The Hottest Questions About Air Curtain

Do you want to know about air curtain? Here are some frequently asked questions.

1. Design of a small scale air curtain

Then the velocity along the centre line decays as $L^-1/3$.More clearly, $v_L = bigg( frac3

ho v_0^4 h^232

u L bigg)^1/3$ ; where $

u$ is the kinematic viscosity of air. 3 & 4. You decide what is your need on $v_L$ or constraint on $v_0$, Then the first point will give you the answer. If you need a more detailed answer or if your jet is turbulent rather laminar, I would suggest the great book "Boundary-Layer Theory" by Hermann Schlichting

2. Technology Advancements Create New Air Curtain Applications

There has been a deluge of recent technological advancements that are creating new air curtain applications that were barely imaginable 10 years ago. Advancements have ranged from more efficient electric heaters to manufacturing improvements that now extend lengths up to 16 feet. Air curtains that were once only custom-manufactured with explosion and spark-proof components for hazardous industrial locations are now standardized catalog items. What was once an energy-saving device for industrial shipping doors is now embraced by retailers, hotels, restaurants, and food service operators as tools for saving energy, eliminating flying insect infiltration, and increasing employee air comfort. Air curtains, or air doors as they are also called, typically are mounted inside the top of a doorway and continually discharge a steady stream of air down to the threshold to separate indoor and outdoor environments. The airstream keeps unwanted cold or hot air from infiltrating an open doorway during winter or summer, respectively. They also keep out flying insects and maintain a comfortable working environment for employees. One new technological advancement is the Venturi style heater. Air curtains have offered electric heating coil options for decades; however, their traditional mounting in the airstream disrupts the laminar flow that's critical to its efficacy. Such an obstructing placement can cut airstream efficiency by up to 40 percent. Furthermore, electric heater placements in the airstream disrupt the air curtain's all-important volume, velocity, and uniformity (VVU), which is critical for maintaining an air seal across the entire doorway for ultimate efficacy. Besides in the discharge air, electric heaters have also been mounted at the inlet screen where air is drawn into the air curtain. While this positioning does not affect discharge, it's less energy-efficient because the air curtain enclosure itself becomes heated. This causes up to a wasteful 5 percent heat loss radiated through the cabinet that does not reach the targeted area. One recent invention that has corrected these inefficiencies is the Venturi style heater, which is a hemispherical electric element array that's strategically mounted at the air curtain blower's inlets. Instead of a an obstructive mounting in the discharge air, the elements' heat is drawn naturally into the blower via the Venturi effect, which is named for Italian 19th century physicist Giovanni Battista Venturi. Essentially, the heating element is on the incoming side versus the discharge end of the fan/blower. The result of the Venturi effect heater is an electrically-heated air curtain with no discharge obstruction, thus the air curtain gets nearly 100 percent of the airstream's aerodynamic potential. Petroleum refineries, food processing, pharmaceutical plants, chemical facilities, compressed natural gas (CNG) bus garages, and other hazardous locations (HL) are restricted by codes that allow only electrical components that are explosion proof, spark-proof, and other safeguards. For years, custom-built HL-rated air curtains were available for this type of clientele, but they were custom-manufactured. Now air curtain manufacturers are offering them as a standardized product line item, which lowers cost significantly and improves availability and lead times. HL air curtains feature explosion-proof motors, spark-resistant fans, HL electrical components and construction, and other precautions required by ANSI/NFPA-70 National Electrical Code (NEC) regulations. Standard construction complies with Class I, Division 1 and 2, Groups C and D for gases; and Class II, Division 1 and 2, Groups F and G for dust. Optional construction is available for Groups A and B. HL applications now offer extra large door coverage with explosion-proof motors ranging from to 15-hp and heavy-duty blowers to protect doorway heights of up to 20-feet-high are offered. Another standardization of air curtain product lines is length. Previously doorways wider than 12 feet typically had modular units bolted together or custom-made single unit constructed air curtains, the latter of which carried expensive manufacturing costs. However, now technological manufacturing advancements make 16-foot-long lengths possible as standardized catalog items for some manufacturers, which makes them proportionately priced to any other shorter length air curtain. Industrial doorways very commonly span widths of 12 to 16 feet. The important aspect of single unit construction is installation ease and performance. Versus multiple short units bolted together, single construction air curtains typically do not need intermediate supports, which can increase installation time and costs. Furthermore, the space between bolted units typically create air voids. Single construction units designed for 16-foot lengths use blower and nozzle airstream widths that cover the entire span without any interruption or turbulence. The VVU of the airstream, which can only be accomplished with a single construction unit, is critical to air curtain performance and efficacy. Recent updates to the 2015 International Energy Conservation Code (IECC), will now allow certified air curtains as a vestibule alternative. This is good news for commercial buildings that in the past were mandated to use vestibules as energy-saving air locks. This code change offers both a new construction and a retrofit perspective especially for retailers. Substituting a vestibule with a comparably less expensive alternative such as an air curtain can cut new construction costs by up to $60,000. In retrofit examples, installing an air curtain and using the vestibule for merchandising space can add to a retailer's bottom line. The IECC-2015 code also stipulates air curtains must be tested in accordance to standard ANSI/AMCA-220 and certified by the Air Movement and Control Association International (AMCA), Arlington Heights, Ill., a not-for-profit organization that tests and certifies manufacturer's stated performance of fans, blowers, air curtains, and other air movement devices. Walk-in cooler air curtains have been shown to surpass the energy-saving potential of alternatives, such as swinging hinged doors and strip curtains, and they produce a quick payback of less than two years, depending on the amount of door cycles. While they are now predominantly appearing as options on new models from walk-in cooler manufacturers, several air curtain suppliers make retrofitting easy with a kit that includes an air curtain designed specifically for the unique size and configuration of walk-in coolers. Included in some kits are a pre-wired 24V control/load center in a small enclosure and a magnetic reed on/off door switch. Once 120V power is extended to the area, the pre-wired kit can be installed in as little as 15 minutes with conventional tools and basic electrical knowledge. Besides walk-in coolers, another trend in the foodservice and restaurant industries is the new drive-thru window air curtains, which are being used for a variety of purposes in many restaurant chains. They minimize both flying insect and outdoor air infiltration, protect the indoor drive-thru station employee from idling vehicle fume inhalation as well as cold air in winter climates, which are employee health and comfort issues, respectively. The U.S.'s Occupational Safety and Health Administration (OSHA) specifically recommends a "reverse-flow fan system" at the www.osha.gov website's "Teen Worker Safety in Restaurants" page. As technological advancements move forward, even more new air curtain applications are expected to emerge. What is barely imaginable today will become common building construction concepts in the future. 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 airstream that meets the floor approximately at the threshold of the door opening. A properly-sized and AMCA-certified air curtain can contain approximately 70 to 80 percent of that air and return it to the space. Because the air curtain discharges air at velocities generally in the range from 1,000 to 3,000 ft/min., it effectively prevents outside air and flying insect infiltration. Volume, velocity, and uniformity (VVU) of the airstream are critical factors in an air curtain's effectiveness. Air curtains are typically activated by a limit switch that's triggered when the door opens and deactivated when closed. Want more HVAC industry news and information? Join The NEWS on Facebook, Twitter, and LinkedIn today!