In the age of the paperless—and near-paperless—hospital, it is essential that doctors, nurses, and healthcare technicians can access data 24/7/365. Whether located within the hospital, in stand-alone buildings on a hospital campus, or even sited remotely, these data facilities have special power requirements because they serve unique systems and services.
Data centers for healthcare maintain not only general computer data and patient records, but nowadays also manage electronic radiology imaging files and monitoring equipment. Without the data center operating, most modern hospitals also would have difficulty operating. Even if the hospital does not have a data center as such, it most likely has a main distribution frame room (commonly known as an MDF room), or rooms that house the active electronics and main computer systems essential to hospital operations.
The principle is the same, regardless of the size: Backup power must operate systems reliably when utility power fails.
Although hospitals are already required to have Level 1, Class 10 emergency generators and emergency power distribution systems that comply with NFPA 99, the data center must have access to plenty of emergency power.
The system's reliability is already halfway home just by virtue of being located within a hospital. But Class 10 emergency systems are required to be online and serving their loads within 10 sec—an eternity for computer equipment. Ten seconds may be sufficient for general power and lighting loads, but it might as well be 10 min as far as electronic data and computers are concerned. Even 1 sec. without power and everything shuts down—and shuts down hard.
MAIN EMERGENCY POWER
Before discussing the value of uninterruptible power supply (UPS) systems for short-term power ride-through and essential protection of critical healthcare data centers, let's review the hospital's main emergency power systems.
Hospital emergency power systems come in all shapes and sizes, from the simplest single-engine, single-transfer switch arrangement to a complex system of multiple-paralleled generators serving multiple transfer switches—and everything in between. The goal is the same: to power the hospital when utility power is lost. The key components of the emergency power system include:
The engine-generator, the emergency system's main source of power. A diesel or gas engine drives an electrical generator.
Paralleling switchgear, the brains of the emergency power system, provides electrical control and distribution when multiple engine-generators are paralleled to serve a common bus.
Automatic transfer switch switches loads between normal and emergency power sources.
Accessories, including all critical components that keep the engine-generator operational, such as generator batteries, battery charger, fuel tanks, and fuel pumps.
“So, how many engine-generators do I need? And what size?” the hospital administrator asks. Unfortunately, there is no one right answer to these questions. Every facility is different, every facility's needs are different, and there are countless combinations of sizes and numbers of engine-generators.
For example, if the emergency load is 2,500 kW, do you need a two-paralleled 1,250 kW engine-generators? Or a three paralleled 900-kW engine-generators? A single 2,500-kW unit? An experienced engineer can wade through the myriad calculations to provide hospitals with cost-effective environmentally responsible and sustainable emergency power solutions.
Now enter the UPS—the backbone of data center backup power. Usually by means of batteries, or sometimes by using the inertia of a rotary disc, the UPS provides a constant source of clean, reliable, and uninterruptible power to ride through the time until the emergency generator systems can pickup to loads.
Battery UPS systems are the most familiar types. Modern battery UPS systems use nickel-cadmium batteries wired in parallel to provide the emergency power through static transfer diodes. Batteries are sized in amp-hours, so the more load, or amps, you need, or the more time in hours you want the load to be served, the more batteries you need. The capacity of the UPS is really limited only by how many batteries you can fit into the room.
Rotary UPS units use the inertia of a spinning flywheel to provide power for short durations. How does that provide emergency power? When power is provided to the UPS, a small electric motor spins a large, massive flywheel. Then, if the UPS loses its power feed, the inertia of the disc keeps it spinning, which turns the motor into a small generator, generating electrical power until friction overtakes the disc's inertia and stops it from spinning. The advantage is that the rotary UPS takes up far less space than the batteries of a traditional UPS. The disadvantage is that the duration of the power is usually short—about 15 to 20 sec. But how much time to you really need?
Many hospital CIOs believe they need enough UPS power to be able to perform a safe shutdown of all of the equipment —often 20, 30, even up to 40 min. That's a lot of batteries. However, if the hospital has multiple engine-generators, if the engine-generators are properly maintained, and the UPS systems are fed by a high-priority emergency branch (usually the critical branch)—in other words, if the emergency system and UPS can be reasonably relied on to come back online within 10 sec. of a power outage—40 min. of battery power might not be necessary.
Remote monitoring of UPS and the batteries is another essential piece of the reliability pie. Too often, an unknown and undiscovered problem within the UPS or battery system can cripple the data center when power is lost. Everyone thinks the data center equipment is being safely supported and backed up by the UPS. In reality, it may not be the case, because the battery charger has failed, or the batteries have been drained, or any one of a dozen problems have happened that nobody knows about—until it's time for the UPS to do its job—and then it's too late. By specifying and designing remote alarm features in the UPS—power availability, battery status, charger status—and tying these alarms into the building automation system (BAS) or other 24-hour monitored system, the hospital can easily keep an eye on the status of the UPS system and know they can count on the unit when they need it.
In the coastal Southeast, susceptible to the wrath and fury of hurricanes, emergency power systems often go above and beyond code minimum requirements. Many hospital administrators and facility directors are asking themselves and their engineers: What do we need in emergency power in order to continue to operate our hospital if utility power is out for a week or more? While things like lighting and power for medical equipment are at the top of the list, HVAC systems (including cooling), water supply, sanitary systems, and even data are also essential for a modern hospital to operate and be fully functional during an extended utility power outage.
Is the data center located above the flood plane or in the basement? We advise our clients to locate their critical systems and equipment above the 100-year flood plan and where they will be protected from the impact of flying debris during a hurricane.
In addition to the power that backs up the data, the room itself is just as important. For data centers, providing dedicated reliable cooling is key. If the rooms get too hot, the electronics will not operate, no matter how much emergency power is flowing to the racks. Are air-handling units (AHUs) serving the room that is on emergency power? Are the chillers on emergency power? AHUs connected to emergency power without chillers connected to emergency power will just end up blowing hot air through the data center, and the equipment won't function for long under these conditions.
The case studies that accompany this article teach us an important lesson: No single thing makes a data center's power safe and reliable, even in a hospital. It takes the right pieces, parts, equipment, location, and design to ensure the system's reliability.
Hospital hardens to hurricanes
A 60,000-sq-ft. data center is located in a stand-alone building on the hospital campus. One of the main construction focuses of the building was the hurricane hardening of the building. The data center is not served by the campus central utility plant, but instead has a single 1,000-kW generator dedicated to that building. Additionally, UPS is provided by multiple battery-powered power distribution units (PDUs). Each data rack is served by two PDUs—one primary and one redundant. This arrangement provides maximum reliability on the UPS side, but minimal reliability on the generator side. If the single generator fails to start, the batteries in the PDUs provide only enough power for a controlled shutdown.
Reliable system saves cash
At a newly constructed hospital, the 30,000-sq-ft. data center is located on the fourth floor of the main hospital building. The data center is served by three battery-powered UPS units (no redundancy), which are fed by a dedicated critical branch automatic transfer switch (ATS). This critical branch ATS is fed by the hospital's emergency distribution system—the heart of which is three 2-MW paralleled engine-generators. Because of the high reliability of the engine-generator system, the hospital was able to downsize the size of the UPS systems in the data center to 14 min. of backup time, which resulted in a significant cost savings.
O&M trips up hospital
Recently at one hospital, the existing emergency distribution, installed many years ago, included the UPS units serving the data center feed from the equipment branch of the emergency distribution system. On the same distribution panel as the UPS were several air-handling units, elevators, and compressors. One of these motors had a fault, but instead of the breaker directly upstream of the motor tripping as it should have, the fault carried upstream two levels of distribution and tripped an upstream distribution breaker, which turned of power to a significant portion of the equipment branch, including the equipment distribution panel feeding the UPS units in the data center (the tripped breaker was on the load side of the ATS, so the generators and ATS were not a factor). After the batteries in the UPS depleted their 45 min. of capacity, the data center was without power. If the UPS units had been served by a critical branch of the emergency distribution system, completely isolated from any motor loads, this would not have happened. Even though all the pieces were in place—emergency power, multiple generators, ATS, and UPS systems—a single failed motor and a malfunctioning breaker, neither of which had anything to do with the data center, were the weak point in the data center's reliability. Design and maintenance are essential to system reliability.
|Gelfo is the director of the Jacksonville, Fla., office of TLC Engineering for Architecture. This office focuses on hospital design.|