With restaurants and other food service facilities fully opening, albeit with reduced capacity, key questions have arisen regarding best practices for ventilation systems. We questioned Dr. Andrey Livchak, Halton’s Global Technology Director, and member of ASHRAE for some answers.
Q: What are your recommendations for starting up the HVAC system that may have been idle for an extended period?
Idle for extended time ventilation system may have accumulated dust. Start the ventilation system before you do space cleaning because dust may come out of the vents. If you detect some unusual smell coming from ventilation vents, change the filter in the AC unit if it is equipped with one. If, after changing filters, the smell is still detected, order service company to clean the cooling coil in the AC unit. Follow ASHRAE (American Society of Heating Air Conditioning and Refrigeration Engineers) guidance. https://www.ashrae.org/about/news/2020/ashrae-offers-covid-19-building-readiness-reopening-guidance
Q: Kitchens may have been active for take out or delivery, yet dining rooms have been unoccupied, how would you recommend they start?
If the dining room has a separate ventilation system, the same recommendations as above, if there is a common ventilation system used for both kitchen and dining room and it was used regularly, no action is needed.
Q: How can you be assured of improved ventilation, keeping in mind the current pandemic? Additional exhaust?
You can’t add exhaust without bringing more outside air; this is the law of physics. Adding exhaust will only increase uncontrolled infiltration – unconditioned and unfiltered air coming through doors and windows. This is undesirable because it will compromise thermal comfort in space, change pressure distribution making opening or closing doors difficult. Conditioning all outside air to compensate for increased exhaust will require an upgrade of the air conditioning equipment and will significantly increase energy consumption and costs to run it, especially in hot and humid climate conditions.
In recent publication associated COVID-19 outbreak with air conditioning in a Guangzhou restaurant in China https://wwwnc.cdc.gov/eid/article/26/7/20-0764_article. Unfortunately, some “ventilation experts” interpreted this publication wrong and started recommending shutting down the ventilation system altogether. This is bad advice. Getting many people in a confined space without ventilation is a call for disaster. It may only increase the concentration of air-borne pathogens and increase the risk of disease transmission. The minimum action facility owner should take to verify the ventilation system is designed and maintained correctly, outside air damper is open and brings at least minimum, governed by code, amount of outside air per person. Bringing outside air is critical because it is less likely to contain viruses.
World Health Organization defines COVID19 as a respiratory infection that can be transmitted through droplets of different sizes https://www.who.int/news-room/commentaries/detail/modes-of-transmission-of-virus-causing-covid-19-implications-for-ipc-precaution-recommendations. Exhaled aerosols range in diameter from 0.01 to 1000μm, with the median mass represented by particles in the size range of 0.7 to 1.0μm” Bake et al. Respiratory Research (2019) 20:8 https://doi.org/10.1186/s12931-019-0970-9. These are very small aerosol particles and can be suspended in the air for hours.
The majority of restaurant air conditioning systems in North America use systems with return air; this air is taken from the space, heated or cooled, and returned to space with very little filtration (Fig. 1). Since aerosol particles containing virus may stay air-borne for hours, there is a high probability of them getting into return ductwork. Typical filters used in AC units are not effective in removing particulate below 1.0μm, and aerosols containing viruses in return air are most likely to be re-introduced back into the space with supply air. Only outside air, free from a virus is working to ventilate the space and reduce the concentration of air-borne pathogens. In my opinion, the best strategy for existing buildings to reduce the risk of air-borne exposure is to inactivate viruses in the return air. This is a much less costly and more energy-efficient option compared to converting the HVAC system into 100% outside air in hot and humid climate conditions. Halton is testing such systems and will be able to offer them within a couple of months.
Q: What is the correct balance for improved ventilation?
I’m afraid this is a subject for a separate article, challenging to give a short answer. Most restaurants use mixing-type air distribution systems. This is ventilation by dilution; clean air is supplied at high velocity to enhance mixing of supply air with room air to dilute contaminants and provide uniform temperature throughout the air-conditioned space. There is an alternative air distribution method called Thermal Displacement Ventilation (TDV) that stratifies air-borne contaminants rather than mix them within the space. It is a unique system as it improves indoor environmental quality and saves energy for space cooling simultaneously. A combination of TDV together with local exhaust near a table within breathing level in the dining room allows to contain air-borne contaminants and not spread them throughout the space. We almost need to think of a localized ventilation system containing people sitting around a table. Space relative humidity plays an important role in the spread of aerosol pathogens; it should be maintained within 45-60%. Dry air will facilitate aerosol evaporation, makes air-borne contaminants smaller and more volatile.
It is important to understand that proper ventilation is only one of the mitigation methods that can reduce exposure to air-borne pathogens. Surfaces’ disinfection, social distancing, and personal protection (wearing masks) are still valid and essential mitigation methods. Unfortunately, the latter two are difficult to implement in a dining room environment.
Q: What is your advice to facility operators and building owners?
Add this link to your favorites https://www.ashrae.org/technical-resources/resources and check for regular updates. ASHRAE put together the Task Force of qualified experts providing valuable advice for building owners and operators on how to best reduce the risk of air-borne exposure.
A special thank you to Dr. Andrey Livchak for taking the time to answer some of the important questions. If you have more questions please leave your comments below or send us your questions by using our “Ask The Expert“
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