Message-Id: <199811081532.JAA06276@arnet.arn.net>
Date: Sun, 08 Nov 1998 09:32:15 -0600
To: lancair.list@olsusa.com
From: Hannes & Benita TRNKA <hbtrnka@arn.net>
Subject: Lancair IV A/C System
Mime-Version: 1.0

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When I decided to install an A/C system in my IV-P I initially planned to
go with the engine-driven system that was available as an option for the
EngineAir V-8 I have on order. Unfortunately it turned out that the
compressor takes the place of the second alternator I wanted to install
(Two alternators are important to me since both engine ignition systems and
all my gyros are electrically powered). I checked into electrically powered
systems and found one that is made by EnviroSystems in Oklahoma and is
optional equipment in Commander 114's. Its motor/compressor unit consists
of a big 28VDC motor connected to a automotive-type piston compressor with
a V-belt. Next to being quite large, its current draw is 80 A and it weighs
34 lbs (capacity is 12000 BTU). This was not acceptable to me and I started
doing research about a custom-designed system. I found out that the main
reason for the high current draw is the low volumetric efficiency of piston
compressors at high back pressures. (overall efficiency ~45%). 

I decided to go totally different route on this system and chose an 115 VAC
powered hermetic vane-type compressor. The compressor is very small and
works similar to a vacuum pump except that it has only one vane made out of
steel that is stationary. Its efficiency is supposed to be close to 90%.
The AC motor doesn't have brushes and since it is the area filled with
refrigerant, there are no shaft seal that might start to leak. This motor
compressor unit weighs 20.5 lbs and is powered by a 1200 VA inverter that
weighs 7 lbs. The inverter also supplies power to a 115 VAC outlet in the
cabin that can be used to plug in a laptop computer (or a microwave, if you
want to... :) ...). The compressor was designed for R-22, but I'm going to
use R-411, a R-22 replacement that should provide higher efficiency.
Although it will only provide between 9000 and 10000 BTU/hr it will only
draw about 35A at 28V.

Since I haven't hooked up the evaporator yet I can't say for sure that all
the numbers will be right and everything will work like planned. I'll write
an update when I get there.

Hannes Trnka.