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.