HVAC Indoor Air Quality and Filtration 2 — Questions and Answers
Question 1: What does a MERV rating measure in air filters?
- Filter thickness in inches
- Minimum Efficiency Reporting Value — particle capture efficiency (Correct answer)
- Maximum energy recovery ventilation
- Mean energy reduction value
Correct answer: Minimum Efficiency Reporting Value — particle capture efficiency
MERV (Minimum Efficiency Reporting Value) rates a filter's ability to capture airborne particles on a scale of 1–16.
Question 2: Which IAQ pollutant is a naturally occurring radioactive gas that can accumulate in basements?
- Carbon monoxide
- Nitrogen dioxide
- Radon (Correct answer)
- Formaldehyde
Correct answer: Radon
Radon is a colorless, odorless radioactive gas that seeps from soil and rock and can reach dangerous concentrations in poorly ventilated lower levels.
Question 3: What is the primary purpose of an energy recovery ventilator (ERV) compared to a heat recovery ventilator (HRV)?
- ERV only transfers heat; HRV transfers both heat and moisture
- ERV transfers both heat and moisture; HRV transfers heat only (Correct answer)
- ERV filters particles; HRV does not
- ERV is used in cooling climates only; HRV in heating climates only
Correct answer: ERV transfers both heat and moisture; HRV transfers heat only
An ERV transfers both sensible heat and moisture (latent energy) between exhaust and supply airstreams, while an HRV transfers heat only.
Question 4: A MERV 13 filter is generally recommended for which application?
- Pre-filtration in industrial settings
- Residential and commercial buildings requiring hospital-level filtration
- General residential use with standard HVAC equipment (Correct answer)
- Cleanroom manufacturing environments
Correct answer: General residential use with standard HVAC equipment
MERV 13 filters capture particles as small as 0.3–1.0 microns and are widely recommended for improved residential and light commercial IAQ.
Question 5: What condition results when a building's HVAC system creates a negative pressure differential relative to the outdoors?
- Stack effect reversal
- Backdrafting of combustion appliances (Correct answer)
- Increased filtration efficiency
- Reduced volatile organic compound levels
Correct answer: Backdrafting of combustion appliances
Negative building pressure can cause combustion gases from furnaces or water heaters to be drawn back into the living space instead of exhausted outside.
Question 6: Which measurement unit is commonly used to quantify CO2 concentration when assessing ventilation adequacy?
- Micrograms per cubic meter (µg/m³)
- Parts per million (ppm) (Correct answer)
- Cubic feet per minute (CFM)
- Grains per pound (gr/lb)
Correct answer: Parts per million (ppm)
CO2 concentration in indoor air is measured in parts per million (ppm); levels above 1,000 ppm often indicate inadequate ventilation.
Question 7: What is the recommended action when an electronic air cleaner's collection cells become dirty?
- Replace the entire unit
- Wash the cells with water and mild detergent, then dry completely (Correct answer)
- Vacuum only — never use water
- Apply a coating of activated carbon before reinstalling
Correct answer: Wash the cells with water and mild detergent, then dry completely
Electronic air cleaner collection cells should be removed and washed with water and mild detergent, then fully dried before reinstallation to restore efficiency.
HVAC Indoor Air Quality and Filtration 2
What does a MERV rating measure in air filters?