Another Energy Solution
While air curtains are better known for their long-time use as energy savers in industrial uses, their newfound expansion into more commercial applications such as hotels, retail stores, office buildings, and restaurants is escalating as quickly as today’s energy prices.
Air curtains are typically mounted inside a doorway and continually discharge a steady stream of air to separate indoor and outdoor conditions. They can be a quick and inexpensive long-term fix to substantial open doorway energy losses as well as indoor air comfort issues.
Air curtains are also useful in controlling infiltrations of dust, insects, and humidity. In these times of escalating energy costs, air doors have become invaluable in preventing the infiltration of warm outdoor air in the summer and cold air during the winter.
Many contractors and engineers have the misconception that air doors are useful only in winter to minimize energy losses and add comfort with internal hot water or steam coils and electric heating elements. But, energy losses through open doorways in summer air conditioning months are typically more costly than during winter operation. Thus air doors are useful beyond winter months.
A CASE HISTORYThe Café at the Frick is an upscale restaurant housed in a former coach house on the museum grounds of former industrialist Henry Clay Frick’s estate in Pittsburgh. An air curtain solved an indoor air comfort problem there. Wintertime patrons were chilled from a nearby single entrance door that was continually held open by long lines of people waiting for a table in the 500-square-foot dining spot.
With the installation of a 3-foot-wide aesthetic-looking air curtain that color-coordinates with the interior side of the door, the resulting airstream eliminates cold air infiltration and keeps nearby patrons warm at their tables with supplemental electric heating. The air curtain is activated when the door opens. The onboard electric heater is thermostatically controlled to run until temperature setpoints are reached after the door closes.
Air curtains have the option of a hot water coil and/or electric heating that not only reduces equipment costs, but also lowers operating costs especially when adding a control package.
SIZING & SPECIFYINGAir curtains typically take air from inside the facility and discharge it through factory-aligned, field-adjustable ±20°F nozzles to produce a nonturbulent airstream that meets the floor approximately at the threshold of the door opening. Approximately 70 to 80 percent of the air returns to the space. Because air curtain discharge velocities generally range from 3,000 to 6,500 feet per minute at the discharge, the strong airstream prevents outside air and insect infiltration.
Selecting the proper air curtain is critical and there are great variances among manufacturers and their equipment performance claims. Therefore, an air curtain model should have certified air performance data in accordance with Standard 220 - Testing Methods for Air Curtain Units from the Air Movement and Control Association (AMCA) International (www.amca.org) to ensure its claims are accurate.
Air curtain manufacturer salespeople and/or Websites should be able to provide assistance in selection sizing, energy-savings calculations, and payback. Typical air curtain paybacks range from one to three years.
CONTROL PACKAGESNot all air curtain models have controls or control packages that are equal to one another, but the ones that do can save additional energy. Control packages have many options such as two- to 10- fan speed selections, built-in thermostats, door switches, off-on switches, and built-in timers. At the high end of control packages, there is the option of a programmable digital LED display switch that functions almost like a mini building automation system for its respective air curtain.
Extra control equates to money savings. For example, instead of just one or two speeds, the fan can be set to operate at a speed that provides the optimum air comfort and air barrier, but at the least possible operating expense. Additionally, the timer can save huge amounts of energy if it is programmed to operate only during occupancy hours, which will eliminate the need for store managers to turn it on or off.
The continuing escalation of energy prices will undoubtedly send many building owners to contractors for solutions to energy losses. Contractors that have experience or the knowledge in marketing and selling air curtains as a viable energy-saving alternative will undoubtedly satisfy these requests by lowering energy bills, while simultaneously adding to their profit margins.
Publication date: 09/08/2008