Air Purifier Glossary: D-G

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 "D" to "G." with my attempts at clarification.

----------- D -----------

dB(A)

Abbreviation for Decibel, see next.

Decibel

The standard metric for sound pressure level - noise.

For complete details see Quiet Air Purifier?

DC Motor

Direct current motor. A stepped down voltage, usually 12 Volts, is used to reduce noise, energy use, and electromagnetic field emissions in the most modern air purifiers.

The majority of air cleaners still use 120 Volt, 60-cycle/second (60 hz) alternating current.

See also BLDC.

Delivered Airflow

The actual air going through an air cleaner with all filters installed and covers closed. For machines not AHAM certified, it is an approximation of CADR rate. Many manufacturers will quote unobstructed free airflow to make their air purifier seem stronger.

Compare Free Airflow, below.

Depth Loading

Filters can have a progressively tighter matrix of fibers, designed to capture successively finer particles deeper into the filter, or have a uniform fiber spacing throughout.

Depth loading can reduce the need for a series of filter stages, making filter changing extremely convenient.

The Blueair "HEPASilent" filters are a leading example.

Diffuser

Air exhaust designed to create airflow patterns for quiet or efficient air circulation. Usually a louver arrangement.

DOP - Dioctylphthalate

DOP is the Military Standard used to rate HEPA filters.

A HEPA's efficiency is evaluated by the percentage of 0.3 micron sized DOP smoke particles captured in laboratory conditions.

Ductwork

Air channels, made of metal or plastic/fiberglass, used to carry air to and from heat exchangers and cooling coils in HVAC systems.

Duct Cleaning

The controversial process of removing accumulated dust and mold from HVAC ducting. Every situation is different and often more complex than homeowners and even contractors specializing inHVAC understand.

Sometimes, duct cleaning does more harm than good.

Dust Mite

House dust mites are tiny, but borderline visible, household insects.

Dust mites feed on flakes of human skin, which is constantly shedding, and prosper in humid areas with ample food, especially mattresses and pillows.

Mites contribute to asthma and allergy on a global basis.

Dust Mite Allergens

Dust mite droppings, tiny fecal pellets, contain enzymes.

It is these enzymes, not bites, which cause allergy symptoms,

Droppings can become airborne with strong air currents, but they are primarily transferred by breathing with one's face close to a pillow. Air purifiers cannot intercept this mode of transmission, and therefore cannot completely prevent dust mite allergy.

Dwell Time

Time air spends in close proximity to ultraviolet radiation and photocatalytic surfaces. Air cleaners using these technologies must slow down airflow in order for the germicidal and oxidative effects to work. Many builders are simply adding low powered UV and PCO to existing designs without engineering for dwell time.

----------- E -----------

Efficiency

Efficiency might be the most misapplied concept in air purifier marketing.

Filtration efficiency consists of a specific particle size and a percentage: "99.97% at .3 microns."

"Captures 99% of a list of pollutants..." is completely meaningless marketing jargon.

Ideally, tho rarely, a table of efficiencies at various particle sizes is published.

Only the best of the premium class air purifiers actually realize near 100% efficiency on sub-micron sizes. Good air cleaners might get 80%, average maybe 60%, poor 30%.

High efficiency air cleaners take less time to reach acceptable particle levels. Those with low efficiencies, the majority sold today, will never reach these levels.

Efficiency of chemical and odor filtration is completely unrelated to particle efficiency.

Electrostatic Precipitator

Commonly mislabeled as "ionic" air cleaners, precipitators have both a charging field and a collection grid.

Formerly the best selling air cleaner technology, these machines are plagued with ozone emissions and declining efficiency when not fastidiously kept immaculate inside.

Examples; Oreck Xl, Ionic Pro, Ionic Breeze, Honeywell IFD, abd Friedrich.

EN1822

European Norm 1822 is a more exacting HEPA standard. Typical HEPA tests assume that .3 micron is the most penetrating particle size.The EN1822 two part test first determines the most penetrating size, and rates the filter at its weakest efficiency.

Only a few premium air purifiers can excel at this test.

EnergySTAR

A US Environmental Protection Agency (EPA) program that issues energy efficiency ratings to air cleaners and other appliances.

Air cleaner ratings are based on Clean Air Delivery Rate numbers, and expressed as Dust CADR per Watt.

To qualify 2.0 CADR/W is required.

Currently the leading energy-efficient air purifier is Blueair's ECO10 at a miserly 19.66 C/W.

Evaporator Coil

Part of an air conditioning system, resembling an automotive radiator, where cold refrigerant gas absorbs heat from the passing airstream.

While modern condensers are usually outdoors, evaporator coils are commonly inside the home, attached to the furnace.

Condensation of water makes the evaporator coil, and its drain pan, a collecting place for debris and a breeding ground for microbes.

----------- F -----------

Free Airflow

Air flow (CFM) tested without filters or other restrictions installed, often just the fan rating. Manufacturers and vendors will sometimes incorrectly state this as the machines throughput.

See Delivered Airflow, above.

----------- G -----------

Gas Phase Pollutant

Chemicals and odors, at the molecular size level, are gas-phase pollutants. These go right through HEAP filters.

Carbon and other gas adsorbents, present in very small amounts in the majority of air cleaners, are required to collect gaseous contaminants.

Gasket

Material inserted between an air filter and its supporting frame or case to prevent bypassing. Gaskets can be rubber, urethane foam, or even paper.

Many air cleaners are built without proper sealing to keep costs down and airflow up to support the appearance of higher performance.

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