313A Refrigeration Fundamentals & Thermodynamics 1 — Questions and Answers
Question 1: What is the primary purpose of the refrigeration cycle in an HVAC system?
- To generate heat through combustion
- To transfer heat from a low-temperature region to a high-temperature region (Correct answer)
- To convert mechanical energy into electrical energy
- To increase the pressure of ambient air
Correct answer: To transfer heat from a low-temperature region to a high-temperature region
The refrigeration cycle transfers heat from a cool space to a warmer environment by using a refrigerant that absorbs and releases heat as it changes phase.
Question 2: In the vapour-compression refrigeration cycle, at which component does the refrigerant absorb heat from the space being cooled?
- Condenser
- Compressor
- Evaporator (Correct answer)
- Expansion valve
Correct answer: Evaporator
The evaporator is where the low-pressure liquid refrigerant boils and absorbs latent heat from the surrounding space, providing the cooling effect.
Question 3: What is the unit of heat energy used in Canadian HVAC calculations?
- BTU
- Calorie
- Joule (J) or kilojoule (kJ) (Correct answer)
- Foot-pound
Correct answer: Joule (J) or kilojoule (kJ)
Canada uses SI (metric) units, so heat energy is measured in joules (J) or kilojoules (kJ) in accordance with Canadian standards.
Question 4: What does 'latent heat' refer to in refrigeration?
- Heat that causes a temperature change
- Heat absorbed or released during a phase change without a temperature change (Correct answer)
- Heat generated by electrical resistance
- Heat lost through conduction in metal pipes
Correct answer: Heat absorbed or released during a phase change without a temperature change
Latent heat is the energy absorbed or released when a substance changes phase (e.g., liquid to vapour) at a constant temperature, which is the principle behind refrigerant phase changes in the cycle.
Question 5: What is superheat in a refrigeration system?
- The temperature of refrigerant above its boiling point in the vapour state (Correct answer)
- The excess pressure above design operating pressure
- The temperature difference across the condenser
- The heat added by the compressor motor
Correct answer: The temperature of refrigerant above its boiling point in the vapour state
Superheat is the number of degrees the refrigerant vapour is above its saturation (boiling) temperature at a given pressure, measured at the evaporator outlet or compressor suction.
Question 6: What is subcooling in a refrigeration system?
- Cooling the suction line below ambient temperature
- The number of degrees the liquid refrigerant is cooled below its condensing temperature (Correct answer)
- Reducing compressor speed below design RPM
- Lowering evaporator pressure below design
Correct answer: The number of degrees the liquid refrigerant is cooled below its condensing temperature
Subcooling refers to cooling the liquid refrigerant below its saturation temperature at the condenser outlet, which prevents flash gas in the liquid line and improves system efficiency.
313A Refrigeration Fundamentals & Thermodynamics 1
What is the primary purpose of the refrigeration cycle in an HVAC system?