Screw Compressor Central Chiller
Chapter 3: Installation
19
Making Tank Piping Connections
If you have purchased the Screw Compressor central chilling station with the
optional
integral pump tank, please proceed with this section.
Note:
Thermocouplings for chillers must be installed on both the hot and cold
sides of the tank.
Freezestat Control
The unit can be equipped with a freezestat control which shuts down the compressor if the
chilled water temperature approaches the freezing point. The chilled water pump on the
system will continue to run. It is factory-set at 40°F (4ºC) or 10°F (6ºC) below the rated
capacity operating temperature of 50°F (10ºC).
If you want lower chilled water temperatures (minimum of 30°F (-1ºC), you’ll need to mix
process water with industrial- (not automotive) grade ethylene or propylene glycol with rust
inhibitor to provide protection down to 20°F (12ºC) below the operating temperature you
want. Figure 1
below shows the proper mixtures needed to provide protection to 20°F (12ºC)
below the operating temperature you want. You can then reset the freezestat cutout
temperature to a temperature 10°F (6ºC) below the operating temperature you selected.
Caution!
Make sure all freezestat adjustments are performed by a qualified
refrigeration service technician.
The manufacturers product warranty does not cover system freeze-up!
Figure 1: Freezing Protection Curve
Example: Desired leaving temperature = 35°F (1.7ºC),
Glycol % by volume = 35%
This will provide protection to 15°F (-9.4ºC)
Ethylene glycol required for evaporator freeze protection
Ethylene
glycol
percent by
volume
Chilled water operating temperature ºF / ºC
60
50
40
30
20
10
0
-50ºF -40ºF
-40ºC
-30ºF -20ºF -10ºF 0ºF
10ºF 20ºF 30ºF 40ºF 50ºF 60ºF
16ºC
10ºC
4ºC
-1ºC
-7ºC
-12ºC
-18ºC
-23ºC
-29ºC
-34ºC
-46ºC
