Hybrids: A/C and Heater Usage in MPG Ratings?
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Question

Hybrids: A/C and Heater Usage in MPG Ratings?

RossABQ (Mechanical)

(OP)

17 Feb 09 00:11

One thing I've noticed on the hybrid versions of normal gas-engine cars (i.e., Civic, GM's soft hybrids, etc) is that "climate control" or automated HVAC is part of the package. The recent cold weather made me wonder, do hybrids run their gas engines constantly just to provide cabin heat? Likewise, in the summer do they run the engine to cool ? It seems like they must, but how is this figured into the EPA ratings cycles? I guess I'd be surprised if there is an HVAC component to the testing,but it would seem to have a definite impact on the scores.

I'd also be interested to know if their little gas engines are able to maintain a warm cabin in really frigid weather, keeping the windows clear and occupants comfortable?

Enlighten me, please!

MikeHalloran (Mechanical) · Answer 1 · 2009-02-17 00:36:26

A couple of years ago, Miami Beach got a small fleet of all-electric buses.

They were not, as you might expect, silent.

The propane- powered engine that ran the air conditioner droned continuously....

Mike Halloran
Pembroke Pines, FL, USA

GregLocock (Automotive) · Answer 2 · 2009-02-17 03:55:43

The lack of HVAC in the EPA cycles is one of the criticisms - EVs and PHEVs should also include an allowance for HVAC in their range claims.

I can't remember what the Prius does for coolth, but since its engine is always kept at or near operating temp then yes, you effectively have a gasoline powered heater in your greenmobile.

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

waross (Electrical) · Answer 3 · 2009-02-17 07:13:23

That question deserves a star!

Bill
--------------------
"Why not the best?"
Jimmy Carter

BrianPetersen (Mechanical) · Answer 4 · 2009-02-19 19:58:25

There are a couple different ways to deal with this.

The Prius has a little "thermos bottle" that stores warm coolant for the next engine cycle. I don't know how long the heat in the "thermos" lasts. The new Prius has exhaust-heat recovery. But, ultimately, in extremely cold weather, whenever I see those cars (or Camry hybrids which are more popular here) there is always exhaust steam coming out.

It's possible to operate the A/C electrically, but I'm not sure if they are actually doing that yet. The upcoming Honda Insight doesn't, but it's got an "econ" button on the dash to give the driver the choice. If it's not in "econ" mode then the A/C has priority ... if the A/C is on and it's not in "econ" mode, then the engine runs all the time to drive the A/C. If it is in "econ" mode then the economy has priority. If the A/C is on and the engine happens to be running, you get A/C. If the driving conditions are such that they call for engine stop ... you don't, until the engine starts again. On that car it's not a big deal, the engine is only stopped when the car is stopped anyway.

In the real world with today's hybrids it probably doesn't matter. I've driven a Prius, and I couldn't do what it takes to stay in all-electric mode ... too slow by far.

The upcoming all-electric vehicles are going to have a BIG problem with this. How far is that electric car going to make it in -40 degrees in Winnipeg with the heater cranked, and what happens when the car runs out of juice? Driver freezes to death?

RossABQ (Mechanical) · Answer 5 · 2009-02-19 20:06:24

Quote:
The upcoming all-electric vehicles are going to have a BIG problem with this. How far is that electric car going to make it in -40 degrees in Winnipeg with the heater cranked, and what happens when the car runs out of juice? Driver freezes to death?

How is battery capacity affected by those temps, too?! But I doubt Winnipeg is their target audience. (On the other hand, everyone up there already plugs their car/truck in at night, to run a block heater!)

GregLocock (Automotive) · Answer 6 · 2009-02-19 21:32:13

"How is battery capacity affected by those temps, too?!"

Roughly speaking a LiPo battery loses about 20% of its nominal capacity per 10 deg C fall in temp - so at -30, it is a brick.

The GM Volt boys are currently sucking their teeth over this one. Their latest public proposal is that if you try and drive off with a fully charged battery that is at less than 50 deg F (10 deg C) then the engine will start, and the battery will just provide balancing current until it has warmed up.

Quite how they are going to deal with airport long-stay carpark syndrome I am not sure, but having dug my car out of the snow I'd be a tad peeved if it didn't start. Maybe they'll fit a timer and the thing will warm itself up in readiness for your return.

Cheers

Greg Locock

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rmw (Mechanical) · Answer 7 · 2009-02-19 21:39:50

Maybe they will furnish them with a starter rope.

Seriously, does anyone know the answer to the OP question for the Toyota Camry Hybrid?

rmw

DanEE (Electrical) · Answer 8 · 2009-02-20 08:22:06

The Prius AC system is all electric.. The combined air conditioning scroll compressor and AC PM 3 phase compressor drive motor is mounted on the engine for noise/vibration isolation, with only electrical and refrigerant connections. It is powered by the inverter.

When parked for example waiting for someone with the the vehicle "on", the engine will cycle on and off to keep the traction battery above the minimum charge level. 12 volt accessories are powered by a DC-DC 100amp inverter, which also charges the small 12 volt battery used to boot up the system, and power 12 loads.

The heater will run the engine as needed, but also has a supplemental electric "heat strip" heater to produce additional heat.

The thermos bottle is capable of storing heat for a good 24 hours.. When restarting the next morning after a previous day's drive, the heater is producing heat very quickly.

On a cold start, getting the catalytic converter up to operating temperature is the priority factor in determining how long the engine runs, and then cabin heat demands..

geesamand (Mechanical) · Answer 9 · 2009-02-28 08:45:05

I dunno about the Camry Hybrid, but my wife's Escape Hybrid loses about 1-2mpg when either the A/C or heater is in regular use.

Dave

GregLocock (Automotive) · Answer 10 · 2009-02-28 17:50:16

The heater?

Cheers

Greg Locock

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RossABQ (Mechanical) · Answer 11 · 2009-02-28 22:40:05

Yes, because the heater needs hot water, and to make hot water the engine needs to make waste heat, whether the car otherwise needs the engine to run or not. Of course the double whammy is that these are very efficient engines, so they need to run even more to make a given amount of waste heat...

patprimmer (Publican) · Answer 12 · 2009-03-01 01:31:04

Could cooling air from the electric motor be diverted to the cabin for heat. There is no risk of CO contamination like the heaters in the old air cooled VWs, but possibly some extra ozone, but surely if that might be a problem, that can be avoided with simple consideration in duct design.

Regards
Pat
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GregLocock (Automotive) · Answer 13 · 2009-03-01 05:21:23

Doesn't the Escape use a stored hot water system, like the Prius?

When I worked on an efficient vehicle I caught a certain amount of flak from t'management because I put heating the engine up as a higher priority than heating passengers.

Cheers

Greg Locock

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Hybrids: A/C and Heater Usage in MPG Ratings?
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