A purge unit on a low-pressure chiller cycles and discharges through a line to the outdoors. What is in that discharge?
Correct Answer
D) Air and other non-condensable gas, with water vapor and a trace of refrigerant
A purge collects the gases that gather at the top of the condenser because they will not condense at the pressures and temperatures inside the machine. That is air drawn in through the vacuum side, along with the water vapor that came in with it. A well-built purge condenses the refrigerant out of the mixture and returns it to the machine, so only a trace goes out with the air. An old or failing purge sends far more refrigerant out, which is why efficiency matters.
Why This Is the Correct Answer
The purge exhaust is mostly atmospheric air that leaked into the machine, plus the water vapor that came with it. Refrigerant is meant to be separated out and returned, so a small trace is all that should leave. Understanding the composition explains both why the discharge is not treated as venting and why a poor purge costs the owner refrigerant.
Why the Other Options Are Wrong
Option A: Oil vapor carried up from the compressor sump by the rising condenser temperature
Oil is not volatile at these temperatures and does not travel to the top of the condenser as a gas.
Option B: Refrigerant vapor that the machine has no room for at current condenser pressure
A condenser does not run out of room for refrigerant, and a purge is not a pressure relief device.
Option C: Chilled water vapor that has crossed the tube walls into the refrigerant space
Water crossing the tube walls means a tube has failed, which is a fault rather than a description of normal purge discharge.
Memory Technique
Whatever leaked in, leaks back out through the purge, and it should take as little refrigerant with it as possible.
Reference Hint
Purge exhaust consists of non-condensable gas drawn into the machine, with water vapor and a small amount of refrigerant.
More epa-608-type-3 Questions
Some jobs on a chiller count as a major repair under the refrigerant rules, which changes what a technician is allowed to do with a badly leaking machine. Which job falls into that category?
An owner asks how many pounds of refrigerant the rules allow to be left inside a chiller once the recovery has been signed off. What is the correct answer to give him?
The motor of a hermetic centrifugal chiller sits inside the pressure boundary rather than outside it on a shaft. What follows from that construction?
An oxygen monitor is used to decide whether a chiller machine room is safe to enter after a refrigerant release. Below what oxygen reading is the atmosphere treated as oxygen deficient?
A low-pressure chiller's rupture disc has a discharge line running from it. Where does that line have to terminate?
A refrigerant vapor detector in a chiller machine room reaches its alarm level. Besides sounding, what is that alarm expected to do?
Which piece of equipment requires a technician to hold Type III certification before it may be serviced?
What property of the refrigerant is what actually places an appliance into the low-pressure category?
During normal operation, what condition exists inside the evaporator of a running low-pressure centrifugal chiller?
In what unit is the required final recovery vacuum for a low-pressure appliance normally expressed?
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