Top MEP considerations when designing for elevator systems
In recent years, there has been a growing trend toward architectural projects that focus on building upward instead of sprawling outward. When land is limited, particularly in urban areas, this is the most efficient use of space and resources. In Chicago alone, the number of active high-rise construction sites more than doubled (from 14 to 34) from October 2014 to January 2016.
Designing multistory buildings requires architectural teams to carefully plan elevator systems that meet current safety standards as well as address the unique needs of the space. This whitepaper will discuss mechanical, electrical, plumbing, and fire protection (MEP/FP) considerations for designing a safe and efficient elevator system.
Types of elevators
Hydraulic vs. traction elevators
When designing for an elevator system, it is important to first determine which type of elevator suits the project’s needs. Hydraulic and traction elevators have different requirements and specifications, and building height is a major factor in which one is appropriate for a project.
Pumps that are generally 30 to 40 hp move hydraulic fluid under a piston to raise this type of elevator and then return fluid back into the tank to lower the elevator. Hydraulic elevators are advisable for shorter buildings, up to 5 stories. They also contain flammable liquid and must feature appropriate fire alarm and protection devices.
Traction elevators, on the other hand, are suspended by tensile cable and balanced by counterweights equal in weight to a half-loaded elevator. They are raised and lowered by moving the cable. Traction elevators are commonly installed in buildings that have more than 5 stories and use motors that are generally 15 to 20 hp.
Traction elevator machinery has traditionally been located in penthouse spaces above the elevator shaft; however, "machine roomless" elevators are now available for buildings up to 150 ft tall. This centralizes all machinery within the shaft, saving the client the cost of building a dedicated penthouse space.
Smoke control and pressurization
Modern buildings are designed to contain a fire to the location where it starts, and floor plates generally are rated to prevent movement of smoke and growth of a fire. For this reason, care must be taken with shafts that penetrate multiple floor levels, because they are susceptible to collecting smoke from a fire or transferring smoke from floor to floor.
Smoke control normally is operated automatically by the fire alarm system, but firefighters need the ability to override the system. Because of this, smoke control is required to be annunciated and manually operated from a firefighter’s smoke control panel.
In the past, hoistway ventilation was the main approach to smoke control. When smoke was detected in an elevator shaft or lobby, vents in the top of the shaft would open to discharge smoke. Hoistway ventilation is becoming less preferable because it can exacerbate problems through stack effect, drawing smoky air from the fire floor through the shaft.
Pressurization is an alternative smoke control solution, which begins when a building’s fire alarm system is activated. It works by positively pressurizing the hoistway and pushing air outward through any opening, avoiding smoke infiltration.
Emergency power is a primary concern in new building design, especially since high-rise buildings are becoming more commonplace, and they are simply not accessible without elevators.
Electrical power requirements
In most jurisdictions, a high-rise is defined as a building with an occupied floor set more than 75 ft above the lowest level of access from a fire department vehicle. Backup power systems are required for high-rise buildings and are usually powered by generators. Emergency lighting including elevator cab lighting is considered an emergency load, while elevator motors are backed up by generators as standby loads.
All high-rise buildings must have standby power for elevators, but not all elevators have to be capable of running at once during an outage. Generators should, therefore, be large enough to operate only one elevator in a group. Elevator controllers should also be programmed to operate just one elevator at a time while on backup power.
Fire safety for elevator system design has changed dramatically in recent decades. Modernizations have been developed to solve life-threatening problems present in older systems.
Elevator recall is a control system that prevents occupants from unwittingly riding an elevator to a floor with a fire. It is now required among almost all elevators, both old and new.
In the first phase, emergency recall, the elevator descends to the level of egress (primary-level recall). If the fire is on the main floor, the elevator goes down to another level (alternate-level recall).
The second phase of elevator recall, in-cab operation, enables firefighters to use recalled elevators to reach a fire. A warning light will alert firefighters if a fire in the elevator machine room has made an elevator ineligible to use.
The need for this critical system component has become clear in situations where fires have broken out in older buildings without recall. In a 2012 case in Chicago, a fire in a 21-story building resulted in the death of a resident when the elevator took her to the floor containing the fire. The building was constructed in 1952 and lacked elevator recall.
Lobbies and fire service access
Fire-rated, enclosed elevator lobbies are required for hoistways in nonsprinklered buildings with more than 3 floors,as well as institutional-occupancy buildings or sprinklered high-rises.
High-rise buildings with an occupied floor located more than 120 ft above the lowest level of fire department access must also have at least two fire-service access elevators (or one if there’s only one elevator in the building).
Buildings with a height greater than 420 ft need to have an extra egress stairway, unless occupant self-evacuation elevators (with standby power) are available.
Awareness about the importance of self-evacuation elevators has grown since the Sept. 11, 2001, attacks. Typically, during an emergency, building occupants are urged to evacuate using the stairs. But in the case of a high-rise with more than 100 stories and thousands of occupants—some of whom may not be able-bodied—this is not a feasible option. Stairwells get backed up, and evacuation is slowed dangerously down at a time when every second counts. Egress from a building 40 stories or higher can take more than an hour.
Sprinkler systems and fire alarmsNew high-rise constructions are now including self-evacuation elevators that are protected from fire and smoke, allowing occupants to flee a building safely much more quickly than using the stairs. Building self-evacuation elevators also represent a far more economical option than adding egress stairways to every floor of a high-rise.
Earlier versions of fire protection codes for elevator systems required sprinklers in all hoistways, elevator pits, and machine rooms. But newer code requirements are less focused on sprinkler systems and have more emphasis on fire-resistant and non-flammable construction. Newer codes also discourage sprinklers in elevator spaces, leaving them open for evacuation or fire department operations during a fire.
Smoke detectors are usually obligatory for all elevator operation or access spaces as well as within 21 ft of any hoistway door and in elevator machine rooms.
Shunt trips must be in place wherever sprinklers are present inside the elevator hoistway or machine room. This is a precaution to allow removing power before the sprinkler system is activated.
-This article originally appeared on RTM. RTM is a CFE Media content partner.