Question

minimum out side air changes per hour how to acheive

Answer 1

Air changes per hour, or air change rate, abbreviated ACH or ACPH, is a measure of the air volume added to or removed from a space (normally a room or house) divided by the volume of the space.[1] If the air in the space is either uniform or perfectly mixed, air changes per hour is a measure of how many times the air within a defined space is replaced.In many air distribution arrangements, air is neither uniform nor perfectly mixed. The actual percentage of an enclosure's air which is exchanged in a period depends on the airflow efficiency of the enclosure and the methods used to ventilate it. The actual amount of air changed in a well mixed ventilation scenario will be 63.2% after 1 hour and 1 ACH.[2] In order to achieve equilibrium pressure, the amount of air leaving the space and entering the space must be the same. A C P H = 60 Q V o l {\displaystyle \quad ACPH={\frac {60Q}{Vol}}} Where:ACPH = number of air changes per hour; higher values correspond to better ventilationQ = Volumetric flow rate of air in cubic feet per minute (cfm), if using Imperial units, or cubic meters per minute if using SIVol = Space volume L × W × H, in cubic feet if using Imperial units, or cubic meters if using SI.