The infectious disease and HVAC engineering communities have been grappling with the complexities of COVID-19 transmission for the past nine months. Increased HVAC fresh air has the potential to dilute and remove the aerosol droplet particles of COVID-19 that many experts believe is one of the main sources of transmission. Now the building science community is starting to contribute to the discussion. Insulation Institute talks this week with Paul Grahovac, LEED AP, about the ventilation solution to COVID-19.

The Fresh Air Component

Paul Grahovac is a 30-year veteran of the construction industry, an attorney and manager of building codes, standards, and field support for PROSOCO, Inc. and the related company, Build SMART, LLC. He’s written an article for a construction journal and recorded a presentation for Massachusetts Passive House advocating for adding increased fresh air using mechanical ventilation to reduce COVID-19 transmission in indoor environments.

Grahovac recommends tightening the building envelope using techniques employed in Passive House construction for buildings of all types and sizes and adding energy recovery ventilators that would cycle fresh air through a building. While 100 percent fresh air is desirable, that much wouldn’t be required to dilute and remove aerosolized particles in the building air, he said. In fact, one study determined that increasing the fresh air component of the fresh and recirculated air mix indoors to 16 percent (3ACH per) would be as effective in mitigating outbreaks as vaccinating approximately 50 percent of a building’s occupants. This is for short-range droplets and aerosolized particles mixed Grahovac noted. For long-range aerosols, such ventilation would be even more effective, virtually eliminating the chance of transmission, according to the study.

U.S. Center for Disease Control and Prevention (CDC) now recommends 100 percent fresh air ventilation, if it can be achieved. Grahovac believes that Passive House construction, with its extreme energy efficiency, is the best route to offset the cost of such a ventilation program. Also, the American Society of Heating Refrigeration and Air-Conditioning Engineers (ASHRAE) recommends increased airtightness and has an extensive position document on controlling infectious aerosols relative to COVID-19. ASHRAE also recommends two hours of 100 percent fresh air flush each morning and evening.

The Retrofit Process

Grahovac recommends that buildings be blower-door tested to determine the extent of air leakage. As a less expensive alternative to testing the entire building, a portion of the building could be tested, or one could assume that the building lacks airtightness. The project team would recommend measures to increase airtightness, such as sealing leaks and penetrations. Energy modeling can be used to estimate the energy savings from the retrofit work and compare that to the retrofit costs to determine the feasibility of completing the work.  

The additional benefits of increasing air tightness include reduction of stale air, allergens and dust, more uniform building temperatures, and reductions in condensation, water leaks, and mold.

Ultimately, Grahovac suggests that building enclosure consultants meet with local or state health regulators to discuss their plans to modify the building air tightness and add fresh-air mechanical ventilation. The consultants could then request modifying the social distancing and/or mask requirements for the specified facility as a result of the feasibility study. Addressing the air tightness and the fresh-air ventilation could allow safer public outings.

Implications for New, Existing Construction

With consumers increasingly worried about indoor air quality, health, and everyday environmental exposures at home, builders can meet consumer needs with fresh-air and energy recovery ventilation. For example, with Passive House construction and ventilation, the incoming air is virtually allergen-free. While the increased energy costs associated with increased mechanical ventilation use may be a concern, those costs are mitigated by increased building energy efficiency achieved through an airtight envelope.

“The more outdoor air is brought in, the higher your energy bills will be. That is why an energy recovery ventilator is a good idea, Grahovac said. “That is also why it is a good idea to seal leaks in existing buildings because doing so saves energy dollars.”  

Grahovac added that some people find it hard to understand why building owners should not rely on leaky walls to provide outdoor air ventilation. The U.S. Department of Energy’s Berkeley Lab demonstrated that airtightness and ventilation work together to provide energy efficiency and healthy air. In tight buildings, the ventilation system and not unintended air leakage, provides virtually all the building’s fresh air.  

The more airtight the building envelope and the HVAC ducts, the more precisely the ventilation system can provide the correct amount of fresh air. Ventilation works more effectively in airtight buildings than in leaky buildings.

A DIY Portable Air Cleaner

In a recent blog post, Dr. Allison Bailes of Energy Vanguard provided step-by-step instructions on building a DIY portable air filter for your home using a simple box fan and MER-13 air filters. Bailes notes that while filtration isn’t the whole answer, social distancing, mask wearing ventilation are also very important to reducing the transmission of COVID-19 in your home when visitors are there.

Wearing a mask and keeping the portable air cleaner in the middle of the room should greatly reduce the risk of transmission if someone is infected, Bailes noted.