Whether it is a supermarket, shop or business, the trick to lure in customers is to utilise sights, sounds and smells. This has led to most commercial buildings leaving their main doors open, to appear welcoming and increase footfall.   

However, operating this way comes at a cost – either by heating the building in winter or keeping it cool in summer. In fact, research from Cambridge University found that closing the main doors of a typical UK shop in winter can reduce energy consumption by as much as 50%, cutting annual CO2 emissions by around 10 tonnes [1].  

With sustainability at the top of the agenda, reducing energy consumption is now an important part of a business’s corporate responsibility. But what if a company wants to keep its doors open?  

Well, following the success of the EcoBlade, which reduces the energy consumption of supermarket fridges by 25%, Wirth Research have now developed AirDoor to help tackle this problem.

Keeping The Outside Air Out

Preventing the outside air from entering a building ensures a more comfortable environment for staff and customers and improves energy efficiency. ‘In cold countries keeping the outside air out reduces the need for heating and in hot countries, reduces the need for air conditioning, leading to energy savings,’ explains Rob Rowsell, Engineering Director at Wirth Research.  

‘The benefits are particularly significant in humid countries. The water rich air requires more energy to either heat or cool, and when it is cooled can cause moisture on the floor, creating slip hazards. Also, any refrigerators have to work harder to dry this humid air out and therefore consume more energy.’  Separating the outside and inside air also helps to improve safety. Slip hazards are further reduced because wind and rain does not circulate around the entrance. While airborne pollutants, sand or insects are also prevented from entering the building. 

Conventional Overdoor Air Curtains

The typical approach to stopping the outside air from entering a building, whilst keeping the doors open, is to install overdoor air curtains, blowers or heaters. These devices sit above the door and force temperature-controlled air vertically downwards. This attempts to create an air curtain across the door opening which acts as a barrier between the outside and inside air.

However, the distance between the blower and the ground means that the air curtain becomes progressively less effective as you move downwards. Consequently, outside air infiltrates inside at an increasing rate towards the floor; escalating the risk of slip hazards. Furthermore, these devices can require up to 18 kW [2] to operate, leading to high energy consumption and costs.

Introducing the AirDoor

To provide a more effective air curtain, which consumes minimal energy, Wirth Research have utilised their aerodynamic expertise to develop the AirDoor. ‘This is an archway that goes around the inside of the doorway, replacing traditional overdoor air curtains,’ explains Rowsell.  

‘Fans located around the arch blow jets of internal air across the doorway, creating a robust air barrier which prevents infiltration. Pressure sensors inside and outside the building measure the speed of the wind coming into the building and a controller automatically adjusts the fan speeds, within half a second, to match it. The net result is no airflow in or out of the store, keeping the inside air in and the outside air out.’

By exploiting the natural flow of air in this way, no heating or cooling elements are required. Therefore, the only energy consumed is the 1 to 2 kW necessary to drive the fans, compared to 18 kW for conventional overdoor air curtains.

Air Curtain CFD Analysis with HELYX

The key to developing this innovative archway was to fully understand the aerodynamic behaviour of both the external and internal air flows. To achieve this, the engineers at Wirth Research combined their aerodynamic experience with HELYX CFD software. 

‘We have always invested heavily in the latest CFD technology and computing power to model things in as much detail and accuracy we need,’ highlights Rowsell. ‘This ethos has come from our motorsport background where we optimised the aerodynamic performance of racecars for Formula 1, Le Mans 24 hours and IndyCar.’ 

‘Our approach is to go down to the finest resolution on every detail of a design so that our simulations can account for any changes,’ continues Rowsell. ‘This gives us the confidence to develop things digitally and know that the finished product will not only work, but also deliver the performance we promised.’ 

This strategy of using the finest resolution requires CFD software that can cope solving meshes consisting of hundreds of millions of elements in fast computational times. HELYX achieves this with its advanced hex-dominant automatic mesh algorithm which can run in parallel to create large computational grids. 

‘Having this fast, robust and reliable meshing means we can give the software whatever resolution geometry we want, and we know that it will capture the details with a good quality mesh and make a valid CFD prediction,’ says Rowsell. ‘Whereas poorer quality meshes can lead to instabilities so you can’t always trust the results.’

‘We’ve got our own queueing system as well, so we can run simulations on the cluster overnight, come in the next morning and the results are ready,’ continues Rowsell. ‘In those scripts we also have some additional checks on mesh quality as well as on the velocities, temperatures and pressures for automated quality control. This drastically speeds up throughput because our engineers are not wasting time second guessing whether the answer is right, instead they can believe in the results.’

How Much the AirDoor Can Save

The AirDoor is currently installed in a range of shops and supermarkets across the UK including Waitrose, John Lewis, Sainsbury’s and Morrisons. However, this device can benefit any building entrance or exit which is temperature controlled and experiences significant footfall.  

‘This can range from warehouses to office buildings,’ concludes Rowsell. ‘We have found that our mid-sized supermarket customers have saved up to 31% on their annual gas use. While some boutique retail stores have reduced their winter electricity costs by around 54%. The AirDoor can transform any temperature-controlled environment and improve comfort, safety and energy efficiency.’

References

[1] M.B., M.O., 2010. Interim report on the energy appraisal of retail units [Online]. University of Cambridge. 

[2] New 18kW Commercial air curtains [Online]. BN Thermic.