For many HVAC contractors, updates to ASHRAE Standard 90.1-2019 “Energy Standard for Buildings Except Low Rise Residential Buildings” on air curtains this summer didn't exactly make for “breaking news.”
However, the newly-revised approval of air curtains as substitutes for vestibules is big news for mechanical engineers, commercial building owners and HVAC contractors.
The approval allows retail, health care, hospitality, office and other commercial building owners to retrofit vestibules and repurpose the space (anywhere from 40 to over 300-square-feet) for more productive uses.
Besides additional space, studies prove that air curtains are equal or more efficient than two-door vestibules as energy-savers. Also, air curtains protect against the infiltration of outdoor air, fumes, flying insects, wind and dust through open doorways.
Besides retrofit opportunities, HVAC contractors can recommend air curtains as value engineering advantages on new construction projects. Why? Because they are roughly 10 percent of the cost of vestibules in labor and materials.
Why air curtains are better than vestibules
Two-door vestibules have been an energy code conservation mandate for commercial buildings the last several decades. However, the concept’s efficacy depends on the sequential opening and shutting of doors manually or automatically in an entryway.
The vestibule maintains an air lock and discourages an open wind tunnel effect where conditioned air rushes through two doors open simultaneously. Unfortunately, the concept is easily defeated by both doors opening at the same time.
Air curtains are more effective. The technology draws interior air from the facility and discharges it through linear nozzles that "seal" the doorway. Meanwhile, non-turbulent air streams meet the floor approximately at the door opening threshold.
A properly sized air curtain can contain approximately 70 to 80-percent of the conditioned indoor air and return it to the space. Also, the air curtain separates the indoor/outdoor environments by maintaining AMCA-certified minimum velocities of 2.0 m/s (400-fpm) at the floor.
Typically, a limit switch activates them in conjunction with a smart controller (or factory-mounted controls) that includes a variety of opening and closing functions.
When the door is closed, the air curtain can provide supplemental heat from an optional on-board electric, gas-fired, steam or hot water coils.
Energy saving superiority over vestibules was proven with two third-party lab studies by Montreal-based Concordia University professor, Dr. Liangzhu Wang. The studies include, "Investigation of the Impact of Building Entrance Air Curtain on Whole Building Energy Use" in 2013, and "Energy Saving Impact of Air Curtain Doors in Commercial Buildings" in 2016.
On average, air curtain-protected doorways were proven to save total building energy usage by a factor of 0.3 to 2.2-percent more over that of vestibules, according to Wang’s studies.
The studies led to the ASHRAE 90.1-2019 changes. However, the standard stipulates that only compliant air curtains are those tested and certified in accordance with ANSI/AMCA Standard 220, which assures a minimum 400-ft/min. airstream velocity at the floor.
How to properly install air curtains
HVAC contractors, and sometimes electrical contractors, typically install air curtains.
Air curtains require 240V electric. They are generally hung by threaded rod from the ceiling or attached via brackets installed above the doorway.
HVAC contractors are preferred because air curtain can often include an internal hot water, steam or electric heating coil. The former two typically require mechanical hookups from a central plant.
Additionally, sheet metal contractors are also involved to fabricate and attach plenums that efficiently draw stratified high ceiling heat for redistribution back into the occupied zone.
Overall, ASHRAE 90.1-2019’s approval of air curtains as vestibule substitutes offers new business opportunities for HVAC contractors. And, if marketed correctly, HVAC contractors can easily take advantage of this new standard.
