Thermal destratification is the process of mixing the internal air in a building to eliminate stratified layers and achieve temperature equalisation throughout the internal space. It is the reverse of the natural process of thermal stratification which is the layering of differing (normally rising) air temperatures from floor to ceiling.
In a stratified building, temperature differentials of up to 10 degrees Celsius can be found over a height of 10 metres on average. In extreme cases, temperature differentials of 10 °C have been found over a height of 1 meter. In a destratified building, temperature differentials can be reduced to 1 - 2 °C or less from floor to ceiling.An experiment with a 3 meter high room yielded a temperature difference of 0.86 °C. Computational fluid dynamics (CFD) may be used to calculate the distribution. A faster method is the Volume element method (VEM). The ASHRAE standard 55 (2004) prescribes 3 °C as the limit for the vertical air temperature difference between head and ankle levels. Local discomfort from warm head or cold feet is the primary reason for discomfort, not stratification per se which can be up to 6 °C without discomfort. A minimum of 23 °C at the feet and maximum of 26 °C at head was found comfortable in a test.
This method has the most benefits through its application in the HVAC industry and in heating and cooling for buildings and utility specialists DTE Energy found that "stratification is the single biggest waste of energy in buildings today." By incorporating thermal destratification technology into buildings, energy requirements are reduced as heating systems are no longer over-delivering in order to constantly replace the heat that rises away from the floor area, by redistributing the already heated air from the unoccupied ceiling space back down to floor level, until temperature equalisation is achieved. As a result, destratification technology has great potential for carbon emission reductions due to the reduced energy requirement, and is in turn capable of cutting costs for businesses. This is supported by The Carbon Trust which recommends destratification in buildings as one of its top three methods to reduce carbon dioxide emissions.
There are a number of types of destratification fan on the market offering varying degrees of efficiency and energy savings. Over the past few years destratification fan technology has moved on dramatically from the traditional paddle and box type fans to the new third generation Axial Turbine Fan.The more advanced systems maximise are capable of maximising the performance of existing heating and cooling systems and equipment, and are designed to be installed alongside all types of heating and cooling equipment to optimise the hot or cool air produced - creating uniform temperatures, whilst reducing energy costs and carbon emissions.
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