Hi Justin,
I have worked with both kinds of systems. In general I think the water-cooled
systems are more robust, and the responses already posted give a couple of
reasons why. I wanted to add a few more points for consideration:
1) Seasonal variability -- This is famously a problem for the air-cooled
compressors. The necessity of exposing the system to the external environment
means that the air-cooled compressors can dramatically lose efficiency in
summer (this was a big problem at Brandeis until Tom Pochapsky built a gazebo
over the compressor). In winter, excessive cold can also cause the system to
have problems, which I experienced on several occasions at Brown. Due to
AGW I expect these sorts of problems to get worse. Of course, one could put
an air-cooled compressor inside and force conditioned air through it (Doug
Lyons once told me about such a system set up in Brazil), but this would seem
to me to introduce about as many problems as it solves. NB that switching to a
water-cooled system does not entirely insulate you from this issue; many
chilled-water systems will adjust their temperature setpoint with the seasons,
particularly if they are campus-wide loops used for AC, and you may see changes
in your cooling efficiency as a result. Make sure to check these setpoints and
base your calculations on the higher temperature (usually delivered in winter).
2) Maintenance -- For the water-cooled compressors the maintenance burden is
less, but keep in mind that a Haskris or other secondary loop is not maintenance-free.
Haskris units also require regular filter cleaning (ideally semi-annual) and
occasional pump maintenance, and you will likely need occasional pump replacement
or maintenance on a custom-built loop. As well, you will want to monitor the water
quality and other parameters yourself on a regular basis. It has also been my
experience that maintenance teams working on building-wide or (especially)
campus-wide PCW are incredibly bad at communicating with stakeholders when
significant maintenance operations or "experiments" are going to be performed.
I once had rotating anode X-ray system completely die in the middle of an
important experiment because facilities decided (on a random afternoon in early
March) to see if they could generate PCW solely through air cooling. Gentle
reader, they could not.
Sparky
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Received on Fri Mar 01 2024 - 08:02:40 MST