What Are Destratification Fans?

BSRIA Test Report Showing the Effectiveness of Airius Destratification

So how exactly can destratification fans benefit buildings?

We all know that hot air rises but what some of us don’t know is why.

Usually, the air at the ceiling is warmer than the air at the floor.

This is basic physics.

Destratification fans reverse this phenomenon.

The term ‘Destratification’ relates to a process called Thermal Stratification, which is a naturally occurring phenomenon whereby temperature gradients in a space, created simply by natural convection, often result in a temperature difference between the roof or ceiling and the floor.

Thermal Buoyancy

So, what is thermal buoyancy and how does this work?  In enclosed spaces cold air, which is denser and therefore heavier than warm air, will sink to the lowest point, pushing the lighter, warmer air upwards through displacement. This warmer air will continue to rise up to the highest point in the space, which is usually the roof or ceiling.

The outcome of this process is that you end up with a temperature difference between the floor and ceiling, known technically as the ‘Delta T’’ or the thermal differential between floor and ceiling temperatures.

This thermal difference is caused by a range of factors, including the temperature of the air you are supplying into the space  (known as supply air temperature) or just the existing air temperature and the height of the space. The warmer the supply air temperature and the higher the space, the greater the accumulation of warm air at your roof or ceiling.

Additionally, stratification can also be affected by factors including the building shape, type and area, floor plan layouts, weather, as well as any type of artificial heating or cooling.

Differences in temperature from floor to ceiling can vary from 2°C to 10°C or more.

During the cooler months of the year, temperatures in the space usually need to be increased to improve thermal comfort for occupants, removing uncomfortable chill from the space.

In winter, due to stratification, people who are working or living in say a mezzanine floor usually find they are warmer than those living or working at floor level. A great example is when one has to climb up a ladder to change a light globe. As you ascend the ladder you can experience the temperature becoming warmer and warmer. That is because the warm air has risen up to under the roof or ceiling.

Or when you walk up the stairs at a house or building you can feel how much warmer it is up higher in the space than at the floor level.

That is thermal buoyancy creating ‘stratification’.

The higher the space the greater the thermal buoyancy and the more stratification there is.

Let’s put this theory in practice.

Imagine its winter and the outside temperature is 10°C. Your building is 5 metres high and you want the inside temperature to be 22°C.  (A typical thermally comfortable temperature in a building) Your heater is running at full capacity however, you find that your floor temperature is only at 16°C even though the roof temperature is 35°C.

This is because all that warm air that is being supplied to the space is continually rising up to sit under the roof or ceiling where it escapes through the roof , creating minimal effect on the building users.

This is a bit of a loose, loose situation because 1) you’re still feeling cold and 2) your power bill is through the roof (no pun intended).

This is stratification at its worst, causing expensive over delivery of warm air just to ensure comfort at ground level.

If you could get that warm air to the floor easily, then your supply air temp can be reduced and the related heating load will drop significantly, because you are harnessing all that heated air up at the ceiling and gently pushing it to the floor continuously, optimising thermal comfort.

Cross Section Diagram Of How The Airius Destratification Process Works

Destratification Fans

Destratification fans reverse stratification. It is the process of pushing the lighter, warmer air down to the floor and mixing it at floor level.

By destratifying spaces and circulating all the warm air sitting under the roof or ceiling back down to where it is needed, you can significantly reduce your heating costs, as you are no longer oversupplying or wasting warm heated air to ensure comfort. Continue this throughout the heating season and huge savings can be made on a building’s energy costs.

Gentle circulation of lighter, warm air back down to the floor, through the heavier, denser cool air, and mixing it thoroughly, has the greatest winter comfort outcomes for building users.

There are a few methods that achieve this, either via the use of specifically designed circulation fans or by the use of expensively designed air conditioning systems.

With stratification, no matter how you place warm air into a space, either at floor or roof level, it will always rise to the top of that space. A large amount of cost in design and equipment is often allocated to ensuring that air conditioning systems master this phenomenon, but it is often not very successful or is very expensive to purchase and operate.

When destratification techniques are implemented, winter comfort is improved and heating bills significantly reduced, in most cases by a minimum of 20% but we have also recorded savings of up to 50% and more.

Internal comfort temperatures are reached faster and at a much lower cost. Building users are much happier.

For example, when you are destratifying a space, your supply air temperature may now only need to be 18 Deg. C.  to ensure a comfortable internal temperature, instead of the 30 Deg. C. plus you were pumping into the room previously.

BSRIA Test Report Tests On Airius Destratification

BSRIA Report Showing a Stratified Room
BSRIA Report Showing Room After Airius Destratification

Thermal Loss

Another downside of stratification is related to the accumulation of heat at the top of the space, creating a greater ‘Delta T’ between indoor and outdoor temperatures.

As basic physics tells us, thermal energy always transfers from hot to cold to equalise. The greater the ‘Delta T’ or difference between warm and cold temperatures, the faster the rate of heat transfer.

Therefore, if you have a stratified space with a roof or ceiling temperature of 35°C and the outdoor temperature is 10°C giving a Delta T of 25°C, then the rate of heat loss through the roof is much faster, than if the roof and floor temperature difference was only 5°C.

By destratifying the space, you are significantly reducing the temperature difference between the roof zone and the outside temperature, thereby significantly reducing the amount of heat loss through the roof.

This is applicable regardless of insulation ‘R’ or ‘U’ values. With higher insulation levels the rate of heat transfer is slower but it still occurs, causing significant loss of all the heat you have been supplying to the space.

The Worlds Most Popular Destratification Fan Range From Airius

Airius – The World’s Leading Destratification Fan & Airflow Circulation System

Destratification is usually carried out using fans, but only the Airius® range of patented air turbine destratification fans are able to destratify at floor level. This is what they are designed to do.  All other fan types mix and destratify the air primarily at ceiling level, often resulting in poor outcomes and large amounts of noise or air movement.

One of the key success indicators of a successful destratification fan system is the ability to gently force the higher warmer air down to the floor. This easier said than done.

Certainly, if you apply large amounts of power and volume to a space you may achieve destratification, but the higher the space and the greater the temperature difference, the harder it is for a non-turbine type fan to force lighter, warmer air down to the floor.

Competing systems include large, bladed fans as well as cheap, tube type fans, but they all struggle to ensure the lighter (cooler) air is successfully forced to the floor and also evenly mixed across the floor zone despite consuming vast amounts of energy and creating loud, disturbing levels of noise – See this demonstrated in comparison testing here. You can also view our full library of destratification fan comparison tests on our Videos page.

Some of the cheaper tube or bucket type destratification fans, because they are simply a fan in a tube with a  poorly engineered or non-existent air delivery mechanism, don’t have the thrust or the efficacy to push that lighter warm air anywhere down near the floor. Therefore, they cannot effectively destratify and they also will not effectively mix the air across the space. This may result in cold spots and areas of discomfort.

Effective destratification is a very simple and low-cost solution to massively improve comfort and save large amounts of heating energy in colder winter climates.

Ranked by the Carbon Trust UK as one of the top three energy saving initiatives in buildings, it is recommended that if you have high heating costs, uncomfortable building users in winter or both, to consider the use of a suitable destratification fan solution.

Returns on investment are very short and can be often under 24 months.

Destratification has been successfully implemented in a huge range of facilities including Supermarkets, Sports Halls, Climbing Gyms, Indoor Pools, Theatres, Museums, Aircraft Hangars, Green Houses, Gymnasiums, Big Box retailers, Airport Terminals, manufacturing and warehousing and numerous other facilities or building types.

For more information regarding the Airius destratification system, or if you would like to discuss how Airius destratification can benefit your building please feel free to contact us on +61 (2) 6608 2736 or email info@airius.com.au.
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