Doorway air curtains were approved June 25 as alternatives to vestibules on most commercial building entries in the upcoming ASHRAE Standard 90.1-2019 “Energy 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.
The approval is good news for retail 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. Vestibules cost construction projects for retail stores, healthcare facilities, hotels and other commercial buildings upwards of $100,000 per site. Air curtains cost less than 10% of a vestibule’s expense.
Consulting engineers and architects, who previously were hesitant to supplant 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., US-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,” says David Johnson, president of AMCA, and director of engineering for air curtain manufacturer Berner International in New Castle, Pa, US.
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: 1) Investigation of the Impact of Building Entrance Air Curtain on Whole Building Energy Use in 2013; 2) Energy Saving Impact of Air Curtain Doors in Commercial Buildings in 2016; and 3) Wind Effects on Air Curtain Aerodynamic Performance in 2018 (also co-authored by Ted Stathopoulos). 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-sq.-ft. and larger.
Decades ago, two-door vestibules were code-mandated to save building energy. Theoretically they created an air lock 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 to 2.2% more over that of vestibules, according to Wang’s studies. This illustrates that they’re equal or more effective at separating outdoor and indoor environments regardless of door opening styles or cycles.