CRD Ground Loop & Heat Pump Configuration 3 — Questions and Answers
Question 1: When designing a multiple-bore vertical loop field, what is the minimum recommended bore spacing to prevent thermal interference?
- 5 feet
- 10 feet
- 20 feet (Correct answer)
- 50 feet
Correct answer: 20 feet
IGSHPA guidelines recommend a minimum of 20 feet between vertical bores to limit long-term thermal interference and ground temperature change.
Question 2: A geothermal heat pump system has a COP of 4.0 in heating mode. If it delivers 48,000 BTU/hr of heat, how much electrical power does it consume?
- 3,500 W
- 3,517 W (Correct answer)
- 4,000 W
- 12,000 W
Correct answer: 3,517 W
Power = Output/COP = 48,000 BTU/hr ÷ 4.0 = 12,000 BTU/hr input; converting: 12,000 / 3.412 ≈ 3,517 W.
Question 3: Which grout characteristic is most important for optimizing vertical bore thermal performance?
- Compressive strength above 5,000 psi
- High thermal conductivity (Correct answer)
- Low permeability to prevent moisture migration
- Rapid set time under 4 hours
Correct answer: High thermal conductivity
High thermal conductivity grout reduces borehole thermal resistance, allowing more efficient heat exchange between the pipe and the surrounding formation.
Question 4: In a two-stage geothermal heat pump, what is the primary advantage of first-stage operation at partial load?
- It allows the system to run without antifreeze
- It improves efficiency by operating the compressor at a lower compression ratio (Correct answer)
- It bypasses the reversing valve to reduce wear
- It reduces groundwater consumption in open-loop systems
Correct answer: It improves efficiency by operating the compressor at a lower compression ratio
At partial load, the first stage runs at a lower compression ratio, yielding higher COP because the temperature lift between source and load is reduced.
Question 5: What does the term 'ground thermal conductivity' (λ) describe in loop field design?
- The temperature gradient between surface and deep earth
- The rate at which soil or rock transmits heat per unit thickness (Correct answer)
- The total BTU capacity of the ground volume
- The freeze depth of the soil in winter
Correct answer: The rate at which soil or rock transmits heat per unit thickness
Thermal conductivity (W/m·K or BTU/hr·ft·°F) describes how readily a material transfers heat, directly affecting bore length calculations.
Question 6: A desuperheater connected to a geothermal heat pump primarily recovers heat from:
- The ground loop return line before the heat exchanger
- Superheated refrigerant leaving the compressor (Correct answer)
- The condenser fan motor waste heat
- Domestic hot water entering the storage tank
Correct answer: Superheated refrigerant leaving the compressor
The desuperheater captures waste heat from the hot, high-pressure refrigerant gas leaving the compressor to pre-heat domestic water.
Question 7: Which loop configuration is best suited for a site with limited land area but access to a nearby pond at least 8 feet deep?
- Horizontal trenched loop
- Vertical borehole loop
- Pond/lake closed-loop coil (Correct answer)
- Standing column well
Correct answer: Pond/lake closed-loop coil
Closed-loop pond coils are submerged in a body of water, requiring no land trenching and effectively using the water body as a heat sink/source.
CRD Ground Loop & Heat Pump Configuration 3
When designing a multiple-bore vertical loop field, what is the minimum recommended bore spacing to prevent thermal interference?