Air Conditioning Info.

[skygazer6033]

Atomic13 --- I believe you were given some bad info on several fronts. We were told sometime back about the Chrysler minivan rear A/C unit however we were later told the supplier could not supply the numbers needed. Same with the rear unit for the Nissan Quest unit. I believe both the Chrysler and Nissan units are not electric but operate from the same compressor as the front A/C. The IAV engine clearly shows the compressor mount beneath the water pump housing.

 

[JEBar]

The IAV engine clearly shows the compressor mount beneath the water pump housing.

I'm not an automotive mechanic nor do I play one on TV but I was wondering about that.

 

[skygazer6033]

The tour people are PR guys and when asked engineering questions may not have totally accurate answers. The last I heard on the HVAC was they have been unable to find a US built unit and may need to go to an offshore supplier. Paul doesn't want to do this because that would lower the "made in USA" percentage but they may have no choice.

 

[Craig]

AC will have no effect on the stated MPG for the Elio once on the road.
Will it be better when off, yes, so that is a plus.
The AC is included in the test.

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

Just drive with the tachometer like I do. Find out what's the minimum RPMs required to shift into second and try not to pass that by much when accelerating.

 

[CrimsonEclipse]

An electric compressor would help fuel economy.
More importantly, in the long term, it would require less maintenance.
With a belt driven compressor, it is either ON or OFF and rotates at a speed set by the engine. (a magnetic clutch creates quite a force when the compressor is engaged at speed. This requires more strengthening thus more mass)
An electric compressor can turn at optimum speed at all times.
Translation: ware on the compressor would be a lot less and it could be made lighter.

An electric compressor MIGHT be more expensive.

 

[karl]

Every vehicle that I own with AC cuts the compressor when you use a lot of throttle. They all have a clutch on the compressor that lets it cut out under high load. How they do is is not a concern to me. Will the AC cool the vehicles cabin? I think so. No real world testing in Death Vally yet but I still have confidence they will get it done.

Lets get a list of things to obsess about: Who will provide the 1. compressor 2. condenser 3. evaporator 4. lines 5. controls 6. duct work may the speculation begin...

 

[UCF'73]

I remember some of those underpowered small cars from the 70s. When you turned on the AC belt, your head almost went crashing into the steering wheel.

 

[JEBar]

I remember some of those underpowered small cars from the 70s. When you turned on the AC belt, your head almost went crashing into the steering wheel.

oh dear .... Kung Fu level flashbacks

Jim

 

[karl]

The cars in the 80's where soo much "better?"

 

[CrimsonEclipse]

Are you speculating or can you point to any data?

The reason I ask is modern belt-driven compressors last the life of the car and all the non-electric high MPG cars to-date still use belt-driven compressors. Many modern compressors are also variable-displacement instead of "On/Off". Also electric compressors suffer a penalty for the double energy conversion from mechanical to electrical and back to mechanical. The question is if that penalty is more than made up for by the presumed efficiency of variable speed electric compressor.

Also remember There ain't no such thing as a free lunch. The fact that electric energy conversion is not 100% efficient means that a larger alternator is required, and the load on the alternator belt when the electric compressors kicks on will be 100% + conversion inefficiency. So figure the mechanical shock load on the alternator will be ~120% of the load on a belt-driven compressor. So the alternator mount will have to be stronger thus more massive.

TL;DR: Efficiency gains from an electric compressor are dubious at best and they will be more expensive. If they were better, automakers would be flocking to them to help meet CAFE standards.

So many points to make.... Where do we start?

"Many modern compressors are also variable-displacement"
Apples to apples please. Most cars do not use these. They have more moving parts and are more expensive.

"There ain't no such thing as a free lunch."
First year physics. Conservation of energy. Yes I seem to recall.
Yes there are energy losses, just like using a belt.
An electrical motor can be brought up to speed gradually and if necessary, modulate the power for the load, reducing the line losses. Thus reducing your "shock load".

Another advantage of an electrical system is its location can be placed anywhere there is space.
A stronger alternator is not likely necessary. The biggest draw would be on start up and the battery can easily compensate.

"modern belt-driven compressors last the life of the car and all the non-electric high MPG cars to-date still use belt-driven compressors"
Many modern compressors do NOT last the life of the car. Even in the high quality cars, replacement at 150,000 is pretty high.

Some mini vans have a separate electrically powered A/C system in the back. Ever wonder why? Is it due to the length of the freon lines? Line loss? extra weight? Complexity?

Why have cars gone from a belt driven fan to an electrical fan? The same arguments apply. In reality, an electrical system commonly beats belt driven and hydraulic and mechanical on many levels.

In aviation, many systems are being removed from the parasitic nature of engine driven sub systems to an All Electric aircraft.
See B-787.

Frankly, the only remaining argument is:
"Is an electrical A/C system financially viable with the early model Elio?"

We'll see.