Figure 1.

Schematic illustrating ventilation flows with the various flow elements such as the body plume, inlet flows, stratification and arrows indicating entrainment and mixing. (a) Mixing ventilation, the hot air rises to the ceiling and, except near the inlets and vents, the indoor conditions remain approximately uniform. (b) Displacement ventilation when the occupant does not wear a mask. The secondary breathing plume stratifies below the hot upper layer, and the fluid in the secondary layer gets entrained into the body plume and exhausted out of the indoor space. (c) Displacement ventilation when the occupant wears a mask. In this scenario, near its origin, the breathing plume gets caught into the body plume and exhausted out from the upper layer. (d) When we turn off the mechanical ventilation input and instead open the doors and windows of space with a top-level opening, ignoring the effect of the wind, it effectively creates a displacement ventilation scenario (here shown when no mask is worn).