BPI Heating, Ventilation & Air Conditioning (HVAC) 3 — Questions and Answers
Question 1: What is the purpose of measuring static pressure in an HVAC duct system?
- To determine the age of the air filter
- To assess airflow resistance and identify restrictions that reduce system performance (Correct answer)
- To calibrate the thermostat set point
- To measure indoor humidity levels
Correct answer: To assess airflow resistance and identify restrictions that reduce system performance
Static pressure measurements reveal how much resistance exists in the duct system; high static pressure indicates restrictions that reduce airflow and system efficiency.
Question 2: Which refrigerant replaced R-22 as the standard for residential air conditioners due to lower ozone depletion potential?
- R-410A (Correct answer)
- R-134a
- R-407C
- R-11
Correct answer: R-410A
R-410A became the dominant replacement for R-22 in residential systems because it does not deplete the ozone layer, though it still has a high global warming potential.
Question 3: In a balanced ventilation system, what must be true about supply and exhaust airflows?
- Supply airflow must exceed exhaust by 10%
- Exhaust airflow must exceed supply by at least 10%
- Supply and exhaust airflows are approximately equal (Correct answer)
- Only supply airflow matters; exhaust is passive
Correct answer: Supply and exhaust airflows are approximately equal
A balanced ventilation system maintains approximately equal supply and exhaust airflows to avoid pressurizing or depressurizing the building envelope.
Question 4: What is the function of an expansion valve (TXV) in a refrigeration cycle?
- To compress refrigerant from low to high pressure
- To meter refrigerant flow and reduce pressure before the evaporator (Correct answer)
- To remove heat from refrigerant in the condenser coil
- To sense indoor temperature and cycle the compressor
Correct answer: To meter refrigerant flow and reduce pressure before the evaporator
The thermostatic expansion valve (TXV) meters refrigerant flow into the evaporator and drops refrigerant pressure, enabling heat absorption at the evaporator coil.
Question 5: According to BPI standards, what CO level measured in ambient air during combustion appliance testing requires immediate action?
- 9 ppm
- 35 ppm
- 70 ppm (Correct answer)
- Any level above 0 ppm
Correct answer: 70 ppm
BPI protocols require immediate action (stopping work, evacuating, notifying the homeowner) when ambient CO reaches or exceeds 70 ppm during testing.
Question 6: What does ACCA Manual J calculate?
- The efficiency rating of installed HVAC equipment
- Heating and cooling loads for proper equipment sizing (Correct answer)
- Duct system layout and sizing
- Seasonal energy use of the HVAC system
Correct answer: Heating and cooling loads for proper equipment sizing
ACCA Manual J is the industry standard procedure for calculating residential heating and cooling loads to ensure equipment is properly sized for the structure.
Question 7: A technician measures a temperature difference of only 10°F across an evaporator coil during cooling mode. Normal split is 15–22°F. What is the MOST likely cause?
- Oversized ductwork causing excessive airflow
- Low refrigerant charge or restricted airflow across the coil (Correct answer)
- High outdoor temperature reducing system capacity
- Thermostat set point too high
Correct answer: Low refrigerant charge or restricted airflow across the coil
A low temperature split (delta-T) across the evaporator typically indicates insufficient refrigerant charge or restricted airflow, both reducing heat transfer at the coil.
BPI Heating, Ventilation & Air Conditioning (HVAC) 3
What is the purpose of measuring static pressure in an HVAC duct system?