As the healthcare construction industry grows, associated technology continues to advance, bringing with it a large number of emergency power system options. Older, existing emergency power systems are being upgraded to take advantage of this availability and meet modern code requirements. In fact, it’s no longer uncommon for healthcare facilities to harvest technology comparable to that of a power plant to switch between normal and emergency power without even so much as a blip in the lights—and it can all be done remotely.
Hospitals have been required to have emergency power for years, similar to all normally occupied buildings, as dictated by international and local building codes. However, in addition to the requirements for a standard building, a hospital’s emergency power system must keep critical care rooms and equipment powered in the event of any power outage, ranging from a power dip, commonly referred to as a “brown-out,” to a full power outage lasting up to 96 hours per NFPA 110. Advancements in technology pave the way for improved emergency power provisions, including redundancy and control.
Hospitals that were originally constructed with emergency battery packs (i.e., individual battery packs on each emergency light fixture) and other localized uninterruptible power supplies (UPS) supporting the critical equipment now have those same power circuits connected to a remote generator. This single-source power supply for emergency systems allows for simplified maintenance and testing, which therefore allows for better reliability. Some systems utilize large UPS, battery banks, and inverters for back-up power. A UPS is a single piece of equipment that contains both the battery and inverter along with the circuitry required to switch between DC and AC power. The DC batteries in these systems retain their charge from the normal power system. A battery bank is a massive rack of DC batteries, wired together in series or parallel acting as a power reserve. A battery bank requires an inverter to convert the DC power to AC power for delivery to a connected system. The inverter has the circuitry required to pass through AC power or utilize the DC batteries for the load. The benefit of these devices is the instantaneous response. They switch immediately with no indication of a loss of power to the connected load, whereas a generator supported system requires seconds to start. However, these systems have a short operating time limit. They can be sized for a full 90 minutes to support life safety systems, but they’re mostly useful to cover a power outage of a few seconds while emergency generators are starting.
Regardless of the location and complexities of an emergency power system, the same primary requirements hold true: Power must be restored within 10 seconds to the life safety systems. Here are some ways to achieve that.
The case for consolidation
Most major hospitals have grown over the years, building addition after addition. Each time a space is added, so too are emergency power provisions. The result is several emergency generators located at various points around the facility, and oftentimes there’s no cross connection or redundancy if one generator fails to start. Recently, hospitals have been performing major renovations in order to consolidate their emergency power to a central power station.
Consolidation of emergency power is the act of standardizing emergency power equipment and achieves several operational improvements. First, it provides new emergency power equipment. All equipment has a life expectancy and must be replaced before a critical situation. And while one can’t predict critical situations, having a thorough understanding of life expectancy can help keep equipment up-to-date. For example, battery life expectancy ranges from three to five years, while a power generator can last from 20 to 30 years if well maintained.
Consolidation also creates interchangeability. Most existing emergency power systems in various wings of a hospital don’t match one another, substantially increasing the spare parts and maintenance knowledge necessary for upkeep. Once equipment has been consolidated or standardized, facilities will require only one size and type of each piece of equipment. This will make it easier to swap parts among equipment and maximize the efficiency of operating units. Fewer spare parts have to be stocked because the same spares will work for any of the redundant equipment.
Consolidation presents the opportunity for N+1 redundancy, too, which refers to the capacity of the emergency electrical plant. If three generators are required to power the emergency systems, four generators will ensure N+1 redundancy, where “N” is the number of required generators and one extra generator is a spare in case any of the others are down for service or fail to start. Reaching N+1 redundancy ensures that backup power is not lost in the event of a technical failure.
Considering control options
Control options, such as generator control, closed transition switching, and load shedding, must be thoroughly considered when installing a new emergency power system. These systems have a vast array of options and flexibility. More sophisticated emergency power switching is performed through switchgear, utilizing controls and operable circuit breakers to connect and disconnect power sources and loads.
Generator control through the switchgear is similar to an automatic transfer switch (ATS)—a piece of electrical equipment that senses a loss in power, then calls for the generators to start and switches to the back-up power source as soon as it’s stable. The switchgear performs the same operation. The sophisticated controls can dictate which generators and how many generators need to energize. Often the sequence will call for all generators to start, and as soon as the first one is running, the loads are connected to that generator. As additional generators come on line, they automatically synchronize, and the intelligent switchgear connects them to the building loads. The benefits of this option include better load management, remote monitoring, and full customization.
A closed transition switch is used to momentarily feed a load from two sources simultaneously, usually from the normal utility and the emergency generators. The sequence calls for the new source to be closed to the load while the original source is still connected. After the new source closes, the original source opens. This is most beneficial when normal utility power is restored to a hospital, because the system can transfer back from emergency power without the slightest interruption to the hospital power supply. Special relays and controls are required to ensure this is performed safely, with closed transition switching preventing the power distribution system from seeing the slightest loss in power. This is a great feature for serving critical equipment if it doesn’t have a UPS. However, it’s important for systems with this sophistication to have well-trained maintenance personnel to operate them.
Load shedding is the act of disconnecting load from the emergency power system due to potential overload conditions. If the connected load exceeds the load capability by the connected generators, part of the load is disconnected by opening up a controlled circuit breaker. In order to do this, the loads must be prioritized and separated onto individual-controlled circuit breakers. This feature is great for prioritizing loads. If there aren’t enough generators available to power the connected load, low-priority loads are shed, such as HVAC. It’s the responsibility of the designer to organize the various types and priorities of loads on the power distribution.
Staying in control
These systems must be fully designed by the designer of record, rather than requirements described to the manufacturer to complete, as performance-based systems are dependable only if the performance is thoroughly defined. One very important element of the emergency power system is often underdesigned: system controls.
Emergency power systems require mechanical operation in order to properly function. Whether utilizing intelligent switchgear or ATS, the internal mechanics of this equipment require complex controls with a detailed sequence of operations. ATS come equipped with internal controls, but the designer must still identify sequences and specific features such as override capabilities, response actions, timer settings, relays to connected equipment, etc. The designer must also define which control signals will be remote and where those signals are to be relayed. Most ATS are fully capable of communication with a building automation system (BAS) and controlling the generators that serve them.
For example, the ATS or switchgear should signal the BAS in the event of a power loss because the BAS is typically powered through a UPS and doesn’t otherwise know the power has been lost. If the BAS doesn’t recognize the power has been lost, it will respond by alarming every system component that has just stopped working. The designer must work with the hospital representatives to define the system requirement, first by defining the needs of the facility, then organizing those needs from most to least critical, identifying the system options to accommodate those needs, and selecting the best options for the hospital in terms of effectiveness, maintainability, and cost.
While it’s important that the designer select all of the control options and define the sequence of operations, without proper quality control, there’s no guarantee that those controls will be integrated into the system. Commissioning the emergency power system will ensure the design will work. Completing quality control tests are a great way to ensure the system is installed as designed. However, in order to achieve exactly the level of testing depth desired, a commissioning agent should be involved to oversee functional testing of the system and run it through multiple scenarios. It’s just as important to define thorough and appropriate quality control as it is to provide a thorough, in-depth design.