ASHRAE Standard 90.1-2019: Air Curtains Allowed as Vestibule Substitute

Good news for building owners, engineers/architects, and HVAC contractors who can now save energy, construction costs, and space in commercial facilities with this latest approved code addition.

Doorway air curtains were approved June 25, 2019 as alternatives to vestibules on most commercial building entries in the upcoming ASHRAE Standard 90.1-2019Energy Standard for Buildings Except Low Rise Residential Buildings.” The professional association’s approved addition requires that the air curtain performance be tested in accordance with ANSI/AMCA Standard 220 to ensure it provides a minimum 400-ft/min. airstream velocity at the floor.

This is good news for retail, restaurants, healthcare, hotels, office, and other facility owners, because they can now opt to forego the expense of vestibules in new construction, or repurpose significant square footage for more productive uses by retrofitting existing vestibules. Consulting engineers and architects, who previously were hesitant to replace vestibules with air curtains due to inconsistent code language, now have the support of ASHRAE Standard 90.1-2019 which will be published this fall. Furthermore, HVAC contractors will see a spike in air curtain installations to accommodate facilities looking to prevent energy loss through their main entries and meet building codes. Air curtains also protect against the infiltration of outdoor air, fumes, flying insects, wind, and dust through open doorways, and contribute to occupant air comfort.

The addition’s “Air Curtain Effectiveness” task force was sponsored by AMCA (Air Movement and Control Association–International), an Arlington Heights, Ill.-based trade association dedicated to certifying manufacturers’ air performance statistics.

“This is the most significant recognition of air curtains as an effective energy conservation device since the International Energy Conservation Code (IECC) approved air curtains as vestibule substitutes in 2015.”

– David Johnson, president of AMCA, and director of engineering for air curtain manufacturer, Berner International, New Castle, Pa. 

Inclusion in ASHRAE Standard 90.1 required more than eight years of air curtain research and presentations. The IECC code and the high-performance overlay code, the International Green Construction Code (IgCC), helped initiate the path to Standard 90.1 acceptance by allowing AMCA-certified air curtains as substitutes for vestibules.  However, ASHRAE’s mechanical, building envelope, and other subcommittees required additional research of real-world air curtain situations such as wind loads and building pressure differentials on an annual national-weighted average basis. Subsequently, the subcommittees accepted AMCA’s commissioned research represented by three third-party lab studies by Montreal-based Concordia University professor, Dr. Liangzhu Wang. All three studies proved air curtains that maintained a minimum 400 ft/min. airstream at the floor (as per ANSI/AMCA Standard 220), were equally effective or better than vestibules in buildings 3,000-square-feet and larger.

On average, air curtain-protected doorways were proven to save total building energy usage by a factor of 0.3-2.2% more over that of vestibules.

AMCA Certified Product Seal
Look for the AMCA certification seal on product documents.

Decades ago, two-door vestibules were code-mandated to save building energy. Theoretically, they created an airlock as one door would open and close before the second door opened. However, the emergence of automatic door opening sensor requirements, smaller space-saving dimensions, and other infringements on vestibule effectiveness, helped make air curtains an attractive energy-saving alternative. On average, air curtain-protected doorways were proven to save total building energy usage by a factor of 0.3-2.2% more over that of vestibules, according to Wang’s studies. This illustrates they’re equal or more effective at separating outdoor and indoor environments regardless of door opening styles or cycles.

For a list of AMCA certified Berner air curtains recommended for the main entrance, click here.