Monitored labs can run overall air change
rates as low as 2 ACH when the air is clean, but can increase the airflow rates to 8 to 16 ACH when contaminants are sensed.
An additional standard of interest to designers of laboratories is ASHRAE Standard 129-1997, Measuring Air Change
Effectiveness, which provides a method for determining the age of air in a space (or how well the outdoor air in the space is mixed within the space).
After determining the total air volume flow into (or flow out of) the building cluster, the air change
rate of the building cluster can then be defined as,
Grade B can handle aseptic preparation and filling, and operates with a minimum of 40-50 air changes
The air change
rate is in both cases is equal to 4 [h.
Particularly for life sciences labs, air flow is often dictated by the minimum air change
rate for the space.
This analysis indicates that minienvironment cleanrooms may be operated at lower air change
rates without significantly affecting the cleanliness of the minienvironment, provided that the resulting higher particle concentrations in the cleanroom are of less concern.
When considering the operational air change
rate, it is important that the design air change
rate is correct for the activities and occupancy within the room.
In general, the discharge takes place through the chimneys and the compensation through the building body, which means that the air change
rate in the studied buildings depends on their air tightness.
This ventilation strategy uses sensors to monitor spaces for a range of pollutants, allowing minimum air change
rates during unoccupied periods to be reduced when pollutant levels are below some threshold value, saving thermal and fan energy related to once-through air.
Through comparing this result with the result of the ventilation measurement using the PFT technique, which determines the average air change
rate during the entire period, the air change
rate during periods of use--i.
The performance and energy efficiency of mini-environment cleanrooms depend on several factors including the design of mini-environment chamber, particle generation rate, associated air change
rates for the mini-environment chamber as well as for the surrounding cleanroom space, and location and number of airflow supply and air return in the space.