During normal operation, what condition exists inside the evaporator of a running low-pressure centrifugal chiller?
Correct Answer
B) Pressure below atmospheric pressure
A low-pressure refrigerant such as R-123 has to be below atmospheric pressure to boil at the chilled water temperatures a building needs, roughly the upper thirties. That means the evaporator of a running centrifugal sits in a vacuum. The practical consequence is that a hole in the low side does not spray refrigerant out into the room; it pulls air and moisture into the machine. That is the whole reason these chillers carry a purge unit, and it is why a Type III leak hunt is done differently from a high-pressure leak hunt.
Why This Is the Correct Answer
To produce chilled water around forty degrees, the refrigerant in the evaporator must be a few degrees colder still, and at those temperatures a low-pressure refrigerant's saturation pressure is below atmospheric. So the low side runs in a vacuum any time the machine is loaded, which is exactly why air and moisture migrate inward through any opening.
Why the Other Options Are Wrong
Option A: Pressure well above one hundred psig
Pressures that high belong to high-pressure equipment such as R-410A or R-22 systems. A low-pressure centrifugal never sees anything close to that on either side during normal operation.
Option C: Pressure identical to the compressor discharge pressure
The evaporator is the low side and the discharge is the high side; if the two were equal the compressor would be doing no work and no refrigeration would take place. There is always a pressure difference across a running machine.
Option D: Pressure held steady at forty-five psig by the purge unit
The purge unit does not regulate or hold system pressure. Its job is to pull non-condensable gases out of the condenser, and it has no control over the evaporator's operating pressure.
Memory Technique
Vacuum cleaner rule: a low-pressure chiller is a vacuum cleaner, it inhales air and moisture through its leaks.
Reference Hint
Low-pressure appliances operate below atmospheric pressure on the low side; this drives the purge and leak-test rules in 40 CFR Part 82, Subpart F.
More epa-608-type-3 Questions
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?
In what unit is the required final recovery vacuum for a low-pressure appliance normally expressed?
What should a technician do about the water in the chiller tubes before pulling a deep vacuum on the machine?
What happens if the internal pressure of a low-pressure chiller is driven past the rating of its rupture disc?
Which refrigerant was the original factory charge in most low-pressure centrifugal chillers built during the nineteen sixties and seventies?
A running low-pressure chiller develops an opening in a section of shell that is below atmospheric pressure. What passes through that opening?
A technician is assigned to recover the charge from a large water chiller holding nine hundred pounds of R-134a. Which certification does that job require?
Into which appliance category does a machine charged with R-13 for very low temperature service fall?
On a low-pressure centrifugal chiller running at load, how do the evaporator and condenser sit relative to atmospheric pressure?
People Also Study
Business & Financial Management
120 questions · 70% to pass
Contract Administration
60 questions · 70% to pass
Project Management
60 questions · 70% to pass