CRD CRD System Commissioning & Performance Testing 2 — Questions and Answers
Question 1: What is the purpose of a pressure test performed on a closed-loop geothermal ground loop before system startup?
- To verify loop integrity by detecting leaks before backfilling or system connection (Correct answer)
- To measure the static ground pressure at loop depth
- To calibrate the heat pump refrigerant circuit
- To determine soil permeability for loop sizing
Correct answer: To verify loop integrity by detecting leaks before backfilling or system connection
Pressure testing the loop prior to backfill and connection confirms there are no leaks in the piping that would cause fluid loss and system failure.
Question 2: According to IGSHPA standards, what minimum pressure is recommended for loop pressure testing, and how long should it be held?
- 100 psi for at least 30 minutes with no pressure drop (Correct answer)
- 10 psi for 5 minutes
- 50 psi for 2 minutes
- 200 psi for 60 minutes
Correct answer: 100 psi for at least 30 minutes with no pressure drop
IGSHPA recommends at least 100 psi for a minimum of 30 minutes to reliably detect small leaks in the ground loop before backfilling.
Question 3: During commissioning, a technician purges air from the closed loop using a high-velocity purge cart. Why is complete air removal critical?
- Air pockets reduce heat transfer efficiency and can cause pump cavitation (Correct answer)
- Air improves freeze protection in the antifreeze solution
- Air increases system pressure to design levels
- Air acts as a thermal buffer improving COP
Correct answer: Air pockets reduce heat transfer efficiency and can cause pump cavitation
Air in the loop disrupts flow, reduces heat transfer, and can damage the circulating pump through cavitation, so thorough purging is essential.
Question 4: What antifreeze concentration is typically verified during commissioning of a closed-loop system in a US climate where ground temperatures may drop below 32°F?
- Sufficient concentration to provide freeze protection to at least 10°F below the minimum expected EWT (Correct answer)
- Plain water with no antifreeze since loops stay warm
- 100% antifreeze for maximum protection regardless of climate
- Any concentration as long as some antifreeze is present
Correct answer: Sufficient concentration to provide freeze protection to at least 10°F below the minimum expected EWT
Antifreeze must be concentrated enough to protect the loop fluid to at least 10°F below the minimum design entering water temperature to prevent freeze damage.
Question 5: Which performance metric is used to evaluate a geothermal system's cooling efficiency during commissioning?
- Energy Efficiency Ratio (EER) or Cooling COP (Correct answer)
- Heating Seasonal Performance Factor (HSPF) only
- Annual Fuel Utilization Efficiency (AFUE)
- Seasonal Energy Efficiency Ratio (SEER) measured in isolation
Correct answer: Energy Efficiency Ratio (EER) or Cooling COP
EER or Cooling COP compares cooling output to electrical input at specific test conditions, giving an instantaneous measure of cooling efficiency.
Question 6: What action should a commissioning technician take if the measured system COP is significantly below the manufacturer's rated value under similar conditions?
- Investigate loop flow rate, refrigerant charge, air handler airflow, and entering water temperature before accepting the system (Correct answer)
- Accept the system and note the discrepancy without investigation
- Increase the thermostat setpoint to compensate
- Replace the heat pump immediately without further diagnosis
Correct answer: Investigate loop flow rate, refrigerant charge, air handler airflow, and entering water temperature before accepting the system
A low COP has multiple potential causes that must be systematically diagnosed before the system is accepted or equipment replaced.
CRD CRD System Commissioning & Performance Testing 2
What is the purpose of a pressure test performed on a closed-loop geothermal ground loop before system startup?