Role of HVAC&R Systems in Infectious Disease Transmission Addressed by ASHRAE
This announcement was excerpted from ASHRAE's August 31st press release.
Role of HVAC&R Systems in Infectious Disease Transmission Addressed by ASHRAE
For more information, contact: Jodi Dunlop, ASHRAE Public Relations (678-539-1140, firstname.lastname@example.org)
As health and school officials deal with a second wave of the H1N1 virus, commonly referred to as swine flu, new information is available on health consequences of exposure to such airborne infectious diseases and the implications on the design, installation and operation of HVAC&R systems.
?While the long-standing public health view is that influenza transmission occurs through direct contact or large droplets, newer data suggests it also occurs through the airborne route, meaning HVAC&R systems may contribute far more to transmission of the disease and, potentially, to reduction of that same transmission risk,? said Gordon Holness, president of the American Society of Heating, Refrigerating and Air-Conditioning Engineering (ASHRAE) that developed the guidance.
ASHRAE?s Airborne Infectious Diseases Position Document addresses the impact of ventilation on disease transmission, the disease for which ventilation is important for either transmission or control and the control strategies that are available for implementation in buildings. The paper can be read at www.ashrae.org/positiondocuments.
Since the first reported case in the spring of 2009, the H1N1 virus has spread to nearly 170 countries, resulting in 1,154 deaths and some 160,000 illnesses. With a better understanding of ventilation?s effect on the transmission of disease, future incidents of the H1N1 virus may now be easier to prevent, according to Holness. He said several technical solutions are available to assist in avoiding transmission. These include:
dilution ventilation, airflow strategies, room pressurization, personalized ventilation, source control, filtration and ultraviolet germicidal irradiation.
Airborne transmission through building ventilation systems can be significantly reduced by provision of adequate air filtration and pressurization, Holness said. ASHRAE?s other guidance of relevance includes Standard 170, Ventilation of Health Care Facilities, and Standard 611, Air Quality Within Commercial Aircraft.
Last edited by genesis; 09-08-2009 at 01:09 PM.
Wouldn't UV pretty much do the trick? You don't even have to put them IN the AHUs. Put them in the ductwork. You could retrofit an entire K-12 school over the weekend. Just put a big UV unit in the return duct right before the AHU.
Interesting info, I'm surprised there has not been more comments.
Last edited by jimj; 11-20-2009 at 11:11 PM.
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I agree with you on that one. I deal mainly with commercial and industrial IAQ. The majority of the HVAC service techs have no clue how important IAQ has become in HVAC design and operations. Filters are no longer to just protect the equipment. The two money market trends in HVAC that are progressing faster than anything else are Energy Management and IAQ. Both are changing HVAC design considerations.
Originally Posted by jimj
Airanone UV lights by themselves are useless in an airstream for IAQ. But they do and exellent job in reducing the biofilm on an evaporator which in turns raises the efficiancy of the equipment. There simply isn't enough residence time in the airstream to properly reduce or eradicate a mold spore or biologic.
Here are some thoughts:
1. Viruses do not exist very long on their own. They need a "host" and thus the target size for virus disease transmission is not the .01 microns of the virus itself but rather the 5 micron and above size of the droplet nuclei in which they reside. The chances of disease transmission through surface contact is much greater than airborne transmission.
2. The number one thing to do to reduce the transmission of H1N1 is to wash your hands!
3. Medical facilities, in particular, need to use all of the tools available including isolation, differential pressure, air flow direction, filtration and UV lights.
4. UV lights do not take the place of filtration. However, they could have some benefit in reducing airborne transmission of viruses. There have been some good studies done on upper room UV reducing the spread of TB.
5. Medical facility hygiene is critical. You could have the best engineered HVAC system with all of the airborne transmission controls and still have a major outbreak of nosocomial H1N1 flu just by the improper use and cleaning of floor mops!
6. Take your flu shot as soon as possible.
Steve Wilmer of the National Center for Energy Management and Building Technology made a good presentation to the EPA CIAQ at the June 3rd meeting titled Transmission of Flu Virus in Indoor Air: HVAC System Protection Options. He brings up two methods of transfer that are not normally mentioned: toilet water viral aeroization (how the SARS virus got out) and infectious droplet nuclei (<.3΅M) tavel. The presentation is attached.
You mean Steve Welty who is an IAQ consultant.
I think he makes some good points. However, I am not sure where he derived the data on viral transmission through fecal fumes - I thought I read somewhere that the original SARS virus spread through plumbing leaks in that building.
But what I really don't understand is the 0.3 micron droplet nuclei. I am not aware of any studies confirming this size. In fact what I have seen is more along the lines of 10 times that level.
It is true that 0.3 microns has been determined to be the most easily respirable particle size. Thus HEPA filters are measured at this particle size. (In fact HEPA filters are more efficient at both larger and smaller sizes than 0.3microns.)
However, I do agree with Steve's conclusions on using a multi-faceted approach including filtration and UV light (and the right type of PCO) in medical facilities concerned about the spread of viruses.
Another difference between the H1N1 and the influenza A strain is its ability, when inhaled, to make it into the lower sections of the lungs to start causing trouble. That correlates to the resent research demonstating that the proverbial flu season is more about lower humidity levels than people understood before. The lower rh levels allows the viral hosts to stay airborne longer allowing more opportunity to be inhaled. The attached chart confirms your statement about the abundance of viral hosts in common atomspheric air. The map show how where you live matters.
You want evidence of long range transmission of a virus. Ever herd of the PRRSV virus. I have an ongoing project with several universities on this subject as we speak.
PRRSV is why pig farmers are so paranoid about visitors. The better feeder lots have gone to great lengths to protect their stocks from one house to the next and one farm to the next.
When a homeowner complains about too much dust in the house it usually is a result of poor construction, poor maintenance and the lifestyle of the owner more than anything else. Resent studies have shown that all kinds of things we don't like come in on our shoes, clothes and hair riding in the dust, and not just viruses. Trace amounts of bad chemicals that are blown in the air from manufacturing plants states away can be found floating around. There can be traces of chemicals found in the dust on your TV screen that havent been made in years just now settling to the ground. No one knows what the eventual accumulative effect will be. That is why IAQ is getting more attention every year.
I am not sure what to make of the attachments. One is a map of areas in the US with high PM2.5. This is a common indicator of outdoor pollution.
The other is the strangest distribution of particle sizes I have seen. The particle counts are well over 100 times what one would expect to see. Typically one would see somewhere between 800,000 and 1,200,000 particles at 0.3 microns per cubic foot. Your chart shows something like 500,000,000. Where were these counts taken? Wherever it is, you don't want to go there!
By the way rh has not been a good predictor of disease transmission. However, the most recent study found that absolute humidity had very high correlations with disease transmission. The hypothesis of lower humidity resulting in smaller droplets that remain in the air longer seems to be valid.
Interesting article. To me this points out the necessity of using all of the tools available to reduce the transmission of disease. It would be foolhardy to rely only on an HVAC system to stop the spread of airborne disease when you only have 1 to 4 ACH in the average medical facility. That is why it is so important to use the other tools of air flow and particularly differential pressure to protect other patients from being infected.