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HVAC-related airborne infection control procedures have proved to improve air quality and prevent the spread of contagious diseases. Read more.
For the past six months, the world has been fighting the novel coronavirus, COVID-19, and yet nothing tangible is known about the transmission of the virus. Researchers around the world have been conducting studies to analyze the stability of the viruses in aerosols and on surfaces. A National Institute of Health study indicated that the coronavirus remained viable for hours in aerosols.
Many other researchers have simulated the transmission of the virus when airborne to further strengthen the urgency for people to wear masks in public.
"Without a mask, a turbulent jet forms (during the time of coughing or sneezing), and droplets with a broad size distribution are ejected. Large droplets (greater than about 125 microns in diameter) fall to the ground within about 2 meters, while turbulent clouds transport a mist of small aerosolized droplets over significant distances (approximately 5 meters). A loosely fitted simple cotton cloth mask qualitatively changes the propagation of the high-velocity jet, and largely eliminates the turbulent cloud downstream of the mask. The spread of the ejecta is also changed, with large droplets trapped at mask surface," a study suggests. This clearly indicates the potency of the virus to travel to significant distances through the air.
ASHRAE, a globally-acknowledged professional association involved with advanced HVAC systems recently announced the best HVAC practices for the healthcare facilities to combat the coronavirus that stressed the importance of proper ventilation systems. The important strategies that it recommended to effectively address the disease transmission involve differential room pressurization, dilution ventilation, personalized ventilation, laminar and other in-room flow regimes, source capture ventilation, filtration (central or unitary), and UVGI (Ultraviolet germicidal irradiation).
ASHRAE's guidelines are also in line with those given by the CDC, which also support the role of HVAC implementation to prevent the spread of contagious virus and diseases.
Apart from healthcare facilities and hospitals, if used in commercial establishments or individual spaces, can MEP and HVAC implementation cut down airborne transmitted diseases?
HVAC manufacturers and professionals are making the people aware about the various technologies available that have been proven to contain the spread of the diseases that are airborne. However, common logic and reasoning must be applied by the people here. They ought to understand the limited study that has taken place to understand the scope of prevention of the virus through HVAC systems. Another important consideration that the people interested in adopting HVAC for their living spaces must refer to is this - Coronavirus is a disease that can be transmitted through multiple ways, airborne being just one of them. So, even if HVAC controls the airborne transmission, they will need to adhere to other disciplinary guidelines to prevent the spread of the virus.
This being said, one needs to fully understand the role of HVAC systems in curbing the airborne transmission of contagious diseases like coronavirus to be able to effectively implement them.
There are three key HVAC implementation methods, as documented by the ASHRAE journal, that can help in controlling the spread of transmissible diseases. It involves ventilation, particle filtration, and HVAC UV light.
Maintaining indoor air-quality through HVAC ventilation and disinfection system implementation includes humidity modification mechanisms, fans, ductwork, air exhaust systems, diffusers, grilles for optimum air distribution, etc. The American Institute of Architects (AIA) has also shared the guidelines for indoor air quality standards required to be maintained by healthcare facilities and other zones in order to deter the spread of airborne diseases and includes variables like ventilation rates, temperature levels, pressure ratio, minimum air changes per hour (ACH), humidity levels, etc.,
The physical removal of particles through filtration is the elementary step in the process of maintaining optimum indoor air quality. Depending on their principle of performance there are many types of filtration methods that are variably used bearing in mind the conditions and needs.
High-efficiency particulate arrestance (HEPA) filters are generally being used in hospitals and critical care environments and they hold a record of trapping down the particles that are 0.3 microns in size, accounting for their 99.97% effectiveness range.
But studies have shown that many viruses, including COVID-19, measure somewhere between 0.6 and 0.14 microns in size and that means even the HEPA filters may lead to some level of virus penetration in absence of supplementing UV-C lights HVAC system implementation discussed below.
Ultraviolet germicidal irradiation systems are complementary to UV disinfection and filtration systems but are one of the most crucial as they are effective in inactivating the pathogens and viruses. As mentioned above, the viruses are so small in size that some may even pass through filters, and this is where UV-C lights come to aid.
Due to its composition in general, all UV light will kill bacteria and viruses, but the UV-C light has 254 to 260 nm range that makes it a very powerful germicidal and is much more potent in killing microbes and viruses that are smaller in size. UV-C deactivates the DNA of the bacteria, viruses, and other pathogens, by damaging the nucleic acid of microorganisms, thereby, destroying their ability to replicate themselves, ultimately dying.
As noted by ASHRAE, "the germicidal wavelength of UV-C light can kill 90 percent of all microorganisms living on HVAC air ducts and evaporator coils, depending on wavelength intensity and length of exposure. Although the germicidal wavelength was effective in killing other varieties of coronaviruses, such as SARS and MERS, scientists do not yet know about the impact of UV-C on COVID-19."
"However, we have no reason to believe it will be much different than other similar type viruses," added the ASHRAE spokesperson, indicating that after all, UV-C light may serve as the breakthrough in curbing of the coronavirus spread via air.
After taking everything into account, answering to the general query, of how HVAC can help cut down airborne transmitted diseases, one must look at HVAC as a system for risk reduction and not as a tool for elimination of the virus itself. People can transmit viruses to each other even after taking preventive measures to control or to give optimal time for HVAC systems to eliminate the viruses that became airborne during the transmission.
Hence, whether it is a commercial establishment, a healthcare facility, or an individual home space, applying HVAC systems should be incorporated as an additional preventive measure and should not in any way lead to undermining the importance of practicing other precautions like wearing masks, maintaining at least a 2-meter distance from other people, and other suggested preventive actions suggested by CDC and WHO.
O2I is a leading HVAC and MEP design and drafting company in the world. We extend our expertise to any commercial, industrial, or residential establishments looking to implement this technology to combat the spread of airborne diseases like COVID-19. Our specialization includes HVAC and other MEP design review solutions, developing detailed 2D and 3D drawings, generating as built drawings, and creating retrofit kit and shop drawings.
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