X-Message-Number: 2107
Date: Wed, 14 Apr 93 18:27:50 CDT
From: Brian Wowk <>
Subject: CRYONICS Polycold Systems
Polycold cryogenerators: The Best Alternative to LN2! (company motto)
I received fascinating information in the mail today from
Polycold Systems, the company that sells refrigeration units that
might be useful to us. It turns out that they are far from a backroom
operation. They have been around since 1974 and sell hundreds of
"cryogenerators" each year, racking up $10 million in annual sales.
They have sales and technical support spread across 15 states,
including California, Nevada, and Arizona. Their primary market? The
microchip industry (and other vacuum deposition people) who use
cryogenerators to "cryopump" water vapor from their high vacuum
systems. This is good news because it means that this industry is
here to stay, and cryogenic refrigeration systems and service will be
available from multiple vendors for decades to come.
The units of interest to us are their "P" series of
"cryocoolers" described below:
The Polycold P Cryocooler features a patented single
compressor refrigeration process. It directly cools baffles
and cold traps as low as -140'C using a safe, non-flammable
non-CFC refrigerant mixture in a closed loop system. The
Crycooler requires only power and water utility service, and a
typical operation exceeds 50,000 hours with only occasional
condenser cleaning.
The cold refrigerant output is circulated through a heat exchanger
that they supply or that the OEM user can fabricate themselves (as we
will want to).
Notice the reference in the paragraph above to "water utility
service". This answers the question of what happens to waste heat
from the system. They want 20'C water circulated through their unit
at about 10 liters per minute (14000 liters per day). Since water
from utilities is expensive and unreliable, it will be necessary to
build our own closed circuit water cooler to dump heat into a ground-
based heat sink. This sounds expensive, but it needn't be. Water
pumps and pipe are cheap.
Included in their information package was a nice set of graphs
that show how their inlet and outlet refrigerant temperatures change
for various amounts of heat absorbed. I can now tell you exactly what
performance to expect from their units in our application without any
handwaving. The units of interest are:
Model Cooling at -135'C -130'C -125'C Power Consumption Cost
---------------------------------------------------------------------
P-550 100 W 250 W 400 W 4.8 kW $12,430
P-660 200 W 400 W 600 W 5.7 kW $16,050
Note how dramatically performance deteriorates as the termperature
drops. It is clearly not economical to store below -130'C with these
systems.
Suppose we store at -130'C. I recommend purchasing two P-550s
for $25,000 total. These two units running simultaneously will easily
hold the Cold Room at -130'C, and leave a bit extra pull-down capacity
for *slowly* cooling patients from dry ice temp to -130'C. Now here
comes the nice part. If one of these units fails, the other running
*by itself* could hold the room at -123'C indefinitely. Also, the
rise from -130'C to -123'C would take about one month, giving ample
time for servicing. And of course, if everything breaks down, you
could always go back to pouring good ole' LN2 in the heat exchanger
tank
Operating costs for running two P-550s simultaneously will be
$7000 per year at 8 cents per kilowatt-hour. This is half the price
of LN2. If times really got tough you could operate only one of the
units for $3500 a year and hold at -123'C. This is $25 per patient
per year in a full room ($2.50 for neuros). Not bad eh?
---- Brian Wowk
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