Product Manual AGR-3
AGR 070A through 100A
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flow rate (GPM) for comfort cooling applications. For process applications where the load can change
quickly, contact the factory for recommendations. A water storage tank (provided by others) may be
required to increase the system water volume in some systems.
Evaporator Freeze Protection
Evaporator freeze-up can be a concern in the application of air-cooled water chillers. To protect against
freeze-up, insulation and an electric heater cable are furnished with the unit. This protects the
evaporator down to -20°F (-29°C) ambient. Although the evaporator is equipped with freeze
protection, it does not protect water piping external to the unit or the evaporator if there is a power
failure or heater cable burnout. Consider the following recommendations for additional protection.
1.
If the unit will not be operated during the winter, drain evaporator and chilled water piping and
flush with glycol. Drain and vent connections are provided on the evaporator to ease draining.
2.
Add a glycol solution to the chilled water system to provide freeze protection. The freeze point
should be approximately ten degrees below minimum design ambient temperature.
3.
Continuous circulation of water through the evaporator and piping.
4.
Insulation and heat tracing the chilled water piping.
The evaporator heater cable is wired to the 115 volt circuit in the control box. This power should be
supplied from a separate source, but it may be supplied from the control circuit. Operation of the heater
cable is automatic through the ambient sensing thermostat that energizes the evaporator heater cable for
protection against freeze-up. Unless the evaporator is drained in the winter, the disconnect to the
evaporator heater must not be open.
Extended Shutdown
This unit is equipped with a recycling pumpdown control system. This permits the compressors to run
and re-pumpdown following a 2 hour “off” cycle if the refrigerant evaporator pressure is high enough to
close the low pressure switch (57 to 60 psig). If the unit is expected to be off for an extended period of
time, completely de-energize the unit except for piping and chiller vessel heat tape.
Refrigerant Piping
Introduction
Proper refrigerant piping can represent the difference between a reliable, trouble free system and
months or years of inefficient, problematic performance. The following section is based on ASHRAE
information.
System concerns related to piping are:
1.
Refrigerant pressure drop
2.
Solid liquid feed to the expansion valve(s)
3.
Continuous oil return
Of the three listed, the most important and least understood is number 3, “Continuous oil return”. The
failure of oil to return at or close to the rate of displacement from the compressor can result in oil
trapping and ultimately to compressor failure.
On the other hand, the instantaneous return of a large volume of compressor oil, as a slug, can be
equally damaging to a compressor.
Also more oil is displaced at start-up of a compressor than occurs during a normal running period.
Thus, if a compressor experiences excessive starts because of recycling pumpdown control, the larger
quantity of oil pumped out is trapped in the condenser with the refrigerant charge, and may not return
regardless of the adequacy of the piping system.
A similar problem to a lesser extent occurs when the equipment is oversized for the available cooling
load.