Air Purifier Glossary: B-C

With so many acronyms and terms, the air purifier space can get confusing. Here are some frequently encountered stumbling blocks which begin with the letters "B" and "C." with my attempts at clarification.

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Black Wall Effect

Black Wall is attributed to "ionic air purifiers," a nonexistent class.

In reality it occurs primarily with simple negative ionizers, not air purifiers, installed near light colored walls in very sooty environments.

The “Black Wall Effect” occurs as negative ions flocculate (clump together) soot particles, causing them to stick to positively charged surfaces, including the wall behind the ionizer.

This is an overblown marketing ploy, used by vendors of competing technologies like ozone generators.

Where there is enough airborne soot to blacken walls near a table top ionizer, soot will also stain walls near HVAC vents and registers, slowly discolor carpets, and inflame lungs and eyes.

BLDC

Acrynom for Brushless Direct Current Motor. Stepped-down voltage BLDC motors are quiet, frugal on energy, friction free, run cooler, and last longer than the 120 volt alternating current motors still common in most air cleaners.

British Allergy Foundation

The British Allergy Foundation, around since 1991, but now known as Allergy UK, awards a "Seal of Approval," endorsing selected products for a fee.

Leading the list of approved air cleaners is the 3M Ultra Clean Filtrete less-than-HEPA, reviewed here as merely acceptable, for mild seasonal pollen allergy only.

Bypassing

Bypassing is internal leakage through cracks in filters and gaps between housings. Sealing tightly raises costs dramatically.

This is why so many lesser quality air cleaners are advertised as collecting "99% of particles that pass through the filter."

AHAM, the Association of Home Appliance Manufacturers, authorizes independent laboratory tests and rates air cleaning products. Called the AHAM Clean Air Delivery Rate (CADR), it is properly based on particle capture efficiency.

But efficiency testing requires a particle size distribution emphasizing sub-micron fine particles.

AHAM has neglected to test for fine particle, chemical, and odor interdiction.

Full details are available at CADR: "Clean Air Delivery Rate"

Centrifugal Fan

Also called a "squirrel-cage" fan, the centrifugal fan has a paddle wheel with blades mounted around the hub.

Air enters from the side(s) of the fan wheel and exits through a circular housing with one exit port.

Commonly used in HVAC systems and low to mid cost air purifiers, the plastic centrifugal fan is a common source of problems, mostly balance issues.

Carbon Monoxide

Carbon Monoxide (CO) is a colorless, odorless, tasteless toxic gas. CO is created by burning, including that in gas stoves and water heaters.

Acute CO poisoning much less common of late, but chronic exposure is a subtle health hazard many are unaware of.

CFM

Acronym for Cubic Feet per Minute, a measure of airflow, see below.

Clean Air Delivery Rate

See CADR, above.

Contiuous Source Emission

A continuous source emission is any pollutant that is continuously broadcast into a room. Smoking, candles, mold colonies, and exposed asbestos are examples.

No air purifier can effectively work where these chronic insults to air quality are allowed to persist.

Corona Discharge

Corona Discharge is the blue flame-like aura surrounding high voltage connections at conditions just short of outright arcing.

Early ionizers and most electrostatic air cleaners are prone to ozone and nitric oxide emissions produced when the discharge interacts with air molecules.

Many ozone generators use coronal discharge, but it is unacceptable in air purifiers sold today.

Cubic Feet per Minute

Air cleaner throughput (airflow) is measured in Cubic Feet per Minute (CFM).

CFM is handy for calculating room size for non-CADR certified air cleaners, but is just part of the equation. Airflow is meaningless without particle size specific efficiency data.

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