Air change per hour and effective temperature

Air change per hour (ACH)

Air change per hour is the number of times the whole volume of air in a room is replaced by fresh air in one hour.

$$ACH = \frac{Q}{V}$$

where $Q$ is the volume of air supplied or removed per hour (m³/h) and $V$ is the room volume (m³). For example, a 4 m × 5 m × 3 m room with a supply of 360 m³/h has $V = 60$ m³, so $ACH = 360/60 = 6$. Typical values: living rooms 3 to 6, kitchens 15 to 30, toilets 6 to 10, assembly halls 8 to 12.

Effective temperature (ET)

Effective temperature is an index that combines dry-bulb temperature, humidity and air movement into one number. It is the temperature of still, saturated air (100 % RH, no air movement) that gives the same feeling of warmth or cold as the actual conditions. It is read from the ET chart (Yaglou and Houghton) using dry-bulb and wet-bulb temperatures and air velocity. The comfort zone is about 20 to 27 °C ET for most people, with the preferred ET at 22 to 25 °C.