Ventilation & Filtration

Building Ventilation and Filtration

This webpage provides information about the heating, ventilation and air conditioning (HVAC) systems in our buildings and how we are managing them in response to major events such as the COVID-19 pandemic.

Because many buildings are connected to a centrally controlled HVAC system, building occupants have little ability to modify their systems, including increasing ventilation or filtration. UC Davis Facilities Management is evaluating the performance and capabilities of these HVAC systems individually, prioritizing buildings with currently higher occupancy levels.

HVAC Systems

The coronavirus spreads primarily through respiratory aerosols and droplets produced through breathing, speaking, coughing and sneezing. The risk of transmission by droplets and aerosols generally decreases as the distance between people increases, since large droplets fall and aerosols are diluted. Wearing masks or face coverings helps to decrease the risk of direct person-to-person transmission.

HVAC systems cannot prevent the spread of the coronavirus, but they can mitigate risk of infection in the following ways:

1. Air Exchange Rates

Over time, respiratory aerosols can build up in rooms. The time aerosols spend in a given room is largely controlled by a room's air exchange rate, typically characterized as the number of air changes per hour. In a typical room on campus, the number of air changes per hour varies based on space and system type, but is typically 4 air changes per hour or less for offices and 6 air changes per hour for laboratories.

2. Ventilation

Ventilation is the intentional introduction of outside air into a space to improve air quality. Many HVAC systems recirculate some air to save energy, and mix in some outdoor air based on the code requirements for the space type and its designed occupancy (a typical ventilation rate is 15 cubic feet per minute of outdoor air, per person.) In these systems, both the outdoor air and the recirculated indoor air are filtered by the HVAC system before being supplied to the occupied spaces.

Other HVAC systems (primarily those serving lab and animal spaces) operate at 100% ventilation rates, meaning they supply only outside air to occupied spaces and do not recirculate any air.

Airflow through a laboratory space is 100% outside air.

See how heating and cooling works in different types of spaces.

Check out animated graphics of HVAC systems in laboratory (wet labs) and non-laboratory buildings to see how they bring in ventilation and filter air supplied to occupied spaces.

3. Filtration

We also maintain air conditioning and ventilation systems and replace air filters on a schedule throughout the year. Filtration further mitigates risk of transmission in buildings with recirculated air. As air moves through a building's HVAC system, air filters trap and collect large and small particles such as dust, allergens and microorganisms.

Many of our buildings are already served by systems with MERV 13 rated filters. Systems with lower rated filters (typically MERV 8 or 11) are being evaluated for upgrade where feasible. Upgrading HVAC system filters is not always feasible due to system limitations.

Learn more about MERV Filter Ratings
MERV stands for minimum efficiency reporting value (MERV) and the rating number is a measure of how effectively the filter stops dust and other contaminants from passing through the filter and into the air stream. Filters with higher MERV ratings are denser and trap small particles more effectively than filters with lower MERV ratings.

In general, filters with a rating of MERV 16 or below are considered to be HVAC-system-grade filters for residential, commercial and general hospital use. MERV 17 through MERV 20 filters are typically used in surgical operating rooms, clean rooms and other contexts that require absolute cleanliness.

4. HVAC System Evaluation

Below you will find a link to more information about the specific ventilation and filtration levels of the HVAC systems serving campus buildings. Systems serving classrooms are listed first.

Building-Specific Information

Key: RA = recirculated air and OA = outside air
Drill down to learn more about the ventilation and filtration units in hundreds of campus buildings in this table created by Facilities Management's Energy and Engineering office. This team will continue to add details including descriptions of the specific areas served.

If your building is not listed, if you need more information about the unit serving a specific room or area in your building or you have questions about your HVAC equipment's settings and capabilities, please contact us.

5. Desk and Floor Fan Use

Although fans can increase ventilation if installed where they bring in outside air, fan use is not recommended anywhere multiple people may be present in an indoor environment. A fan blowing across a sick person can increase risk of infection for others in a room. Learn more in article: UC Davis experts detail common mistakes about COVID-19.

6. Opening Windows & Doors

This may be possible depending on your space, but you’re encouraged to consider that:

Opening a window or propping a door open may not necessarily improve air circulation (e.g., it depends on outdoor air currents and whether a cross-draft can be achieved by opening windows or doors on opposite sides of room).
Opening a window or door may interfere with the ventilation provided via the HVAC system by changing the pressurization or air balance of the room. It could also cause other spaces served by that system to be overcooled or overheated if unconditioned outdoor air affects a thermostat.
Opening windows and doors presents other security and cleanliness issues (e.g., dust, particulates).

For fire prevention and life safety reasons, do not prop open:

Entry doors
Security access doors
Fire doors | read SafetyNet on fire door regulations
Laboratory doors
Doors to rooms with fume hoods

Before propping open doors, please consult Fire Prevention Services at fireprevention@ucdavis.edu or (530) 752-1493.