Thermal destratification is the process of mixing the internal air in a building to eliminate stratified layers and achieve temperature equalization throughout the building envelope. Thermal stratification in buildings Destratification is the reverse of the natural process of thermal stratification, which is the layering of differing (typically increasing) air temperatures from floor to ceiling. Stratification is caused by hot air rising up to the ceiling or roof space because it is lighter than the surrounding cooler air. Conversely, cool air falls to the floor as it is heavier than the surrounding warmer air. In a stratified building, temperature differentials of up to 1.5°C per vertical foot is common, and the higher a building's ceiling, the more extreme this temperature differential can be. In extreme cases, temperature differentials of 10°C have been found over a height of 1 meter. Other variables that influence the level of thermal stratification include heat generated by people and processes present in the building, insulation of the space from outside weather conditions, solar gain, specification of the HVAC system, location of supply and return ducts, and vertical air movement inside the space, usually supplied by destratification fans. Computational fluid dynamics can be used to predict the level of stratification in a space. Effects of thermal stratification In a study conducted by the Building Scientific Research Information Association, the wasted energy due to stratification increased consistently based on temperature differential from floor to ceiling (ΔT). The study indicates that stratified buildings tend to overheat or overcool based on the temperature at the thermostat, which tends to be lower than the overall heat energy present in the room. The study also showed that energy waste due to stratification was present at ceiling heights ranging from 20 ft. to 40 ft, and higher ceilings caused higher energy waste, even at the same ΔT. Since ΔT tends to be higher in taller ceilings, the effect of stratification is compounded, causing substantial energy waste in high-ceiling buildings. Definition of destratification Since stratification and the costs associated with it are linear, the definition of destratification will differ based on opinion and use case. Full destratification, or a 0° ΔT from floor to ceiling, is unlikely to occur in any building. Since the costs of stratification decrease linearly as ΔT approaches 5.4°F, and no study has yet looked at the effects of stratification below 5.4°F, it is not uncommon to consider any space