ASHRAE Epidemic Task Force releases updated Building Readiness Guide
ATLANTA, Georgia, 02 February 2021: With the performance of many HVAC systems in buildings still being evaluated, the ASHRAE Epidemic Task Force has updated its reopening guidance for HVAC systems to help mitigate the transmission of SARS-CoV-2, ASHRAE said through a Press release.
“The Building Readiness Guide includes additional information and clarifications to assist designers and commissioning providers in performing pre- or post-occupancy flush calculations to reduce the time and energy to clear spaces of contaminants between occupancy periods,” said Wade Conlan, Lead, ASHRAE Epidemic Task Force Building Readiness team. “New information includes the theory behind the use of equivalent outdoor air supply, method for calculating the performance of filters and air cleaners in series, and filter droplet nuclei efficiency that help evaluate the systems’ ability to flush the building.”
According to ASHRAE, major updates to the building readiness guidance include the following:
- Pre- or post-flushing strategy methodology: The strategy has been updated to include the use of filter droplet nuclei efficiency, which is the overall efficiency of filter, based on viable virus particle sizes in the air, to assist in determining the impact of the filter on the recirculated air on the equivalent outdoor air. This allows the filter efficiency as a function of particle size, using ASHRAE Standard 52.2 test results, to be estimated based on the expected size distribution of virus-containing particles in the air. This calculation is currently based on Influenza A data and will be updated as peer-reviewed research becomes available for the distribution of particle sizes that contain a viable SARS-CoV-2 virus. Additionally, a chart has been added to help determine the time to achieve 90%, 95% or 99% contaminant reduction, if the equivalent outdoor air changes per hour is known.
- Flushing time calculator: There is now a link to a view-only Google Sheet that can be downloaded for use, to help determine the available equivalent outdoor air changes and time to perform the flush. This sheet is based on a typical mixed AHU with filters, cooling coil, with potential for in-AHU air cleaner (UVC is noted in the example), and in-room air cleaning devices. Provided efficiencies of MERV-rated filters are based on the performance of over 200 actual filters from MERV 4 through 16, but the tool also allows users to enter custom characteristics for specific filters.
- The sheet also calculates the filter droplet nuclei efficiency, based on the cited research but allows a user to adjust the anticipated distribution of virus, as desired. It also allows specification of the zone (room) air distribution effectiveness from ASHRAE Standard 62.1 to account for the impact of the HVAC system air delivery method on the degree of mixing. Default calculations assume perfect mixing. Finally, the tool allows for the target air changes to be adjusted if an owner wants to achieve a different per cent removal in lieu of the recommended 95%.
- Heating season guidance: The guide now includes data to consider for heating of outdoor air and the potential impact on pre-heat coils in systems.
- Adjustments to align with Core Recommendations: The Core Recommendations were released in January 2021, and this guidance document needed to be updated to ensure that the information provided aligned with the intent of those recommendations. This included minimum outdoor air supply and filter efficiency requirements and their role in an equivalent outdoor air supply-based risk mitigation strategy.
According to ASHRAE, the guidance still addresses the tactical commissioning and systems analysis needed to develop a Building Readiness Plan, increased filtration, air cleaning strategies, domestic and plumbing water systems, and overall improvements to a system’s ability to mitigate virus transmission.
How to kill enveloped viruses in just 30 minutes
Poor ventilation in closed indoor environments is associated with increased transmission of respiratory infections. There have been numerous SARS-CoV-2 transmission events associated with closed spaces, including some from pre-symptomatic cases. The role of ventilation in preventing SARS-CoV-2 transmission is not well-defined – that is, by preventing dispersal of infectious particles in small waterdrops to minimise the risk of transmission or preventing transfer of an infectious dose to susceptible individuals.
SARS-CoV-2 is thought to be primarily transmitted through large respiratory droplets; however, an increasing number of outbreak reports implicate the role of aerosols in SARS-CoV-2 outbreaks. Aerosols consist of small droplets and droplet nuclei, which remain in the air for longer than large droplets. Studies indicate that SARS-CoV-2 particles can remain infectious on various materials, such as air conditioning surfaces in air ducts and air handlers, as well as in aerosols in indoor environments, with the duration of infectivity depending on temperature and humidity.
While HVAC coatings are often the most cost-efficient insurance for the longevity of your air-handling system, there’s much more to them than just increasing your building systems’ lifespan. The rising demand for antimicrobial coatings was triggered by the COVID-19 pandemic and tenants worried about their wellbeing from airborne diseases. In the same category, antimicrobial coatings can make a huge difference for indoor air quality and occupant safety. There are a number of HVAC coatings that drive energy savings, primarily desiccant-coatings.
Found on AHU heat exchangers, coils and in duct systems, they enable recovering heat and moisture, which then helps building owners to save on operational cost. Recent studies have uncovered an extreme antimicrobial effect of desiccant coating systems, in high relative humidity, as present in air conditioning systems. It appears the surfactants can break the exterior protein of a virus or bacteria strain. Once the protein is destroyed, the virus cannot attach to cells and transfer or alter human ribonucleic acid (RNA).
In many circumstances, once microbes have begun to proliferate on a painted surface, constant cleaning and disinfecting is required to keep growth under control, which is highly unwanted inside an air conditioning system. Recognising that the ability to clean constantly is unreasonable in most air conditioning systems, the best weapon against corrosion and microbial growth is an antimicrobial paint that prevents growth of, or eliminates, bacteria and viruses. Both the coating and the possible active ingredient should not produce any environmental, safety or health issues during application. Any off-gas from the film is unwanted, because ideally, the coating must be applied to air conditioning systems in operation without any concern of release of poisonous additives.
Antimicrobial efficacy based on silver ions
Generally, an antimicrobial surface contains an additive, like Agion, which inhibits the antimicrobial property that is composed primarily of silver ions, which have been proven in antimicrobial use throughout history. It incorporates silver ions inside a zeolite carrier, providing an area for these ions to exchange with other positively charged ions – often sodium – from the moisture in the environment.
Once exchanged, these now “free” silver ions are attracted to oppositely charged hydrogen ions, commonly found in most bacteria and microbes. The bacteria and microbes’ respiration and growth are now abruptly halted, since the hydrogen ions are no longer available. Silver based antimicrobial coatings contain a pesticide additive that evaporates slowly from the coating surface and raises questions on the durability of discharge. In Europe and North America, these coatings require a registration by the government authorities.
Antimicrobial efficacy based on desiccation
Enveloped viruses, like the H1N1 influenza virus, Corona (COVID-19) and bacteria have membranes of protein and enzymes to protect the infecting contents. The spreading of the viruses and bacteria in closed spaces and air conditioning systems is carried out by smaller aerosols. Alternative antimicrobial functionality is based on desiccation, a physical process to extract the moisture from the virus and bacteria particles. This approach may seem relatively primitive; however, it is extremely effective in slowing down or even preventing microbes from spreading and transmission. This method is similar to other physical treatments, such as UV irradiation, filtering and heating.
Desiccant coatings inactivate a wide variety of microbes that adhere to the surface through their hydrophilic surface properties. The antiviral functionality of the coating has been tested on the Phi6 virus, which is commonly used as surrogate for enveloped Corona viruses.
A recent study shows that a desiccant coating can have an extremely quick kill-rate of enveloped viruses after just 30 minutes.
Further studies have proven that strong antimicrobial working was additionally confirmed. Surface activity results in full kill-rates of > 99,99%, which were confirmed on the following micro-organism strains:
- Klebsiella Pneumoniae
An important note should be added to this paper: No claim or assertion should be made that the antimicrobial properties in the coating will improve air quality or eliminate the threat of disease-causing microbes in the air supply system. A healthy indoor air system is highly dependent on a combination of design, maintenance and cleaning measurements that are incorporated in the air conditioning system and facility management procedures.
- Knibbs LD, Morawska L, Bell SC, Grzybowski P. Room ventilation and the risk of airborne infection transmission in 3 health care settings within a large teaching hospital. Am J Infect Control. 2011 Dec;39(10):866-72.
- Lu J, Gu J, Li K, Xu C, Su W, Lai Z, et al. COVID-19 Outbreak Associated with Air Conditioning in Restaurant, Guangzhou, China, 2020. Emerg Infect Dis. 2020 Apr 2;26(7).
- Rothe C, Schunk M, Sothmann P, Bretzel G, Froeschl G, Wallrauch C, et al. Transmission of 2019-nCoV Infection from an Asymptomatic Contact in Germany. N Engl J Med. 2020 Mar 5;382(10):970-1.
- World Health Organization (WHO). Natural Ventilation for Infection Control in Health-Care Settings. 2009 [updated 4 May 2020].
- Ong SWX, Tan YK, Chia PY, Lee TH, Ng OT, Wong MSY, et al. Air, surface environmental, and personal protective equipment contamination by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from a symptomatic patient. Jama. 2020;323(16):1610-2.
- Bahl P, Doolan C, de Silva C, Chughtai AA, Bourouiba L, MacIntyre CR. Airborne or droplet precautions for health workers treating COVID-19? The Journal of Infectious Diseases. 2020.
- Dietz L, Horve PF, Coil DA, Fretz M, Eisen JA, Van Den Wymelenberg K. 2019 Novel Coronavirus (COVID19) Pandemic: Built Environment Considerations To Reduce Transmission. mSystems. 2020 Apr 7;5(2):e00245-20.
8 Evaluation of Phi6 Persistence and Suitability as an Enveloped Virus Surrogate Aquino de Carvalho, Nathalia; Stachler, Elyse N.; Cimabue, Nicole; Bibby, Kyle Environmental Science & Technology (2017), 51 (15), 8692-8700CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
Recent outbreaks involving enveloped viruses, such as Ebola virus and SARS COVID-2, have raised questions regarding the persistence of enveloped viruses in the water environment. Efforts have been made to find enveloped virus surrogates due to
challenges investigating viruses that require biosafety-level 3 or 4 handling. In this study, the enveloped bacteriophage Phi6 was evaluated as a surrogate for enveloped waterborne viruses. The persistence of Phi6 was tested in aq. conditions chosen based on previously published viral persistence studies. Our results demonstrated that the predicted T90 (time for 90% inactivation) of Phi6 under the 12 evaluated conditions varied from 24 minutes to 117 days depending on temperature, biological activity, and aq. media compn. Phi6 persistence was then compared with persistence values from other enveloped viruses reported in the literature. The apparent suitability of Phi6 as an enveloped virus surrogate was dependent on the temperature and compn. of the media tested. Of evaluated viruses, 33%, including all conditions considered, had T90 values greater than the 95% confidence interval for Phi6. Ultimately, these results highlight the variability of enveloped virus persistence in the environment and the value of working with the virus of interest for environmental persistence studies.
- The use of bacteriophages of the family Cystoviridae as surrogates for H5N1 highly pathogenic avian influenza viruses in persistence and inactivation studies
Adcock, Noreen J.; Rice, Eugene W.; Sivaganesan, Mano; Brown, Justin D.; Stallknecht, David E.; Swayne, David E.
Journal of Environmental Science and Health, Part A: Toxic/Hazardous Substances & Environmental Engineering (2009), 44 (13), 1362-1366CODEN: JATEF9; ISSN:1093-4529. (Taylor & Francis, Inc.)
Two bacteriophages, .vphi.6 and .vphi.8, were investigated as potential surrogates for H5N1 highly pathogenic avian influenza virus in persistence and chlorine inactivation studies in water. In the persistence studies, .vphi.6 and .vphi.8 remained infectious at least as long as the H5N1 viruses at both 17 and 28 degrees C in fresh water, but results varied in salinated water. The bacteriophage .vphi.6 also exhibited a slightly higher chlorine resistance than that of the H5N1 viruses. Based upon these findings, the bacteriophages may have potential for use as surrogates in persistence and inactivation studies in fresh water.
- Systematic Review and Meta-Analysis of the Persistence and Disinfection of Human Coronaviruses and Their Viral Surrogates in Water and Wastewater, Andrea I. Silverman and Alexandria B. Boehm, April 2020
- Determination of the Antiviral Activity of Water-Based Coating for Air Conditioning Applications against phi6 Bacteriophage using a Method Based on ISO 21702:2019, the laboratories of Industrial Microbiological Services Ltd at Pale Lane Hartley Wintney, Hants, RG27 8DH, UK. December 2020
The writer is with Aqua Aero Coatings and may be contacted at firstname.lastname@example.org