As shown in the illustrated LP centrifugal...

🔍 Key Concepts

• Note that this is a low-pressure centrifugal chiller that normally operates below atmospheric pressure on the refrigerant side • Focus on what a dedicated pressure maintenance system (with tank, heater, pump, check valve, and pressure controllers) would be trying to control when load is very low or the machine is stopped • Compare the functions of surge control in a centrifugal compressor versus air leakage prevention in a low-pressure (subatmospheric) system

💭 Think About

• When a low-pressure chiller is at very low load or idle, what happens to the internal refrigerant pressure relative to atmospheric pressure, and why is that important? • Look at the tank, heater, and pump in the illustration: are they arranged to move refrigerant for cooling, or to adjust system pressure to a safe range? • Which of the choices specifically addresses the problem created when part of the system pulls a deeper vacuum than intended?

✅ Before You Answer

• Identify whether the system shown is acting during low load and idle conditions or mainly during normal, full-load operation • Decide if a pressure maintenance system would primarily change compression ratio in the compressor, or instead limit how far below atmospheric pressure the machine can go • Ask which answer choice most directly addresses air entering a subatmospheric (vacuum) refrigerant circuit under the conditions shown in the illustration

As shown in the illustrated LP centrifugal chiller pressure maintenance system, what is its functional purpose? Illustration GS-RA-40

prevent surging

maintain a relatively low compression ratio under low heat load conditions

prevent the entrance of air into the chiller under low heat load conditions

prevent the entrance of air into the chiller when the chiller is idle

🔍 Key Concepts

💭 Think About

✅ Before You Answer