All buildings require ventilation to keep the indoor air fresh and clean. With underfloor air distribution, fresh air is supplied at a low level, while exhaust air is extracted from the top of a room. If the room contains a heat source, then a temperature stratification develops and occupants are surrounded by fresh air in the lower part of the room, while warmer, stale air accumulates underneath the ceiling.
One might have expected the warmer air to be completely vented from the room when the ventilation flow is increased sufficiently. However, this had not been tested in the laboratory before.
PhD student Dan Toy and professor Andy Woods have now run laboratory experiments that show that the system retains the two-layer stratification even when the rate of ventilation of the room is very large. Their observations suggest that this is the result of turbulent mixing in the room associated with the kinetic energy flux supplied by the plume of hot air rising above the heat source.
Dan and Andy have developed a new model which accounts for this mixing, and which predicts the height of the temperature stratification interface in the limit of very large ventilation.
This article has now been published by the Journal of Fluid Mechanics, and is available here.