CRD Ground Loop & Heat Pump Configuration 4 — Questions and Answers
Question 1: What is the function of the expansion device in a water-source heat pump refrigerant circuit?
- It compresses refrigerant vapor to high pressure
- It reduces refrigerant pressure to enable evaporation at low temperature (Correct answer)
- It reverses refrigerant flow between heating and cooling modes
- It removes moisture and contaminants from refrigerant
Correct answer: It reduces refrigerant pressure to enable evaporation at low temperature
The expansion device (TXV or orifice) drops refrigerant pressure so it can absorb heat by evaporating at low temperature in the evaporator.
Question 2: HDPE pipe used in ground loops must conform to which ASTM standard for pressure ratings?
- ASTM D2447
- ASTM D3035 (Correct answer)
- ASTM D2513
- ASTM F876
Correct answer: ASTM D3035
ASTM D3035 covers HDPE pipe dimensions and pressure ratings for geothermal ground loop applications.
Question 3: A loop field is described as 'thermally imbalanced.' What does this mean for long-term system performance?
- The loop pressure differs between supply and return legs
- Heating and cooling loads extract and reject unequal amounts of heat annually, causing ground temperature drift (Correct answer)
- The bore spacing is uneven, creating hot and cold zones
- The antifreeze concentration varies across parallel circuits
Correct answer: Heating and cooling loads extract and reject unequal amounts of heat annually, causing ground temperature drift
Thermal imbalance occurs when annual heating and cooling loads differ, causing the ground to either warm or cool over years, reducing heat pump efficiency.
Question 4: What minimum flow rate (gpm per ton) does IGSHPA typically recommend for closed-loop ground heat exchangers to maintain turbulent flow?
- 0.5 gpm/ton
- 1.5 gpm/ton (Correct answer)
- 3.0 gpm/ton
- 5.0 gpm/ton
Correct answer: 1.5 gpm/ton
IGSHPA recommends approximately 1.5 gpm per ton to ensure turbulent flow regime and adequate heat transfer in ground loop piping.
Question 5: Which antifreeze solution offers the best combination of freeze protection and low viscosity at operating temperatures for residential ground loops?
- Calcium chloride brine
- Propylene glycol (Correct answer)
- Methanol
- Sodium chloride brine
Correct answer: Propylene glycol
Propylene glycol is preferred for residential closed loops because it is non-toxic, biodegradable, and maintains acceptable viscosity at low temperatures.
Question 6: What is the primary purpose of a flow center in a geothermal ground loop system?
- To regulate refrigerant superheat at the evaporator
- To circulate loop fluid, maintain pressure, and allow fluid addition or purging (Correct answer)
- To separate air from the refrigerant circuit
- To balance flow between multiple heat pump units
Correct answer: To circulate loop fluid, maintain pressure, and allow fluid addition or purging
The flow center houses the circulator pump(s), purge valves, and fill ports needed to maintain proper loop fluid circulation and pressure.
Question 7: In a variable-speed geothermal heat pump, what sensor signal most commonly modulates compressor speed?
- Outdoor air temperature
- Loop entering water temperature (Correct answer)
- Supply air static pressure
- Refrigerant discharge superheat
Correct answer: Loop entering water temperature
The entering water temperature (EWT) from the ground loop is the primary control signal that tells the variable-speed compressor how hard to work.
CRD Ground Loop & Heat Pump Configuration 4
What is the function of the expansion device in a water-source heat pump refrigerant circuit?