Reduce doorway energy losses

As recently as 15 years ago, the use of air curtains–also known as air doors–was typically reserved for industrial settings or backdoor foodservice applications. Today air curtains are seen in retail stores, hotels, hospitals and office lobbies where they help to conserve energy, minimize flying insect control and enhance occupant comfort. In foodservice, air curtains are used to conserve energy at drive-through windows and walk-in coolers.

Air curtains are typically mounted inside a doorway and continually discharge a steady stream of air to separate indoor and outdoor conditions to reduce open doorway energy losses. They offer an alternative solution to forced-air cabinet heaters or the construction of an air-lock vestibule.

Many contractors and engineers have the misconception that air doors are useful only in winter to minimize energy losses and to add comfort with internal hot water or steam coils and electric heating elements. In fact, energy losses through open doorways in summer air conditioning months are typically more costly than during winter operation.

How Air Curtains Work

Air curtain technology draws interior air from the facility and discharges it through field-adjustable (+/-20 degree) linear nozzles that “seal” the doorway with a non-turbulent air stream that meets the floor approximately at the threshold of the door opening. A properly-sized and Air Movement & Control Association (AMCA) International certified air curtain can contain approximately 70 to 80 per cent of that air and return it to the space. Because the air curtain discharges air at velocities generally in the range from 1000 to 3000 ft/min., it effectively prevents outside air and flying insect infiltration. Volume, velocity and uniformity (VVU) of the air stream are critical factors in an air curtain’s effectiveness. Air curtains are typically activated by a limit switch that is triggered when the door opens and deactivated when closed.

Trend: Air curtains as vestibule substitute

Recent updates to the 2015 International Energy Conservation Code (IECC), which is published by the International Code Council (ICC), will allow certified air curtains as a vestibule alternative. In provinces and cities where the IECC’s provisions are adopted, contractors have the opportunity to spec air curtains in new construction and retrofit applications. The suggestion of substituting a proposed vestibule with an alternative such as an air curtain can bring value engineering to a project.

Studies, such as the computer-modeled research study, “Air Curtains: A Proven Alternative to Vestibule Design,” used computational fluid dynamics (CFD) analysis to prove an air curtain/automatic door combination is more efficient than a vestibule. The study compared conventional automatic two-door vestibules to an air curtain/automatic door entrance combination. It confirmed the latter was up to 10 per cent more energy-efficient in environmental separation performance, cost up to 75 per cent less in labour/materials and conserved anywhere from 4.6 to 186 m2 (50 to 2000 sq. ft.) of entryway floor space typically consumed by vestibules (see Figure 1).

In design/build situations, a vestibule could range from 2.3 to 26 m2 (25 to 250 sq. ft.) and larger in size. Using a general retail store construction cost of $150/ sq. ft., for example, a vestibule may be utilizing anywhere from $3,750 to $37,500 worth of space that could be used for product display.

The IECC-2015 code also stipulates air curtains must be tested in accordance to standard ANSI/AMCA-220 and certified by the Air Movement and Control Association-International (AMCA), Arlington Heights, IL, a not-for-profit organization that tests and certifies manufacturer’s stated performance of fans, blowers, air curtains and other air movement devices.

For retrofits, air curtains can make a vestibule re-use possible by retiring the space from traffic and using it for merchandising.

Foodservice Air Curtain Innovations

HVAC/R contractors with refrigeration and/or HVAC foodservice customers can help save them energy, increase sanitation and provide more employee air comfort with air curtains designed specifically for drive-through windows, walk-in coolers and front entrances.

Air curtains are not foreign to foodservice. For decades they were typically used only on foodservice back entrances to eliminate flying insects and improve overall sanitation near the shipping and kitchen areas.

Walk-in cooler air curtains have been proven to surpass the energy-saving potential of alternatives, such as swinging hinged doors and strip curtains, and they produce a quick payback of less than two years, depending on the amount of door cycles. While they are now predominantly appearing as options on new models from walk-in cooler manufacturers, several air curtain suppliers make retrofitting easy with a kit that includes an air curtain designed specifically for the unique size and configuration of walk-in coolers. Included in some kits are a pre-wired 24V control/load centre in a small enclosure and a magnetic reed on/off door switch. Once 120V power is extended to the area, the pre-wired kit can be installed in as little as 15 minutes with conventional tools and basic electric knowledge.

Besides walk-in coolers, another trend in the foodservice and restaurant industries is the new drive-thru window air curtains, which are being used for a variety of purposes in some locations of restaurant chains such as Tim Hortons and McDonalds in Ontario; and Harvey’s in Alberta. They minimize flying insect and outdoor air infiltration, protect the indoor drive-thru station employee from idling vehicle fumes as well as cold air in winter climates, which are health and employee comfort issues, respectively. The U.S.’s Occupational Safety and Health Administration specifically recommends a “reverse-flow fan system” at the www.osha.gov website’s, “Teen Worker Safety in Restaurants” page.  <>

Sites to see

Air curtains are important features in other recent building and retrofit projects across Canada. Check them out if you are in the neighbourhood.

• The Gateway Mail Processing Plant of Canada Post Corp., Mississauga, ON, has five air curtains with photo sensor activation. Installed for environmental protection and employee air comfort by Hawraz Mechanical System Inc. of Mississauga, ON, the air curtains were sold through the western provinces office of manufacturer’s representative, Square-M Group, Burnaby, BC.

• Calgary International Airport recently had 37 10-foot-long and two eight-foot-long air curtains installed for environmental protection and baggage handling, respectively, by contractor, Trotter and Morton Building Technologies Inc. in Calgary, AB.

• Salle André-Mathieu theatre at the College of Mont Morency, Laval, QC uses six-foot-long, in-ceiling mounted air curtains to keep people warm who fill the lobby and to counter the effect propped open entrance doors before productions begin. Designed by Marcel Provost, ing, principal at MLC Associés Inc. in Laval, QC, and installed by Serge Chabot

& Fils Inc. of Marieville, QC, the air curtains also have thermostatically-controlled 20-kW heating coils with modulating devices. These solutions call for the heating coil’s full 20-kW capacity when the lobby temperature drops 1.1C (2F) or more below the set point.

• The Calgary location of trucking company Coastal Pacific Xpress needed 16-foot-long air curtains in a tractor and trailer wash stall entrance to keep equipment from wintertime freeze-ups. Luckily, 16-foot-long single-construction air curtain designs had been developed to surpass the former standard of 12-foot-long lengths. The length was the difference that helped score a sale for Bill Myles, president of the eastern provinces office of Square M Systems, a Richmond Hill, Ontario-based manufacturer’s representative for IAQ and energy-saving products. Shorter modular units bolted together in tandem wouldn’t have been possible for the installation and also would have obstructed the required perfect airstream needed for environmental separation.