Air curtains and energy efficiency

Air curtains are the final complement in an energy efficient building system.

Air curtains are the final complement in an energy efficient building system.

Correctly operated, they can make a building warmer, safer, and more economic to maintain.

Marianne Sibborn of Airbloc explains.

Overdoor air curtains have a very straightforward purpose - to keep warm air inside the building and cold air out (and vice versa in warmer weather, or if the building is air conditioned).

In doing so, they actually achieve much more, not least by enhancing the economic operation of other building systems.

And with increasingly stringent regulations on building efficiency, both from the UK government and Europe, this is becoming a highly significant element in construction and specification.

The trick is to select the right energy efficient air curtain for the doorway.

Most commercial and industrial buildings - whether it's a hotel, office block, supermarket or manufacturing plant need to keep external doors open for some proportion of working hours to maintain the smooth flow of people and goods.

For some businesses, it is important to create a warm, welcoming entrance environment to encourage footfall.

Others, such as distribution centres, train maintenance sheds or aircraft hangars, may require 24-hour door opening, making internal conditions uncomfortable for personnel during cold weather spells.

The moment a door opens, external air floods into the interior, creating a wind tunnel effect and immediately impacting on comfort levels.

In heated buildings, cooler, denser air flows in through the bottom half of the door opening, while warmer internal air flows out at high level.

In warmer weather, when internal air is cooled, the reverse occurs.

Heating or air conditioning systems have to work twice as hard to restore the working environment.

If the doors are in constant use, opening and closing throughout the day, most heating or air conditioning systems are unlikely to cope effectively.

Overall energy consumption increases as internal temperatures fluctuate.

An air curtain can prevent such extremes of environmental change.

Studies have shown that premises without an air curtain show appreciable fluctuations in temperature of between 4C and 10C within the building.

With an air curtain, a difference of only 1C is the norm.

Low energy solution Air curtains work by forcing a 'sheet' of air across the entire doorway.

This forms a barrier that deflects the natural convection airflow, so that gusts of wind cannot penetrate.

Similarly, dust and small flying insects cannot get through - an important factor in protecting doorways to food storage or preparation areas.

To achieve energy efficiency levels high enough to impact the economic running of heating or air conditioning systems, the air curtain must, like Airbloc models, be designed to deliver air across the doorway at critical velocity, volume flow and temperature.

These factors affect the air curtain's capability to deflect external air.

Air jet width and pattern of the airflow are also crucial.

Optimum performance is achieved when the flow across the door is uniform and linear, and when fan speed can be finely controlled.

It is particularly useful to have extra width adjustable air jet for improved wind resistance.

Additional economies can be gained when the air curtain is used to supplement the heating system.

This can be achieved in one of two ways, depending on whether the air curtain is heated or ambient.

When doors are closed, the unit operates at low speed to provide additional heating - ie.

it simply delivers warmed air into the building.

Alternatively, the air curtain can be configured to redistribute warmed air that has risen to high level.

This is a particularly effective method of maintaining comfort conditions in the doorway area, as Airbus Aerostructures found at its Broughton plant.

Flexible and versatile Air curtains are available in three heated forms, powered either by gas, electricity or low pressure hot water.

Ambient models are unheated and are deployed to perform the air curtain's primary purpose of maintaining stable internal temperatures.

This variant is typically installed in spaces where an effective heating system is already in place and there is a requirement to prevent external air from entering the building.

In most applications, the air curtain can be positioned discreetly and unobtrusively above or, in the case of large industrial buildings, down the side of the doorway.

Recessed and surface-mounted models are available for commercial premises.

A recessed air curtain, such as the Airbloc ACR, can be mounted in bulkheads and above false ceilings to serve a doorway without obtruding on the eyeline or aesthetics of the entrance.

A smaller ceiling tile version, such as the Airbloc ACT, will provide effective protection across doorways, yet fit neatly into modular t-bar ceiling tile systems.

The selection of surface-mounted or recessed will depend on the requirements of the building and its use.

In applications where the aesthetics of the air curtain are crucial, some models, such as the Airbloc AC, are available in a range of colours and finishes to match the interior, as the owners of Baroosh Bar in Uxbridge discovered.

This model also complies with Health and Safety regulations for emergency lighting and audible alert, and can be backlit to display company logo or venue name.

Safe environment When safety is an issue, an air curtain can be a useful complement to the protection of personnel and equipment, particularly when used as an alternative to a high-speed roller-shutter door.

With an air curtain, there is no danger of the door trapping employees when it shuts.

It cannot jam during operation and cannot be damaged by fork-lift trucks.

The result is uninterrupted work flow throughout working hours.

Add to this estimated seasonal fuel savings of up to GBP16k in cases where very large doorways are open constantly during winter, and the case for energy efficient air curtains becomes compelling.

Whatever the application, air curtains will retain warm or conditioned air within the building, ensuring that less burden is placed on the heating or air conditioning system.

In a building with high performance services and good insulation levels, the air curtain is the final piece of the jigsaw that completes its energy efficiency credentials.

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