Look for links to printable pdf  literature in equipment specifications sections, above in this column, & on site map.

• Client requires HEPA air filtration for particulates such as dust from jack hammering concrete, compounding drywall, plaster, interior demolition, lead & asbestos remediation, and other construction/renovation activities.
• Client may also need air filtration for gases during construction/renovation.
• The work area may need to be placed under negative pressure to help contain air contaminants to work area.
• The largest expected work area is TBD 

ANALYSIS:   The air contaminants may be broadly classified as either particles or gases.  High efficiency HEPA filters are used to remove the particles.   

A blend of carbon is used to adsorb many gases/odors.  It is important to have the proper ratio of carbon blend to air flow in order to maintain sufficient contact time between the air and carbon for high single pass efficiency through the air cleaner unit.  It is also important to have the proper blend of media to capture a broad range of molecular weight gas molecules, or, to target specific gas molecules.

• Your  application does not currently require carbon, as gases are presumed not an issue.  However, if gases/odors/Volatile Organic Chemicals (VOC's) become an issue, the following air cleaners may optionally be configured for these gaseous air contaminants.

For background information, please refer to our ambient air cleaning sizing table, and, particle filter efficiency standards.

FREQUENCY OF WORK AREA AIR FILTRATIONS

• What is Air Changes per Hour (ACH)
  The simplest way to understand this concept is by example.  Suppose we consider a hypothetical bar/pub which permits smoking.  If only 3 or 4 people smoke, the air does not need to be cleaned as quickly as when the room is packed shoulder to shoulder with about 100 people smoking.  In other words, the faster smoke is created (emitted), the faster the air must be filtered.  If there is not sufficient air cleaning capacity to clean the air faster than the smoke is emitted into the air, then the airborne smoke concentrations will gradually rise rather than fall, and, the air cleaners will eventually be overtaken by the smoke.  So, based on this example we deduce that there is a relationship between the rate that contaminants are emitted into the air, and the rate which the air must be filtered or cleaned.  The more frequently the air is cleaned, the cleaner the air.
  Rule of Thumb:

  • Light Emissions (residential):           Clean the air at a rate of 6 ACH
  • Moderate Emissions(commercial):     Clean the air at a rate of 8 ACH
  • Heavy Emissions(industrial):            Clean the air at a rate of 10 ACH [contractors]
  • Critical Emissions(hospital isolation): Clean the air at a rate of 12 ACH

  Since air cleaner specifications for airflow are cited with clean filters, it's best to overdesign slightly to allow for airflow reduction between filter changeouts.  As the filters backfill with particulates, the blower and motor will incur increased air resistance causing airflow to taper off over time by up to 5-10%.  This reduction will cause a similar percentage reduction in ACH.  For instance, if 10 ACH is achieved with clean filters, then at time of filter change, the air cleaner may be providing about 9.5 or even 9.0 ACH, depending on the degree of filter degradation permitted by the user.

IMPACT OF NEGATIVE PRESSURE REQUIREMENT

• What is negative pressure?
  Negative Pressure Rooms maintain a flow of air into the room, thus keeping contaminants from reaching surrounding areas. The exhaust air is normally filtered through a HEPA (High Efficiency Particulate Air) filter before being exhausted to the area beyond the work area.  Air which is recirculated within the room is also filtered. The exact air pressure differential which is required to be maintained is nominal only, as it merely indicates the airflow direction. It is sometimes stated as 0.001"wg, but this is not a pressure which is practical to measure, and therefore other criteria are given such as maintaining an inward velocity of 100 fpm (feet per minute), or exhausting 10% of the airflow, or exhausting 50 cfm more than the supply. The exact criteria will always be dependent on both the size and the air tightness of the subject facility.
  • Example:
    Assume the work area is completely partitioned off from surrounding areas, except for a single doorway with estimated dimensions of 3 ft wide x 7 ft high, or, 21 sqft.  Using the typical criteria for a chemical hood that the face velocity of air into the hood should be between 75 to 125 ft/minute, and settling on a velocity of 100 ft/min, the required airflow through the doorway to achieve 100 ft/min velocity is 21 sqft x 100 ft/min = 2100 cubic feet per minute (CFM).  Using 75 ft/min, the minimum airflow needed is 21 sqft x 75 ft/min = 1575 cubic feet per minute (CFM). 

    The more tightly the work area is sealed off from the rest of the facility, the less filtered airflow necessary to create sufficient negative pressure to contain the air contaminants to the work area.

The target airflow should be the higher requirement which meets both the ACH needed and the necessary velocity through open area in the workplace partitioning.  Meeting both requirements ensures proper filtration and creation of negative pressure for containment of airborne contaminants.

More information on negative pressure: see Figure 1 & Table 2

PROPOSAL:

The following tables contain pricing which is current as of March 02, 2014.  You may request a formal quote of a particular model with replacement filters, for the quantity of machines desired. 

Contact Us for Formal Quote, Freight, and Orders

• All the following machines have prefilters to trap large particles. The main purpose of the prefilter is to prevent the large particles from clogging the main filter and/or carbon.
• The machines intended for capture of a broad range of particle sizes large and small to submicron, contain high efficiency HEPA filters.  You may read more about the properties of HEPA filters at: http://www.berriman-usa.com/tutorial_2_air_purifiers.htm  In the USA contractors are required to utilize HEPA filters when working in hospitals.

Please let us know if we may be of further assistance.

Additional HEPA Air Cleaning Machines for Construction & Renovation