By Stephen Benes, Regional Sales Manager, Berner International Corp.
HVAC trends are point toward an increasing amount of consulting engineers that specify air curtains for healthcare applications to reduce their clients’ operational costs.
However, those specifications are not the common shipping door or foodservice back door air curtain applications to prevent flying insect infiltration. Instead, air curtains have expanded to the front door, emergency room door and even foodservice walk-in cooler doors
to reduce energy costs.
The trend toward the front doors is very apparent to Don Peterson, P.E.,
a principal at consulting engineering firm, Robert G. Burkhardt & Associates, Chicago, which specializes in total HVAC design for healthcare facilities.
Burkhardt, which has specified HVAC for dozens of projects including Central DuPage Hospital, Winfield, Ill., Edward Hospital, Naperville, Ill., and Saint Joseph Hospital, Elgin, Ill., specifies air curtains on almost every new healthcare project now, according to Peterson. Entry vestibules are the main target in 90-percent of the projects because of the high foot traffic. Automatic doors in emergency rooms are also getting air curtain treatments for energy reduction, but also to minimize idling vehicle emission infiltration that’s inherent in emergency areas.
The trend toward pedestrian doors is a direct result of increasing energy costs and the air curtain industry’s move toward more aesthetic models that either match doorway frames or recess inconspicuously into ceilings with flush-mount designs. The energy saved with an air curtain many times results in paybacks under two years.
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 air curtain can contain approximately 70 to 80-percent of that air and return it to the space. Because an air curtain discharges air at velocities generally in the range from 1,000 to 3,000 ft/min., it separates the indoor from the outdoor environment and effectively prevents outside air and flying insect infiltration. The air curtains are typically activated by a limit switch or a smart control that can be programmed for a variety of opening and closing functions, as well as supplemental spot heating from optional on-board electric, steam or hot water coils.
The main difference between air curtains are manufacturers’ specification claims and the actual performance statistics. For example, an engineer might specify a particular discharge cfm, but an overstated specification in a manufacturer’s catalog might result in poor performance and ultimately lost energy saving potential. Volume, velocity and uniformity of the air stream are critical factors in an air curtain’s effectiveness, therefore it’s important that air curtains perform up to manufacturers’ specifications. The Air Movement & Control Association (AMCA-International), Arlington Heights, Ill., which is a not-for-profit organization that tests and certifies fans, blowers, air curtains and other air movement devices, created a test standard to assess air curtains and certify their performances. Thus, AMCA Standard 220, “Laboratory Methods of Testing Air Curtain Units for Aerody- namic Performance Rating” is now a test standard that’s an American National Standards Institute (ANSI) and ISO standard.
An AMCA rating label should rank as highly with engineers as Underwriters Laboratories, (UL), Northbrook, Ill., or National Sanitation Foundation (NSF), Ann Arbor, Mich., certifications. “We pay close attention to whether an air curtain model is rated by AMCA or not,” added Peterson.
A Vestibule Substitute
Air curtains have proven energy efficiency superiority over vestibules, according to the energy study “Air Curtains: A Proven Alternative to Vestibule Design” verified by second-party research/validation consultant, Blue Ridge Numerics, Charlottesville, Va. The study used computational fluid dynamics (CFD) analysis technology to prove that an air curtain/automatic door combination is 60-percent more effective in environmental separation performance than conventional automatic two-door vestibules.
Furthermore, vestibules cost up to 75-percent more in labor/materials than air curtains, and they also consume more valuable floor space, which in today’s construction environment can carry costs between $100 to $250 per square-foot. While they carry expensive construction costs, vestibules theoretically conserve energy because as one door opens, another closes and prevents a breezeway where heated and cooled air escapes or outdoor environmental elements can infiltrate. Unfortunately, multiple people in the vestibule can defeat the strategy and create a
scenario whereas both doors open simultaneously and create a wind tunnel into the facility.
Specifying air curtains as energy-saving, cost-cutting alternatives to vestibules in 3,000-square-foot buildings and larger are blocked by local jurisdictions that have adopted the International Energy Construction Code (IECC), which doesn’t yet cite air curtains as vestibule alternatives.
However, the recently-enacted International Green Construction Code (IgCC), which was published earlier this year, now allows air curtains as vestibule substitutes. The IgCC provides an approved overlay of green construction products to the IECC’s base code, which is overseen by the International Code Council (ICC), the Washington-based organization responsible for providing minimum safety, sustainability and affordability building codes and standards.