Commercial Refrigeration FINAL
TEST 2024/2025 Questions and
Answers (Graded A)
How is the cooling effect in a mechanical refrigeration system produced? - ANSWER
- Evaporation of liquid refrigerant into vapor
What is the primary purpose of a compressor? - ANSWER - It circulates and
pressurizes the refrigerant vapor before the vapor Is condensed for re use
Name another function that must be performed by the compressor - ANSWER - Is
raise the pressure and temperature of the refrigerant vapor. This allows the
refrigerant to condense into a liquid as it circulates through the condenser
What characteristic defines an "open" type compressor? - ANSWER - Has a drive
shaft protruding from the compressor
What are the two main disadvantages of a hermetic compressor? - ANSWER - If
either the motor or compressor malfunctions, the entire unit must be replaced. The
motor is actually a part of the refrigerant circulation system. This means that a
burnout can contaminate the entire system
In a reciprocating compressor, the piston is connected to the crankshaft by a _____ -
ANSWER - Connecting rod
Name the three elements of performance that are the major factors in evaluating a
compressor - ANSWER - Efficiency, capacity, and economy of operation
If the suction gas superheat is too low, What could be the result? - ANSWER - Liquid
refrigerant might enter the compressor. This causes stress on the compressor
valves, wrist pins, rods, shaft, etc. It also causes excessive foaming of the oil in the
crankcase and other damaging effects. The compressor will not reach its rated
capacity
, What will happen if the suction gas temperature is too high? - ANSWER - Will cause
the compressor to run hot
What purpose do the fins attached to the condenser tubes serve? - ANSWER -
Increase the surface area for heat transfer
What is the purpose of subcooling? - ANSWER - To prevent the liquid from vaporizing
prematurely
If condensing pressure is higher than the corresponding condensing temperature,
what is normally the cause? - ANSWER - Non condensable gases
How is compressor efficiency often judged? - ANSWER - Btu per cubic foot (Btu/ft^3)
of displacement
When the same model of open type compressor is used with both air cooled and
water cooled condensing units, which is usually run at a slightly higher rpm? -
ANSWER - Water cooled
What is the equation for ratio of compression? - ANSWER - The absolute discharge
pressure (psig plus 14.7) divided by the absolute suction pressure (psig plus 14.7)
What type of compressor is found in large applications up to 10000 tons? - ANSWER
- Centrifugal compressors
Which compressor utilizes two helical rotors to compress the refrigerant gas? -
ANSWER - Screw compressor
What is the most outstanding advantage of the hermetically sealed compressor
over the open type? - ANSWER - Has no protruding crankshaft or shaft seal
TEST 2024/2025 Questions and
Answers (Graded A)
How is the cooling effect in a mechanical refrigeration system produced? - ANSWER
- Evaporation of liquid refrigerant into vapor
What is the primary purpose of a compressor? - ANSWER - It circulates and
pressurizes the refrigerant vapor before the vapor Is condensed for re use
Name another function that must be performed by the compressor - ANSWER - Is
raise the pressure and temperature of the refrigerant vapor. This allows the
refrigerant to condense into a liquid as it circulates through the condenser
What characteristic defines an "open" type compressor? - ANSWER - Has a drive
shaft protruding from the compressor
What are the two main disadvantages of a hermetic compressor? - ANSWER - If
either the motor or compressor malfunctions, the entire unit must be replaced. The
motor is actually a part of the refrigerant circulation system. This means that a
burnout can contaminate the entire system
In a reciprocating compressor, the piston is connected to the crankshaft by a _____ -
ANSWER - Connecting rod
Name the three elements of performance that are the major factors in evaluating a
compressor - ANSWER - Efficiency, capacity, and economy of operation
If the suction gas superheat is too low, What could be the result? - ANSWER - Liquid
refrigerant might enter the compressor. This causes stress on the compressor
valves, wrist pins, rods, shaft, etc. It also causes excessive foaming of the oil in the
crankcase and other damaging effects. The compressor will not reach its rated
capacity
, What will happen if the suction gas temperature is too high? - ANSWER - Will cause
the compressor to run hot
What purpose do the fins attached to the condenser tubes serve? - ANSWER -
Increase the surface area for heat transfer
What is the purpose of subcooling? - ANSWER - To prevent the liquid from vaporizing
prematurely
If condensing pressure is higher than the corresponding condensing temperature,
what is normally the cause? - ANSWER - Non condensable gases
How is compressor efficiency often judged? - ANSWER - Btu per cubic foot (Btu/ft^3)
of displacement
When the same model of open type compressor is used with both air cooled and
water cooled condensing units, which is usually run at a slightly higher rpm? -
ANSWER - Water cooled
What is the equation for ratio of compression? - ANSWER - The absolute discharge
pressure (psig plus 14.7) divided by the absolute suction pressure (psig plus 14.7)
What type of compressor is found in large applications up to 10000 tons? - ANSWER
- Centrifugal compressors
Which compressor utilizes two helical rotors to compress the refrigerant gas? -
ANSWER - Screw compressor
What is the most outstanding advantage of the hermetically sealed compressor
over the open type? - ANSWER - Has no protruding crankshaft or shaft seal
