Passive Air Cleaning Methods(top)
Technologies which fall into this category perform the air cleaning operation within an enclosure such as a box usually constructed from wood, metal, or molded plastic rather than outside the box and in the open air of the room or facility.

• Media Filtration(top)
  This method employs a filter usually made from an advance technology paper, textile, metal, synthetic, glass, or other substance.  As air is drawn through the filter, usually with a blower attached to a motor, the particulates such as smoke, pollen, dust, mold spores, and bacteria, become trapped in the filter while the air consisting primarily of nitrogen and oxygen molecules continues through the filter.  The result is that the air is ridded of the pollutant particles.  The air returned to the room is clean.   There are various types of media filters and several popular methods for testing the efficiency of these types of filters.  The efficiency describes how well the filter performs the filtering job.  It is important to understand the various testing methods because an efficiency rating  for a filter from one test can be vastly different from the same type of filter tested with another testing method.  Without knowing the test used to attribute an efficiency rating to a filter the efficiency rating is of very little value in comparing different air cleaners.  This knowledge is often used by marketing departments of air cleaner manufacturers to lure the consumer into the belief they are purchasing a fabulous air cleaner when they may be able to get a much better machine from a competitor for comparable cost.  This type of air cleaner requires periodic filter replacements.  The replacement interval depends on the amount of pollution to which the air cleaner is exposed.  n Click Here for Filter Efficiency Tests.

• Electrostatic Precipitation(top)
  This method employs high voltage electronics to deliberately place an electrical charge on particulates in the air as they enter the air cleaner.  The electrically charged particulates may be "steered" with electrical forces within electronic cells of the air cleaner so that the particulates crash into a metal plate and become stuck.  The particulates then remain in the air cleaner as the cleaned air exits.   This type of air cleaner requires periodic cleaning of the electronic cells with a special electronic cell cleaner.  The cleaning interval depends on the amount of pollution to which the air cleaner is exposed.
  n Click Here for Portable Electrostatic Precipitator
  n Click Here for Hard Surface Ceiling Mounted Electrostatic Precipitator
  n Click Here for Acoustic Ceiling Mounted Electrostatic Precipitator

In general, when using either media or electrostatic precipitation air cleaners the rule of thumb is that all the air in the room or facility should be cleaned at least six times each hour for excellent protection and elimination of pollutants such as allergens.  If the air cleaner is for a bar/restaurant situation where people may be actively smoking then it is advisable to plan on cleaning the air eight to ten times each hour.

• Sorbent Materials(top)
  Media based and electronic air cleaners are limited in their ability to remove particles from the air approaching the size of small gas molecules.  This is easy to observe by realizing that the air is primarily made up of nitrogen and oxygen and that it easily passes through the air cleaner.  Therefore, another method is employed to remove a wide array of gaseous substances from the air.  This method is called adsorption.   Several popular materials used for this purpose are activated carbon or charcoal, zeolite, and alumina potassium permanganate¹.  Each material has a propensity to collect certain pollutants from the air that pass through it.  Carbon is a good adsorber of a wide spectrum of gas molecules but has less affinity for very light gases such as ammonia and formaldehyde .  Carbon is sometimes blended with alumina potassium permanganate or potassium iodide to add adsorption capacity for light gases.  If you suspect you have an air problem due to gases, odors, or Volatile Organic Compounds (VOC) from gas molecules, than you may want to consider an air cleaner that incorporates sorbent materials in the design.  The amount of sorbent material will affect the longevity of the air cleaner to remove gaseous pollutants. The amount of sorbent material may also impact the contact time between the air and the sorbent materials and therefore the single pass efficiency of the sorbent material.   Some air cleaners simply have a molecular thick coating of sorbent material while other air cleaners have 15 pounds or more.
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  ¹ CPZ ™ is a Honeywell Enviracaire^® trademark acronym for Carbon, Permanganate, Zeolite
  n Click Here for Portable Media Filtration with Sorbent Materials 
  n Click Here for More Portables
  n Click Here for Hard Surface Ceiling Mounted Media Filtration with Sorbent Materials
  n Click Here for Acoustic Ceiling Mounted Media Filtration with Sorbent Materials
  n Click Here - to see ceiling fans that act as air cleaners (passive and active methods)

• Ultraviolet (UV) Light(top)
  The germicidal effectiveness of UV lamps is proportional to the exposure time of the microorganism to the UV light and the intensity of the UV lamp.   Different microorganisms require different exposure time to UV lights to be killed.   UV lamps are most effective in still air at an ambient temperature of 77 degrees Fahrenheit.

  According to the Center for Disease Control (CDC) Guidelines,  "The use of UV lamps and HEPA filtration in a single unit would not be expected to have any infection-control benefits not provided by the use of the HEPA filters alone".

  However, certain pathogens such as viruses may be able to penetrate HEPA filters  An air cleaner designed to deliver an appropriate dosage of UVGI light may be able to reduce the ambient pathogen level. 
  Making a case for UVGI: AEROBIOLOGICAL ENGINEERING - HEPA Filtration

  n Click here for further information on UVGI and medical grade air cleanersn
  n Airborne Respiratory Diseases and Mechanical Systems for CONTROL OF MICROBES

• Choosing the Proper Number of Passive Air Cleaners for your Application(top)
  
  A summary table for this section  is available here.
   

  • Select the proper amount of air cleaning capacity(top)
    The first step is to decide how often the air needs to be cleaned (Air Changes per Hour: ACH), in order to maintain air cleanliness.  The following chart provides a good rule of thumb.

    Passive Air Cleaners
    Air Changes per Hour(ACH), Typical Applications

    		ACH
    light load	general offices, residences:	6
    average load	bars, breakrooms, designated smoking areas:	8
    heavy load	bingo halls, cigar bars, extra smoky areas:	10
    special load	dental labs	10-12
    	hospital isolation rooms	12

    The second step is to compute the total volume of air that needs to be cleaned.  First determine the length, width, and ceiling height of the room in feet. Compute the total volume by multiplying the length, width , and height.
    
                VOLUME in cubic feet = Length X Width X Ceiling Height
                            where Length, Width, & Height are in units of feet

    The third step is to compute the amount of air that needs to be processed each minute in cubic feet of air per minute, CFM.  The following table provides a guide.

    For this much ACH:			multiply the VOLUME by this:
    	6			0.1
    	8			0.134
    	10			0.167
    	12			0.2

    The result will be the total required air cleaning rate in CFM.

  • Determine the necessary number of machines.(top)
    First: Determine the air cleaning rate of the passive air cleaner you are intending to purchase by inspecting the product literature for the CFM rating.
    Second: Divide the total required CFM for your room by the CFM rating of the machine and round up.
         Total number of passive machines required = (Required CFM) / (Machine CFM rating)

  Click Here for more information