- Which of the following refrigerant has the lowest GWP?
A. R410A
B. R134A
C. R152a
D. R744
2.Thermostatic expansion valves respond to changes in:
Select one:
A. Pressure.
B. Subcooling.
C. Temperature.
D. Superheat.
The correct answer and explanation is:
Question 1: Which of the following refrigerants has the lowest GWP?
Correct Answer: D. R744 (Carbon Dioxide)
Explanation:
Global Warming Potential (GWP) is a measure of how much heat a greenhouse gas traps in the atmosphere over a specific period, usually 100 years, compared to carbon dioxide (CO₂). Among the listed refrigerants:
- R410A: A hydrofluorocarbon (HFC) with a high GWP of around 2088. It’s commonly used in air conditioning but has a significant environmental impact.
- R134A: Another HFC with a GWP of approximately 1430. It is used in automotive air conditioning and refrigeration but contributes to global warming.
- R152a: This HFC has a much lower GWP of around 124, making it less harmful compared to R134A and R410A, but still not the lowest.
- R744 (CO₂): This refrigerant has a GWP of 1, as it is used as the reference point for GWP calculations. It is natural, non-toxic, and environmentally friendly, making it the refrigerant with the lowest GWP on the list.
R744 is gaining popularity due to its low environmental impact and high efficiency in certain applications, particularly in commercial refrigeration.
Question 2: Thermostatic expansion valves respond to changes in:
Correct Answer: D. Superheat
Explanation:
A thermostatic expansion valve (TXV) is a critical component in refrigeration and air conditioning systems, controlling the amount of refrigerant that flows into the evaporator. It does so by responding to superheat, which is the temperature difference between the refrigerant vapor at the evaporator outlet and its saturation temperature.
The TXV operates based on the balance between three forces:
- Bulb pressure (responsive to the superheat temperature).
- Spring pressure (pre-set to control flow).
- Evaporator pressure (opposing the bulb pressure).
When superheat increases, the bulb pressure rises, causing the TXV to open and allow more refrigerant into the evaporator. Conversely, when superheat decreases, the TXV closes to prevent overfeeding. This ensures the evaporator operates efficiently without liquid refrigerant returning to the compressor, which could cause damage.
Understanding superheat control is essential for maintaining system efficiency and protecting components.