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Heating, Ventilation, and Air Conditioning Frequently Asked Questions

Frequently Asked Questions:

Can SAR-CoV-2 be transmitted via existing air handling systems? How much do HVAC improvements reduce the risk of illness?

While it is clear that the world is still struggling to understand the newly emerged COVID-19 virus, evidence suggests that transmission between persons is typically the result of large droplet transmission at a short-range (e.g., cough or sneeze) with some transmission via touching a contaminated surface. However, case studies of unexplained “community spread” highlight the possibility that smaller aerosolized droplets such as those emitted by all persons when they breathe, speak, or laugh could also transmit the virus. Predicting the transmission methodology of COVID-19 is challenging given that it is a newly emerged public health threat.

Infectious diseases like COVID-19 can be controlled by interrupting the direct and indirect transmission routes used by the pathogen. The direct spread of pathogens is the primary method of disease spread. Controlling direct spread primarily involves managing human factors (distance, density, hygiene, face coverings etc.) and these cannot be effectively managed or controlled via building mechanical systems. However, we can help mitigate the risk of indirect spread of this disease via aerosolized particles by increasing fresh air delivery to spaces and enhancing our building ventilation systems filtration where practical.

What is the process for assessing and making adjustments to HVAC systems in Cornell buildings?

Cornell personnel have been actively engaged in evaluating the hundreds of campus buildings and making alterations to how fresh air is delivered to each. Our initial efforts have focused on evaluating the building as a whole and making adjustments at the building-wide level. An initial evaluation of all university buildings has been conducted. During the evaluation process, we first determine what type of ventilation exists in the building.  Some buildings rely on natural ventilation, while others use mechanical systems of various types. 

Cornell personnel have also been conducting pilot studies focused on finding low-cost, low-tech methods to increase fresh air delivery to classrooms on campus that typically rely on natural non-mechanical ventilation. Facility Managers and campus community members will work together to identify individual classrooms within buildings that rely on natural ventilation where we can explore deploying these individual space interventions.

What can be done to reduce the risk of COVID-19 transmission via air handling systems? Is there a set of guidelines/recommendations you can share for how to improve air circulation in classrooms, residence halls, and common areas like dining halls where possible?

In general, reducing the risk of pathogen spread via building systems include the following methods:

  • Increase fresh outdoor air delivered to a space.
  • Provide highly effective air filtration within mixed air systems.
  • Identify areas not served by mechanical ventilation systems. Find possible ways to mitigate risks in those spaces.

Cornell personnel have developed a flowchart (shown below) that outlines the methodology the team is following to evaluate a building’s ventilation system. At the building level, all campus buildings have been examined. In spaces where mechanical ventilation is provided, the team is evaluating these systems and making interventions when possible to provide additional fresh air and to improve building filtration when possible. For spaces without mechanical ventilation, the team is exploring ways to use natural ventilation and, where appropriate, finding solutions that temporarily increase fresh air delivery. Exhaust systems in dormitory restrooms may be operated to provide additional ventilation.

HVAC Restart Recommendations

Should HEPA filters be used in all Air Handling Systems?  Is Cornell updating filtration in buildings?

Unless a building air system is designed to accept a HEPA filter, installing one may actually cause so much resistance that it actually lowers airflow to a space, and can damage installed systems. New York State, SUNY, and ASHRAE instead recommend installing higher MERV (Minimum Efficiency Reporting Value) air filters. NYS and SUNY recommend installing MERV-11 filters in mixed air systems when possible. Cornell is exceeding that recommendation and upgrading filtration to MERV 13 rated filters where feasible, based on the physical constraints of the HVAC system. Many of our facilities already utilize MERV 13 or higher filtration and do not require upgrades.

What operational modifications could be made to existing HVAC systems to help during this time?

Cornell personnel have adjusted the digital control settings of our most modern mechanically ventilated buildings to increase fresh air delivery to the buildings. We have also adjusted the occupancy periods to reflect the extended occupancy schedules and the reduced density.

Should campuses run HVAC systems at 100% outside air to increase ventilation?

Many of our campus buildings, including most laboratory spaces, already operate using 100% outside air systems (makeup air systems). However, buildings served by mixed air systems have not been designed to run at 100% outdoor air. Doing so could cause conditions that damage building HVAC systems and create unintended indoor air quality issues.

For recirculating air systems, Cornell is implementing alternate strategies that increase fresh air delivery and filtration. In general, most if not all mechanically ventilated buildings on campus supply fresh air at rates that exceed industry best practice (ASHRAE 62.1). These ventilation rates are based on typical occupancy patterns. Since our building density will be significantly reduced due to physical distancing and scheduling, fresh air rates supplied per person are multiple times higher than the recommended minimums.

Should campuses run HVAC systems 24/7?

Operating all building HVAC systems 24/7 during unoccupied periods of the day would be wasteful and would not provide benefit to facility occupants when the building is empty. Instead, we have executed building programming changes that provide an extended building flushout before occupants arrive for the day, and after they leave in the evening. These flushout periods have been scheduled recognizing that some facilities have unique and extended hours of operation, and have been tailored to fit those occupancy patterns.

Should campuses disable Demand Controlled Ventilation?

Demand controlled ventilation systems sense the level of carbon dioxide produced by occupants in a space, which then triggers building systems to ramp up air delivery to the space. Cornell has programmed building spaces served by demand-controlled ventilation to activate at carbon dioxide levels well below the industry recommended limits. This will result in more fresh air being delivered to a space when it is occupied by fewer people as Cornell requires lower density in buildings.

Should we bypass Energy Recovery ventilation units?

Energy recovery ventilation units recover heating and cooling energy from exhaust air to temper incoming fresh outdoor air. Cornell technicians have inspected all campus ERV units to identify cross-contamination risks. Units identified as deficient will be deactivated until they can be repaired.

Should Ultraviolet (UV) light systems be installed as a means to reduce virus transmission?

Feasibility of installation, research, and discussions with our campus Environment, Health and Safety professionals have caused us to decline to install UV light sources within recirculating HVAC systems due to safety and efficacy concerns.

What are the ideal temperature and humidity values?

At this time, there is no definitive research that identifies the ideal temperature and humidity values that would discourage the survival of SARS-COV2, the virus that causes COVID-19 in the indoor environment. Very few buildings located in our regional climate zone have the capability to control humidity through the HVAC system. In the absence of more definitive research on the efficacy of this approach, we do not recommend altering building temperature and humidity settings at this time.

Should air purifiers or fans be used? I want to purchase an air cleaner for my dorm or office, what should I purchase?

The installation of an “air cleaner” does not provide sufficient protection from the COVID-19 virus alone. Cornell Facilities Engineering does not recommend the installation of these units campus-wide due to numerous concerns about safety and efficacy. Installation of these units may be appropriate in areas that include all of the following: there is no make-up air (just recirculating air), no operable windows, small spaces (<300 SF), and high-risk spaces due to specific space use or occupancy limitations for physical distancing. Certain technologies within commercially available air cleaning units may actually be harmful if not operated or installed correctly.

Parents and students interested in purchasing an air cleaning or sanitizing unit should be aware that some dorm locations have limited electrical service capacity and the operation of these types of units could trip electrical service breakers, causing a loss of power. Also, this type of equipment when operating will generate heat, which during certain times of the year could make a space quite uncomfortable. Lastly, please consider that a unit with a fan operating is pulling air from one space to another. While ideally, it may just be causing airflow to circulate within a dormitory room, it could also just as easily end up pulling air into the room from an adjacent hallway or restroom.

Should ductwork be cleaned?

Cleaning ductwork is not an effective or necessary strategy to control the spread of SARS-CoV-2.

Should people open windows to get fresh air exchange. Is this true for all rooms?

Opening windows can provide additional ventilation in some spaces, and would be entirely appropriate in locations such as private offices or dorm rooms. However, this practice in some cases can cause issues around temperature, humidity and airflow. Users and facility managers will need to evaluate the effectiveness of opening windows and make sure that there are no significant unintended negative consequences when doing so.

How is Cornell evaluating individual spaces?

Cornell personnel have been evaluating campus building HVAC systems at the whole building/facility level. We examine the mechanical systems to ensure that we are delivering plenty of fresh outdoor air to all building spaces served by these systems while also upgrading filtration when possible. If you feel that a certain location in your building is not receiving sufficient ventilation, have a discussion with your facility manager and they can help evaluate individual spaces within a building.

Is Cornell following the CDC recommendations for operating buildings?

Yes. Facilities and Campus Services has evaluated and improved facility HVAC systems according to CDC recommendations.

If the HVAC system is upgraded, do I still need I still need to wear a face covering?

Yes, it is essential that we keep wearing a face coverings and maintaining physical distance as required by both University policy and New York State requirements. Improving HVAC system ventilation does not interrupt the direct transmission of COVID-19 from person to person. Direct transmission appears to be the primary method of COVID-19 spread.

How are SUNY schools addressing HVAC recommendations?

Cornell University has reviewed guidance by our peer institutions and SUNY facilities professionals at the SUNY Operations and Maintenance COVID19 Workgroup. In general, Cornell’s COVID-19 risk reduction activities align with or exceed the SUNY recommendations relating to building HVAC systems.