Here are my two cents:

Here at Tech we use both home-made and commerical heat-exchangers with
great sucess for all our chilled water requierments.  Before I arrived our
SIRA at first utilized regular house chilled water which was extremely
corrosive.  This and mandates requiring water saving measures (West Texas
is DRY) led to the installation of a couple Neslab chillers which
repeatedly burnt out.  Several years ago the University installed a second
dedicated closed loop chilled water system (approx. 5C) in our building.  I
managed to get my hands on a "pre-owned" Neslab heat exchanger that we have
used for our SIRA-12 and MM 903 ever since.  We have had to change the
motor once but that easy and cheap since the motors are availbe locally.
My technician James Browning built a couple heat-exchangers to run the prep
lines and they have been wonderful.  The first heat-exhanger was a 10
gallon plastic paint bucket filled with distilled water that we ran a
chilled water metal coil through.  We used a cheap fish tank recirculator
pump to circulate the water from the bucket through the diff pumps,  This
systems was very quiet since the cirulator pump is submerged in the water.

Good luck,

Hal Karlsson

Dr. Haraldur R. Karlsson
Associate Professor of Geosciences
Department of Geosciences
Texas Tech University
Box 41053
Lubbock, TX 79409, USA

(806)-742-3130 office
(806)-742-3112 lab
(806)-742-0100 Dept. fax