Commercial Refrigeration FINAL TEST
Exam Questions with Complete
Solutions
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
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
How are the disadvantages overcome in compressors that are employed in low
temperature applications? - Answer-Use supplementary cooling
How are the disadvantages overcome in water cooled hermetic compressor systems? -
Answer-Have water jackets, or water coils around the compressor/motor shell or
housing
Is the condenser load greater or less for compressors designed for low temperature
applications than for compressors designed for high temperature applications? -
Answer-The condenser load is less for the low temperature applications
Name the two most widely used desiccants today - Answer-Alumina and zeolites
Why is a drier installed in a refrigeration system? - Answer-The primary property in the
drier is desiccant which removes moisture and acid
Why must a desiccant act rapidly? - Answer-Because it must reduced moisture to a
sufficiently low level in one pass through the drier
What is the criterion for stability of a desiccant? - Answer-To stay in its original solid
state
What standard determines the moisture holding capacity of a drier? - Answer-ARI
Standard 710-86
ARI Standard 710-86 specifies flow rates through a filter drier at a pressure drop of
_____ - Answer-1 Psig
Where should a moisture liquid indicator be installed? - Answer-Installed in the liquid
line, either upstream or downstream from the drier
How many sources of heat have to be rejected from the vapor in the condenser? -
Answer-Three, the heat absorbed in the evaporator, the heat picked up in the suction
line, the additional heat of compression caused by compressor operation
Exam Questions with Complete
Solutions
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
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
How are the disadvantages overcome in compressors that are employed in low
temperature applications? - Answer-Use supplementary cooling
How are the disadvantages overcome in water cooled hermetic compressor systems? -
Answer-Have water jackets, or water coils around the compressor/motor shell or
housing
Is the condenser load greater or less for compressors designed for low temperature
applications than for compressors designed for high temperature applications? -
Answer-The condenser load is less for the low temperature applications
Name the two most widely used desiccants today - Answer-Alumina and zeolites
Why is a drier installed in a refrigeration system? - Answer-The primary property in the
drier is desiccant which removes moisture and acid
Why must a desiccant act rapidly? - Answer-Because it must reduced moisture to a
sufficiently low level in one pass through the drier
What is the criterion for stability of a desiccant? - Answer-To stay in its original solid
state
What standard determines the moisture holding capacity of a drier? - Answer-ARI
Standard 710-86
ARI Standard 710-86 specifies flow rates through a filter drier at a pressure drop of
_____ - Answer-1 Psig
Where should a moisture liquid indicator be installed? - Answer-Installed in the liquid
line, either upstream or downstream from the drier
How many sources of heat have to be rejected from the vapor in the condenser? -
Answer-Three, the heat absorbed in the evaporator, the heat picked up in the suction
line, the additional heat of compression caused by compressor operation
