Bringing Down the Curtain on Infiltration
Fairborn, a distributor of loading dock, industrial door, and specialty industrial plant products, reviewed several technology options to solve its food manufacturing client’s doorway energy and maintenance challenges.
The client had already installed a high-speed, insulated rollup door that reduced -5°F freezer air emigration and 60 to 95° summertime ambient air infiltration from the shipping door area, which is 50 feet away. Despite the high-speed door, humid ambient air still infiltrated through the top of the 12- by 12-foot doorway during its hundreds of daily cycles. The greatest concern was a freezer temperature fluctuation of 8 degrees, which is unacceptable to the client’s internal product quality, refrigeration equipment wear-and-tear, and energy conservation standards.
The significant energy losses are no surprise according to the refrigeration standards handbook of ASHRAE, which states that air infiltration in open doorways is the leading cause of increased refrigeration loads at cold storage facilities. Bob Hare, general manager of Fairborn’s Columbus, Ohio, office, estimated his client’s energy losses combined with maintenance costs amounted to thousands of dollars per month.
Besides energy losses, humidity infiltration also required periodic ice removal from the ceiling-hung ammonia refrigeration system’s piping, coils, valves, and controls just inside the 20,000-square-foot freezer’s doorway. The fire door roller tracks also were continually iced. Additionally, the potential for forklift accidents loomed due to icy floors near the threshold, which also required ongoing maintenance.
Options to Energy Loss Solutions
The client relied on the expertise of the design and engineering departments of Fairborn as well as its air curtain supplier, Berner International. Fairborn began as a dock seal and shelter manufacturer in the 1970s and later became a full-line loading dock and door dealer.
One option Fairborn offered was a full-perimeter door that recirculates air horizontally. At a price of more than $30,000, however, the full-perimeter door was a cost-prohibitive retrofit. A more economical and equally functional option was a Berner 12-foot-wide, two-speed, 2,304-cfm Model VSB air curtain mounted above the doorway at one-fifth the cost. Like the full perimeter recirculating air doorway, an air curtain is up to 80 percent efficient at separating two environments, it was said. This resulted in an air curtain and rollup door combination — the latter of which the client already had already purchased and installed.
Custom Engineering Solution
To eliminate the need to cantilever the air curtain away from the high-speed door mechanism, Berner recommended installing the air curtain vertically. Because the unit was originally designed for horizontal mounting, Berner’s engineering department modified the air discharge nozzles to produce a thinner, higher-velocity airstream, so that the air curtain reaches the volume, velocity, and uniformity required to seal a doorway. The modification helps minimize doorway air balance issues between adjoining rooms with significant temperature differentials that are inherent in cold storage facilities.
“We sell and install 10 to 20 air curtains annually, but this is the first time we’ve installed a vertical mounting,” said Hare.
The freezer door activation is now executed with the following sequence:
• A Falcon motion sensor detects an oncoming forklift and activates the air curtain, which needs one second to ramp up to full air velocity.
• A second Falcon sensor activates the rollup door, which opens after the air curtain is at full velocity.
After the forklift passes through, the door closes and the air curtain shuts off one second later.
The result of the air curtain installation is that it has reduced the 8° freezer temperature fluctuation to less than 2°. Subsequently, ice maintenance costs have been reduced and the potential for slippery floors has been eliminated, the customer said.
Most importantly, Fairborn is realizing energy and maintenance cost reduction of thousands of dollars per month, it was reported. Managing better environmental separation at the freezer entry has also prolonged refrigeration equipment lifecycles by cutting back on operational wear-and-tear. The cost of the project is equally impressive for the client because the payback on the air curtain is less than one year, according to Hare.
For more information, go to www.berner.com.
Publication date: 7/30/2012