HVAC Systems – Designing during & after COVID-19

March 17, 2021

By: Chad Musselwhite, P.Eng., LEED® AP BD+C, Engineering Manager, Mechanical

HVAC systems provide ventilation and air circulation in buildings and play a critical role in indoor air quality. Because of the COVID-19 pandemic, building owners and operators might have concerns about their building’s HVAC system and its effectiveness. As a building owner or property manager looking to re-open a building, you want to ensure that the HVAC system is working effectively to provide the healthiest possible indoor air quality for building occupants.

Are current HVAC systems adequate to help prevent the spread of airborne diseases?

There are so many factors to consider that there is not a one-size-fits-all answer to this question. Every building is different and serves a unique purpose. The types and ages of HVAC systems vary widely and will also operate differently from building to building. For example, a hospital or emergency response facility will require more advanced ventilation and filtration than a walk-up apartment building, school, retail facility, office building, or fitness centre. To the extent that an HVAC system can provide additional clean, fresh air, more complete distribution of that fresh air, and offer optimized space temperature and humidity, it will support better health outcomes for those who use the facility.

HVAC system design is just one part of the strategy

A building’s HVAC system design and operation is only one part of the strategy for preventing the spread of airborne viruses in an indoor environment.

Other considerations include:

  • The type of virus and its primary modes of transmission.
  • Building occupancy levels. How many people will be in the building during and after the pandemic?
  • How people use, move through, and congregate in the building. For example, a learning institution will require a different strategy than a supply warehouse.
  • The development and implementation of other mitigation strategies. These include mask-wearing, the distance between workspaces, and hand sanitation.

How can HVAC system design contribute to preventing the spread? 

The HVAC systems help set the scenes where people live their lives at home, at work, and at play. When those environments contain clean air and optimal temperature and humidity, two things happen. First, the growth and viability of viruses, bacteria, and molds are discouraged or suppressed. Second, the baseline resilience of occupant immune systems is actually bolstered, improving their health outcomes even if they have become infected within the building or elsewhere.

Key things to look at include fresh air intake quality and quantity, air circulation, airflow patterns, humidity, and temperature. Depending on the function of your building, you could also consider air filtration or air treatment strategies.

Let’s look at some key points that building owners and property managers can investigate further to ensure their HVAC system operates adequately and safely.

Understand how the building’s ventilation system works

The first step is gaining an understanding of how your HVAC system works. If you don’t have the knowledge yourself and don’t have a team of building operators, there are some places you can look to find the information you need.

Depending on the building’s age, you should have access to ventilation system drawings and the Operations and Maintenance (O&M) Manuals assembled at the time of construction. These documents will contain information on the system’s function, how it works as a whole system and technical information about each of the primary system components.

If you don’t have access to these documents, contact a commercial HVAC company that has provided service to your building in the past. They might not have the answers for your specific HVAC system, but they can guide you towards an HVAC consulting engineer or building operator that can help.



When learning about your system, it’s essential to understand airflow patterns, fresh air intake, filtration, and air treatment. 

Airflow patterns

Check the direction of airflow patterns, including how air circulates throughout various areas in the building. What direction does air move within or through a space? Is the air flowing from one person’s location to another person’s location? Is the air coming into each room and then being drawn up and away without mixing with the air in another area?  Different supply diffusers are designed to induce different airflow patterns. So it is not always as simple as connecting the dots between the supply diffuser and the exhaust or return grille.

Fresh air intake

In most buildings, the air is continuously moving and mixing around. The HVAC system injects a certain amount of outdoor air into the mix to “freshen” that air and dilute the present contaminants within each space. At the same time, an equivalent portion of the current indoor air is expelled from the building. Ensure that the building is drawing in an adequate amount of fresh air – according to ASHRAE Standard 62 – and it is being distributed effectively to all occupied areas. We will go into greater detail regarding fresh air balancing further in this article.

Filtration and air treatment strategies

Most commercial building HVAC systems recirculate a significant portion of air. Filtration or air treatment is the most relevant solution for improving the quality of recirculated air. Early research suggested that the COVID-19 virus would not survive very long in the air and especially not the long trip through the ductwork from one space to the air handling unit and back again. However, it depends on the many specific variables of your building, and we can also not assume that new variants of the virus or future viruses will share this characteristic.

Most HVAC filters are designed to capture small dust particles and will not capture particles as small as viruses. Nonetheless, these filters play a role in air quality. Check to make sure your system is using the correct type of air filters for your application. O&M Manuals will often contain a record of the initial filter types and performance criteria targeted when the HVAC system was commissioned. Ensure that the type and quality of the current filters match what is in the original design. In some cases, additional higher-efficiency filtration might be needed.

If your facility requires the HVAC system to be capable of removing viruses from recirculated air, a combination of HEPA-grade filters and active air-cleaning devices would be required. Active air-cleaning systems can include Ultraviolet Germicidal Irradiation and other specialized air-cleaning techniques within rooms, ceiling spaces, or ductwork.

Perform a maintenance and cleanliness check

Have the interior air handling units and ductwork inspected by a commercial HVAC company that offers HVAC and duct cleaning. Pre-COVID, the recommendation was to clean the ductwork every three to five years. If you’re re-opening a building or acquiring a building, you should have them cleaned as a fresh start.

An inspection will also determine if the filters in your HVAC system need to be cleaned or replaced. Check the pressure gauges across the filter bank. Replace the filters when the pressure drop suggests that the filter is dirty or “loaded.” Always remember to use Personal Protective Equipment (PPE) when removing old filters.

Ensure there is an adequate fresh air intake

As mentioned, fresh air is vital to healthy indoor air quality. Determine the amount of fresh air drawn into the system and how and where it’s distributed. Inspect the operation, control sequence, and positioning of fresh air intake dampers and mixed air dampers to ensure you have the right balance.

An air balancing agent may be engaged to measure the amount of fresh air being drawn into the building for each operating mode and measure the volumes of air being delivered throughout the system. If ventilation drawings or original balancing reports are available, the agent can reset all the balancing dampers to match the HVAC system’s original design or to suit what is appropriate for how your facility currently functions. If your building is newer, you might notice that the dampers were marked at construction. If the dampers aren’t at those positions, it could mean that the system has been changed since the building was commissioned. This could be for a good reason or could be a sign that things have drifted out of tune.  Perhaps you would like to increase the ratio of fresh air being provided; a mechanical consulting engineer can help determine how much more fresh air could be brought in within the constraints of your system and the climate conditions and how to implement those upgrades.

Inspect the air diffusers and return air intakes throughout the building. Ensure they are clear of blockages and that they have not been tampered with since the last inspection.

Don’t skip humidification equipment maintenance

If your HVAC system includes humidification equipment, ensure that the humidifier is maintained, cleaned, and is operating correctly. Humidifiers require considerable maintenance, and building operators may have chosen to defer maintenance efforts or costs by decommissioning them.

It is strongly encouraged to maintain proper humidity levels in a building that people frequently occupy. Maintaining a relative humidity level between 40 to 60 percent is ideal for immune system performance and overall human health. However, in frigid winter climates, the effects of indoor humidity on the building envelope must also be considered to make an appropriate compromise. As noted earlier, the proper humidity and temperature can support better immune system performance.

Review the control system sequences and set-points

The control system contains the algorithms that bring the mechanical systems in a building to life. It is the brain and nervous system of your HVAC system. Without it, you’d have an ineffective collection of pipes and ducts. You need a well-designed, dynamic system that provides heating, cooling, and ventilation in response to changes in climate and indoor activities. The system turns on, starts, and stops at the correct times and conditions.

The way a system is controlled and how it is operated has a significant impact on its effectiveness. If the programming and decision points built into the control system aren’t set correctly, then the system won’t run efficiently or effectively according to its intended design.

If you’re not sure, a professional engineering consultant can help you assess the system and recommissioning it for optimal performance. A professional can help ensure that the system is reacting appropriately at the right time of day and when certain conditions occur. If necessary, upgrade the control system. You should see significant improvements in effectiveness, energy efficiency, and indoor air quality.

Review energy consumption data

Heating, cooling, humidifying, and ventilating a building takes energy. Reviewing energy consumption data will allow you to benchmark appropriate consumption and see any spikes or step changes that have occurred over time. If the energy consumption is on an upward trend, it’s a sign that the building’s systems have drifted from their original, efficient operating points. If this is the case, it’s worth having an engineering professional come in to determine why or to perform an Energy Audit of the facility.


Considering COVID-19, other viruses, or other threats when planning HVAC system design in new buildings

Resilience to a pandemic is a subset of the larger concept of resilience in building design. The first step in HVAC system design in a current and post-pandemic situation is to define the purpose of the building and what known or unknown threats you will require it to operate through.

Do you need the building to be resilient against epidemics or pandemics? Do you want to future-proof it against other crises’ like wildfires, floods, extreme wind events, or interruptions to power or fuel supplies? Once you’ve determined the building’s goals and tolerances, your consultants can start to design the HVAC system to meet those goals.

Incorporating risk mitigation strategies will indeed add to the construction or building retrofit costs. What’s important to you and your organization? No one strategy can make your building or HVAC system “bulletproof,” but you should incorporate the level of resilience appropriate to the building and its function.

If you’re interested in doing more research, there are valuable resources about HVAC system operation and design through organizations like the American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE). 

As the world begins to come out of the COVID-19 pandemic slowly, building owners and managers will need to continue to be vigilant with their strategies to ensure their systems support tenant health and safety and that their buildings operate as expected. Keeping ourselves and our clients informed of the latest trends remains crucial to our team’s ability to deliver quality engineering solutions. Our proactive, collaborative, and multi-disciplined approach helps solve our client’s greatest challenges. It enables our team to live out our purpose of brightening people’s lives by engineering sustainable cities that are safe, inclusive, and resilient.