Never has the need for the installation and maintenance of efficient filtration systems been such a high priority as it is today. Health and productivity are closely related to ambient air quality. Recent studies reveal disturbing facts:
The growth of global trade has significantly increased the danger of contamination in the air.
There is an increase of atmospheric polluants, gases and volatile compounds released by new materials, as well as an augmentation of virus and bacteria in the ambient air of buildings.
We are withnessing an exponential increase in all types of respiratory problems such as asthma.
These studies will force government agencies to tighten filtration standards concerning air filtration.
MERV classification SYSTEM
Minimum efficiency reporting value, commonly known as MERV rating, is a measurement scale designed in 1987 by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) to rate the effectiveness of air filters.
The scale "represents a quantum leap in the precision and accuracy of air-cleaner ratings"[1] and allows for improved health, reduced cost and energy efficiency in heating, ventilation and air conditioning (HVAC) design. For example, a HEPA filter is often impractical in central HVAC systems due to the large pressure drop the dense filter material causes. Experiments indicate that less obstructive, medium-efficiency filters of MERV 7 to 13 are almost as effective as true HEPA filters at removing allergens, with much lower associated system and operating costs.
The scale is designed to represent the worst-case performance of a filter when dealing with particles in the range of 0.3 to 10 micrometers. The MERV rating is from 1 to 16. Higher MERV ratings correspond to a greater percentage of particles captured on each pass, with a MERV 16 filter capturing more than 95% of particles over the full range.
The image above briefly demonstrates the type and size (in microns) of the particles filtered by each type of filter.
PrE-FILTER
Filter placed upstream of a filter with greater efficiency to ensure pre-filtration of the particles beforehand, which will thus avoid too rapid saturation of the filter at medium and high efficiency.
MEDIUM EFFECTIVENESS
Filtering particles of 3 μm (microns) and more at an efficiency ranging from 35% to 75%, this type of filter can have a MERV classification ranging from 8 to 12.
HIGH EFFICIENCY
Filtering particles of 0.3 μm (microns) and more at an efficiency ranging from 85% to 95%, this type of filter can have a MERV classification ranging from 13 to 14. This type of filter can be used as a pre-filter to a HEPA and ULPA filter.
HEPA
HEPA meaning High Efficiency Particulate Air Filter. This type of filter removes at least 99.97% of airborne particles equal to or larger than 0.3 μm (microns).
ULPA
ULPA meaning "ultra low penetration air". A ULPA filter can remove at least 99.999% of dust, pollen, mold and any particle in the air equal to or greater than 0.12 μm (microns), at a minimum.
aCTIVATED COAL
Coal that has been purified by steam heating to adsorb certain elements. In air filtration, activated carbon filters are mainly used to filter unwanted odors in offices and laboratories.
Ultraviolet
Especially used in the hospital environment, UV light filtration releases a quantity of energy necessary to break molecular links of micro-organisms. When these microorganisms (microbes, germs, viruses, bacteria, molds, etc.) pass through the UV rays of ultraviolet lamps, there is a breakdown of molecular links, which results in cellular or genetic damage that leads directly to the destruction of these.
EFFICIENCY
The ability of a device to remove particulate or gaseous material from a stream of air by measuring the concentration of material upstream and downstream of the device.
DURABILITY
Ability to retain dust in the filters with the least possible harm to the flow of air.
RELIABILITY
Filter capacity to perform its function well thanks to a construction of superior quality.
Micron OR MICROMETER (ΜM)
Unit measuring the length of the international system of 10-6 meters, which corresponds to a millionth of a meter.
bag filters
Filter whose filter layer is in the form of polyester or fiberglass bags.
pleated bags
Generally a filter consisting of a mixture of cotton and polyester or synthetic media folded several times to increase the filtration area.
cleanrooms
Airtight enclosure in which the properties of the atmosphere (temperature, hygrometry, content of particles and micro-organisms, pressure and movement of air, etc.) are controlled.
containment units (Bag In / Bag Out)
Bag In / Bag Out systems are containment units that have an option that allows the user to include a filter replacement device using polyvinyl chloride bags with handles. The addition of this type of bag for the replacement of filters makes it possible to avoid any contact with hazardous materials picked up by the filters.
GRAVIMETRIC EFFECTIVENESS TEST
Test often used to compare very low efficiency filters, such as pre-filters. This test uses a synthetic dust that has a particle size distribution much larger than those found outside, in the ambient air. The gravimetric efficiency is calculated with the following formula:
GRAVIMETRIC EFFECTIVENESS = GAIN BY FILTER WEIGHT
Weight of synthetic dust emitted
In summary, if we sent 10 pounds of synthetic dust and the filter, after the experiment, weighs 9 pounds more than the original, the filter will have an efficiency of 90%, since it has captured 9 pounds out of 10.
D.O.P. TEST
The D.O.P. uses uniform particles of hot or cold dioctyl phthalate with a diameter of 0.3 microns and requires a penetration analyzer. For a filter to be classified as "HEPA", the results of the DOP test must be greater than 99.97% on a dust of 0.3 microns.
In order to obtain a HEPA efficiency, the filtration system must be tested with a DOP test to detect any leakage between the filter and its frame.
There is also another type of test for HEPA filters: