BPI Heating, Ventilation & Air Conditioning (HVAC) 4 — Questions and Answers
Question 1: What is the primary risk of installing an oversized air conditioner in a humid climate?
- Higher upfront equipment cost
- Short cycling that prevents adequate dehumidification (Correct answer)
- Excessive noise from large supply registers
- Tripping circuit breakers due to high startup current
Correct answer: Short cycling that prevents adequate dehumidification
An oversized AC cools the space quickly and shuts off before running long enough to remove sufficient moisture, leading to high indoor humidity despite comfortable temperatures.
Question 2: When assessing duct leakage with a duct blower, what does 'duct leakage to outside' (CFM25-out) measure?
- Total leakage in the duct system at 25 Pa
- Leakage from ducts located outside the conditioned space only (Correct answer)
- Air leakage through the building envelope
- Return duct leakage pulling in unconditioned air
Correct answer: Leakage from ducts located outside the conditioned space only
CFM25-out measures only the leakage from ducts located outside the conditioned building envelope (e.g., attic, crawlspace ducts), which directly affects energy loss.
Question 3: Which of the following best describes the role of the economizer in a commercial HVAC system?
- Recovering heat from exhaust air to pre-condition incoming air
- Using outdoor air for free cooling when conditions are favorable (Correct answer)
- Reducing refrigerant pressure during peak cooling demand
- Staging compressors to match part-load conditions
Correct answer: Using outdoor air for free cooling when conditions are favorable
An economizer uses outdoor air for cooling when outdoor temperature and humidity are below set thresholds, reducing or eliminating mechanical cooling energy.
Question 4: What is the recommended method to verify adequate combustion air supply for a naturally drafted appliance?
- Check the appliance BTU rating against the room square footage
- Observe flame color — blue means sufficient air
- Perform a draft test with a manometer before and after closing interior doors (Correct answer)
- Confirm the gas pressure at the manifold is within specification
Correct answer: Perform a draft test with a manometer before and after closing interior doors
Measuring draft pressure before and after closing interior doors reveals whether the appliance loses adequate combustion air supply under realistic building conditions.
Question 5: A homeowner's energy bills are high and the duct system is located in an unconditioned attic. What is the MOST impactful improvement?
- Replace the air handler with a higher-efficiency model
- Seal duct leaks and insulate ducts to at least R-8 (Correct answer)
- Add a programmable thermostat
- Install a two-stage compressor
Correct answer: Seal duct leaks and insulate ducts to at least R-8
Ducts in unconditioned attics lose substantial energy through both leakage and conduction; sealing leaks and adding R-8 insulation typically yields the greatest energy savings.
Question 6: What does a negative reading on a manometer connected to measure appliance zone pressure indicate during a depressurization test?
- The appliance is firing at full capacity
- The zone is depressurized relative to outdoors, increasing backdraft risk (Correct answer)
- The duct system has excess return capacity
- The heat exchanger is operating within safe parameters
Correct answer: The zone is depressurized relative to outdoors, increasing backdraft risk
A negative pressure reading in the appliance zone means that zone is depressurized relative to outside, which can cause backdrafting of combustion gases into the living space.
Question 7: According to BPI, which ventilation strategy is considered most appropriate when tightening a leaky house?
- Relying on existing envelope infiltration for ventilation
- Installing a continuous exhaust fan sized per ASHRAE 62.2 (Correct answer)
- Opening windows seasonally to provide fresh air
- Increasing return duct area to improve natural air exchange
Correct answer: Installing a continuous exhaust fan sized per ASHRAE 62.2
BPI requires that when a house is air-sealed, mechanical ventilation must be installed per ASHRAE 62.2 to maintain indoor air quality since natural infiltration can no longer be relied upon.
BPI Heating, Ventilation & Air Conditioning (HVAC) 4
What is the primary risk of installing an oversized air conditioner in a humid climate?