[Vwdiesel] Diesel vanagon A/C

[LBaird119 at aol.com]

In a message dated 8/28/2004 6:35:54 AM Pacific Standard Time, 
Libbybapa at wmconnect.com writes:

> My 
> question is why is the engine used to run a compressor (robbing hp and 
> economy, 
> and increasingneccessity for cooling when it's hottest out) instead of the 
> waste heat from the exhaust?  The only explanations I see are that the 
> exhaust is 
> not hot enough, or the system would be initially more expensive.  How about 
> a 
> small stirling compressor run off exhaust heat?
> 

  The biggest problem is heat transfer capacity.  I asked an A/C friend 
how many btu a car A/C was, 10K?  He replied it was more like 2 to 3 
ton in size!  That's one BIG refirgerator.  Those propane refrigerators 
are a mix of gasses, I've been told, rather than just amonia.  A couple 
catches.  ALL of the plumbing must be steel, which isn't very resiliant 
for automotive vibrations.  That adds a lot of weight, bulk and expense. 
Much cheaper to put a compressor on the engine.  My TD Jetta feels 
like it loses about 5 hp when the compressor kicks in.  Some of the 
newer compressors can hardly even be felt.
  The A/C doesn't add that much load to the engine as much as the 
condensor sitting in front of the radiator reduces the capability of the 
radiator to dissipate heat.  As far as the rad is concerned, ambient 
temp takes roughly a 30 to 40F jump behind a condensor.  Never 
measured it, just a guess as to what it'd be at speed.
     Loren