Plant features four new generators
The new central plant, located across the street from the main hospital in a free-standing building, houses four new 2,500 kW generator sets from mtu. With a total capacity of 10 MW, the four units could provide the average power consumed by almost 1,000 homes with 200 amp service panels, according to Smith. The generator sets are powered by mtu 20V Series 4000 engines that have a proven record of dependability and performance. These engines feature greater cylinder displacement than comparable generator-drive engines, giving them greater reserve horsepower for better load acceptance, as well as precise voltage and frequency control. Voltage and frequency control are important in healthcare applications because medical imaging and other equipment are especially sensitive to power quality.
Like many mission-critical facilities, the hospital has provided for several layers of protection against power outages. For redundancy, the central energy plant is supplied by utility feeds from two separate substations. In the event that power from one utility feed is interrupted, power would be automatically supplied by the other utility feed. The standby generators get a signal to start if one of the utility feeds fails, however if the second utility sources remains stable, the generators shut down and return to a standby state. A generator equipment failure won’t cause problems for what Smith describes as a “totally redundant” system. “If any piece of equipment in this plant fails, there’s a backup piece of equipment that will do its job,” he says. “So you’d actually have to have multiple failures before the plant wouldn’t operate.”
The mtu generator sets generate power at 12,470 volts, which is fairly unique for standby power systems. However, 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, less energy is lost as the electricity travels 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 four generator sets are arranged so that the exhaust vents from the engines and the cooling air intake vents for the radiators are located on the same side of the building. While care was taken to make sure that the exhaust gases do not reenter the building, the arrangement 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-inch digital display that projects a one-line diagram of the plant. Fuel for the generators is supplied from four 400-gallon day tanks housed in the plant building. Fuel for the day tanks is pumped from a 20,000-gallon tank on the hospital side of the street. Although the hospital plans to add additional fuel storage capacity, the new generators actually use 30 percent less fuel than the old units for a given load, according to Smith.
Since completion of the installation, the generator sets have performed exactly as designed during several power outages. The units also run more quietly than their predecessors, thanks to the unique building design and hospital-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,” reports Eddie Oliver, a sales engineer for W.W. Williams, the local mtu distributor that provided the units to The Medical Center.
Flexibility gives hospital new options
The central energy plant has many advantages over the former collection of standby generators. For one thing, the new plant has the capacity to power to all electrical loads in the hospital, not just critical life-safety systems, says Smith. Among other things, 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, for example, 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, there could be breaks in power to the hospital that would cause lights to flicker and/or disrupt the operation of critical medical equipment.
Similarly, during the approach of a severe storm that might cause a power outage, the hospital can preemptively run its generators in parallel with the utility until the storm passes. The hospital has already done this once in the brief time the plant has been up and running. “We didn’t lose power in that case, but it was still worthwhile,” Smith says. “All you do is burn a few gallons of fuel, so 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.”
“Demand response” capabilities reduce power costs
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 hospital can run its backup generators to take some load off the grid and potentially save money on the cost of electricity. Whether the hospital will save money by doing so depends 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 was able to save approximately $5,000 per day in power costs, Smith reports. And, while there are limits established by the U.S. Environmental Protection Agency on how many hours per year the hospital can run its generators for load management, Smith says “We don’t come anywhere close to the limit.”
Extra generating capacity has its advantages
One of the plant’s most impressive features is its 10 MW generating capacity. At present, The Medical Center runs on about 4 MW of power. “So even if two of the plant’s 2.5 MW generators were to fail, we could still run on the other two and not have any issues as a result,” Smith says.
According to Oliver, The Medical Center originally planned to purchase just three generators and leave room in the plant for a fourth. Instead, however, “they bought for the future” by purchasing four units. This means, he says, that the hospital’s power needs could grow by 80 percent and still leave one redundant generator for more convenient maintenance and reliability purposes.
Soon, The Medical Center will call on its central energy plant to provide backup power for a sister hospital across the street that was acquired several years ago. And more growth is undoubtedly ahead for the region’s main healthcare facility. But with a quartet of powerful new generators at his disposal, Smith sounds 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.”