Years ago I was shown a system that supposedly optimized efficiency by
monitoring the line from the condenser to the compressor and keeping the
refrigerant's phase change as close to the compressor as possible without
trying to pump liquid. We were working with fixed speed compressors
(on/off) so it wasn't practical for our use. Have you seen that scheme?

Roger

http://home.insightbb.com/~derbyrm

wrote in message
ups.com...

The reason we want to control compressor speed is to use the lowest
amount of daily onboard power and maintain the box temperature we want
at all times. We by a compressor that can produce the results we want
and generally more capacity output most of the time. Cutting down on
capacity by lowering compressor speed improves SCOP (System Coefficient
Of Performance). Whenever the box temperature can be maintained at the
compressors slower speeds and still have it cycle off the end result
will be fewer daily amp-hrs consumed. What all three of these speed
controllers do is compensate for day night and seasonal temperature
changes. They all will change speed but slowly when warm product is
added to the box. The SSC and ASU both can be set to manual to speed up
the cooling process. I believe only the SSC will provide actual
compressor speeds at the panel. All of these units change the milliamp
flow in the thermostat circuit to control compressor speed.