Traffic doors: speed or sustainability?
When it comes to equipment, life on the plant floor is often an endless series of choices with unsatisfying results or dubious outcomes. That can be the case for operations when choosing doors for high-traffic doorways, especially if there are temperature differentials on either side of the wall.
A common dilemma that plant managers face is when beefing up the panel to prevent heat transmission, you risk slowing down traffic. On the other hand, when installing a high-speed metal slat door on the exterior doorway, you risk having to excessively crank up the hot air blowers.
For plant managers, conventional wisdom used to make it an either/or decision. But thanks to recent research from the Door and Access System Manufacturers Association (DASMA), it may, in fact, be possible to save energy while making sure that product briskly gets out the door.
Manufacturers embrace sustainability
It’s no surprise that energy efficiency is top of mind with managers. At their PROMAT national convention in 2011, the Material Handling Institute of America (MHIA) released a study of its members, "Sustainability in Warehousing, Distribution, & Manufacturing." The findings indicated 48% of the respondent companies have a sustainability initiative underway and 88% of respondents say sustainability will be of even greater importance in the ensuing 14 to 18 months.
A growing number of manufacturing and processing plants are becoming U.S. Green Building Council LEED-compliant, putting to rest the classic image of carbon-laden, smoke-belching factories. In 2012, a number of major manufacturers formed the LEED Manufacturing User Group to share resources, expertise, and best practices. As of the close of 2013, there were 738 LEED-certified manufacturing facilities worldwide, representing 195 million sq ft, with another 343 million sq ft in the pipeline.
Speed vs. sustainability
One approach to deciding between a thicker door and a faster door is found in a recent report by the DASMA High-Performance Door Division. The study, "High-Speed Doors and Thermal Performance," discovers that today’s industrial and commercial buildings can deliver high door speed while at the same time-saving energy, depending on doorway factors.
The DASMA research revealed this new perspective in evaluating door energy efficiency and took into consideration common U-factor, air leakage, and motor horsepower values in a comparison of high-speed doors with conventionally operating insulated doors. High-speed doors become more efficient when cycled 55 or more times per day, according to this analysis.
While 55 cycles is the minimum, high-speed doors are typically specified for applications requiring much more than 100 cycles daily. Thus, the doors studied demonstrate superior overall energy efficiency when meeting the demand for high-cycle operation in a building.
This new approach views doors as dynamic parts of a building. High-speed doors, in addition to providing rapid access, also contribute to the thermal efficiency of a building through dynamic thermal performance characteristics when the door is not closed.
The bottom line is, no matter how well-insulated and tightly sealed a door may be, neither matters if the door is rarely closed because of frequent use. Rapid closing speed means a reduction in air infiltration for doors that are used often.
Annualized energy consumption analysis. Courtesy: Rytec High Performance Doors
High-speed doors are excellent at controlling air exchange-the air flowing through an opening when a door is not fully closed. In fact, when taking thermal transmittance (i.e., U-factor), air leakage, and door power usage into consideration, air exchange can be the most significant part of the total energy loss for a door, depending on the application.
Based on the research, the group proposed changes to ASHRAE 90.1, ASHRAE 189.1, Standard for the Design of High-Performance, Green Buildings, and the IECC. These changes include the following specification:
"A high-speed door is a nonswinging door used primarily to facilitate vehicular access of material transportation and having an automatic closing device, with an opening rate of at least 32 in./sec and a closing rate of at least 24 in./sec."
Now, a high-speed door specified for a building should comply with the new performance standard set for high-speed doors. With this in mind, the door manufacturer should be able to supply the opening and closing speeds, as well as U-factor and air leakage performance values, and should be able to make a more accurate assessment of doorway need based on actual or projected usage.
Since high-speed doors tend to have a roll-up design, there are other features that save energy and keep traffic moving. At the same time, these doors greatly reduce maintenance costs.
Getting the door out of the way
Typically, a vehicle rushing through the doorway in too much of a hurry might collide with the door panel. That is not a problem with high-speed doors for two reasons. First, the door is so fast that it is nearly impossible for the vehicle to catch up with it. If the vehicle does stop in the threshold, door-safety devices such as electric eyes will prevent the door from closing.
Second, if somehow the door panel sustains a collision, high-speed fabric-panel door design enables the panel to be quickly reset in the guides. Traditional doors sustain accidents all the time, so the facility has to do one of two things-either leave the door open until the repair crew shows up, exposing the doorway to significant energy loss, or manually open and close the door, slowing traffic to a crawl. Either way, the overall costs to the facility can go far beyond repair costs.
Speaking of door guides, for most designs the guides envelop the edge of the door panel to stop energy from escaping the room. Combined with a floor-hugging gasket and brush gaskets along the header, HVAC energy is well-contained between rooms or between the exterior and the interior.
Deciding which door is best
When it comes to building management, the answers to many questions are not always straightforward. This is true in the case of door selection for traffic doorways.
Here are some questions to consider when evaluating door style choices.
- What is the area of the doorway?
- How often is the door cycled in a typical day?
- What is the temperature differential on either side of the wall?
- Even if the temperature differential is not significant, do temperature, debris containment, drafts, and other issues impact product sensitivity, worker comfort, or the production process?
- How important is material-handling speed to your operation?
The analysis criteria as presented by the DASMA study may not yield a clear yes or no in terms of energy savings, but bringing these and other factors into consideration may justify installing a high-speed door.
Of course, if traffic speed is important to operation, the energy savings could be icing on the cake. An expert from local door dealers can help walk through the alternatives to find a fit for your doorway and operation.
– Michael Watkins is vice-president of marketing with Rytec High Performance Doors. Edited by Joy Chang, digital project manager, CFE Media, firstname.lastname@example.org.