Health care facilities rely on emergency standby generators to ensure uninterrupted electrical power during utility outages. When utility power is lost, patients’ lives literally depend on backup power systems to keep operating rooms, nurseries, and life-sustaining medical devices working. Backup systems also power emergency egress lighting and fire-protection equipment.
The generators at The Medical Center of Columbus Regional Healthcare System, Columbus, Ga., were adequate to power critical loads during utility outages — despite some that were more than 30 years old — but they lacked the capacity to handle the hospital’s total electrical load, including HVAC, at the 400-bed hospital. Currently, The Medical Center runs on about 4MW of power. Despite taking precautions, utility outages at The Medical Center over the years have ranged from a few seconds to several hours.
Rather than add to the mix of existing standby generators, which had been cobbled together as the hospital grew, The Medical Center decided to replace all of them with a new central power plant, located across the street from the main hospital in a free-standing building, equipped with four 2,500kW gen-sets from MTU Onsite Energy.
With a total capacity of 10MW, the plant is more than capable of meeting the hospital’s energy needs. “Even if two of the plant’s 2.5MW generators failed, we could still run on the other two and not have any issues,” says Mark Smith, the hospital’s director of facilities management.
Smith describes the new system as “totally redundant.” Utility feeds from two separate substations supply power to the main switchboard. If power from one utility feed fails, the other utility feed automatically supplies the power. The standby generators get a signal to start if one of the utility feeds fails; however, if the second utility source remains stable, the generators shut down and return to a standby state.“If any piece of equipment in this plant fails, there’s a backup piece of equipment that will do its job,” Smith says. “So you’d actually have to have multiple failures before the plant wouldn’t operate.”
The gen-sets generate power at 12,470V. The ability of the generators to operate at this high voltage enables them to match the incoming utility voltage and avoid energy-wasting transformers between the utility and the central plant. Also, by generating at this high voltage, electricity travels more efficiently through the underground cables connecting the central plant to the hospital across the street.
Even the layout of the new central plant contributes to the system’s efficiency. For example, the design engineer arranged the four gen-sets so that the exhaust vents from the engines and the cooling air intake vents for the radiators were located on the same side of the building. This design makes sure that the exhaust gases do not reenter the building, and it allows all of the switchgear to be grouped together along the other side of the building, resulting in more efficient use of space and easier maintenance access.
Control equipment for the standby power system is located in both the central plant and a power center inside the hospital. Facility management personnel can take full control of the generator plant from the power center, which includes a 52-in. digital display that projects a one-line diagram of the plant. Four 400-gal day tanks housed in the plant building supply fuel for the generators. A 20,000-gal tank on the hospital side of the street resupplies the four day tanks. Although the hospital plans to add additional fuel storage capacity, the new generators actually use 30% less fuel than the old units for a given load.
The units also run more quietly than their predecessors, thanks to critical-grade mufflers installed on each unit. “There’s an HVAC cooling tower nearby, and you can hear the water running in the cooling tower over the noise made by all four generators,” says Eddie Oliver, a sales engineer for W.W. Williams, the local MTU Onsite Energy distributor that provided the units to The Medical Center.
The new plant has the capacity to power all electrical loads in the hospital, not just critical life-safety systems, said Smith. Among other advantages, this gives the hospital greater flexibility in managing power use and cost. At any given time, the facility can be totally on the power grid, partially on the grid, or totally off the grid, depending on the situation. During routine testing, hospital personnel can start the generators and briefly operate them in parallel with the utility while the facility transitions from full utility power to full generator power. Without this paralleling feature, power breaks could cause lights to flicker and/or disrupt the operation of critical medical equipment.
Similarly, during the approach of a severe storm, the hospital can preemptively run its generators in parallel with the utility until the storm passes. “All you do is burn a few gallons of fuel,” said Smith, “There’s little cost involved, but the payback could be tremendous. If we did it 10 times and lost power just once, it would be well worth it.”
The Medical Center’s new central power plant can also be put to use during extremely hot summer days, when power demand soars and utility rates jump. At such times, the backup generators can take some load off the grid and potentially reduce electrical costs, depending on the price of diesel fuel and the price the utility is charging for electricity at any given time. To determine whether dropping off the grid makes financial sense for the hospital, Smith plugs the spot price of diesel fuel into a formula for calculating the price at which the hospital can generate its own electricity. Then he compares that price to the price being charged by the utility at that particular time.
If the utility’s price for electricity is higher than the cost to generate power onsite, Smith flips the switch on the new power plant. As a result, during some recent hot periods, the hospital saved approximately $5,000 per day in power costs, according to Smith. The U.S. Environmental Protection Agency (EPA) limits the number of hours per year the hospital can run its generators for load management, but that’s not a problem. “We don’t come anywhere close to the limit,” says Smith.
The Medical Center originally planned to purchase three generators and leave room in the plant for a fourth. Instead, it purchased four units. This means, says Oliver, the hospital’s power needs could grow by 80% and still leave one redundant generator for more convenient maintenance and reliability purposes.
Since completion of the installation, the gen-sets have performed exactly as designed during several power outages. In the near future, The Medical Center plans on using this central energy plant to provide backup power for another hospital across the street. Despite these increased demands on the power, Smith is confident about meeting any challenges that arise. “This emergency power plant will serve our needs today and carry us into the future for years to come,” he says.