Indoor Air Quality and Filtration Flashcards

What does MERV stand for in air filter ratings?

Answer: Minimum Efficiency Reporting Value; higher = more efficient at capturing smaller particles

MERV (Minimum Efficiency Reporting Value) rates filter efficiency on a scale of 1-16+. Higher MERV numbers capture smaller particles more efficiently.

What is 'sick building syndrome' (SBS)?

Answer: Occupants experiencing health symptoms linked to time spent in a building, primarily caused by poor ventilation and indoor air contaminants

SBS refers to situations where occupants experience acute health symptoms (headaches, irritation, fatigue) that appear linked to time spent in the building—often related to inadequate ventilation and indoor pollutants.

What is the primary purpose of outdoor air ventilation in commercial HVAC systems according to ASHRAE Standard 62.1?

Answer: To dilute indoor contaminants and provide fresh air for occupant health and comfort

ASHRAE 62.1 establishes minimum ventilation rates to dilute and remove indoor-generated contaminants and provide outdoor air for occupant breathing.

What CO2 concentration is generally considered the threshold above which occupant comfort begins to decline?

Answer: 1,000 ppm

CO2 levels above approximately 1,000 ppm are associated with noticeable declines in comfort and emerging impaired cognitive performance.

What is 'bioaerosol' contamination in HVAC systems?

Answer: Airborne biological particles (mold spores, bacteria, viruses) generated by HVAC system components or building sources

Bioaerosols are airborne biological particles including mold spores, bacteria, viruses, and allergens. In HVAC systems, they most commonly originate from wet cooling coils, condensate drain pans, and humidifiers.

What type of filter is required to achieve HEPA filtration?

Answer: True HEPA filter rated at 99.97% efficiency on particles ≥0.3 μm

True HEPA filters must capture 99.97% of airborne particles at 0.3 micrometers—the standard used in hospitals and clean rooms.

What is the purpose of a UV germicidal irradiation (UVGI) system in an air handling unit?

Answer: To inactivate microorganisms by disrupting their DNA using UV-C light

UVGI systems use UV-C light (typically 254 nm wavelength) to disrupt the DNA/RNA of microorganisms on cooling coil surfaces and in airstreams.

What is a 'volatile organic compound' (VOC)?

Answer: Carbon-based chemical gases emitted from materials and products, with common indoor sources including new carpet, paint, and cleaning products

VOCs are carbon-based chemicals that evaporate at room temperature, emitted from building materials, furniture, cleaning products, and office equipment.

How does an energy recovery ventilator (ERV) improve indoor air quality while reducing energy consumption?

Answer: By transferring heat and moisture between outgoing and incoming air streams, conditioning fresh air with minimal energy

An ERV uses a heat exchange core to transfer both heat and moisture between outgoing stale air and incoming fresh air, pre-conditioning incoming outdoor air while exhausting indoor pollutants.

What does 'demand-controlled ventilation' (DCV) do?

Answer: Modulates outdoor air intake based on actual occupancy, typically using CO2 sensors

DCV adjusts outdoor air ventilation rates in real time based on actual occupancy, using CO2 sensors as a proxy for occupant density, saving significant energy in variable-occupancy spaces.

What is the difference between 'air changes per hour' (ACH) and 'cubic feet per minute' (CFM)?

Answer: ACH measures how many times per hour the entire room volume is exchanged; CFM measures volumetric flow rate

ACH represents how many complete room volume exchanges occur per hour. CFM is an absolute volumetric flow rate. ACH = (CFM × 60) ÷ Room Volume (cubic feet).

What is 'radon' and why is it an indoor air quality concern?

Answer: A naturally occurring radioactive gas that seeps from soil and rock, accumulating in buildings and increasing lung cancer risk

Radon is a naturally occurring radioactive gas (decay product of uranium/radium) that seeps into buildings through foundation cracks—the second leading cause of lung cancer after smoking.

What is 'stratification' in a large space HVAC system?

Answer: The tendency for warm air to rise to the ceiling while conditioned fresh air stays near the floor

In tall spaces, warm air naturally rises (buoyancy), causing temperature and pollutant stratification—conditions at the breathing zone near the floor may differ significantly from ceiling level.

What IAQ hazard does a malfunctioning heat exchanger in a forced-air furnace pose?

Answer: Carbon monoxide (CO) poisoning from combustion gases leaking into the supply air stream

A cracked or corroded heat exchanger allows combustion gases—including deadly carbon monoxide—to mix with the circulated air supply, posing serious carbon monoxide poisoning risk.

What does ASHRAE 62.1's 'ventilation effectiveness' (Ev) factor account for?

Answer: How effectively the ventilation air actually reaches the breathing zone based on air distribution method

Ventilation effectiveness (Ev) accounts for the fact that not all supply air effectively reaches the breathing zone—Ev ranges from 0.5 to 1.2 depending on air distribution method.

What is the minimum ventilation rate specified by ASHRAE 62.1 for a typical office space?

Answer: 5 cfm per person plus 0.06 cfm per square foot of floor area

ASHRAE 62.1 uses a dual-parameter formula: people-related component (5 cfm/person for offices) plus building-related component (0.06 cfm/ft²), accounting for human bioeffluents and building material emissions.

What is the 'dilution ventilation' approach to IAQ, and when is 'source control' a better strategy?

Answer: Dilution adds clean air to lower pollutant concentration; source control is better when the source can be eliminated or isolated

Dilution ventilation uses increased outdoor air to reduce pollutant concentrations; source control (eliminating or isolating pollutant sources) is more effective and energy-efficient when sources can be directly addressed.

What is a 'pressure relationship' between spaces in a building?

Answer: The relative positive or negative pressure between spaces that determines which direction air flows through gaps and openings

Pressure relationships (positive or negative pressure between adjacent spaces) determine the direction of air movement through cracks, gaps, and penetrations—critical for controlling contaminant migration.

What is 'formaldehyde' and why is it a significant indoor air quality concern in new construction?

Answer: A VOC off-gassed from composite wood products, insulation, and adhesives, classified as a known human carcinogen

Formaldehyde (HCHO) is a VOC off-gassed from pressed wood products (MDF, particleboard), insulation, adhesives, and finishes—classified as a Group 1 carcinogen by IARC.

What does an 'electronic air cleaner' (electrostatic precipitator) use to capture particles?

Answer: High-voltage ionization to charge particles, which are then attracted to collector plates of opposite charge

Electronic air cleaners use a high-voltage ionizer section to charge particles, which are then attracted to collector plates of opposite charge—effective for very fine particles that pass through mechanical filters.