Ventilation in the COVID Era – Airborne transmission of SARS-CoV-2

Author: Lou Vogel, PE, LEED AP, President
Published: October 5, 2020
Last updated: October 5, 2020

As expected on Friday, September 18, the World Health Organization (WHO) changed its recommendations regarding airborne transmission of SARS-CoV-2 (the virus that causes COVID-19) and now confirms that it is an airborne illness that can be transmitted by aerosols, not just respiratory droplets. As defined in Part I of this series of posts, aerosols are small particles that, unlike droplets that will land on a surface, continue floating in the air and will follow any air movements that may be present.

And still, the most important method to reduce transmission is to stop it at its source; wear the mask, and don’t go out if you aren’t feeling well. 

There is a new study (published August 28, 2020, from April 2020 measurements) that circumstantially points to a lack of outdoor air contributing to an outbreak in a nursing home in the Netherlands. One of the HVAC units in the ward that had the outbreak was set up with CO2 control of the outside air damper. This is a very common energy saving measure that only provides the maximum code required outside air when there are enough people in the space to trigger the CO2 sensor. We generally call this Demand Controlled Ventilation (DCV) and it can save substantial amounts of energy in large occupancy spaces that are not always full of people. In times of low occupancy, when the sensors do not call for ventilation, the fallback should be set to a minimum amount based on the size of the room, which was likely not the case in this nursing home ward.  

In this case, it says that the setting was 1000 ppm of CO2. This is higher than usual, and it is entirely possible that the outside air damper would never open up, depending on the size of the room and number of people. Currently, the atmosphere is listed as being 414 ppm (it is going up, according to So, the air in the room would progressively have more concentration of virus if there was an infected person in the space and no windows open. Another factor that should be considered is whether or not the CO2 sensor was properly calibrated so that it was reading correctly.   

The other 6 wards in the building did not have an outbreak and had no positive test results. Evidently, the other 6 wards did not have the DCV control and the other HVAC units in each space were providing outside air, though it’s hard to be sure from the write-up. 

There’s still no evidence that the virus traveled in ductwork, but a complete lack of fresh air or good filtration may have contributed to the high transmission rates. In this case, it can also be considered that if the HVAC unit had a good filter (MERV 13 or higher) it likely would have reduced the concentration of virus in the air.   

For future posts, I will go into what impact your HVAC system layout has on reducing aerosols in your building. As new information is released, I will continue to respond here and help navigate new guidelines set forth by the CDC and ASHRAE as they relate to building ventilation. If there are any questions you have, feel free to ask here

How COVID 19 Spreads. September 21, 2020. National Center for Immunization and Respiratory Diseases (NCIRD), Division of Viral Diseases and the Center for Disease Control and Preventions.

Ventilation in the COVID Era

Author: Lou Vogel, PE, LEED AP, President
Last updated: September 11, 2020

There is a great deal of discussion and research going on right now to understand what enables the transmission of the SARS-CoV-2 virus. In this multi-part series, I will work toward clarifying some of the recent findings on how the virus moves and rests in indoor spaces from the perspective of an HVAC engineer and what that means for building designers and occupants. The following series of posts will look at several facets of ventilation systems including:

  • how HVAC systems might disperse, transfer, or dispel the virus concentrations;
  • how the building industry is responding through improved design and enhanced filtration measures; and 
  • what these shifts in building design and filtration mean for the energy usage of our buildings. 

Part I

In this introduction, I will define respiratory droplets and aerosols, and begin the discussion of what we are learning about the transmission of the virus through the air and how HVAC systems impact that. There are still ongoing discussions of how much of the virus gets transmitted to other people by aerosols. The World Health Organization (WHO) hasn’t changed its guidance on this yet, but it seems likely that it will eventually do so. 

Droplets Defined

The WHO currently states that the “COVID-19 virus spreads primarily through droplets of saliva or discharge from the nose when an infected person coughs or sneezes.” Infectious droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs. The WHO sizes up respiratory droplets as between 5 μm and 10  μm (micrometers) in size and aerosols at less than 5 μm. However, there is a continuum of airborne particle sizes; they don’t suddenly switch from one to the other. The droplets are aptly named, as they are small particles that eventually  “drop” down onto a surface, mostly within 6 feet, some a little farther. 

What Are Aerosols?

There is a growing consensus among researchers that aerosols also contribute to the transmission of the virus. Interestingly, droplets can dry out and become a droplet nucleus type of aerosol. Aerosols will continue floating in the air and will follow any local currents or air movements that may be present. These air currents can be caused by HVAC grilles, open windows, or any other movements in the space. 

Ductwork, Filters, and HVAC System Design

As of September 10, 2020, there are no documented cases of virus transmission through a building’s ductwork into other spaces. There are case studies that suggest the flow of air in a room spreads the virus to nearby people, there are studies that have found the virus on the return air grille of HVAC systems, but there are none that show cases of the virus traveling from one room to another.  

What’s Next?

Next, I will look at how the layout of an HVAC system can affect the potential transmission of the virus and examine a case study that provides an example of the SARS-CoV-2 virus moving through indoor space. 

What does that air movement mean for transmission of the virus? Does ductwork harbor droplets and aerosols? Will an enhanced filtration system help reduce exposure to SARS-CoV-2 virus in indoor spaces? 

Modes of transmission of virus causing COVID-19: implications for IPC precaution recommendations: Scientific brief. March 29, 2020. World Health Organization.

Ventilation systems can help reduce COVID-19 exposure

Our team has been attending webinars, collecting data, and closely monitoring the research around the transmission of SARS-CoV-2 as it relates to building ventilation requirements. Understanding up-to-date guidelines for improving will support building owners and building occupant safety as we move toward reopening businesses and public spaces in NYS.

Most recently, ASHRAE’s (The American Society of Heating, Refrigerating and Air-Conditioning Engineers) Executive Committee and Epidemic Task Force released two statements around COVID-19 summarized as follows:

Transmission of SARS-CoV-2 through the air is sufficiently likely that airborne exposure to the virus should be controlled. Changes to building operations, including the operation of HVAC systems, can reduce airborne exposures.

…Ventilation and filtration provided by heating, ventilating, and air-conditioning systems can reduce the airborne concentration of SARS-CoV-2 and thus the risk of transmission through the air…

There are many variables that can affect the impact your HVAC system has on reducing exposure to SARS-CoV-2. Here are some common issues that we’ve seen in the field that can be remedied fairly simply. 

  • Check your HVAC systems for missing air filters. It’s surprising how often filters are overlooked for replacement or simply never installed. 
  • Consider installing high-efficiency filters.
  • Check for any leaks in air filter covers and doors.
  • Look for any air bypass around the air filters.
  • With office spaces shifting, it would be a good time to assess the location of your system’s return air grilles in relation to how building occupants use the space. 

Taitem has been designing HVAC systems that meet or exceed ASHRAE design guidelines and will continue to provide building owners with the most advanced strategies for reducing the risk of transmission of airborne exposures in their buildings. If you have questions about improving your existing system operations or designing a new system that will reduce the airborne concentration of SARS-CoV-2, please reach out to our team.

Saving Energy in Unoccupied Buildings

With a workforce at home, is your office building powered down? Taitem put together a list of tips for safely shutting down your building systems to conserve energy, save money, and further reduce our greenhouse gas emissions. Please take a moment to review the list and spread the word to your network. Click the image below to link to a shareable .pdf.


To meet the carbon reduction goals set forth in the Green New Deal, policymakers at the national-state-county and city levels are adopting whole-building electrification policy standards that have already been set in some trailblazing cities in the U.S. Electrifying our building stock will have the most dramatic impact on our carbon reduction goals.

The engineers at Taitem are already designing buildings in NYS that will be free of fossil fuel use onsite and able to take advantage of an increasingly cleaner electric grid. This is an important step in addressing local and regional carbon emission reduction goals and one that is becoming more attainable as demand for products that support electrified buildings increases.

As buildings designers, developers and engineers, we will all play a role in the electrification of our building stock in NYS and helping to reduce the amount of carbon emissions our buildings create.

Efficient air source heat pump systems for heating and cooling have already been widely adopted state-wide and are greatly improving the efficiency of our buildings. We’re seeing consumers comfort with these systems grow and contractors offering to install them as design/build, as well as other indicators that building electrification has moved beyond early adoption. However, one area that has been especially challenging to efficiently electrify is domestic hot water for multifamily and commercial buildings. Electric resistance hot water heaters are inefficient and result in high electricity demand while gas systems still rely on the use of fossil fuels.


With all the forward movement, there have been hurdles in electrifying hot water heating systems. Storage tank-type, heat-pump water heaters also have several issues, including taking up lots of space, stealing heat from the space, and slow recovery. Our engineers have overcome these challenges by designing innovative solutions using air to water heat pumps that are currently on the market. Air to water heat pump systems work like a reverse air conditioner, taking heat from outdoors and pumping it into water.

The design on one of our most recent projects included a cutting-edge air to water heat pump technology for domestic hot water generation, which we hope will set an example for other building designers. The Sanden SANCO2™ Heat Pump Water Heater we used for this design is not only more efficient than standard gas, but it also uses carbon dioxide as the refrigerant, which has the lowest global warming potential of all refrigerants on the market.

This system is comprised of (16) Sanden units, 1,000 gallons of storage and two additional 119-gallon tanks with electric elements. The entire system is located in the mechanical room on the first floor with the Sanden units on the adjacent exterior wall. Water is stored at 150°F and is mixed down to 135°F for distribution throughout the building. The Sanden system also incorporates drain back for freeze protection.


While there are a limited number of air to water heat pump products available, we’re feeling confident that competition in the market for these products will soon shift. We’re seeing utilities state-wide encouraging whole building electrification and empowering consumers to move toward electric systems which will, in turn, drive manufacturers to bring additional product options to the market. However, even with the limited number of products available, we’re already designing high-efficiency heat pump water heating systems that work in our cold climate.


Not only are air to water heat pumps 200-400% more efficient than traditional gas or electric resistance water heaters, they also rely solely on electricity. This means that they help our high-performance buildings save money now while significantly reduce our carbon emissions. As our electricity grid continues to become cleaner, buildings utilizing these technologies will also have lower carbon emissions.



Taitem tabling at the Sustainable Energy Expo, October 28 in Syracuse

Sustainable Energy Expo | Syracuse Monday, October 28.

The buildings of the very near future will run on clean energy. The Sustainable Energy Expo is where building owners, developers, contractors, architects, engineers, and local government officials will come together to learn about latest advances in non-fossil fuel energy solutions and the financing options available for retrofits and new construction. Please stop by Taitem’s booth to meet our energy engineers during your visit to the Expo.

Studies continue to show cost-effectiveness of commissioning buildings

The Lawrence Berkeley National Labs (LBNL) recently released a year-long meta-analysis of costs and benefits of commissioning that more than doubles the number of building and project area on which the previous studies were based. The latest study, conducted in 2018 and released this summer, is an update to their previous reports:

The Building Commissioning Association (BCxA) helped collect data for the most recent study by reaching out to its members and asking for project data. As members of the BCxA, Taitem submitted extensive project data for the commissioning of new systems at a site in Brookhaven, NY. The request was for a substantial amount of data including a retro-commissioning audit, pre-construction utility bills to verify savings post-construction, information on equipment costs, change orders, schedules, and more.

We took a closer look at the 2018 report and compiled some key metrics for building professionals to consider:

2009 Study 2018 Study 2009 Study 2018 Study
Median building energy savings 14.5% Energy Savings
(non-utility EBCx+MBCx)
19% Energy Savings
(non-utility EBCx)
13% Energy Savings (not yet reported)
Median simple payback times 1.1 years 2.2 years 4.2 years (not yet reported)
Median commissioning costs $0.30 per square foot $0.26 per square foot $1.16 per square foot $0.82 per square foot
Median commissioning costs as % of construction cost N/A N/A 0.57% 0.25%


This collaboratively compiled data from certified commissioning agents shows, even more markedly, that commissioning may be the single most cost-effective strategy for reducing energy, costs, and greenhouse-gas emissions in buildings today.

Here are some other things we’ve seen that indicate growth in the field:

  • More incentive programs, codes, and standards are including or requiring commissioning.
  • Commissioning costs are decreasing for both new construction and existing buildings.
  • Non-energy benefits of commissioning are extensive and often offset part or all of the commissioning cost.
  • New tools are available to supplement commissioning, tapping into complex and digitized building systems to automate fault detection and monitoring and ensure persistence of savings.




Industrializing Deep Energy Retrofits

phbcoverDeep energy retrofits of existing structures are an absolute must for meeting any reasonable carbon emission reduction goals, but cost-effective retrofits are challenging, to say the least. Taitem teamed up with King + King Architects to bring a five-building, 40-unit, two-story, wood-framed apartment complex in upstate New York to a net zero energy and Passive House level of performance.

Read more about the details of the project and the long-term phased plan of retrofit measures at


Over the last 20 years, Taitem’s team has performed blower door tests on countless buildings. Blower door testing supports optimal system design and provides paybacks. Blower door testing is also required in New York.

New York State Energy Conservation and Construction Code (NYS ECCC) sets minimum requirements for air tightness. Both residential and commercial buildings are required to have a continuous air barrier to prevent air passing through the building’s thermal envelope.


Detached one- and two-family dwellings and multiple single-family dwellings (townhouses) as well as Group R-2, R-3, and R-4 buildings that three or fewer stories above grade.

Any building that is not considered a residential according to the above definition.


To measure that the air leakage rate of the building thermal envelope is not greater than 0.40 cfm/ft2 at a pressure difference of 75 Pascals, commercial buildings must:

1.  Meet a list of prescriptive requirements OR
2. Perform a blower door test

Residential buildings must be tested and verified as not having an air leakage rate exceeding three air changes per hour at a pressure difference of 0.2 inch w.g. (50 Pa), also known as 3 ACH50. Note: There are no changes in the 2018 International Energy Conservation Code (IECC) regarding air barrier requirements, but we can expect enforcement of the NYS ECCC to increase.


Blower Door Testing can help identify building air tightness issues which, in turn, can

• reduce energy usage due to air leakage,
• improve occupant comfort by reducing drafts caused by air leakage, and
• reduce moisture condensation problems.

While commercial buildings can comply with code without blower door testing, blower door testing ensures that the construction is adequate and can be key part of envelope commissioning.


Blower door testing is an excellent diagnostic tool. You can locate and find leaks in the building envelope during the test so they can be properly addressed before these areas are covered. With higher levels of insulation, less heat is being driven through walls, reducing drying potential.

Air leakage is a major source of water vapor transport. Reducing air leakage is critical to ensuring that moisture doesn’t reach undesired areas in the building and thermal envelope.


Get in touch with Taitem or your blower door consultant EARLY in the design and construction process so that a test plan can be developed to make best use of the technology and service.

Commissioning Code updates in NYS – Taitem presents at NYS Green Building Conference

Taitem was happy to be among the top green building researchers, educators, and practitioners at the New York State Green Building Conference in Syracuse, New York. One team presented on the progress of its RetrofitNY project, and another led a session on updates to the NYS Commissioning Code.

Lou Vogel, President, and Nate Goodell, Senior Engineer, presented “Shifting the Baseline: An update on Cx Construction Code in NYS.” As of October 2016, the New York State Commercial Construction Code was updated to align with international standards for energy efficiency and building performance. Part of this alignment added a requirement for certain buildings to receive commissioning per the 2015 International Energy Conservation Code. This change has shifted commissioning from an activity usually limited to high-performing buildings to one that will be part of many new commercial construction projects. With this shift comes the need for education and outreach to stakeholders who might not be familiar with commissioning or with the new code requirements. Lou and Nate explored which buildings are impacted by the new code, what commissioning entails, and why it is required. They concluded with lessons learned through their extensive field experience on how to make the commissioning process easier.

Click here to download the complete presentation.

About NYS Green Building Conference

As the premier green building conference in the Northeast, the New York State Green Building Conference’s progressive advisory council has fostered growth by consistently bringing together top green building researchers, educators, and practitioners. Conference participants represent many industries including architecture, engineering, construction, consulting, deconstruction, landscape architecture, government, higher education, K-12 education, state agencies, real estate, and management firms.