What Are Air Changes Per Hour?

Ventilation times = room air supply volume / room volume, the unit is times / hour. The number of air changes is not only related to the nature of the air-conditioned room, but also to many factors such as the volume, height, location, air supply method, and degree of indoor air deterioration, which is an empirical coefficient.

The number of air changes is an important parameter for measuring the dilution of the space, that is, the degree of mixing achieved by the dilution, and it is also the basis for estimating the ventilation of the space. For a function-determined space, such as a building room, you can find the empirical value of the number of ventilations by checking the corresponding data sheet, and estimate the ventilation volume of the room based on the number and volume of ventilations. ^[1]

Two types of tracer gas methods are commonly used to measure the number of ventilations: ascending method and descending method. ^[1]

The ventilation times of residential buildings should be selected according to Table 1, and the ventilation times of hospital buildings should be selected according to Table 2. ^[2]

Table 1 Minimum ventilation times for residential building design

Living area per capita	Number of air changes per hour
10	0.70
10 <20	0.60
20 <50	0.50
> 50	0.45

Table 2 Minimum ventilation coefficient of hospital building design

Function room	Number of air changes per hour
Clinic	2
Emergency room	2
pharmacy	5
Radiation room	2
Ward	2