Building Ventilation and Filtration

UC Berkeley is working to  make sure that campus ventilation and filtration systems provide appropriate air-borne pathogen risk mitigation. 

HVAC systems cannot prevent the spread of pathogens, but they can mitigate risk of infection by providing filtration and air exchanges.   Wearing a mask and being vaccinated are the most effective methods of increasing your personal safety.  

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.

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HVAC System & Ventilation

HVAC SYSTEM

Facilities Services has adjusted HVAC systems to provide the maximum possible outside air in most buildings.  We have also performed additional mechanical maintenance and repairs to ensure the continued function of the systems.

VENTILATION

Ventilation is the introduction of outside air into a space. Under normal operations, most HVAC systems recirculate some air to save energy.  The system will 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.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.

During the Covid-19 pandemic, Cal OSHA guidelines required the campus to “maximize ventilation and filtration” where feasible.   

Facilities Services accomplished this by changing most buildings to 100% outside air, meaning no recirculation, in all buildings in which the system can perform this way.  In the very few buildings which require some recirculation, the amount of outside air has been maximized as close as possible to 100%.  Some campus buildings do not have mechanical ventilation at all.  In most cases, these buildings have operable windows which can be used to provide air flow. 

Facilities Services replaces building air filters as necessary to keep them at their highest capacity. Additionally, FS performs repairs and preventive maintenance of fans and air handlers to make sure they are functioning as they should. 

Opening Windows & Doors

Opening windows and doors can be used to increase airflow in a space. Before doing so, it is important 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 the 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:

Before propping open doors, please consult Fire Prevention Services at ehs@berkeley.edu or (510) 642-3073. 

Many windows in campus buildings have restrictions in place. If you would like a restriction modified, please fill out the Window Change Request Form

Smoke

Wildfire events can create hazardous air quality.  In normal operations, campus buildings can be configured to limit outside air intake during smoke events to reduce the amount of smoke being pulled into a building.   Under Covid restrictions,  Cal OSHA guidelines require that outside air be maximized until the air quality index reaches 100.  At that point, Facilities Services will adjust the building ventilation systems to limit outside air where possible.  Some buildings, such as lab buildings, will remain on 100% outside air under all conditions.


For more information on campus operations during smoke events, please see the UHS website: UHS Wildfire Smoke/Air Quality

Filtration

Filters clean the air that moves through a mechanical system.  Each building has been designed to have a certain level of filtration, known as a MERV rating.  The MERV rating is part of the system design and cannot be increased without negatively affecting the system and its performance. 


A map of the MERV rating for campus buildings can be found here

Air Exchange Rates

Air exchange is defined as the number of times the air in a space is replaced in an hour.  UC Berkeley buildings were designed and built over many years and each met the code requirement for ventilation in its time period.

Many of our buildings  were built when specific ventilation and air exchange rates were not a requirement in the building code.   The buildings simply had to provide some fresh air, either mechanically or by operable windows.   Their systems were never designed to move a lot of air, unlike more modern buildings.  They do not have the internal systems or infrastructure to support high levels of air flow.

Modern buildings tend to have more mechanical ventilation and are able to move more air. On our campus, lab spaces must meet a requirement to have six air changes per hour when occupied but most other spaces are designed to meet much lower rates and the requirement is dictated by the type of use and the occupancy.  It can vary widely. 

In order to gather information about ventilation in GA classrooms, FS has performed physical assessments in higher density classrooms to determine the air exchange rates. 

Classrooms have been the focus of the assessments because they are used by groups of people.  

Other kinds of spaces, such as offices, are not being assessed as they already meet the Cal OSHA requirements for maximized outside air supply and increased filtration efficiencies. 

An important thing to note is that temperature and air exchange rates do not always correlate.  A room can have a high ventilation rate but if the air being moved is heated, the room will be hot regardless of the air exchanges. 

HEPA Filters

BACKGROUND

The campus response to the Coronavirus pandemic included a combination of protective measures with vaccination and masking being the most important. 

The use of high-efficiency purified air (HEPA) cleaners has been suggested by agencies like the California Department of Public Health (CDPH) and the Centers for Disease Control (CDC) for improving ventilation indoors when there is insufficient fresh air introduced by HVAC systems, or natural ventilation from windows.

While the use of HEPA air cleaning devices may reduce the presence of airborne viral particles in a room, their use should be carefully considered before using.

VENTILATION IN CAMPUS BUILDINGS

Facilities Services has increased the percentage of outdoor air in campus buildings where feasible, per CDC and CDPH guidance, as part of the multi-layer strategy to limit the spread of Coronavirus. There remain buildings without mechanical ventilation that rely on windows for fresh air that should be opened when spaces are occupied.  

WHEN TO USE A HEPA AIR CLEANER

The campus has generally assessed whether the use of portable or mounted High Efficiency Particulate Air (HEPA) filtration units, or other air cleaning systems, would reduce the risk of COVID-19 transmission and concluded that in some cases they should not be used because of the following: 

  • Air currents that can spread untreated air to other people in the space

  • Noise that increases with the fan speed

  • Maintenance and filter replacement considerations

  • Energy consumption and potential power failures

  • Theft of unattended devices

If you are interested in using filtration units, please contact EH&S at 510-642-3073 or EHS@berkeley.edu(link sends e-mail)(link sends e-mail) to assess if using HEPA air cleaners in your location would be helpful.  Please also contact Facilities Services at 2-1032 to submit a work order to confirm that your area has sufficient electrical capacity if several HEPA filtration units are to be considered.

  • Portable HEPA filtration units must be approved for use in California (look for the label CARB-compliant(link is external); this means they are tested for electrical safety and ozone emissions). 
  • Ensure the unit is sized appropriately for the intended space. Some large classrooms may require more than one unit. One method for selecting the appropriate size unit is checking that the Clean Air Delivery Rate (CADR) is at least 2/3 of the room's floor area (in square feet), with adjustments made for high ceilings. A list of units with CADR ratings can be found on AHAM's "Verifide"(link is external) website.
  • For classroom use, look for quieter models with a noise level < 50 dBA if possible.

In all cases, it is recommended that each use of a HEPA air cleaner be thoughtfully reviewed before purchase.  Remember that ventilation is only one part of many strategies that limit the spread of Coronavirus and other air-borne pathogens.  Weigh the above considerations before contacting EH&S to determine whether a HEPA filter could be an option.  

PORTABLE FANS

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.

RESOURCES

The following websites offer more information on HEPA air cleaner devices and COVID-19:

Corsi-Rosenthal DIY box filters  These Do It Yourself air filters offer a low cost option for filtering room air, but they don’t quite match the performance of a HEPA air cleaner. Materials to construct a Corsi-Rosenthal box filter include a typical 20” box fan, one or more pleated filters (preferably MERV-13 rated) to fit the box fan, and some tape to hold the filters in place.  There are different ways to construct these boxes. Here are a couple of resources:

DIY Box Filter - link requires CalNet Authentication

How to Build A Corsi-Rosenthal Box Filter (UC Davis)

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