A revolving door is used to control traffic or heating and air conditioning in a building. The revolving door structure consists of individual door panels (or wings), a center shaft with the hardware needed to support the door wings, a circular structure called a "rotunda" or "drum" that is usually fitted with glass, and the ceiling (supported by the rotunda) that contains either a mechanical braking device (used to control the speed of the doors) or an electronic device that uses a motor to drive the doors automatically.
The main benefit of a revolving door is that it is always closed and always open. This means that the design of the system is such that there is at least one door wing sealing the opening at all times reducing the amount of heating volume and air conditioning (HVAC) that escapes from a building and these savings in energy costs can be considerable. The revolving door achieves these savings because the curved walls of the rotunda allow the seals to fit tightly as the door wings rotate.
Each wing is fitted with a rubber and felt weather seal. With time and use, these weather seals on the door wings must be replaced because their effectiveness diminishes with age. This process is also a part of the design of the revolving door system.
The exact first use of revolving doors is unknown. However, it is known that they have been in use since about 1790 in Chicago where they are still widely used today. Revolving doors solved the problem of how to automatically close the door opening in order to keep from losing heating or cooling. Early revolving doors were manufactured using wood because the technology and materials needed to economically manufacture them from metal was either not yet available or prohibitively expensive.
The materials used in the construction of a revolving door consist of aluminum extrusion, steel tubes, machined steel hardware pieces designed to attach the doors to the structure, marine grade plywood, glass (curved and flat), felt and rubber, and the mechanical devices used to control speed or a motor driven operator device to move the doors in response to a signal from a sensor.
Each basic revolving door design is modified (with respect to dimensions, number of door wings, whether the function is manual, automatic or security, and finish or color) to suit the users requirements. The basic design of the revolving door system is not changed, but it is available in several configurations. When an architect specifies a revolving door, he or she is primarily interested in the best design that will conserve energy but also one that will bet suit the traffic requirements of the finished building. From this basic idea, the architect specifies the revolving door system and configuration, and manufacturers can adapt their designs to comply with the specifications.
- All aluminum members are cut to length depending on the overall final dimensions
of the revolving door. Aluminum extrusions are manufactured utilizing a very large press device called an extrusion press. The press forces pre-heated aluminum cast billets through a steel die that has a shape cut to the requirements of the user. Much the same as a cake decorator who uses a sack of icing forced through a small nozzle to create designs and shapes, an extrusion takes the shape of the cut out in the die and these shapes can be made to very exact tolerances. These extrusions are the main components used in revolving door manufacturing—they are designed to lock together and provide a very solid framework to support the rest of the system.
Revolving door systems can also be manufactured using exotic metals like brass or stainless steel to enhance their appearance. These systems do not use aluminum extrusions. Instead, sheets of metal that are cut and formed to wrap around a steel skeleton (sub-frame) are welded in place. They can easily cost as much as three times that of a standard aluminum revolving door.
- The circular rotunda walls are formed from aluminum extrusions that are repeatedly fed through a bending machine until the correct radius is achieved. The radius depends on the required size of the revolving door. The most common size (width) is 8 ft (2.4 m), but these systems can be manufactured to much larger widths. Larger systems are usually motorized because the structure would be very difficult to push manually.
The bending machine consists of three rollers through which the straight piece of aluminum is fed. After each bend, the rollers are moved closer together and the material is fed through again until the correct radius is achieved. This process is critical because the door panels must not only fit inside the rotunda, but they must also evenly rotate 360 degrees without hitting the rotunda walls. The seal between the door panels and the rotunda must also be maintained to reduce the amount of hot and cold air entering and leaving through the door.
- All aluminum parts (doors, frames, etc.) are welded together and prepared to receive the hardware components that make up the emergency breakout system.
- The circular ceiling is cut from 1 in (2.54 cm) thick marine grade plywood and then laminated with 0.125 in (0.318 cm) thick aluminum sheet to form the interior ceiling.
- The ceiling is prepared for the light fixtures (cut-outs) and the center shaft hole is cut at the very center.
- Steel angle is welded together in a grid pattern to provide the support for the ceiling and to secure the mechanical speed control device. The grid is installed on top of the ceiling.
The speed control device is a system of spring loaded brake shoe assembly that rotates inside a drum. As the rotational speed of the revolving door increases, so does the brake shoe assembly and the pressure of the brake shoes against the drum slows the revolving door down preventing the "freewheeling" effect. The speed control device can be mounted in the ceiling or in the floor. Floor mounted speed controls are used on systems that have glass ceilings or have insufficient clearance at the top of the door system.
- The center shaft is fabricated and fitted with the balance of the breakout hardware. Revolving door systems (in the United States) must be fitted with a "panic collapsing mechanism" or "breakout system" that permits the door frames to fold against one another. This bookfold position permits an unobstructed exit from the interior to the exterior of the building in the event of a fire or other emergency. The Uniform Building Code (adopted by most municipalities in the United States) requires the breakout system together with another manual or automatic swinging or sliding door next to the revolving door for emergency exit and handicap access.
The breakout mechanism consists of two breakout plates that are attached to each end of the center shaft. They are slotted because the door frames are fitted with pivot bars that allow the door frame to fold out of position as described above. The breakout plates have removable access gates that allow the door frame to be hung to the assembly using a pivot bar assembly.
The revolving door panels rotate with the center shaft assembly and the center shaft assembly is, as previously discussed, fitted with breakout plates at the top and bottom. There are additional hardware devices at each end of the center shaft and these devices are the actual center shaft pivot points. They are referred to as stub shafts.
The bottom of the center shaft assembly sits inside a bearing assembly that is secured to the floor of the building. The bearing permits the revolving door to rotate smoothly and is necessary to prevent mechanical breakdown due to wear.
- The entire revolving door is assembled at the factory for testing. Once cleared for shipment, the revolving door is disassembled and wrapped in protective plastic. A wood crate is built and the revolving door components are packed and secured for their journey to the job site.
When the revolving door assembly is erected, a series of tests and measurements are made in order to verify that the product conforms to the requirements of the customer. The system is checked for correct height and width, all functions of the revolving door are tested (speed control, breakout system, weather stripping, etc.) and adjustments are made where needed. In the case of security systems or automatic systems, each computer function or mode of operation is checked and re-checked for proper operation. The quality control inspector must sign off on an inspection form before the door system can be disassembled.
All waste materials are recyclable and consist of wood, aluminum and steel. All waste material is stored and sent to a recycling center. There are no harmful chemicals used or wastes in the manufacturing process.
Designs are being examined that would incorporate enhanced security features for specialty applications such as airports and prisons to include metal and chemical detection systems as well as new video recognition systems. Although the revolving door basic design remains the same after over 200 years of use, some new door systems are very large (20 ft [6.1 m] in diameter) and their design incorporates elaborate and exotic electromechanical devices designed to allow several people to transverse the opening at once, where most revolving door designs accommodate one or two people at a time. The mechanical limitations of the equipment make the large door systems expensive to own and troublesome to maintain and repair. Revolving doors will always be the best way to control HVAC loss in areas that experience extremes of climate but they will also remain effective for access control and traffic control well into the future.
Where to Learn More
Manfredi, Bob. Revolving Doors: An Open And Shut Case. December 2001. <http://www.greendesign.net/bcnews/SEPOCT96/rvlvgdrs.htm>
Sierra Automatic Doors, Inc. Web Page. December 2001. <http//:www.autodoors.com>.
re·volv·ing door • n. an entrance to a large building in which four partitions turn about a central axis. ∎ used to refer to a situation in which the same events or problems recur in a continuous cycle: many patients are trapped in a revolving door of admission, discharge, and readmission. ∎ [usu. as adj.] a place or organization that people tend to enter and leave very quickly: the newsroom became a revolving-door workplace. ∎ used to refer to a situation in which someone moves from an influential government position to a position in a private company, or vice versa.