2 years post rebuild my AC compressor died(bearings), How about electric compressor?

Fellas,

For quite a while now I've been interested in the potential to change my AC compressor from the belt driven type to one of the brushless DC electric compressors. I could imagine this may add a bit of efficiency, and also allow the use of AC without the engine running for short periods of time(watching battery charge of course). I see that some electric vehicles are using them now and wonder about the potential for a swap. Things that I can think of that may be sticky points:

1) Ensuring cooling capacity is comparable(may require two E compressors to do this)

2) Would need to make an AC delete bracket with idler pulley

3) Would need to come up with a solution to hook two compressors in parallel together and then to the stock lines.

4) Would need to figure out the control scheme of the brushless compressors so the system would adjust refridgerant flow(by changing the brushless motor speed) according to cooling demand.

5) Would need to be mindful of the space that two electric compressors might take



I know this is really far fetched, but Im now at the point that I must do something(at least before summer time) whether go stock or go for an upgraded system. I'm looking for some technical guidance on what cooling capacity I would want to shoot for, and whether or not the stock expansion valve would play nicely with the electric compressors among other things. Thanks!

120 amperes at 14.8 volts (maximum alternator power output) is a bit under 1.8 kW. The Sanden compressor draws a bit over 2 kW.

With an 80 amp-hour battery, you are looking at 40 minutes to fully drained battery, ignoring Peukert's Law which in reality means substantially less than 40 minutes.

Stick with the stock system. The variable displacement compressor is more efficient than a variable speed DC system. EV air conditioning systems will always be far under-sized.

As far as the stock ALH AC system refrigeration capacity, it is about 3 tons. Cars have lots of glass and little insulation thickness so they need refrigeration capacity equivalent to a 3000 square foot house.

Great technical perspective "Keith_J" for I too was pondering the use of
low maintenance/hermetically sealed electric compressors...!!?
Thanks for your perspective... but
what about:
(a) install the 120A alt,
(b) a 2nd battery system isolated electrically
..... and located in the trunk,
(c) Do you know if Sanden or some other Co. mfg. a smaller
..... compressor that would satisfy the load in more moderate climates!??
Happy "enthalpy"... " ˈenTHalpē " !
Sam Ross

Keith_J said:

120 amperes at 14.8 volts (maximum alternator power output) is a bit under 1.8 kW. The Sanden compressor draws a bit over 2 kW.

With an 80 amp-hour battery, you are looking at 40 minutes to fully drained battery, ignoring Peukert's Law which in reality means substantially less than 40 minutes.

Stick with the stock system. The variable displacement compressor is more efficient than a variable speed DC system. EV air conditioning systems will always be far under-sized.

As far as the stock ALH AC system refrigeration capacity, it is about 3 tons. Cars have lots of glass and little insulation thickness so they need refrigeration capacity equivalent to a 3000 square foot house.

Click to expand...

I'm guessing you mean that the Sanden SD7V16 compressor draws 2KW mechanical equivalent from the engine when it is at max displacement pumping? I'm not planning on running my stock AC compressor with a 12 volt motor. I was under the impression that some of the brushless DC operating air conditioning compressors had higher efficiency over their belt driven counterparts. Then again, it may be an efficiency gain in the fact that under acceleration or low cooling demand it can be turned off or have it's energy demand reduced.

Also, quite a few of the compressors I saw require more than the 12 volts that the battery would supply. I would need to create a sub system off of the alternator to supply the higher voltages needed.

Yes, the mechanical load on the engine remains about the same IF you have 100% efficiency. The parasitic load from the belt is also the same, since you would need additional alternator load or possibly, a second alternator which runs at higher voltage to reduce losses in the copper.

Brushless DC are more efficient but then you have the electronic speed control/commutators which introduce their own reliability issues and inefficiencies.

I'll take variable displacement over variable speed any day for air conditioning.

There must be a creative way to use the available waste energy from the exhaust heat, coolant heat, or the addition of a regenerative breaking sytem or a combination of all three to allow conditioned air to be produced. I understand that there is very little "excess" coolant heat(per my "hybrid 205 T-stat experimentation) and that the turbo makes use of exhaust heat to aid efficiency, but that is not too say that a bit more can't be eeked out.

I'm not looking for folks to necessarily comment with seemingly insurmountable obstacles that would deter folks from trying something, but to perhaps think a bit outside the box to acheive a goal. I would just bet that some properly placed and well though out systems added to these cars would make them a bit more fuel efficient or at the very least allow comfort with no additional energy consumption.




Ways to cool air:


Ammonia based refridgeration cycle
Zeolite/dessicant based refridgeration
Peltier devices(pretty much automatically dismissed)
Evaporative cooling
Stirling cycle cooling





What we have available:

1) Coolant heat(perhaps anything over 205 deg F)

2) Exhaust heat(perhaps construct a bypass exhaust loop that allows us to make use of the available EGR gas cooler for other purposes)

3) Vacuum(although not free energy, can be usefull for some processes)

4) Create a regenerative breaking system(maybe pump refridgerant into an accumulator while breaking)

5) pressure bled from intake during overboost(instead of having the VNT vanes adjust the angle early for instance bleed a small amount to a pressure vessel until it reaches a certain pressure and then let the computer adjust the vane angle a bit later than it would normally do)





..

I designed and built an experimental absorption refrigeration unit using waste heat in that temperature range. It was heavy, cumbersome and just not suited to automotive use. It was in the 350 Watt range (1/10th of a ton).

It just cannot be done and packaged to fit under the hood. Availability just isn't suited for mobile applications.