Air Curtains: A Proven Alternative to Vestibule Designis a newly released, three-month-long research study funded by air curtain manufacturer Berner International. The certified results used computational fluid dynamic (CFD) analysis from second-party research-validation consultant Blue Ridge Numerics, Charlottesville, Va.
When compared to conventional automatic two-door vestibules, the study’s results confirmed that an air curtain/automatic door entrance combination is up to 10 percent more energy efficient in environmental separation performance, costs up to 75 percent less in labor and materials, and conserves 50-2,000 square feet of entryway floor space typically consumed by vestibule designs.
CONFIRMATION“If you ask most engineers or architects if air curtains are more energy efficient or less expensive than vestibules, they probably don’t know for sure, but this study reveals what we’ve known for some time,” said Timothy Londeree, R.A., architect, David A. Levy and Associates, Akron, Ohio, a retail design and development firm that has specified air curtains on dozens of commercial projects to save clients construction costs.
Berner executives said they hope the certified research will open a dialogue between the industry and the International Energy Conservation Code (IECC). Currently the IECC doesn’t accept air curtains as viable alternatives in its Air Leakage - Section 802.3. Thus, the research study is another example of Berner providing customers with custom solutions to real market issues.
“Our clients want to save operating costs by using air curtains and eliminate the $20,000 to $60,000 cost of vestibules in their store designs, but they also want to stay within the IECC code,” said Berner project engineer Phil Thomas, who oversaw the project with engineering manager David Johnson.
The study also confirmed that building owners save more than energy, construction costs, and floor space. Air curtains use less supplemental heat than vestibule heaters; they help enhance employee comfort, and reduce liability by maintaining drier entryway floors during inclement weather. This helps keep traffic flow unhindered, and improves sanitation by reducing insect entry.
The culmination of energy and construction savings adds up to a one- to three-year payback for an air curtain, according to the study.
The Air Movement and Control Association (AMCA), Arlington Heights, Ill., a nonprofit organization that creates standards for, and tests/rates everything from air curtains to dampers, louvers, outside air grilles, fans and other air-side HVAC equipment, hopes to change codes to address air curtains as a vestibule substitute. Armed with the research study, the association is currently lobbying code committees.
Architects, engineers and specifiers can still comply with codes and use air curtains as vestibule substitutes, but it’s usually done at the local inspection level.
MORE ADVANTAGESAnother sometimes-overlooked advantage of air curtains is employee comfort. Because point-of-purchase (POP) stations typically are located near entryways for security reasons, POP employees don’t enjoy the same air comfort of their interior counterparts. Cashiers tend to get the brunt of unchecked wind in the absence of vestibules or air curtains.
In the case of vestibules, cold outdoor air can penetrate the entryway, especially when both sliding door entrances open simultaneously during heavy traffic periods. Supplemental space heaters, which can be costly to install and operate, temper the vestibule space air that infiltrates the POP area. Air curtains can be specified with built-in electric heaters or heating coils that are supplied by the building’s central heating supply loop to temper the air.
In the summer, hot, humid air infiltrates the space and makes work areas near doors uncomfortable for employees.
BEYOND VESTIBULESAir curtains also have a variety of other applications. For example, the extension of the TD Banknorth Garden’s commuter foot traffic area 100 feet into the adjacent train shed of the Massachusetts Bay Transit Authority’s (MBTA’s) North Station was an energy-saving opportunity.
Architect Sasaki and Associates, Boston, and HVAC project engineer Jeff Fleishman, Cosentini Associates, Cambridge, Mass., were concerned with energy efficiency as much as aesthetics. Consequently, Sasaki’s idea of a 12-foot-high lobby/soffit design now presents an environment that’s comfortably separated from the outdoor air of the mammoth train shed via 12 air curtains at the mouth of 12 automatic sliding doors. During rush hour when the automatic doors are constantly open with passing commuters, the air curtains keep cold air from infiltrating the new train station lobby area at a great savings to the building owner, Delaware North Companies Inc.
Summertime operation prevents hot, humid air from infiltrating the lobby space. Except for the gentler airstream at the entrance, commuters don’t notice the air curtains, which are flush-mounted above into the new lobby’s perimeter soffit.
Cosentini custom ordered factory-installed coil-filter combination options that all have hot water coils that tap into the soffit’s heating supply loop. The 95,600-Btuh coils supplement the new entrance area’s main HVAC system by providing thermostatically controlled heating near the door areas when needed.
Each air curtain also includes a control package, which includes a thermostat; three-speed fan with maintenance access from an onboard control panel; a timer delay function; and a low-voltage relay for tapping into direct digital control (DDC) building automation systems.
MCCORMICK PLACEAnother innovative use of air curtains is Chicago’s new McCormick Place West convention center. When officials of the Metropolitan Pier and Exposition Authority (MPEA), which owns and operates the facility, were presented with energy conservation estimates of $70,000 annually and equipment cost paybacks of less than two years, choosing air curtains looked like a good thing.
Air curtains were one of several energy-conserving technologies that helped the project achieve two of its Leadership in Energy and Environmental Design (LEED) points from the U.S. Green Building Council (USGBC) in the Optimized Energy Performance category.
The $850 million exposition facility has more than 375 linear feet of freight and pedestrian doors, which are typically open 10 to 14 hours daily during the five-seven days of setup prior to major winter events. Many air curtain manufacturers can perform an energy savings estimate for customers by gathering and calculating dozens of site conditions data. Some of McCormick Place West’s data calculations considered a 26-week heating season, with each door open 10 hours weekly for a total of 260 hours annually. Besides the annual savings and payback, there was also a calculated hourly savings of $269.79 when all the doors are open simultaneously.
Air curtains also have an impact on indoor air comfort in the facility’s 470,000 square feet of open exhibition space. Without the air curtains on all large roll-up doors and main doors, temperatures would drop dramatically during set-up and tear-down, and it would require a minimum of 24 to 48 hours to regain the target temperature of 73° to 75°F for an event, according to Susan Van Klompenburg, senior mechanical design engineer, A. Epstein and Sons International Inc., which performed consulting engineering for the McCormick Place West expansion as a member of the joint venture, McCormick Place Design Team, Take II LLC, Chicago.
Furthermore, employee air comfort can affect productivity significantly. Shows are set up more efficiently in cold, wintertime months at McCormick Place West because employees are more comfortable. Moreover, forklifts can pass freely through freight doors without waiting for them to cycle.
IN THE STUDYThomas and Johnson recorded and compiled hundreds of statistics based on the geometry and scale of conventional vestibule architecture used by three national pharmacy chains. Three building configurations (vestibule only, air curtain only, and vestibule and air curtain) were simulated with wintertime ambient temperatures of 20°F under a variety of wind loads and traffic frequencies. The dozen scenarios were 3-D modeled in SolidWorks 2007 and launched into CFdesign upfront CFD software by Blue Ridge Numerics.
CFdesign was chosen because of its ability to model moving solids in numerous scenarios and to allow recorded measurements in a multitude of scalar and vector quantities in a precise and repeatable manner. Similar test results would have been impossible with other testing methodology such as simple mathematical equations.
“Physical lab testing procedures might have given a similar result, but CFD analysis cut test time by as much as 60 percent, not to mention the additional production costs of building a vestibule test site,” said Jason Pfeiffer, director of engineering services, Blue Ridge Numerics, which is a world leader in upfront CFD and engineering services.
For more information, visit www.berner.com.
Sidebar: Air Curtains and LEED CreditsBerner air curtains, which have been certified by the Air Movement and Control Association (AMCA), can help to achieve Leadership in Energy and Environmental Design (LEED) Energy and Atmosphere points, as well as Indoor Air Quality points. Here are a few of the main areas in which the proper use of an air curtain can help a building achieve LEED points.
Energy and Atmosphere Points (EA Credits 1)
Credit EA 1- While air curtains are not a major part of an HVAC system, used properly, air curtains can increase a space’s energy efficiency when the doors are opened - decreasing energy consumption and increasing occupants’ comfort. For this credit (good for up to 10 points), the LEED certification process requires a whole building project simulation that shows the percentage improvement in the proposed building performance rating compared to the baseline building performance rating per ASHRAE/IESNA Standard 90.1-2004.
Indoor Air Quality Points (EQ Credits 6.2 and 7.1)
Credit EQ 6.2- Air curtains provide a high level of thermal comfort system control by individual occupants or by specific groups in spaces that are surrounding openings (i.e., loading dock doors, customer entryways) to promote the productivity, comfort and well being of building occupants (Thermal Comfort: Controllability of Systems, Credit 6.2).
Credit EQ 7.1- By preventing thermal drops or rises due to a system’s reaction to cross contamination of airstreams near an open doorway, air curtains can help an HVAC system comply with ASHRAE Standard 55-2004, Thermal Comfort Conditions for Human Occupancy. For example, cold winter air near the door may kick the heat on, causing spaces away from the door to be overheated (Thermal Comfort: Compliance, Credit 7.1).
Innovation in Design Points (ID Credits):
Credit ID 1-1.4 (good for 1 point)- Because doors are already closed when a building is commissioned, air curtains are not always included in the mechanical testing process. However, when used properly, air curtains help to increase energy performance (decrease energy use), and it is common to see a payback period of one-two years depending on location and use. It has been recommended that if the benefits of air curtains are not being captured elsewhere by the LEED-NC Green Building Rating System, air curtains should be submitted for this credit.
Some air curtains can also be used for insect control. If a client is putting together a Low Environmental Impact Pest Management Policy to minimize the use and cost of chemicals, air curtains can help achieve Indoor Environmental Quality points in the LEED for Existing Buildings Rating System.
Indoor Environmental Quality Points (EQ Credits 10.4 and 10.5)
Credit IEQ 10.4 and 10.5- Low Environmental Impact Pest Management Policy.
For more information, visit www.usgbc.org.