Commercial Refrigeration Ch. 4
Questions and Answers (Graded
A)
The discharged vapor picks up which of the following two more additional sources of
sensible heat as the suction vapor is processed through the compressor? - ANSWER
- Motor heat and the heat of compression
What is "clearance volume" and how can it affect compressor efficiency? - ANSWER
- The area of high pressure gas between the top of the piston and the bottom of the
valve plate.
What is "volumetric efficiency"? - ANSWER - How well a compressor is operating
compared with its design capacity
If an R404A commercial freezer has design conditions of -20° evaporator and +125°
condensing, what is the compression ratio? - ANSWER - 10.5 to 1
In the example above what is the compression ratio if the customer lowers the box
temperature so that the evaporator is operating at -30° with the same head
pressure? - ANSWER - 14.1 to 1
Assume the above freezer evaporator temperature remains at -20°, but the
condenser is designed for a 25° condenser split and the condensing temperature
drops to 120°. What is the compression ratio? - ANSWER - 10.5 to 1
Which situation will damage the above freezer compressor quicker, lowering the
suction pressure by 5 psig or raising the head pressure by 20 psig, and why? -
ANSWER - Lowering the suction pressure because it raises the compression ratio
more than raising the head pressure
In the above question what kind of damage will occur to the compressor? - ANSWER
- Overheating
Questions and Answers (Graded
A)
The discharged vapor picks up which of the following two more additional sources of
sensible heat as the suction vapor is processed through the compressor? - ANSWER
- Motor heat and the heat of compression
What is "clearance volume" and how can it affect compressor efficiency? - ANSWER
- The area of high pressure gas between the top of the piston and the bottom of the
valve plate.
What is "volumetric efficiency"? - ANSWER - How well a compressor is operating
compared with its design capacity
If an R404A commercial freezer has design conditions of -20° evaporator and +125°
condensing, what is the compression ratio? - ANSWER - 10.5 to 1
In the example above what is the compression ratio if the customer lowers the box
temperature so that the evaporator is operating at -30° with the same head
pressure? - ANSWER - 14.1 to 1
Assume the above freezer evaporator temperature remains at -20°, but the
condenser is designed for a 25° condenser split and the condensing temperature
drops to 120°. What is the compression ratio? - ANSWER - 10.5 to 1
Which situation will damage the above freezer compressor quicker, lowering the
suction pressure by 5 psig or raising the head pressure by 20 psig, and why? -
ANSWER - Lowering the suction pressure because it raises the compression ratio
more than raising the head pressure
In the above question what kind of damage will occur to the compressor? - ANSWER
- Overheating
