NATE Refrigeration 1 — Questions and Answers
Question 1: What is the refrigeration effect and how is it calculated?
- Heat rejected at the condenser; calculated as condenser enthalpy minus compressor inlet enthalpy
- Heat absorbed in the evaporator; calculated as evaporator outlet enthalpy minus evaporator inlet enthalpy (Correct answer)
- Work input to the compressor
- Heat gained by subcooling the liquid line
Correct answer: Heat absorbed in the evaporator; calculated as evaporator outlet enthalpy minus evaporator inlet enthalpy
The refrigeration effect is the heat absorbed per pound of refrigerant in the evaporator, equal to the enthalpy difference across the evaporator.
Question 2: What refrigerant is commonly used in medium-temperature commercial refrigeration cases in the US?
- R-410A
- R-404A / R-448A (Correct answer)
- R-134a only
- R-22
Correct answer: R-404A / R-448A
R-404A has been the standard for medium-temperature commercial refrigeration, and R-448A is the common lower-GWP replacement.
Question 3: What does a suction line accumulator protect in a refrigeration system?
- Liquid line from high pressure
- Compressor from liquid refrigerant slugging (Correct answer)
- Condenser from excess load
- Expansion device from debris
Correct answer: Compressor from liquid refrigerant slugging
The accumulator traps liquid refrigerant on the suction line, boiling it off slowly rather than allowing it to enter and damage the compressor.
Question 4: At what temperature range does a medium-temperature refrigeration system typically maintain a reach-in display case?
- -10°F to 0°F
- 0°F to 10°F
- 28°F to 40°F (Correct answer)
- 45°F to 55°F
Correct answer: 28°F to 40°F
Medium-temperature refrigeration maintains product temperatures between 28°F and 40°F for dairy, deli, and produce applications.
Question 5: What is the purpose of a filter-drier in a refrigeration system?
- Reduce system sound levels
- Remove moisture and contaminants from the refrigerant circuit (Correct answer)
- Increase subcooling of liquid refrigerant
- Regulate refrigerant mass flow
Correct answer: Remove moisture and contaminants from the refrigerant circuit
The filter-drier contains desiccant that absorbs moisture and a filter screen that traps particulates to protect the metering device and compressor.
Question 6: What does a high discharge temperature on a refrigeration compressor typically indicate?
- Low compression ratio
- High compression ratio due to high head pressure, low suction pressure, or high superheat (Correct answer)
- Properly operating system
- Overcharged refrigerant
Correct answer: High compression ratio due to high head pressure, low suction pressure, or high superheat
High discharge temperature (above 225°F for most systems) results from high compression ratios or excessive superheat entering the compressor.
NATE Refrigeration 1
What is the refrigeration effect and how is it calculated?