IMM AGS-2 21
Evaporator Freeze Protection
AGS chillers are equipped with thermostatically controlled evaporator heaters that help
protect against freeze-up down to -20°F (-28°C).
NOTE: The heaters come from the factory connected to the control power circuit. The
control power can be rewired in the field to a separate 115V supply (do not wire directly to
the heater). See the field wiring diagram on page 42. If this is done, mark the disconnect
switch clearly to avoid accidental deactivation of the heater during freezing temperatures.
Exposed chilled water piping also requires protection.
For additional protection, at least one of the following procedures should be used during
periods of sub-freezing temperatures:
1. Adding of a concentration of a glycol anti-freeze with a freeze point 10 degrees F below
the lowest expected temperature. This will result in decreased capacity and increased
pressure drop.
Note: Do not use automotive grade antifreezes as they contain inhibitors harmful to
chilled water systems. Use only glycols specifically designated for use in building
cooling systems.
2. Draining the water from outdoor equipment and piping and blowing the chiller tubes
dry from the chiller. Do not energize the chiller heater when water is drained from the
vessel.
CAUTION
If fluid is absent from the evaporator, the evaporator heater must be de-energized
to avoid burning out the heater and causing damage from the high temperatures.
1. Providing operation of the chilled water pump, circulating water through the chilled
water system and through the evaporator.
Table 12, Freeze Protection
Percent Volume Glycol Concentration Required
For Freeze Protection For Burst Protection
Temperature
°
°°
°F (°
°°
°C)
Ethylene Glycol Propylene Glycol Ethylene Glycol Propylene Glycol
20 (6.7) 16 18 11 12
10 (-12.2) 25 29 17 20
0 (-17.8) 33 36 22 24
-10 (-23.3) 39 42 26 28
-20 (-28.9) 44 46 30 30
-30 (-34.4) 48 50 30 33
-40 (-40.0) 52 54 30 35
-50 (-45.6) 56 57 30 35
-60 (-51.1) 60 60 30 35
Notes:
1. These figures are examples only and cannot be appropriate to every situation. Generally, for an extended margin of
protection, select a temperature at least 15
°
F lower than the expected lowest ambient temperature. Inhibitor levels
should be adjusted for solutions less than 25% glycol.
2. Glycol of less than 25% concentration is not recommended because of the potential for bacterial growth and loss of
heat transfer efficiency.
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