The current situation raises all sorts of questions among building managers and their tenants. "Can people catch the virus by breathing the air? Is the air filtration system up to the task? Does the system require special maintenance? Will there be additional energy costs?", etc. The information webinar on June 10 organized by Réseau Énergie et Bâtiments, in collaboration with BOMA Quebec, provided some answers to those questions. It was presented by Eddy Cloutier (Bouthillette Parizeau), Roland Charneux (Pageau Morel) and Maxime Drolet (Ivanhoe Cambridge). A PDF version of the presentation is available in the "Activities" section of the Réseau Énergie et Bâtiments website (reseaueb.com).

Contamination and Reducing Risk 

Social distancing is on everyone's minds and lips these days. Two meters is the distance required for the vast majority of droplets emitted by one person to settle on surfaces before being breathed in by another person. Current research suggests that droplet transmission of the virus is the primary means of transmission. Droplets are emitted when a person coughs, sneezes, screams, breathes, sings or talks. The more an individual is in contact with others, the greater the risk of contamination. Someone working in an office will be less at risk than a person working in retail.

The dose of SRAS CoV-2 required to infect a person and cause COVID-19 is currently unknown. It is expressed as the result of the intensity of contamination multiplied by the duration of exposure. It is difficult for a property manager to limit the "duration of exposure" factor once tenants return to their work spaces. It is easier, however, to reduce the "intensity of contamination" factor, i.e. diluting contaminants by introducing more fresh outdoor air into HVAC systems and reducing contaminants by thoroughly filtering the air. 

Ventilation and Outdoor Air Supply 

It has been shown that an individual with COVID-19 can generate significant viral loads in indoor air (Buonanno et al., 2020). In that context, authorities recommend proper ventilation to extract contaminants from indoor air and to dilute them by introducing outdoor air, regardless of the type of building or service area (CDC, 2020a; ASHRAE, 2020a). The chief recommendations have been grouped according to ventilation system type. For free cooling central ventilation systems, the recommendations are as follows:

• Operate systems at their rated speed for two hours prior to the arrival of occupants.
• Operate systems at low speed for two hours after occupants leave.
• For fresh air ventilation systems, lower the CO₂ set point to 400 ppm.
• Keep washroom air evacuation systems in continuous operation (24 hours a day, 7 days a week).
• For variable flow distribution, set the system at the highest possible temperature to maximize circulation of fresh air throughout the premises.

For minimum outside air systems or fan coil ventilation systems with outside air intake, the recommendations are: 

• For fresh air ventilation systems, lower the CO₂ set point to 400 ppm and keep the systems in continuous operation (24 hours a day, 7 days a week). Systems may be kept at reduced flow rates during periods when the building is unoccupied.
• Keep washroom air evacuation systems in continuous operation (24 hours a day, 7 days a week).
• For variable flow distribution, set the system at the highest possible temperature to maximize circulation of fresh air throughout the premises. 

For fan coil systems without outdoor air intake, the recommendation is to shut down the systems and not to use premises that rely on the fan coil ventilation system. Individual standing or office fans should also be turned off to prevent droplets from contaminating other people. As for indoor parking, ventilation systems should be turned on two hours before users arrive. Energy recovery equipment such as thermal wheels (rotary heat exchangers) can remain in operation. 

Applying these recommendations will have an impact on system operating costs. The quantity of outdoor air introduced into the building will increase, as will system operation time, both of which will increase energy costs. For example, for buildings with free cooling central ventilation systems, the additional annual energy cost would be approximately $1.85 per square metre. For buildings with outside air supply systems feeding fan coil units on each floor, the increase would be about $1.12 per square metre. 

Filtration and Cleaning

The SARS-CoV-2 virus is small, about 0.1 µm, similar in size to most viruses. For particles of that size, the ASHRAE 52.2-2016 standard recommends using MERV 13 level filters. They are suitable for the control of viruses and droplets in suspension. Adding MERV 13 filters to ventilation systems will create an additional loss of pressure, which must be compensated by an increase in fan power. The additional energy expenditure over one year will be approximately $0.83 per square metre.

There does not appear to be any benefit to changing duct cleaning practices during the pandemic. Existing maintenance plans may remain in place. The same is true for the frequency of filter replacement. The frequencies recommended prior to COVID-19 are thus still valid. On the other hand, additional protective measures should be taken when replacing the filters. Systems  should be shut down and filters placed in sealed bags. The person changing the filters should wear disposable gloves, eye protection and an N95 respirator mask.

Humidification 

Relative humidity of less than 40% can potentially contribute to transmission of the virus, which explains in part why influenza and cold viruses come back every year. Most commercial buildings maintain relative humidity levels between 20% and 30% to avoid condensation problems on the exterior envelope and to reduce energy costs. If the building can tolerate a relative humidity of 40% down to an outdoor temperature of -10°C, then 85% of the winter period will be in humidity conditions that reduce the life span of viruses. That change in humidity will increase annual energy costs by approximately $0.49 to $0.88 per square metre.

 

Yan Ferron, ing., P.Eng., M.Env., RCx
Certified passive building designer, director and partner
Pageau Morel et associés inc.

Membrer BOMA Québec's Integrated Technical Management committee.