Just to chime in – we have four devices chilled by campus chilled water,
with different plumbing for all four.
Our “best” system has:
* A process loop similar to what Alex described
* Two pumps in parallel on the process loop. Only one is running, the
other is a hot spare.
* A 20-micron water filter with a see-through casing on the process loop,
with a bypass so the filter can be swapped while the system is running.
* A domestic water backup system on the process loop.
* Electronic valves to control the flow of chilled water to the process loop,
so that it does not get too cold and produce too much condensation.
* Controls software and remote monitoring from our central plant.
The supply and return temperatures and pressures on the process loop are
constantly monitored. If anything goes wrong, the domestic water backup turns
on, and we get an email. We check the filter monthly, but it almost never
needs replacing. If I were building it again and had to save a few dollars
on the system, I would skip the hot spare pump.
Our worst system is a direct tie-in to campus chilled water with no controls
or electronics. We added a 300-micron filter, and it still gets gummed up
regularly with iron oxide. If campus chilled water loses pressure for ~30
seconds our equipment shuts down (this occasionally happens on hot days
when our campus utilities adjust the central system).
Best,
Sameer
--
Sameer Al-Abdul-Wahid, Ph.D.
Manager, Nuclear Magnetic Resonance Centre<
http://nmr.uoguelph.ca/>
University of Guelph
519-824-4120 x58914 / s.wahid_at_uoguelph.ca
> From: main_at_ammrl.groups.io on behalf of Todd Rappe via groups.io
> Date: Tuesday, July 29, 2025 at 15:33
> To: main_at_ammrl.groups.io <main_at_ammrl.groups.io>
> Subject: Re: [AMMRL] Coolant for He Compressors
Our chilled water loop is similar to the one Alex describes at NMRFAM. It had
been problem-free for the past 14 years until this past winter we had a catastrophic
failure. Here's my cautionary tale. Over the Christmas holiday, one of our
helium compressors failed in a manner that leaked oil into our chilled water
lines. The contaminated chilled water ultimately caused the failure of three
other compressors on the loop. I will note that all the compressors that
failed all had over 100,000 hours so we knew that replacement was somewhat
imminent but we weren't expecting to have to replace them all at the same
time. Four "younger" compressors survived. We contracted with a local company
to service our chilled water system and clean out the oil. Everything is back
up and running now. The moral of this story: think about your replacement
schedule for helium compressors and there may be some value in having each
cryocooler on its own isolated cooling system (we still don't). Also, I
believe the initial compressor failure was caused by a corroded/clogged
quick-connect fitting on the chilled water input to the compressor. I've
replaced all of the Bruker-provided quick-connect fittings on our compressors
with wider diameter hose barbs to hopefully prevent such clogging in the future.
_____________________________________
Todd Rappe
Minnesota NMR Center <nmr.umn.edu>
612-625-9147 (office)
651-321-TODD (rings office and mobile)
612-624-8892 (magnet lab)
On Tue, Jul 29, 2025 at 1:52 PM Alex Paterson via groups.io wrote:
Hi Luke,
Re 2, is it possible for you to split the difference and have a heat exchanger
between your building chilled and your process loop? That’s how we
do it at NMRFAM.
Our process chilled water loop is closed and exclusively serves our equipment
(approx. 14 helium compressors). It has dedicated redundant lead-lag circulation
pumps. Physical Plant does periodic maintenance on the pumps and the loop itself.
The process chilled water loop rejects heat to the campus chilled water system
via a pair of heat exchangers.
It’s a non-trivial amount of space, but we’ve found this arrangement
to be highly effective. Keeping our process loop closed allows us to keep the
working fluid within helium compressor specifications (no algae!) while reducing
the amount and complexity of equipment we need to maintain.
Best,
Alex
Alex Paterson
The National Magnetic Resonance Facility at Madison (NMRFAM)
University of Wisconsin-Madison
alpaterson_at_wisc.edu<mailto:alpaterson_at_wisc.edu>
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Received on Wed Jul 30 2025 - 09:03:04 MST