By Glen Tracy*, Boon Edam
The built environment is an energy-guzzler.
Commercial buildings account for approximately 24% of national electricity consumption and approximately 10% of national greenhouse gas production, according to the latest Commercial Baseline Building Study (CBBS) prepared for the Australian Department of Climate Change, Energy, the Environment and Water.
Further, the total non-residential building stock count is larger than previously understood, comprising more than 1,000,000 energy-consuming non-residential buildings at the start of this decade. These growing figures include categories such as offices, warehouses, transport buildings, retail and wholesale trade buildings, factories, entertainment, and recreations buildings, short- term accommodation buildings, agricultural buildings, educational buildings, religion buildings, and age care facilities.
Australia's 830 million square metres of gross floor area existing at the start of this decade grew at an annual rate of new construction of 16 million sq m, equivalent to 2 per cent of the total floor area, according to the CBBS. Total floor area demolished annually was 1.8 million sq m. So the problem is growing – both here and internationally.
Because, despite wider local and global investment in building energy efficiency, a recent UN Global Status report for Buildings and Construction growth in floor space outpaced efficiency efforts, leaving the sector off-track to decarbonise by 2050.
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 at which the door revolves is limited. Other sensors can prevent or minimise 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.
Because they provide a "tighter" seal, 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.
How do you measure this?
A landmark study in 2006 by 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 the swinging door involved allowed as much as eight times more air to pass through the building than the revolving door with which it was compared.
This validation was taken a major step further recently by Boon Edam by software developed in partnership with one of the world's leading technical universities.
Delft University of Technology (TU Delft) – ranked in the top 10 engineering and technology best universities in the world by the globally respected QS rankings – partnered with 150-year-old architectural global revolving door leader Boon Edam to give architectural, building and facility management companies a scientifically validated yardstick to measure the savings of their energy-saving doors.
Now available throughout Australia, New Zealand, and Papua New Guinea, a first theoretical use of the software was applied to Sydney, Melbourne, and Brisbane building models.
It shows the payback period for installing a revolving door, instead of a less energy-efficient sliding door, is shrinking rapidly as energy prices accelerate quickly. At current energy prices – which are due to rise again this year – Melbourne has the quickest payback time of four years, with Brisbane next at 4.9 years and Sydney at 5.7 years and shrinking.
Naturally savings will vary with real-world applications developed in partnership with architects, builders, managers, and specifiers can now make some science-based ROI comparisons that consider the comfort and sustainability objectives of the spaces they create.
Further key elements of revolving door design – Façade
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 – as does the dramatic use of colour such as bronze or black (as used in an installation for the Petersham RSL in Sydney).
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 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 the elements as they enter the door.
Dimensional elements
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 optimised 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
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 times of the year, building overhangs provide shelter from weather and keep 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 authorisation before entering a security revolving door.
Adequate attention should also be paid to flooring.
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 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 achieve greater energy efficiency ratings.
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.
Capacity can range from larger doors – such as those at transport terminals – to intimate, welcoming and security-enabled spaces common throughout Australian commercial, industrial, financial, data, hospitality, health, and age care facilities, where stable temperatures, prevention of HVAC losses and ease of access (including wheelchairs) can be determining factors.
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.
The various factors affecting capacity and user comfort include:
- Diameter of the drum
- Throat opening
- Manual or automatic operation
- Compartment size and number of door wings
- Building and safety code requirements for maximum rotation speed and safety sensors
- Positioning drive on manual revolving doors.
Traffic-type capacity
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 (12sq ft). 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.
Diameter
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.
Throat opening
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.
Manual or automatic
Another parameter to consider in determining capacity is whether manual or automatic doors are utilised. Automatic doors most widely applied in Australasia 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 sometimes most suitable for low-traffic applications. However, this is not always the case – for example, many tall buildings in Chicago with multiple entrances have stood the test of time with four-wing, 2m diameter manual doors for 50-plus years.
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 that 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. For example, both the International Building Code (IBC) and NFPA 101, specify 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. Australasia's own standards must be considered in the local equation.
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 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:
- Determine the capacity needed for each entrance and consider the benefits of a larger-diameter door.
- Decide if a manual or automatic revolving door is necessary.
- Make specifications consistent with architectural details.
- Make specifications consistent with the manufacturer's door model selected as the basis of specification.
- Choose the number of door wings – two, three or four – and detail the plan view consistently.
- Indicate the desired dimensions for diameter, door opening height, and height under canopy as well as canopy height.
- Specify a finish for the canopy of the revolving door system. The basics to consider are whether the canopy will be visible from above and whether it is exposed to the outside elements.
- Determine security needs. Will night sliding doors be required? Prevention of tailgating or piggybacking? Do security concerns warrant remote locking and card readers?
A final word
At the outset of this article, I spent some time expressing the environmental and sustainability benefits of revolving doors, before also going on to catalogue their wider benefits in terms of their style, functionality, and flexibility.
I did this because a lifetime of experience in the industry in the US – the birthplace of revolving doors – has convinced me of their enduring benefits as a "green building" technology, which demonstrates performance in both hot and cold environments, in States ranging from Washington and New York in the North to Texas in the South.
Similarly, revolving doors' sustainability, style and practicality benefits are also widely appreciated across Europe (home of our global HQ in Edam, the Netherlands, serving 27 nations worldwide) and increasingly in Asian nations concerned about emissions and global warming.
Their performance, which can be scientifically assessed, is also highly worthy of consideration in Australasia and Papua New Guinea, which encompass a similarly broad range of climatic conditions as in the regions where they are widely accepted.
Like my colleague and friend in Australia – Michael Fisher, Managing Director of Boon Edam Australia – we don't claim revolving doors alone are a silver bullet for energy conservation, that is a multi-faceted question.
But we do believe it is becoming increasingly apparent that revolving doors' performance deserves deep and serious consideration in Australasia, with benefits that are too good to ignore in many applications.
*About the Author – Glen Tracy
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 23 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.
Like his colleagues at Boon Edam Australia, Glen works closely with architects, glazing contractors, consultants, and key customers.
About us:
About Royal Boon Edam With work environments becoming increasingly global and dynamic, smart, safe entry has become the centre of activity in and around many buildings. Royal Boon Edam is a global market leader in reliable entry solutions. Headquartered in the Netherlands, with 150 years of experience in engineering quality, we have gained extensive expertise in managing the transit of people through office buildings, airports, healthcare facilities, hotels, and many other types of buildings. We are focussed on providing an optimal, sustainable experience for our clients and their clients. By working together with you, our client, we help determine the exact requirements for the entry point in and around your building. Please take a look at our range of revolving doors, security doors & portals, speed gates, tripod turnstiles, access gates and full height turnstiles to ensure the security of your entry and perimeter.
