With flu season among us and the different diseases going around today, it is important to know how your HVAC system can protect you from spread of these contagions. Read the article below to get the breakdown of how all the components work in the HVAC and how they protect you and your family.
A sick person sneezes. Even in a well-ventilated room, airborne droplets containing infectious agents can remain viable for as long as six minutes.
One infectious disease that’s been in the headlines this year is measles, which has made a comeback since being declared eliminated in the U.S. in 2000. In the first half of 2019 (Jan. 1 to July 11), 1,123 individual cases of measles were confirmed in 28 states across America. Per the Center for Disease Control (CDC), it’s the largest number of cases reported in the U.S. since 1992.
Measles is a highly contagious virus, and it lives in the mucus of the person who’s infected. It spreads through coughing and sneezing. When someone coughs or sneezes, the virus can linger for two hours.
“If other people breathe the contaminated air or touch the infected surface, then touch their eyes, noses, or mouths, they can become infected,” wrote the American Red Cross. “Measles is so contagious that if one person has it, 90 percent of the people close to that person who are not immune will also become infected.”
Unless precautions are taken, the virus — or any pathogen, really — can be distributed throughout a building by the HVAC system, or even recirculated through the ductwork. One way to reduce that risk is through the use of technology that employs UV-C (short-wavelength ultraviolet) light.
Ashish Mathur is vice president of innovation and technology at UVDI, a technology supplier to Johnson Controls Inc.
“There is peer-reviewed literature giving evidence of UV-C effectiveness in reducing measles transmission,” he said. “UV-C is typically combined with conventional air quality control methods, including dilution, ventilation, and particulate filtration, to optimize cost, energy use, and performance.”
HOW IT WORKS
Typically, UVGI systems are employed in three configurations: cooling coil disinfection, duct and upper air airstream disinfection, and whole-room surface disinfection.
Coil-irradiation and airstream disinfection systems are installed within HVAC equipment and help maintain a clean evaporator coil, drain pan, and surfaces, preventing mold and other contamination from being introduced into the airstream via the HVAC equipment.
“The coil and surrounding area are often the source of microbial contamination,” said Engel. “Maintaining a clean AHU [air-handling unit] will ultimately reduce what is introduced into the air.”
As well as improving air quality by continually ensuring the airstream is clean when it leaves the equipment, coil-mounted systems can potentially save energy.
UV lights placed inside an AHU to disinfect the airstream.
“The insulating nature of biofilm can … increase static pressure and reduce heat transfer across the coil fins,” Engel said. “The microbial coating causes the system to work harder, and resulting biological blow-off is then distributed back into the facility.”
Keeping cooling coils in AHUs free of biofilm buildup can reduce pressure drop across the coils and improve the efficiency of the heat exchanger.
“Commercial IAQ problems vary from application to application, but they often stem from a poorly maintained HVAC system, whose organic-rich environment is an ideal breeding ground for microbial buildup on surfaces and in the airstreams they condition,” Jones said. “Thus, this is one of the first areas that a contractor should check when isolating an IAQ problem.”
In-duct and upper-air systems keep the air clean once it’s circulating. They are installed in waiting rooms, classrooms, cafeterias, gymnasiums, locker rooms, child care centers, emergency rooms — anywhere infectious agents may exist, Jones said.
Upper-air systems are installed in occupied spaces to control bio-aerosols in the upper part of an occupied room.
“In-duct UVC systems distribute UV energy uniformly in all directions throughout the length of the UV duct or AHU [in which they are installed] to deliver the appropriate UV dose to air moving through the irradiated zone,” explained Mathur.
Typically, upper-room fixtures are wall mounted at a height of 7 feet or above and employ louvers to direct the UV-C energy emitted from the lamp upward and outward to create an intense zone of the UV-C wavelength in the upper-air while preventing dosage in the lower (occupied) portion of the room or area, Jones said.
“Operating 24 hours a day, upper-air/room systems can use the natural convection of airflow or mechanically directed airflow in a room to bring potentially infectious microbes through the intense germicidal energy produced by the UV-C fixture,” he said. “Microbes exposed to UV-C can be ‘killed’ in under a second, and these units have been shown to be effective against airborne viruses and bacteria, including chickenpox, measles, mumps, varicella, TB, and cold viruses.”
Upper-air/room UV-C fixtures can also prevent cross-contamination and kill pathogens circulated by cleaning, coughing, sneezing, people entering or leaving a room, or the changing of bed linens.
UV-C disinfection catches what HEPA filters can’t, Engel said.
“Viruses and certain bacteria are so small that they pass through even the highest-efficiency filter like sand through a tennis racket,” he pointed out. “UV-C disinfection is the perfect complement to conventional filtration. The filter removes the particulates from the air, and the UV-C energy deactivates the microorganisms that pass through the filter that would have otherwise been distributed through the HVAC system.”
Coil-mounted and in-duct/upper-air systems work in tandem.
“Installing UV systems in the air handler section will achieve immediate results by disinfecting coil and other surfaces within the AHU (typically within an hour) but will require time for the UV-C light to penetrate deep into the coil, breaking down the biofilm,” Engel said.
How long it will take for the UV-C light to penetrate through the coil depends on how fouled the coil may be.
“Best practices would be to clean the coil first or install the UV system on a new unit,” Engel continued. “If that is not an option, it may take up to a few weeks to months for the UV-C light to break down the biocontaminants within the evaporator coil itself.”
In addition, portable UV-C devices have gained increasing acceptance for whole-room disinfection in hospital settings to reduce nosocomial infections from candida auris and drug-resistant microorganisms such as MRSA, VRE, and C. difficile, Mathur said.