1 Low-Pressure Appliances and Chiller Fundamentals Free Online FlashCards

What makes an appliance low pressure?

It has parts of its refrigerant circuit operating below atmospheric pressure during normal operation.

What happens in a chiller evaporator?

Low-pressure refrigerant absorbs heat from return water and boils, cooling the water that circulates to building coils or process equipment.

What does a low-pressure chiller purge unit do?

It separates and removes accumulated non-condensables from the chiller. Excessive purge activity can indicate air leakage or another system problem.

How do recovery and evacuation differ?

Recovery transfers refrigerant into appropriate recovery equipment and a cylinder. Evacuation brings a system or component to a specified low-pressure endpoint.

Which refrigerant phases must be recovered?

Recover liquid first if useful, but recover vapor as well; follow the recovery machine’s controls and manufacturer-set limits.

Why are inward leaks a concern in low-pressure chillers?

Air and other non-condensables can leak inward. They impair heat transfer and may raise condenser pressure, reducing capacity and efficiency.

What does a centrifugal chiller compressor do?

Its motor-driven impeller raises the refrigerant vapor’s pressure and temperature.

What happens in the chiller condenser?

Hot refrigerant vapor releases heat to condenser water and condenses into liquid.

What is the expansion device’s role?

It reduces the liquid refrigerant’s pressure before the refrigerant returns to the evaporator.

What is the standard EPA evacuation endpoint for a low-pressure appliance?

The standard endpoint is $25\ \mathrm{mm\,Hg}$ absolute. This is an absolute pressure, not a vacuum reading of $25$ inches of mercury.

What can pressure rebound after recovery indicate?

Pressure rebound can mean refrigerant remains in liquid or oil, so recovery may need to continue.

How should refrigerant be introduced during recharging?

Introduce vapor before liquid to reduce the risk of freezing water in the tubes. On centrifugal chillers, use the designated evaporator charging valve.