September 19, 2017
By Glen Tracy
Revolving doors can be up to eight times more energy-efficient than their hinged counterparts—all while allowing large numbers of people to pass in and out, boosting security, and adding architectural interest. In other words, not only can revolving doors efficiently handle bidirectional pedestrian traffic and reduce energy costs by maintaining an airlock, but they can also improve comfort for building occupants and offer more usable space at entrances compared to vestibules.
A revolving door generally consists of door wings that hang on a central shaft and rotate around a vertical axis within a cylindrical enclosure called a ‘drum’ (Figure 1). There are usually two, three, or four wings, typically incorporating glass. The opening of the drum enclosure is referred to as the ‘throat.’
Manual revolving doors rotate with push-bars, which cause all wings to move. Large-diameter revolving doors use a motor to rotate automatically, and can accommodate strollers, wheelchairs, and wheeled luggage. A speed control device (or ‘governor’) mounted in either the ceiling or floor prevents the door from moving at an unsafe speed.
Automatic revolving doors are powered above or below the central shaft, or along the perimeter. Sensors in the door wings and the enclosure frame ensure the speed with which the door revolves is controlled. Other sensors can prevent or minimize the force of impact of the door wing on users.
Revolving doors were invented in Philadelphia in 1888 by Theophilus Van Kannel to reduce air infiltration. His company’s original motto—“Always open, always closed”—refers to how these doors are always open to people, but closed to the elements.
A basic understanding of the way air behaves in a building sheds light on the benefits of revolving doors. Generally speaking, per the stack effect, air flows in and out of a building because of differences in air pressure and humidity. In the winter, heated air rises toward the top of the structure; as long as there are openings on the ground floor, cold air rushes in to replace the heated air. The opposite happens in the summer.
In 2006, a team of graduate students at the Massachusetts Institute of Technology (MIT) conducted an analysis of door use in one building on campus, where they found just 23 per cent of visitors used the revolving doors versus the available adjacent swinging doors. According to MIT’s calculations, the swinging door allowed as much as eight times more air to pass through the building than the revolving door (Figure 2).
According to the April 2009 MIT Tech Talk publication:
students indicated that if everyone were to use the revolving doors in this one building alone, MIT would save almost $7500 in natural gas a year. That’s enough to heat five houses over the same timeframe, and it also adds up to nearly 15 tons of CO2.
The MIT findings on how revolving door usage affects energy consumption are shown in Figure 3. A Toronto hospital project helps further illuminate these doors’ advantages.
Healing the wind tunnel effect
Toronto is known for its cold and blustery winter months. Prior to February 2016, Mt. Sinai Hospital’s employees, patients, and visitors often had to endure freezing wind tunnel conditions within a street-level entrance corridor linking University and Murray Streets. Wind conditions could be so severe, those using a smaller, employee-designated swinging entrance could sometimes not manually open that door.
“On the hospital’s main floor,” explained Tony Khouri, the hospital’s vice-president of facilities and capital development, “there is a long corridor between University and Murray Streets. Formerly, we had double sliding doors at each entrance, and because of the high foot traffic we had lots of problems with blasts of cold air running up and down the corridor.”
The corridor not only connects the two streets to the main entrance of the hospital, but also has retail and other shops located along it length.
The hospital engaged an expert about renovating the entrances, and the consultant recommended installing revolving doors to stop the infiltration of air. One issue to overcome was throughput.
“Compared to other hospitals, we have a high number of users for these entrances, averaging 1000 per hour,” said Khouri.
Mt. Sinai installed a 5-m (16-ft) diameter, dual-wing revolving door at Murray, the larger of the two main entrances (Figure 4). This entrance is more accessible for patients arriving or leaving by car, and can accommodate wheelchairs and patients on stretchers. The smaller entrance, University, is accessed up a flight of stairs and has been fitted with a 3.5-m (12-ft) diameter, two-wing door. Both entrances also maintain one set of push-button activated sliding doors alongside the revolving doors to conform to Accessibility for Ontarians with Disabilities Act (AODA) and for emergency egress. A third, 2.5-m (8-ft) diameter, four-wing manual revolving door is installed at the employee entrance, thereby eliminating the ‘stuck door’ problem.
Due to the relatively large size of its two compartments compared to three- or four-wing doors, the selected revolving door can channel a high capacity of traffic while having a fairly small footprint.
“We try to monitor the sliding door use as much as possible, but we still have some gusting issues,” said Khouri. “The revolving doors are the best solution, given our space and property limitations, and these entrances have cut our wind tunnel effect by 60 to 70 per cent. I believe the revolving doors are the biggest factor in that improvement. They are of good quality, they’re superior to regular doors, and they are helping us achieve our entrance and comfort goals.”
However, what is right for Mt. Sinai may not be right for every building project. In addition to energy and air infiltration, what considerations must design/construction professionals make when selecting an appropriate revolving door?
Key elements of revolving door design
A building’s entrance is its calling card—its first contact with visitors—and its design is critical to its success. To specify the right revolving door for a given project, several factors must be considered.
Connections to the building
Revolving doors can be connected to buildings at the midpost, throat opening, and in several ‘keyhole’ configurations including standard, double-bent glass, and angled (Figure 5). The common connection used is the midpost. However, since half the door protrudes beyond the building envelope, it is not recommended where pedestrian space is limited or without a protective building overhang. An interior keyhole may be used when the lobby is large enough the door will not encroach on a nearby elevator lobby, stairs, or escalators.
With an interior throat opening or keyhole connection, a door is completely mounted into the interior of a building and no part of the door itself is exposed beyond the building envelope. This eliminates any rain or snow accumulating atop the door and greatly reduces accumulation inside it. It also benefits useful life and reduces the amount of maintenance needed. Finally, an interior-mounted door creates a mini overhang or awning effect that protects users from rain or snow as they enter the door.
Security against human and natural hazards is a growing concern, and entry doors are a key focus. Most revolving door manufacturers offer various locking options that can ensure the building is securely closed at night or during non-opening hours. Options include different types of locking mechanisms that secure the door wings in their standard resting position, and night sliding doors that close over the throat opening of the revolving door.
Doors can be locked from a remote location, and access control systems can be integrated with the door to allow authorized users to enter or exit the building. Many employee-only entrances use security revolving doors to prevent ‘tailgating’ and ‘piggybacking.’ Vandal- and bullet-resistant glass is also available.
Recommended surrounding features
A popular strategy in colder sections of the country, building overhangs provide shelter from weather and keep snow and rain from getting inside the door. However, as described earlier, interior throat opening or keyhole connections can create the same benefit within the entry itself—this makes for a simpler, cost-effective solution by requiring less of an exterior overhang to be built. Additionally, if access control is used, an overhang provides protection during the brief pause when a user must gain authorization before entering a security revolving door.
Adequate attention should also be paid to flooring. Although there is no industry standard, most door manufacturers require the floor surface beneath the door’s footprint to be perfectly dead level (or within a few millimetres) to ensure proper operation and correct weather seal along the bottom of the door wings.
Using different flooring materials for the circular footprint of the revolving door itself visually signifies to users the actual path of the moving door wings and makes for less confusion and hesitation upon entering. The installation of the matting materials at the exterior and interior helps avoid slips and falls.
Many buildings also employ stainless steel floor grates on the exterior or interior side of the door or even underneath it to collect dirt and debris before entry and decrease maintenance costs. Grating or matting that continues 3 m (10 ft) or more into the interior space can also help qualify for points under the Leadership in Energy and Environmental Design (LEED) program, working toward Indoor Environmental Quality (EQ) Credit 5, Indoor Chemical and Pollutant Source Control.
Capacity and type of use
While these concerns are certainly important, the biggest issues in specifying a revolving door are capacity and character of expected traffic. Architects will have to consider how many and what type of people are expected to enter and exit a facility. Will rush hours be a challenge or is traffic spread throughout the day? Do doors have to accommodate individuals with luggage or shopping carts? Capacity is based on type of facility and user demographic.
Automatic revolving doors of any wing configurations, with large compartments, safety sensors, and ‘push to slow’ buttons, are generally applicable for facilities accommodating families, children, the elderly, or rolling baggage and carts, including museums, hospitals, airports, large retail establishments, hotels, and casinos. Small office buildings, restaurants, and specialty, high-end retail buildings are ideal for three- or four-wing manual revolving doors. Optimal capacity is reserved for ‘trained traffic’—users familiar with the doors and the building who are either residents or employees and come and go on a regular basis. (Ultimately, there are laws [such as AODA] requiring accessibility be taken into account for all projects. However, facilities want all visitors to maximize the energy efficiency by using the revolving doors; they can complete both objectives by installing automatic revolving doors with large compartments that offer accessibility.)
Factors affecting capacity and user comfort include:
This is expressed in terms of x number of people per direction per minute. For example, ‘1×15’ refers to a one-way door that allows 15 people through in one minute, for a total of 15 people/minute. One-way doors, however, have limited application. The more typical capacity equation is ‘2×24,’ signifying a two-way door that allows 24 people per direction in one minute for a total of 48 people/minute.
When calculating throughput, an individual’s comfort zone should be considered. Most people would prefer a comfort zone around them totalling about 1 m2 (12 sf). To roughly gauge the capacity of a revolving door, one can divide a compartment area by this dimension and then multiply the number of compartments by the recommended number of revolutions per minute (RPMs).
The first element influencing capacity is diameter. With automatic revolving doors, a larger diameter increases capacity (Figure 6). However, with manual revolving doors, increases in diameter generally work to increase user comfort, as they are intended for one user per compartment (Figure 7). The heavier weight of increased-diameter doors actually makes them slightly harder to push, lowering RPMs and thus slightly decreasing the number of people that move through.
It is interesting to note when the diameter of a door is increased by a certain ratio, the area of each compartment increases by a much greater ratio. Thus, for a slightly wider opening in the building envelope, comfort and/or capacity can be greatly improved—this is especially true for automatic revolving doors.
Another factor affecting capacity is the throat opening. By design, a four-wing door has a wider throat opening than a three-wing door of similar diameter. Since the wider throat opening is easier to pass through, it increases user comfort and capacity. In smaller-diameter doors, the throat opening width becomes more of an influential factor in determining capacity.
Manual or automatic
Another parameter to consider in determining capacity is whether manual or automatic doors are used. Automatic doors provide a hands-free experience for users pushing carts, strollers, or luggage, and are the logical choice in such cases. Manual doors are generally smaller in diameter (less than 3 m [10 ft]), designed to accommodate one person per compartment, and are most suitable for low-traffic applications.
Cost is another factor in determining whether an automatic or manual door is selected. Building owners may prefer the lower price point coupled with the lower maintenance costs of a manual revolving door, compared to the higher price and maintenance costs of an automatic door. Finally, real estate constraints may limit the size of the door’s footprint. For example, in downtown areas where space is limited and/or expensive, putting in two manual doors may satisfy capacity needs where a single 3.5-m (12-ft) automatic door would not.
The capacity and safety of automatic revolving doors are enhanced by motion sensors, safety sensors on the top rail and right side of the throat opening to prevent contact, and rubber contact switches, which stop the door on contact (Figures 8 and 9).
Compartment size and shape
Designers should factor in how compartment size affects wheelchair access, rolling luggage, shopping carts, and emergency egress. While larger compartments generally afford more comfort or accommodate higher capacities, there may be caveats in certain situations. For example, if the application is a grocery store and carts are used all the time, the throughput will be reduced significantly. Additionally, the larger an automatic revolving door, the slower it rotates—flattening the curve on the correlation between throughput and compartment size.
Also, as mentioned, in comparing smaller manual doors of the same diameter, the throat opening of the four-wing is greater than that of the three-wing. Smaller three-wing doors may not meet local codes or regulations for egress. For example, both the International Building Code (IBC) and National Fire Protection Association (NFPA) 101, Life Safety Code, require the throat opening of manual revolving doors to accommodate emergency egress. Three-wing doors under 2 m (7 ft) in diameter do not meet the aggregate dimension for egress of 914 mm (36 in.) when the door wings are collapsed during an emergency. (Provincial codes such as AODA may have different requirements.)
Positioning drive and power-assist
In manual revolving doors, an optional, low-energy positioning drive system will slowly rotate the door to the standard ‘X’ position after use, eliminating user confusion upon entering the door and enabling them to step in and keep pushing rather than hesitating. These same positioning drive systems may also incorporate a power-assist function that helps users push the door with reduced effort. The advantages of low-energy positioning and power-assist are a greatly enhanced user experience compared to a plain manual revolving door.
Specifying a revolving door
As a recap, properly specifying a revolving door depends on numerous factors, including:
With rising energy costs and clients’ growing demand for comfortable, safe, and environmentally sustainable buildings, revolving doors can be a true asset. The ‘always open, always closed’ principle of a revolving door ensures conditioned inside air and unconditioned outside air remain separated, preventing drafts, dust, and noise from coming into the building. As less energy is required to maintain the conditioned climate inside the building, revolving doors help reduce the carbon footprint of a building and save both energy and cost—key assets in today’s building environment.
|REVOLVING DOORS AND ESTHETICS|
|Revolving doors are an opportunity to enhance the drama of a building façade. Available in a wide variety of heights and widths, with different canopy heights and heights under the canopy, an all-glass revolving door complements the appeal of a glass façade.
Minimal stainless steel trim and patch fittings contribute to a clean, sleek look. However, it is critical to note all-glass revolving doors are typically manually operated in Canada. This is because automatic doors require safety sensors on the door wings per ANSI/BHMA A156.27-2011, American National Standard for Power and Manual Operated Revolving Pedestrian Doors, and all-glass revolving door wings typically do not include the metal framing elements to mount the safety sensors.
The diameter of the door, the width of vertical stiles, and the height of the door opening, canopy, sidewall enclosure base, and bottom rail sideline can also be optimized to create the desired look and complement surrounding building elements and doors. When these dimensional elements are specified with consideration of surrounding features, a fluid and harmonious sightline is created. For dramatic appeal, an additional curved glass enclosure can be constructed above the revolving door to greatly elevate its visual impact.
Glen Tracy grew up in the revolving door business with his father, Richard Tracy, who manufactured revolving door systems in Chicago for more than 30 years. After nearly 13 years working for his father, Tracy branched out briefly in the automatic door business before joining Boon Edam in 2000. He has held various leadership roles within the company’s outside sales group, including regional sales manager in the Midwest and Southeast, national distribution manager, and his current role as national sales manager for architectural revolving doors. Tracy can be reached by e-mail at firstname.lastname@example.org.
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