ASHRAE Journal - September 2022 - 66

REFRIGERATION APPLICATIONS
COLUMN
Andy Pearson
Less Is More
BY ANDY PEARSON, PH.D., C.ENG., FELLOW ASHRAE
The Herrick Compressor Conference at Purdue University has been held every second
year since 1972 and at the meeting in July this year it was clear that there is as much
to learn as there ever was, if not more. To celebrate the 50th anniversary the plenary
address on the last day of the conference was in the form of a panel discussion,
moderated by the conference chair, Professor Eckhard Groll, and with three representatives
from some of the largest and most successful compressor manufacturing
companies in the world.
One topic divided the room into two distinct camps.
The question was whether there was any prospect of
developing compressors for mainstream refrigeration
applications that had no need for lubricating oil.
I confess that I am firmly in the (oil)less is more camp.
I had never given this much thought
until I started working with small, hermetic,
oil-free centrifugal compressors
in about 2005 and I realized that I had
to recalibrate my thinking about what
" good " looked like. In industrial refrigeration,
draining oil from the evaporators
in an ammonia system is one of the
most hazardous things we ask our technicians
to do, sometimes on a weekly, if
not daily, basis.
finally, because it is there it is often used as a hydraulic
fluid to actuate capacity regulators and other controls.
The question is therefore not " How do we design an oil
free compressor? " but rather " How do we do this at the
same cost of production and with the same reliability
and efficiency as we have at present? " This
question extends beyond the compressor:
many of the other control components in
a refrigeration system, particularly pilot
operated control valves, rely on a spot of
oil to keep them running smoothly.
Oil has been a recurring theme at the
Nick Chopper hoped that oil wasn't going
out of fashion
The compressor guys, not surprisingly, took a different
view. Oil provides several useful functions in refrigeration
compressors. It lubricates bearings, shaft seals and
all other contact surfaces, preventing premature wear
and minimizing frictional losses that would otherwise
impair the machine efficiency. It also provides a sealing
function that reduces internal leakage of compressed
gas back to suction, enabling machines to maintain
a high degree of efficiency without excessively tight
manufacturing tolerances that could make production
expensive, if not impossible. In some types of machines,
the oil also provides a valuable cooling function, again
to preserve efficient operation and minimize losses, and
66
ASHRAE JOURNAL ashrae.o rg
S E PTEM B E R 2022
Herrick conferences for many years, but
it is as relevant now as it ever was because
new materials, new production techniques
and new compressor types have
rekindled the desire to go oil-free. It seems that the only
people advocating oil in compressors at the conference
were the compressor guys and the oil salesmen.
However, they have a point. The main theme I picked
up from the conference in general was that efficiency
is as important as ever. Higher cost of production can
perhaps be justified in terms of savings in operating
expense, although this has always been a difficult argument
to win. On the other hand, if the elimination of oil
means that we would sacrifice a point or two in efficiency
terms, then I suspect that now is not a good time to raise
the topic and we will be oily for some time to come.
Andy Pearson, Ph.D., C.Eng., is group managing director at Star Refrigeration in
Glasgow, UK.

https://ashrae.org/

ASHRAE Journal - September 2022

Table of Contents for the Digital Edition of ASHRAE Journal - September 2022