Many industries have loading or shipping areas that are almost always open to the outdoors. Often the doorway is many feet wide and steady traffic keeps it open most of the time. This allows copious amounts of outside air to enter the building, and conditioned air to escape. This can increase space-conditioning costs manyfold, perhaps to the point of making it uneconomical to condition the shipping area at all.
Other occurrences of this situation are common. An unconditioned warehouse or storage area separated from a fabrication or assembly space has the same problem as the shipping dock, in retaining treated air within a specific zone. Restaurants have an analogous situation, keeping the heat and odors of the cooking area from the public dining space.
A simple and inexpensive fix to these problems is a door with vinyl strips, especially if the traffic flow is not high. In addition to energy savings, this type of thermal barrier is also a sound barrier that can result in quieter and more comfortable working conditions. Vinyl strips are ideal for smaller openings, such as for conveyor passages, or cooler, produce, and personnel doors.
Larger openings may be better suited for air doors. They use forced-air blown down from above the passage to keep the air-conditioning or heat inside. In the summer the hot, humid air is kept out. In the winter the cold air is kept out, and warm air is circulated from the ceiling down to the occupied zone. Some units can even be fitted with a heater to keep the door areas warmed. These are suitable for very cold climates.
Another advantage of these devices is that they prevent dust, insects, and airborne contaminants from entering the work area. In fact, some air doors are designed specifically for insect control, at supermarkets, restaurants, and dairies. Others are tailored for cold-storage use, to reduce refrigeration lost through cooler or freezer meatpacking plants, among others.
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Excerpt from Energy Conservation Projects.