Revolving Doors: A New Spin on an Old Technology

Revolving Doors: A New Spin on an Old Technology  – Copied from Green Spec ( BuildingGreen.com )

Revolving doors were patented in the 1880s to keep dirt, noise, precipitation, and drafts out of buildings and have long been used as the primary entrance into most large buildings. They maintain a reasonably good, constant seal against the outdoors—or as the industry states, are “always open, always closed”—minimizing the loss of conditioned air while allowing traffic flow in a minimal amount of space. In skyscrapers, revolving doors are necessary for maintaining air pressure and reducing air leakage from the stack effect—where cold air from air conditioning on upper floors flows down to lower levels (and out the front door) in summer, and heat rises in winter, pulling cold in through entrances—which can make swinging doors difficult to open or close.

Revolving doors have two to four wings, and are available in both manual and automatic models. Smaller four-wing models and large automatic two-wing models, which have two smaller wings on either end (like a “y”), provide better seals to the vestibule than do three-wing models. All of these wings collapse outward in case of fire, allowing an unrestricted exit.

Important considerations for selecting a revolving door include size of the building opening, number of people using the entrance per minute, handicapped accessibility, luggage usage, and security or control of access.

Manual models are six to ten feet (1.8–3 m) in diameter and are usually the most cost-effective option. They are used for restaurants, banks, universities, libraries, and other buildings where wheelchair access and luggage are not prime concerns. Typically available in three- and four-wing models, these doors can handle 20 to 50 people per minute and use speed reducers that keep the rotations below 8 to 12 per minute (the maximum speed allowable by the National Fire Protection Association), depending on diameter.

Automatic revolving doors come in a variety of sizes, from four-wing models eight to ten feet (2.4–3 m) in diameter to two- and three-wing models over 20 feet in diameter. As with manual doors, maximum rpm is based on door size, with large models spinning at about 3 rpm. Some of these doors can handle 60 people per minute, and are used in hospitals, grocery stores, hotels, and other high-traffic settings because of their large compartment sizes.

A 2006 MIT study showed that using a revolving door rather than a swinging door in its E25 building resulted in one-eighth as much air infiltration (and corresponding energy savings from reduced HVAC demand). Infiltration rates vary widely depending on interior and exterior building factors, and revolving door manufacturer Horton Automatics attempts to incorporate them into the company’s “energy calculator” using local weather data from the National Weather Service along with ASHRAE calculations to determine energy savings.

Elias Campos, vice president of marketing for Horton, compared a ten-foot-diameter (3 m), three-wing manual revolving door to a six-foot -wide (1.8 m) swinging/sliding door, using Chicago as the location along with a building height of 60 ft (18.3 m), entrance use of 3,500 people per day, ten hours of operation, 72ºF (22ºC) indoor temperature, 50% indoor humidity, and 10 mph (16 kph) wind speed. The program calculated peak load reductions of 2,050 tons cooling and 354,000 Btu/hr heating, and 271,000 lbs/yr CO2 emissions.

In this calculation, the revolving door had an installed cost of $75,000 (large, high-end models can cost more than $100,000) compared to only $10,000 for the swinging/sliding door. But the payback was only 26 months—three to five years is typical for a revolving door. Campos’ payback calculations do not factor in potential reductions in the size of mechanical systems.

Though accidents can happen in any entry system, large automatic revolving doors create inertia that could pose a safety risk, particularly to children and the elderly, if not managed properly. To minimize this risk, these doors are equipped with an array of infrared sensors in the wings and vestibule that work in tandem with contact switches on the wings, mats, and at the throat opening to both activate the doors and safely stop them, keeping occupants or luggage from being pinned in the door. (Other sensors can be used in tandem with security systems to verify individual access to secure buildings.) Manual buttons that slow the doors for handicapped access or stop the doors in an emergency are also standard features.

Restaurant chain Bone fish Grill is incorporating manual revolving doors in over 50 of its restaurants. They were chosen primarily to save energy and square footage, but the doors also provide an “upscale, polished” look. “They are a point of distinction between Bonefish Grill and casual restaurants,” according to Tim Martin, senior project manager at OSI Restaurant Partners. The doors empty directly into the restaurant’s lounge, and, Martin said, “We made the revolving door prominent to encourage its use.”

Making sure people use revolving doors is critical. Buildings can’t realize energy savings if occupants use the swinging door—fire codes require these to be within 10 feet of the revolving door—rather than the revolving door; in the MIT study only 23% of the E25 building users opted to use the revolving doors. Fortunately, the study also showed that behaviors can change and that entrance design, like that found at Bonefish Grill, influences revolving door use, as did adding large signage pointing to the revolving doors. In the E25 building, signage placed on an easel in the lobby increased revolving door use from 23% to 63%.

Revolving doors may not be a perfect fit for every building, but because they do such a good job controlling air leakage and the corresponding energy loss, they should be considered for most commercial green buildings