CRST CRST Refrigerants & Thermodynamics 1 — Questions and Answers
Question 1: What is the boiling point of R-134a at atmospheric pressure (14.7 psia)?
- -15.07°F (-26.15°C) (Correct answer)
- 32°F (0°C)
- -40°F (-40°C)
- 20°F (-6.7°C)
Correct answer: -15.07°F (-26.15°C)
R-134a has a boiling point of approximately -15.07°F at atmospheric pressure, making it suitable for medium-temperature refrigeration applications.
Question 2: Which refrigerant is classified as an A1 safety group per ASHRAE 34?
- R-134a (Correct answer)
- R-290 (propane)
- R-717 (ammonia)
- R-1234yf
Correct answer: R-134a
R-134a is classified A1 — 'A' indicating lower toxicity and '1' indicating no flame propagation, making it a non-toxic, non-flammable refrigerant.
Question 3: What thermodynamic process occurs in the evaporator of a vapor-compression refrigeration cycle?
- Refrigerant absorbs heat from the load and vaporizes at constant pressure (Correct answer)
- Refrigerant releases heat and condenses at constant pressure
- Refrigerant is compressed from low to high pressure
- Refrigerant expands from high to low pressure adiabatically
Correct answer: Refrigerant absorbs heat from the load and vaporizes at constant pressure
In the evaporator, liquid refrigerant absorbs latent heat from the refrigerated space and changes phase to vapor at a constant low pressure.
Question 4: What does the term 'subcooling' refer to in a refrigeration system?
- Cooling liquid refrigerant below its condensing temperature at a given pressure (Correct answer)
- Cooling suction vapor below the evaporator saturation temperature
- Reducing the temperature of the compressor discharge gas
- Dropping the refrigerant temperature below 0°F
Correct answer: Cooling liquid refrigerant below its condensing temperature at a given pressure
Subcooling is the number of degrees the liquid refrigerant is cooled below its saturation (condensing) temperature at the same pressure, ensuring all refrigerant is fully liquid entering the expansion device.
Question 5: What does the Global Warming Potential (GWP) of a refrigerant measure?
- Its heat-trapping potential relative to CO2 over 100 years (Correct answer)
- Its toxicity level per ASHRAE 34 classification
- The amount of ozone it depletes in the stratosphere
- Its flammability rating per ASTM standards
Correct answer: Its heat-trapping potential relative to CO2 over 100 years
GWP measures a refrigerant's ability to trap heat in the atmosphere relative to carbon dioxide (CO2 = 1) over a 100-year period.
Question 6: Which refrigerant has an Ozone Depletion Potential (ODP) of zero and is commonly used in new commercial refrigeration systems in the US?
- R-404A (Correct answer)
- R-12
- R-502
- R-22
Correct answer: R-404A
R-404A has an ODP of zero (no chlorine atoms) and became widely adopted for commercial refrigeration as a replacement for ozone-depleting R-502 and R-22.
CRST CRST Refrigerants & Thermodynamics 1
What is the boiling point of R-134a at atmospheric pressure (14.7 psia)?