HVAC Heat Pump Technology 3 — Questions and Answers
Question 1: A ground-source heat pump uses the earth as a heat source in winter. What is the primary reason this is more efficient than an air-source heat pump in cold climates?
- Ground loops use less refrigerant than air coils
- Ground temperature remains relatively stable and warmer than air temperature in winter (Correct answer)
- Ground loops operate at lower pressures, reducing compressor wear
- The earth provides free electricity to assist the compressor
Correct answer: Ground temperature remains relatively stable and warmer than air temperature in winter
Below the frost line, ground temperatures remain relatively constant (typically 45–55°F in the US), providing a more favorable heat source than cold outdoor air in winter.
Question 2: What is the function of the accumulator in a heat pump system?
- To store excess refrigerant charge during low-load periods
- To prevent liquid refrigerant from entering the compressor suction (Correct answer)
- To filter moisture and contaminants from the refrigerant
- To increase refrigerant velocity in the suction line
Correct answer: To prevent liquid refrigerant from entering the compressor suction
The accumulator is installed on the suction line to separate liquid refrigerant from vapor, protecting the compressor from liquid slugging.
Question 3: What type of heat pump system is BEST suited for a home without ductwork?
- Packaged terminal heat pump
- Mini-split ductless heat pump (Correct answer)
- Water-source heat pump
- Dual-fuel heat pump
Correct answer: Mini-split ductless heat pump
Mini-split ductless heat pumps deliver conditioned air directly to individual zones without requiring ductwork, making them ideal for homes without existing ducts.
Question 4: During a defrost cycle on a heat pump, auxiliary heat strips typically energize. Why?
- To assist the compressor in reaching operating pressure faster
- To compensate for reduced heating capacity while the outdoor coil defrosts (Correct answer)
- To prevent the reversing valve from sticking in transition
- To maintain refrigerant temperature above the dew point
Correct answer: To compensate for reduced heating capacity while the outdoor coil defrosts
During defrost, the system temporarily switches to cooling mode to melt frost, so auxiliary electric heat strips energize to maintain indoor comfort.
Question 5: What does HSPF (Heating Seasonal Performance Factor) measure for a heat pump?
- Peak heating capacity in BTU/hr
- Total heating output divided by total electrical energy input over a heating season (Correct answer)
- Efficiency of the defrost control system
- Ratio of indoor to outdoor coil surface area
Correct answer: Total heating output divided by total electrical energy input over a heating season
HSPF is a seasonal efficiency rating for heat pumps in heating mode, calculated as total heating output (BTU) divided by total electricity consumed (Wh) over the heating season.
Question 6: A technician measures suction pressure lower than normal and discharge pressure lower than normal during heat pump heating operation. What is the MOST likely cause?
- Overcharge of refrigerant
- Undercharge of refrigerant or low outdoor ambient temperature (Correct answer)
- Faulty reversing valve stuck in cooling position
- Plugged liquid line filter drier
Correct answer: Undercharge of refrigerant or low outdoor ambient temperature
Low suction and discharge pressures in heating mode typically indicate a low refrigerant charge or very low outdoor ambient temperature reducing the available heat source.
Question 7: What is the purpose of a desuperheater in some heat pump systems?
- To reduce refrigerant temperature before the expansion device
- To recover heat from hot discharge gas to preheat domestic hot water (Correct answer)
- To prevent the compressor from overheating at high ambient temperatures
- To remove superheat from the suction line before it enters the compressor
Correct answer: To recover heat from hot discharge gas to preheat domestic hot water
A desuperheater uses the hot discharge gas from the compressor to preheat domestic hot water, improving overall system efficiency.
HVAC Heat Pump Technology 3
A ground-source heat pump uses the earth as a heat source in winter.
What is the primary reason this is more efficient than an air-source heat pump in cold climates?