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Not surprisingly, evidence continues to emerge that connects health and air quality. A recent study at the Illinois Institute of Technology, funded in part by the National Air filtration Association (NAFA), takes it a step further and correlates risk reductions and operational costs.
The authors analyzed the benefits of preventing one case of influenza in a 1500 cubic meter space with 25 occupants similar in size to a typical classroom. They compared the economics of various levels of risk reduction as provided by either dilution or filters of different efficiencies from MERV 4 to HEPA. Their analysis finds that increased particle filtration provides a reduced risk of infection at a far lower annual cost than increased outside air levels.
Carl Mitchell, Vice-President Sales
cmitchell@DynamicAQS.com
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Which is Better for Controlling Airborne Pathogens - Indoor Filtration or Increased Ventilation?
"Compared to the estimated economic losses of a single influenza case of $375, use of MERV 13 rated filtration could provide a benefit-to-cost ratio of 20 or more."
A paper has recently been published by Dr. Brent Stephens and Parham Azami at the Illinois Institute of Technology entitled "HVAC Filtration for controlling infectious airborne disease transmission in indoor environments: Predicting risk reductions and operational costs". The study estimates the impact of HVAC particle filters and equivalent outdoor ventilation air on the control of infectious aerosols in indoor environments using a model for predicting risks of infectious disease transmission.
Estimates of risk reductions and associated operational costs of both indoor filtration and equivalent outdoor air ventilation were modeled and compared using a case study of airborne transmission of influenza in a hypothetical office space in multiple climates. The study bases its findings on a hypothetical office space with 25 occupants and an HVAC system that needed one 24"x 24" particle filter. The hypothetical office is similar in size to a conventional K-12 classroom.
Overall, recirculating HVAC filtration was predicted to achieve risk reductions at lower costs of operation than equivalent levels of outdoor air ventilation, particularly for MERV 13 -16 filters. Medium efficiency filtration products (MERV 7-11) are also inexpensive to operate but were less effective in reducing infectious disease risks.
Annual Costs
The study used information provided by NAFA to break down the annual filtration costs for the one (1) passive filter in the hypothetical space. The annual cost of a MERV 13 filter was $156.
Cost vs. Risk
Most studies dealing with health benefits for particle filtration analyze the risk reduction for heart and lung diseases. This study is different in that it looks at risks of infectious airborne disease as shown below.
Above: Relative risk (RR) of influenza transmission in the hypothetical office environment with both HVAC filtration and equivalent outdoor air ventilation rates.
As illustrated in the chart shown above, for each level of risk reduction achievable by the use of every level of HVAC filtration except MERV 4, filtration is less expensive on an annual basis than equivalent outdoor air ventilation. MERV 13 and MERV 14 filters appear to achieve the optimal combination of lowest risk reductions at least costs.
A few interesting points from the study:
Particle sizes of concern: While individual viruses are quite small, they are usually part of a larger cluster.
In other explorations of the impacts of particle filtration and other size-dependent processes on virus and bacteria disease transmission, some researchers have assumed that the individual virus or bacteria particles are aerosolized and exist suspended as individual organisms [11,41]; however, it is likely more appropriate to consider the particles as larger expelled droplets that containaggregates of the smaller infectious particles within Refs. [8,35,42,43].
It is commonly believed that droplet nuclei particles average 1e 3 mm in diameter [42], although several recent studies have shown considerable variation in the size distribution of expelled droplets and droplet nuclei.
On average across all of these studies, we estimate that approximately 20% of influenza virus content is associated with particles in the 0.3-1 mm size range in these recent studies; 29% is associated with the 1-3 mm size range, and 51% is associated with the 3-10 mm size range.
In conclusion:
Overall, recirculating HVAC filtration was predicted to achieve the greatest risk reductions at lower costs of operation than equivalent outdoor air ventilation, particularly for MERV 13-16 filters.
MERV 13 and MERV 14 filters appear to achieve an optimal combination of lowest risk reductions at least costs.
Key Conclusions and How the Dynamic V8 Can Help
This study is important to us for several reasons:
- It points out that MERV 13-14 filtration is the most cost-effective filtration level for removing biological contaminants.
- It confirms that the indoor filtration of recirculated air is as effective at removing contaminants as diluting indoor air with outdoor ventilation air.
- It confirms that filtration of recirculated air is significantly less expensive than diluting indoor air with ventilation air.
- Filtration pressure drop and maintenance costs in the study were based on passive filters.
The Dynamic V8 is the most cost-effective way to apply MERV 13-14 filtration and goes beyond to add odor and ultra-fine removal. The V8 offers:
- MERV-NC 15, standard MERV 13
- Up to 99% Ultrafine particle removal
- 50-60% moderate VOC removal
- Clean pressure drop: 0.28" w.g.
- Most economical "final": ~0.65" w.g.
- Holds 8 X more dust there than a cartridge filter at 1.4" w.g.
- Typically no need for pre-filters
- Maintenance cycles measured in years
- OSHPOD Seismic certification
Since according to the authors, MERV 13-14 filtration is the right selection to ensure workplace health, the Dynamic V8 Air Cleaning System is the obvious choice.
Read the entire white paper here.
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Companies renovating, not building
Upgrades seen as less risky
As you likely know, many American businesses are choosing to save money by renovating existing buildings instead of constructing new ones, signaling that caution persists even as the economic recovery enters its fifth year. Amid sluggish demand, energy-efficient upgrades -- such as replacing lighting or HVAC systems -- offer both cost savings and potential tax breaks for companies.
Read the full story here.
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Look for Dynamic at these events
Greenbuild - Booth #2213 in the 50 Mile Pavilion
ASHRAE Show - Booth #1500
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