BPI HVAC Systems 4 — Questions and Answers
Question 1: What does the term 'latent cooling load' refer to in HVAC design?
- Sensible heat removed from indoor air
- Heat required to change the phase of refrigerant
- Energy needed to dehumidify indoor air by condensing moisture (Correct answer)
- Cooling required to offset solar heat gain through windows
Correct answer: Energy needed to dehumidify indoor air by condensing moisture
Latent cooling load is the energy needed to remove moisture from indoor air through condensation at the evaporator coil, without changing air temperature.
Question 2: A technician finds that a gas furnace's heat exchanger surface temperature is consistently below the dew point of the flue gases. What problem can result?
- Flame rollout
- Condensation and acid corrosion of the heat exchanger (Correct answer)
- Incomplete combustion due to excess air
- High stack temperature reducing efficiency
Correct answer: Condensation and acid corrosion of the heat exchanger
When flue gas contacts heat exchanger surfaces below the dew point, moisture condenses along with acidic compounds, accelerating corrosion of the heat exchanger.
Question 3: Which BPI protocol component evaluates the interaction between mechanical ventilation and combustion appliances under worst-case conditions?
- Blower door depressurization test
- Combustion appliance zone worst-case depressurization test (Correct answer)
- Duct blaster pressurization test
- Infrared thermography scan
Correct answer: Combustion appliance zone worst-case depressurization test
The worst-case CAZ depressurization test simulates maximum negative pressure on the combustion zone by operating all exhaust equipment simultaneously.
Question 4: What is the primary benefit of a two-stage or variable-capacity HVAC system compared to a single-stage system?
- Lower initial equipment cost
- Ability to operate at partial load for better comfort and efficiency (Correct answer)
- Simpler installation requiring less ductwork
- Higher rated peak BTU output
Correct answer: Ability to operate at partial load for better comfort and efficiency
Multi-stage and variable-capacity systems modulate output to match actual load, reducing short cycling, improving humidity control, and increasing overall efficiency.
Question 5: When testing duct leakage with a duct blaster, a test-out result significantly higher than test-in indicates what?
- Leakage is mostly to outdoors rather than within conditioned space (Correct answer)
- The air handler fan is cycling improperly
- Return duct leakage is greater than supply leakage
- Equipment was recently serviced and sealed properly
Correct answer: Leakage is mostly to outdoors rather than within conditioned space
Test-out measures total duct leakage to outside; a high test-out compared to test-in confirms most leakage goes to unconditioned spaces like attics or crawlspaces.
Question 6: What ASHRAE standard governs minimum ventilation rates for residential buildings?
- ASHRAE 55
- ASHRAE 62.2 (Correct answer)
- ASHRAE 90.1
- ASHRAE 15
Correct answer: ASHRAE 62.2
ASHRAE 62.2 establishes minimum mechanical and natural ventilation requirements and acceptable IAQ for low-rise residential buildings.
Question 7: Which refrigerant has an Ozone Depletion Potential (ODP) of zero and is commonly used in newer residential air conditioning systems?
- R-22
- R-410A (Correct answer)
- R-11
- R-123
Correct answer: R-410A
R-410A has an ODP of zero because it contains no chlorine, making it ozone-safe, and it replaced R-22 as the standard residential AC refrigerant.
BPI HVAC Systems 4
What does the term 'latent cooling load' refer to in HVAC design?