HVAC Indoor Air Quality and Filtration 4 — Questions and Answers
Question 1: What is the primary difference between a HEPA filter and a standard MERV-rated filter?
- HEPA filters use electrostatic charge; MERV filters use mechanical media
- HEPA filters capture 99.97% of particles ≥0.3 microns; MERV filters are rated on a different efficiency scale (Correct answer)
- HEPA filters are reusable; MERV filters are always disposable
- HEPA filters address gases; MERV filters address particles
Correct answer: HEPA filters capture 99.97% of particles ≥0.3 microns; MERV filters are rated on a different efficiency scale
True HEPA filters must capture at least 99.97% of airborne particles at the 0.3-micron most-penetrating particle size, a standard not defined by the MERV scale.
Question 2: Which chemical, commonly off-gassed by new carpets, adhesives, and furniture, is classified as a Group 1 human carcinogen?
- Toluene
- Formaldehyde (Correct answer)
- Benzene
- Xylene
Correct answer: Formaldehyde
Formaldehyde, found in pressed wood products, adhesives, and some fabrics, is classified by IARC as a Group 1 (definite) human carcinogen.
Question 3: What is the recommended minimum outdoor air ventilation rate per person for office spaces according to ASHRAE 62.1?
- 2.5 CFM per person
- 5 CFM per person
- 10 CFM per person (Correct answer)
- 20 CFM per person
Correct answer: 10 CFM per person
ASHRAE 62.1 requires a minimum of approximately 17 CFM total per person for offices, but the people component alone is 5 CFM per person plus an area component.
Question 4: An activated carbon filter is best suited for removing which type of indoor air contaminant?
- Particulate matter and dust
- Gaseous pollutants and odors (VOCs) (Correct answer)
- Biological agents like mold spores
- Radioactive particles
Correct answer: Gaseous pollutants and odors (VOCs)
Activated carbon adsorbs gaseous pollutants, VOCs, and odors through its highly porous surface structure, but does not effectively capture particles.
Question 5: What is the purpose of a demand-controlled ventilation (DCV) system?
- To maintain constant airflow regardless of occupancy
- To modulate outdoor air intake based on real-time CO2 or occupancy sensors (Correct answer)
- To balance static pressure across supply and return ducts
- To control humidity by varying outdoor air temperature
Correct answer: To modulate outdoor air intake based on real-time CO2 or occupancy sensors
DCV systems use CO2 sensors or occupancy data to increase or reduce outdoor air ventilation rates in response to actual building occupancy, saving energy while maintaining IAQ.
Question 6: Which filter media type uses an electrostatic charge to attract and capture airborne particles?
- Fiberglass flat-panel filter
- Electrostatically charged synthetic media filter (Correct answer)
- Activated carbon granule filter
- Polyester mesh pre-filter
Correct answer: Electrostatically charged synthetic media filter
Electrostatically charged synthetic media filters use an embedded static charge to attract particles similarly to a magnet, enhancing capture efficiency beyond mechanical straining alone.
Question 7: What IAQ issue can result from running a cooling system that removes too much moisture from indoor air in a cold, dry climate during winter?
- Microbial growth in drain pans
- Excessively low relative humidity causing respiratory irritation and static electricity (Correct answer)
- Elevated CO2 buildup from reduced ventilation
- Legionella proliferation in cooling coils
Correct answer: Excessively low relative humidity causing respiratory irritation and static electricity
Overly dry indoor air (RH below 30%) causes respiratory tract irritation, increased static electricity, and can dry out wood furnishings and building materials.
HVAC Indoor Air Quality and Filtration 4
What is the primary difference between a HEPA filter and a standard MERV-rated filter?