine is more efficient and often runs intermittently. Because of this, cabin heat may force the engine to run solely to generate heat. In this situation, efficiency is clearly reduced by running cabin heat.

Tom

 

That's a good point.

 

See the preconditioning restores most of the EV miles (for using heat) for Prius PHV. You can't say the same for the Volt or Leaf.

 

Preconditioning restores all those "EV" miles to the PHEV15 because the model relies purely on ICE-derived heat thereafter.

 

Advantage of having two power sources (hybrid). Why didn't it do the same for the Volt?

 

I suppose but looking at it another way, when you aren't actively trying to raise the temperature of the cabin an ICE is throwing off tons of waste energy (noise, heat, friction, etc...) that doesn't get used for anything.

There is no such thing as a free lunch.

 

Using LiIon battery power to generate heat instead of generating motion is a wasteful use of the batteries.

Even though electric heating is almost 100% efficient, or greater than 100% efficient when using a heat pump, there are many other less expensive methods that can achieve the same thing. One is burning hydrocarbons.

Using gasoline to generate power, and then using its waste product as heat makes a lot of sense. Unfortunately this is in opposition to the design goals of the Volt, which places emphasis on primarily running on battery power. So it is a big trade off to rely on the batteries for heating, because otherwise the ICE would have to run somewhat continuously. So for now drawing battery power for heat is the solution, until another one becomes available that doesn't involve burning hydrocarbons.

I believe the most efficient use of the Prius PHV, when the commute will be much greater than 12 miles and on the highway, is to run in a blended mode (if one exists). This will combine the best aspects of EV and a gasoline burning ICE, while trying to minimize the penalties of each as well. In this mode, the Prius would run the ICE at its highest efficiency, while minimizing the power/current of the battery packs.

I don't want anyone to think this is an indictment of the Volt. All EVs will encounter this problem, including the Leaf.

Though I know there exists some relatively simple innovations that will assist heating in EVs. So I think this will be a moot point in the future.

 

The Prius ICE is a combined heat and power (CHP) plant in the winter; the Volt design (and any pure EV) can only be considered a CHP if the central plant is CHP. In the US that is close to zero.

mfennel: The PHV is more efficient than the Volt in the winter exactly because it will blend petrol and electricity. The petrol consumption is a CHP. Volt marketing as an EV wannabe introduces additional inefficiency in winter. Stealing from an old english saying, the Volt is oil penny wise, and coal pound foolish.

 

Yep, although it actually takes effort to run the ICE efficiently with a full battery pack, at least in my G2 Prius. This is because the programming preferentially draws power from the pack when it is full. The driver has to demand 35 - 45 kw to run the ICE in the best SFC spot when this condition is present. The problem is partially self-correcting though, since maximum power drain decreases with temperature. So while Volt marketeers call this a flaw (ICE on in winter,) I appreciate the improved energy efficiency.

If the programming remains similar in a Prius PHV one successful strategy may be to preferentially run in HV mode the first part of the journey, and then switch to EV mode for the last 12 - 14 miles when the cabin is toasty.

By the way, radiator blocking has really improved my car's winter performance. I'm sorry I waited so long to adopt the practice. A G3 Prius with a radiator block and EGR will do even better.

 

When I say 'so far as I know,' I mean that I have read outlines of the EPA cycles and methodology and have never come across a cold temperature drive cycle that heats the cabin.

Your guess has no basis in fact.

http://www.fueleconomy.gov/feg/fe_test_schedules.shtml

 

Use the right tool for the job. Kill two birds with one stone.

Two power sources functioning together to produce the result not independently obtainable -- definition of synergy.

 

I wonder if EV's could employ some sort of CNG mini-system just for winter heating (not related to propulsion)

 

It would be relatively simple to use small propane canisters. They are used in camping for cooking and heating all the time.

Safety is a different issue, but I don't see why it can not be made to be very safe.