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As 2003 wound to a close, the nation's political and business
leaders continued to focus on curbing the rising costs of
health care. For health-care facility managers, this meant
carefully scrutinizing operating costs and relentlessly searching
for new ways to bring costs down—all the way to the bottom
line.
As if intense pricing pressures and escalating competition
weren't enough, recent wide-reaching power outages, which
paralyzed large regions of the country for days, turned the
spotlight on power reliability. When the lights came up, there
was a new mandate from hospital executives: Make sure our
hospitals keep both life-support systems and important
revenue-generating equipment running amid long-term losses
of power.
On the surface, reducing cost and improving power reliability
appear to directly oppose each other, leaving many facilities
engineers with more questions than answers: How can we justify
investing our finite capital resources in backup generation
equipment that sits idle most of the time? And given budget
constraints, how can we afford to train our staff to run this
equipment and maintain it on an ongoing basis?
The collective answer is quite simple. We can't—at
least not from this point of view.
But if we change our perspective to look at distributed generation
for primary—rather than backup—generation, new,
exciting solutions begin to emerge.
New
Thinking Produces New and Better Solutions
Cooling, heating, and power (CHP), a form of distributed generation
that recycles energy, tops the list.
The basic premise of CHP is one that many of us learned in
grade school: recycling. If we capture the energy lost
in traditional power generation, for example, we can reap
the benefits of reusing it. For the electric-power-generation
industry, this translates to anywhere between 45 GWh and 90
GWh of power lost each year—enough to power 45 million–90
million households or five to 10 cities the size of Manhattan.
These staggering numbers reflect the low efficiency levels
(only about 33%) realized by traditional power generation.
By recycling energy, CHP systems bring energy efficiencies
to upwards of 80%. This energy efficiency generates a host
of benefits for hospitals, including significant energy and
operating cost-savings, optimum power quality and reliability,
significantly reduced environmental impacts, and stronger
relationships with communities—relationships that can
translate into patient loyalty, an increasingly important
competitive advantage in today's health-care marketplace.
Today's Patient Care Depends
on Consistent, Reliable Power
For hospitals today, the importance of providing a consistently
reliable source of power—24 hours a day, seven days a
week, 365 days a year—continues to mount. Information
technology is seen everywhere, from patient rooms that almost
all contain both voice and data ports to diagnostic and electronic
equipment at the core of patient care to transferring patient
information from one area of a hospital to the next.
In addition, hospitals increasingly are becoming health-care
campuses connecting ambulatory care centers with core hospital
operations and even adjacent physician facilities. While these
campus settings are designed to set new standards in quality
patient care and attract the high-quality physicians needed
for growth, they can be a headache for the facility's
management team working to coordinate and manage these seemingly
disparate units. In the end, however, these campus settings
can provide the rationale for new energy solutions that raise
the bar dramatically.
CHP: A Chance to Raise the Bar
Just as high-tech industries are protecting electronic data
and signal processing by improving power quality with ultrahigh
reliability (99.9999% or even higher), information critical
to patient care can be protected. “Some machines and
equipment, such as the MRI units, are unable to be used while
on backup generators. With the onsite generator system, we
have three levels of energy security for our patients,"
says Lamar Davis, director of facilities management at Advocate
South Suburban Hospital.
What “onsite generator system" provides this reliability?
Many technologies are available. Tailored to a specific health-care
facility's needs, engine- or turbine-driven generators
produce electricity on-site. Operating this equipment produces
thermal energy that normally is wasted when electricity is
produced. This waste heat is recycled to generate steam and
to dry humid air and/or to produce hot or chilled water for
use in space heating, domestic water heating, or air conditioning.
This equipment operates in parallel with electric chillers
and heaters or gas boilers. The resulting integrated energy
systems are designed to balance supply with demand to optimize
energy use.
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| Figure 1 |
Internal-Combustion
Engine–Driven Generators
Engine-driven generators that burn natural gas generally are
preferred for power generation because they burn cleaner and
have lower emissions than diesel engines (see Figure 1). Many
installations use “dual-fuel" engines that can burn natural
gas, diesel fuel, or a blend of fuels. Engine generators range
in capacity from approximately 3 kW to 16 MW.
Standard diesel engines frequently are used on emergency
generators because they provide a better “power density"
than alternative engines. These machines operate at higher
speeds than engines designed specifically for base-load power
and consequently have higher maintenance costs and lower efficiencies.
Engine-generated heat can be recovered from the engine cooling
water, the oil or lubricant cooler, or the exhaust. Heat recovery
from the cooling water or lube oil is generally on the order
of 220°F, and exhaust heat can be used to produce low-pressure
steam (about 15 psig).
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| Figure 2 |
Gas
Turbine Generators
Gas turbine generators use an engine resembling a jet aircraft
engine to drive an electric generator. While aircraft engines
are designed primarily for thrust and low weight, industrial
gas turbines are designed for efficiency and improved torque
to turn a generator. In addition to uses in aircraft and stationary
applications, such as power generation and pumps for gas pipelines,
gas turbines are used in marine applications for propulsion
and power generation. Gas turbines can be fueled with natural
gas or diesel fuel. In some instances, biofuels are used,
although biogases must be treated to remove moisture and sulfur
compounds. Gas turbines, which generate power, range from
about 1,200 kW to 60 MW or larger. CHP applications use turbines
with electrical outputs ranging from 1,210 to 13,100 kW (see
Figure 2).
Gas turbines consist of an air compressor and an expansion
turbine. The compressor and turbine usually are mounted on
a common shaft. Air drawn into the gas turbine is compressed,
mixed with fuel at a high pressure, ignited, and then expanded
to atmospheric pressure. The turbine drives an electric generator.
Heat-recovery steam generators can be used to recover heat
from the gas turbine exhaust. These heat exchangers typically
produce steam at 125–150 psig that can be used for processes,
space heating, heating of domestic hot water, or production
of chilled water using an absorption chiller.
Microturbine
Generators
Microturbines were developed by expanding automobile turbocharger
technology to produce small combustion gas turbines that drive
electric generators with 30- to 20-kW capacities. This capacity
range is appropriate for small ambulatory care centers.
The general principles behind operating a microturbine are
the same as those behind operating a combustion gas turbine,
just on a smaller scale. Microturbines operate at 96,000 rpm,
while conventional gas turbines operate at 12,000 rpm. In
the simplest configuration, their electrical efficiency is
around 14–18% versus 24–30% for gas turbines. The
low efficiencies prompted almost all of the commercially available
equipment to incorporate “recuperators" that preheat
the combustion air with heat from the turbine exhaust to reduce
fuel requirements. In the process, the exhaust gas temperature
is reduced from around 900°F to 500°F, and microturbines
with recuperators can have 28% efficiencies.
Heat recovery from microturbines uses exhaust gas–to-water
heat exchangers. Both the microturbine efficiency and the
gas-bearing effectiveness are very sensitive to pressure drops
or flow barriers placed in the exhaust gas, so these heat
exchangers need to be designed carefully. The low temperatures
from recuperated microturbines are not well suited to producing
steam.
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| Figure 3 |
Absorption
Chillers
Large buildings, such as hospitals, frequently use “water
chillers" that produce water at about 44°F and pipe it
to air handlers, providing cool air for air conditioning.
Electricity-driven chillers operate by boiling a liquid “refrigerant"
at low pressure using heat from the chilled water loop. An
electrically driven compressor is used to raise the refrigerant
vapor to a high pressure and temperature so that heat can
be rejected outdoors. Then the cooled, high-pressure liquid
is expanded to a low pressure, and the cycle is completed
(see Figure 3).
Absorption chillers generally are classified as “direct-fired"
or “indirect-fired" systems. Direct-fired chillers contain
a burner and are operated directly from a fossil fuel–like
natural gas or fuel oil. Indirect-fired chillers use heat
from steam or hot water to produce the high-pressure refrigerant
vapor.
Absorption chillers also are classified as “single-effect"
and “double-effect," depending on whether or not they
use internal heat recovery to improve efficiency. Double-effect
chillers are about 50% more efficient than single-effect chillers,
but they are more expensive and require higher steam temperatures.
Both double- and single-effect, indirect-fired chillers are
established technology, and products are available from major
manufacturers of electric chillers.
Today's Possibilities Equals
Tomorrow's Realities
The United States Department of Energy, through Oak Ridge
National Laboratory and in partnership with equipment manufacturers
and engineering firms, is working to standardize CHP packaged
systems that reduce transaction costs associated with CHP
installation. More specifically they serve to
- reduce capital costs,
- lower installation costs and shorten installation schedules,
- optimize system energy and emissions performance,
- improve maintainability.
These integrated energy systems meet a wide range of energy
needs—both thermal and electric. They feature preengineered
components designed, delivered, and installed as a single
unit or modular units. Since custom engineering is reduced,
these systems easily can be replicated for multiple installations.
Teams are developing systems that integrate turbine- or engine-driven
generators to optimize the use of waste heat. Smaller systems
can be installed as a single unit and range from 30- to 300-kW
electrical output that can generate up to 110 tons of chilled
water or domestic hot water from the waste heat. Larger integrated
energy systems can be installed modularly and can generate
from 300- to 5,000 kW of electricity and produce up to 2,500
tons of “free" chilled water (see Figure 4).
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| Figure 4 |
Small
CHP Packaged Systems
Several US equipment manufacturers and engineering firms have
teamed to package ultralow-emission, 30- and 60-kW microturbines
in arrays of up to 20 units. One team coupled two 60-kW microturbines
to provide heating and power to a hotel in Chesterton, IN.
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| Figure 5 |
The hotel company decided to replicate this system in its
hotel chain after the facility provided uninterrupted service
during a four-hour power outage—it was the only open
restaurant in town. Another system features a 110-ton absorption
chiller powered by waste heat from four 60-kW microturbines.
The double-effect absorption chiller produces cooling and
heating within the same unit (see Figure 5).
Large
CHP Packaged Systems
Gas research
institutes, universities, equipment manufacturers, and engineering
firms are collaborating to integrate 290- to 770-kW engines
and 1.2- to 5.0-MW gas turbines with absorption chillers (see
Figure 5). Reference designs will simplify installation by
making design details public. These large systems benefit
from supervisory control used to optimize operations in real
time. The Fort Bragg Army base in North Carolina is installing
a prototype 5-MW gas turbine generator integrated with a waste-heat–fired
or direct-gas–fired 1,000-ton absorption chiller that
produces both chilled and hot water (see Figure 6). The City
of Austin will benefit from another modular system that integrates
a 5-MW turbine generator with a waste-heat–fired 2,500-ton
absorption chiller. The system will provide electricity and
chilled water to a high-tech industrial park. In addition
to improved reliability through onsite generation and free
cooling, the double-effect chiller at times will displace
2,500 tons of chilled water produced by electrical centrifugal
chillers.
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| Figure 6 |
The Bottom
Line
On numerous levels, CHP recycling energy makes sense for hospitals.
It helps health-care facilities reach peak efficiency, which
equates to lower energy and operating costs. This in turn
means lower patient costs. Additionally, because CHP systems
are located on-site, revenue-generating equipment can continue
running during power outages—ultimately making CHP hospitals
more productive.
CHP offers other advantages critical to hospitals' success
with indirect benefits for the bottom line. CHP facilities
pollute less, making them good environmental neighbors, and
CHP hospitals can become “energy centers" for communities
affected by power outages. These benefits influence community
support and the hospital's image. It's time for
hospitals to embrace CHP.
In the next issue, we'll present the second in a series
of three articles on CHP. It will rely on case studies to
provide more in-depth information about how hospitals are
benefiting from these systems today.
JAN BERRY and STEVE FISCHER are with
Oak Ridge National Laboratory in Oak Ridge, TN.
DE - Jan/Feb 2004
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