What is Thermal Destratification in buildings?
Over recent years many products have been introduced which reduce energy consumption in buildings. LED lighting, efficient HVAC (heating, ventilation and air conditioning) systems, sub metering, variable speed drive units, improved building fabrics etc. They all reduce the carbon footprint of a building and reduce energy bills.
However, one of the fastest growing and simplest energy reduction initiatives which can be installed into both new and existing buildings is THERMAL DESTRATIFICATION1, rated by the Carbon Trust2 as one of the top carbon reducing initiatives for any type of building.
The natural process of thermal stratification occurs in all buildings; it results in dramatic differences in temperature from floor to ceiling and wall to wall. Thermal 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. This means that HVAC systems have to constantly cycle on in order to maintain building interiors at a set and even temperature throughout.
HVAC systems are typically over-delivering either heating or cooling to compensate for this stratification phenomenon in an attempt to achieve a required temperature at working/operating level, which is normally only around 1.5 metres to 2 metres from the floor. This costs a lot of money and creates a lot of carbon.
As a result large amounts of wasted heat can build up unseen in ceilings where the difference in temperature can easily rise 14°C or higher than the temperature at floor level depending on floor to ceiling height. The higher the building the more extreme this temperature differential can be (Building Services Research and Information Association3). This heat is also increasing the Delta “T”4 between inside and outside, accelerating the rate at which hot air escapes through the roof.
This heat can easily be captured and reused by the installation of an efficient destratification fan system, which will balance internal temperatures and thus reduce the operation time and workload required of HVAC systems.
Many mechanical engineers will argue that good HVAC design will ensure no stratification occurs within a space or building but anyone who has worked in the roof space of a building will tell you that theory is not born out in practice! That is, no doubt, why thermal destratification systems (such as the Airius® system, www.airius.co.uk5) have been in such high demand in North America, Australia, Asia, the Middle East, continental Europe and here in the United Kingdom
Thermal Destratification Fans
Destratification fans will always compliment the HVAC system in any building as efficient air movement is the key to making sure an HVAC system operates to its maximum potential without wasting energy. Destratification fans can also reduce the amount of HAVC equipment required and some brands will also do away with the need for conventional and relatively inefficient duct work.
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, ineffective paddle and box type fans to the new third generation Axial Turbine Fan.Energy saving, personal comfort and indoor air quality (IAQ6) have become more important and new regulations have been introduced with that in mind. The latest generation axial turbine fan addresses the energy saving issue and is designed to be used in many more environments.
Destratification Fan Applications
Here in the UK major retailers such as Morrisons, Tesco’s, Sainsbury’s and John Lewis are utilising thermal destratification systems, saving significant amounts in operational heating and cooling energy. They eliminate hot and cold spots throughout their stores whilst also improving freezer and chiller aisle comfort levels (measurably increasing dwell times and removing fogging and condensation from fridge doors, quickly drying up floor spills and issues such as condensate drainage) with no impact on fridge or open freezer cabinet performance (Morrisons7, 2007, showed reduced temperature stratification in chiller aisles from 6-8°C to 1-2°C). Morrisons now specify thermal destratification in all stores.
The United States Navy also conducted its own research and found a 40 per cent reduction in energy consumption in two facilities implementing thermal destratification fans. (‘Thermal Destratification Technology at West Bethesda, MD’, April 2010 – International Energy Agency, www.iea.org8)
Paradoxically, thermal destratification also provides significant savings and comfort benefits during summer months by gently and efficiently circulating conditioned cool air fully within a space, significantly increasing HVAC system efficiency and user comfort so that set points can be raised minimising system cycling times, which also means less maintenance and wear and tear on HVAC systems. In addition, as the cool air which is normally sat at ground level is being circulated up to body level and throughout means HVAC systems no longer have to over deliver to compensate for the stratification […]
