Doorway Air Curtains for Commercial, Retail and Industrial Applications

Air curtains minimise the amount of cold air entering a building while keeping the warm air inside. However, misconceptions surrounding their use and a lack of knowledge and understanding means that products aren’t always specified or installed correctly – reducing or even negating the benefits. Here Graham Cree, UK sales manager at Thermoscreens, dispels some of the myths, and explains how electrical wholesalers can help to ensure that air curtains deliver the savings they are designed to achieve.

When specified, designed and installed correctly, air curtains minimise the amount of cold air entering a commercial building, while keeping the warm air inside – saving energy and increasing comfort.

They can be installed on any frequently used entrance, but typical applications include high street stores, shopping centres, hospitals, hotels, banks, factories, warehouses, pubs and clubs, restaurants and airports.

If a frequently used door doesn’t have an air curtain, heat will naturally escape each time it is opened. Because of natural convection, warm air will be pushed out at the top, being replaced by cold air coming in at the bottom.

Air curtains work by disrupting and minimising natural convection, and provide a continuous stream of air circulated across a doorway serving a conditioned space. The incoming cold air is conditioned to reach a temperature of around 20-25°C, with the warm air being derived from various sources, such as direct electric heating and low, medium or high pressure hot water.

Thermoscreens, for example, has developed a range of air curtains to work with 60/40°C low pressure hot water (LPHW) condensing boilers. These have been fitted with larger heating coils to increase their efficiency and allow them to perform to the same standards as air curtains designed for 82/71°C LPHW applications.

An air curtain’s main benefit is that it will reduce the amount of heating required, leading to lower energy usage/costs and lower carbon emissions. It’s estimated that an average double doorway could be losing as much as 32kW of energy every hour, and at 10p per kWh this can equate up to £7,000 worth of energy each year. By installing an air curtain, wastage can be cut by up to 70 per cent.

In addition, because air curtains provide a constant environment around the doorway, employees and also visitors/customers will be comfortable – which is especially important in retail environments.

However, air curtains can only deliver energy savings and comfort if they are designed, sized and installed correctly. And, unfortunately, several myths and misunderstandings about how air curtains work, and how they should be installed, have resulted in a significant number of poor installations.

This is a major concern; the effect that a badly designed, selected or installed air curtain can have on energy consumption can actually be worse than not having an air curtain at all.

In addition, these substandard installations are potentially having a negative impact on the air curtain market. Indeed we hear of some businesses complaining that their air curtain doesn’t work properly and isn’t saving them energy or money – but this usually comes down to poor specification, design and installation practices.

So leading manufacturers are committed to helping architects, specifiers, consultants, contractors and installers to learn more, and we endeavour to provide assistance, guidance and Computational Fluid Dynamics (CFD) illustrations to predict energy savings.

However, with electrical wholesalers being a key source of information for anyone purchasing air curtains, it’s worth getting clued up about some of the issues.

One of the biggest problems we are trying to combat is that air curtains are often incorrectly used, with people treating them as space heaters. While there are over-door heaters available on the market, an air curtain isn’t a heating appliance. An air curtain can contribute to the heating around an entrance because the air stream is warm (unless it’s an ambient/no heat model), but it should only ever work alongside a building’s heating system – it shouldn’t replace it.

There are also installation issues to address. Air curtains are usually fitted horizontally over a door, but are sometimes mounted vertically to the side. However, it’s important to note that an air curtain must be installed inside the doorway, as close to the opening as possible. It must also be just wider than the doorway opening with an overlap at both sides (or at the top if it is a vertical installation). Air curtains should always be specified on the size of the door rather than the kW output.

The design of the air curtain must be suitable to discharge air across the whole height and width of the opening at a supply air temperature that is acceptable for the comfort of those passing through the doorway. Meanwhile, the heat output of the air curtain must be sufficient to temper the volume of air coming in at the entrance.

It is really important to get this jet stream right; if it has too little velocity or is too powerful it won’t be effective. Advice can be found in BSRIA Application Guide 2/97, Air Curtains – Commercial Applications, which includes an engineering design procedure for calculating the supply air flow and thermal capacity of an air curtain.

Anyone specifying an air curtain should also be advised that the characteristics of the building and the outdoor and indoor climate conditions must also be considered, as well as voltage and power supply.

In terms of the products available, electrical wholesalers should find there are plenty of options to recommend, at varying price points. Air curtains can be surface mounted or recessed and are generally available in 1m, 1.5m and 2m lengths – but can be seamlessly joined together if required. Brushed stainless steel is a popular finish, but they can be powder painted in a range of colours if required. We find that many retail stores are keen for them to blend into their entrances or colour schemes.

When an air curtain is purchased it’s also worth recommending the use of controls. As well as being an additional revenue stream for the electrical wholesaler, the end user benefits from reduced energy usage.

Controls are a major area of focus for the air curtain market. Thermoscreens, for example, has just introduced the Ecopower Plus controller, delivering savings in the region of up to £1,466* per year. Ecopower Plus utilises a thermistor sensor to automatically adjust the temperature of the air curtain to meet the desired room temperature – typically 20°C. This minimises the demand for energy, reducing usage and thus costs for the air curtain operator, and lowers carbon emissions. Ecopower Plus also includes an outdoor sensor for weather compensation control, so the air curtain can react to external temperatures.

Air curtains significantly reduce energy consumption and carbon emissions by minimising the amount of cold air that enters a building. However, for energy savings to be achieved, air curtains must be designed, selected and installed correctly – and with specifiers, consultants, contractors and installers often turning to electrical wholesalers for advice, it is definitely worth learning more.

Data obtained from a study of Temp Control test results and 2005 ASHRAE Handbook – Fundamentals (SI), mean temperature for heating season 9.8°C