Air conditioning: what actually is air change per hour?

In controlled environment rooms there is a specification for the number of air changes /hour. This refers to the volume of fresh air put into the room. The total volume of air let into the room in an hour for n air changesis given by nV m[SUP]3[/SUP]/Hr, where V is the volume of the room in m[SUP]3[/SUP].

What Ramani sir said is true.
Sir, just evaluate the statement that I am about to right. This doubt refers to the actual way air air leaves and enters the controlled volume.

Air flows in and out continuously from the air conditioner. We do not change it n times.


It can be calculated by multiplying
(mass flow rate) X (specific volume of air).

@Issue

There is a difference. What I refer to is the amount of fresh air from outside that is separately brought into the room (an equal amount is sent out also). What you refer to is the specification given for clean room air handling systems, where the volume flow rate of the of the blower is calculated by multiplying the room volume by the number of air changes. In this case the entire air is thrown out of the room and not recirculated.

However, it is not clear from Vignesh's post which situation is being considered. Since he mentioned air conditioning in the heading I gave the explanation for that otherwise what you said will apply.