[ausev] electric a/c system

Thu Aug 24 17:55:20 GMT 2006

In considering an electric prius ac compressor,  there are some power management issues such as how much range you are starting off with in the first place, then, of course, subtracting 15 to 20 percent for ac power draw.  When I am servicing any auto 134a system,  it is clear that the way to avoid very high cooldown demands are to prevent the sunlight from building up too much latent heat in the first place.  Management of heat buildup with solar films and reflective barriers placed in windows would help, but there is nothing better than the possibility of parking in a shaded area for long term parking of more than an hour.  
  Generally,  134a systems need to be carefully calibrated in order to prevent refrigerant superheat.   Superheat can have a compressor taking far more power than expected, and reduce range more than expected.   However,  designing in management values in evaporator air transfer volume (not using the high speeds all the time), as well as more refined cycling of the compressor may be the answer since you would not be using all of the compressors' rated power demand at all times, especially in a morning commute, when cycling could be reduced to very minimums.  As well, the system may be designed to refrigerate the cabin for 20 minutes with plugged-in power at home, thus eliminating just about all of the excessive power demand potential, even if it is parked in sunlight.   If there were an outlet available at work, then the same logic could apply.  I really like Mark's Ford Taurus' remote engine start system.  One like that could certainly be used to pre-chill your EV with electric AC compressor refrigeration. 
Dan Petit.
  ----- Original Message ----- 
  From: Chris Cooper 
  To: AustinEV News Announcements and General Discussion 
  Sent: Thursday, August 24, 2006 8:04 AM
  Subject: Re: [ausev] electric a/c system

  Been there. Done that.

  Peltiers are about 40% efficient so you would produce more heat than cool. You would have to sink the hot side outside of the area to be cooled. Car A/C units produce about 10,000-20,000 BTU's and are about 70-90% efficient depending on compressor speed and outside air cooling the condenser. You would need about 20 Peltiers to even crack the heat in a vehicle. That's 960watts best case. If you wanted to experiment with Peltiers, I would go the route of localized cooling; that's my next project. Are we back to a space suit now? Or at least a space helmet? What is the end result? Cooling the air in the cabin, or cooling YOU? Something to think about. One advantage of Peltiers is you can connect them in series and drive them directly with high voltage. A 96V system could directly drive 8 Peltiers. 

  Maybe the comical pictures of vehicles I've seen with a window unit hanging out of the rear window  of a car actually have some merit to them. they are about 90% efficient nowadays. You would need a pretty hefty inverter, but inverters are about 90% efficient too and there are some 48V inverters out there. You can get about 5000BTU's on less than 550 watts. 

  I had the opportunity once to drive one of the GM EV1 prototypes a few years back and I asked the engineer how the A/C worked. It was basically, very basically, a 330V(?) self contained A/C compressor unit similar to  but smaller than a home central unit. It ran full speed continuously eliminating the loss of cooling you get from idling at stop lights, etc.

  Chris Cooper

  Manager, Computer Services

  Department of Biomedical Engineering

  University of Texas @Austin

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  From: ausev-bounces at austinev.org [mailto:ausev-bounces at austinev.org] On Behalf Of Joey Carroll
  Sent: Wednesday, August 23, 2006 4:26 PM
  To: ausev at austinev.org
  Subject: [ausev] electric a/c system

  Hi everyone,
  New guy here. No EV yet, but im looking at converting an 84 CRX, and I had some input on the 12v Aircon systems. I'm not sure if anyone has seen this story before, its about how 2 teenagers made a compressor free air conditioner using peltier thermoelectric chips. I know they aer terribly inefficient compared to phase change cooling, but I think there is some potential there. I recently got 2 of these chips off ebay for around $16, just to play around with, I'll bring them to the next open garage or meet if anyone wants to check them out. 
  link: http://www.treehugger.com/files/2005/07/teens_invent_fr.php

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