June 26, 2015
by Glen Tracy
The built environment is an energy-guzzler. The U.S. Green Building Council (USGBC) states in this country alone, buildings account for 41 percent of energy use, 73 percent of electricity consumption and 38 percent of all CO2 emissions, and 13.6 percent potable water consumption. Globally, buildings use 40 percent of raw materials, or about 3 billion tons annually. Fortunately, the type of doors we select can have a big impact on a building’s energy profile.
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 bi-directional 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.
This article discusses the green features of revolving doors and considers design elements as they relate to user comfort and safety. It also offers a checklist of must-dos in properly specifying a revolving door for a given project.
ABCs of revolving doors
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. There are usually two, three, or four wings that typically incorporate glass. The opening of the drum enclosure is referred to as the throat.
Manual revolving doors rotate with push-bars, causing 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 (or ‘governor’) mounted in either the ceiling or floor prevents the door 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 limited. 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 was, “Always open, always closed”—that is, always open to people, always 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 a building and as long as there are any openings on the ground floor, cold air rushes in to replace the heated air. The opposite happens in the summer.
Energy saved by revolving doors
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 percent of visitors used the revolving 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.
According to the subsequent 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 $7,500 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 1.
Key elements of revolving door design
A building’s entrance is its calling card—its first contact with visitors—and its design is a key element to its success. To specify the right revolving door for a given project, several factors must be considered.
Revolving doors are an opportunity to enhance the drama of a building façade. Today’s all-glass façades are the most popular building design and have virtually universal aesthetic appeal. 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 that all-glass revolving doors are typically manually operated in the USA. 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.
Connections to the building
Revolving doors can be connected to buildings at the mid-post, throat opening, and in several ‘keyhole’ configurations including standard, double-bent glass, and angled. The common connection used is the mid-post. However, since half the door protrudes beyond the building envelope, it would not be recommended where pedestrian space is limited or without a protective building overhang. An interior keyhole may be used when the lobby is large enough that the door will not encroach on a nearby elevator lobby, stairs, and escalators.
With an interior throat opening or keyhole connection, a door is completely mounted into the interior of a building and there is no part of the door itself exposed beyond the building envelope. This eliminates any rain or snow accumulating atop the door and greatly reduces accumulation inside the door. It also greatly 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.
The diameter of the door, the width of vertical styles, and the height of the door opening, canopy, sidewall enclosure base, and bottom rail sideline can 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 elevate the door’s visual impact.
Security against human and natural hazards is a growing concern, and entry doors are a key focus. Most revolving door manufacturers offer various night locking options that can ensure the building is securely closed 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. Along these lines, 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 millimeters) 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 will help avoid slips and falls.
Many buildings also employ stainless steel floor grates on either the exterior or interior side of the door or even under the entire door to collect dirt and debris before entry to 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 USGBC’s rating program, Leadership in Energy and Environmental Design (LEED), working toward Indoor Environmental Quality (EQ) Credit 5, Indoor Chemical and Pollutant Source Control.
Capacity and type of use
While the above concerns are certainly important, the biggest issues in the specification of 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 concern or will traffic be spread throughout the day? Will doors have to accommodate individuals with luggage or shopping carts? Capacity is based on type of facility and user demographic.
Automatic doors of any wing configuration, 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, and 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 who come and go on a regular basis.3
The various 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 throughout, an individual’s comfort zone should be considered. Most people would prefer a comfort zone around them that totals 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.
The first element that influences capacity is diameter. With automatic doors, a larger diameter increases capacity. However, with manual doors, increases in diameter generally work to increase user comfort, as they are intended for one user per compartment. The heavier weight of increased diameter doors actually makes the door slightly harder to push, lowering the 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, the comfort and/or the 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. The wider throat opening is easier to pass through; therefore, it increases user comfort and capacity. In smaller-diameter doors, the throat opening width becomes more of an influential factor in determining capacity.
|Understanding Code Requirements for User Comfort and Safety|
A 1942 fire at the Cocoanut Grove, then Boston’s premier nightclub, sparked modern code stipulations governing revolving doors. Today, national standards for the comfort and safety of revolving doors are found in American National Standards Institute (ANSI) 156.27, American National Standard for Power and Manual Operated Revolving Pedestrian Doors.
This standard stipulates requirements for power-operated revolving doors, which rotate automatically when approached by pedestrians and/or small vehicular traffic, and manual revolving type doors for pedestrians. The objective is to provide performance standards and provisions to reduce the chance of user injury and entrapment.
ANSI requirements set maximum RPM allowances for two-, three-, and four-wing automatic doors for safety, as well as speed control for manual doors, and required safety sensors that, when activated, cause the door to slow down or stop. The standard does not pertain to revolving doors for industrial or trained traffic or custom installation.
Manual or automatic
Another parameter to consider in determining capacity is whether manual or automatic doors are utilized. Automatic doors provide a hands-free experience for users pushing carts, strollers, luggage, etc. and would be the logical choice in such cases. Manual doors are generally smaller in diameter (less than 3 m (10 ft) and 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.
Compartment size and shape
Designers should factor in how compartment size affects wheelchair access, rolling luggage, shopping carts, and emergency egress. While it is generally true larger compartments afford more comfort or accommodate higher capacities, there may be caveats in certain situations. 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. According to both International Building Code (IBC) and NFPA 101, the throat opening of three-wing doors under 2 m (7 ft) in diameter is not wide enough to meet life safety codes (which requires an aggregate dimension for egress of 914 mm [36 in.]) when the door wings are collapsed during any kind of emergency.
ANSI code requirements
ANSI places safety restrictions on the rotation speed of manual and automatic revolving doors and also requires presence detection sensors for automatic doors that can slow or stop the door when objects or people are close to making contact with the door. These requirements are discussed later in regard to safety, but it is worth mentioning here their influence on throughout.
Positioning drive and power assist
In manual doors, an optional, low-energy positioning drive system will slowly rotate the door to the standard ‘X’ position after use, which eliminates user confusion upon entering the door, and enables the user 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. The advantages of low-energy positioning and power-assist include a greatly enhanced user experience compared to a plain manual revolving door, and energy savings of a low-energy drive system compared to the constant running motor of an automatic door.
Specifying a revolving door
As a recap, properly specifying a revolving door depends on numerous factors. A list of key factors to consider:
With rising energy costs and clients’ growing demand for comfortable, safe, and environmentally sustainable buildings, revolving doors can be a true asset. Revolving doors are among the most energy-efficient entrance solutions. The ‘always open, always closed’ principle of a revolving door ensures the conditioned inside air and the unconditioned outside air remain separated, preventing drafts, dust and noise 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.
Glen 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 dad, Glen branched out briefly in the automatic door business, prior to joining Boon Edam in 2000. He has been employed at Boon Edam for over 14 years and has held various leadership roles within the outside sales group, including Regional Sales Manager positions in the Midwest and Southeast, National Distribution Manager, and he currently serves as National Sales Manager. Glen has a long history of working closely with architects, glazing contractors, consultants and key customers across several verticals since 1986. Mr. Tracy resides in Salt Lake City, Utah. He can be reached by e-mail at Glen.Tracy@boonedam.us
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