Flexible Solutions Help Logan Hospital Reduce Natural Gas Consumption by 44 Percent
One-third of a facility’s energy
bill can be directly attributed to its boiler room, and system inefficiency
leads to higher energy costs. Replacing
an older boiler system is one way to achieve energy savings, but it is not the
only option. Retrofitting an existing
boiler is another way to increase efficiency, reducing both operating costs and
When deciding whether to retrofit
or replace a boiler, its overall condition should be the determining factor,
not the boiler’s age. If a boiler’s
water-side and fire-side surfaces show minimal signs of heavy scaling, pitting,
cracking, or stress, its pressure vessel is likely in good shape and
retrofitting is a viable option.
If improving efficiency is the
goal, then it is important to identify the problem. The main cause of energy inefficiency is
system heat loss. If retrofitting is
recommended, the first area to upgrade is the controls system. New developments in boiler controls create
opportunities for substantial efficiency gains.
are options to help an existing boiler system produce measurable efficiency
increases and fuel cost decreases.
Positioning -- Many boiler burners are controlled by a single
modulating motor with jackshafts to the fuel valve and air damper. This
arrangement, set during startup, fixes the air-to-fuel ratio over the firing
range. Unfortunately, environmental changes such as temperature, pressure and
relative humidity alter the fixed air-to-fuel ratio, making combustion
inefficient. To account for these conditions, boilers with jackshaft systems
are typically set up with a high amount of excess air. This higher excess air
level reduces boiler efficiency and, over time, linkages wear -- making
To solve this problem, consider
incorporating parallel positioning into the controls system. It’s a process
using dedicated actuators for the fuel and air valves. Burners that incorporate
parallel positioning can be set with lower excess air levels. Energy savings of
up to 5 percent can be realized by introducing a parallel positioning system.
trim -- Another way to ensure peak efficiency is to use an
oxygen sensor/transmitter in the exhaust gas. The sensor/transmitter
continuously senses oxygen content and provides a signal to the controller that
“trims” the air damper and/or fuel valve, maintaining a consistent oxygen
concentration. This minimizes excess air while optimizing the air-to-fuel
speed drive -- Variable speed drives enable a motor to operate only at
the speed needed at a given moment, rather than a constant 3600 RPM as a drive
runs. This speed variance results in the elimination of unnecessary electrical
energy consumption. A variable speed drive can be used on any motor but is most
common on pumps and combustion air motors of greater than 5 horsepower. These
drives also produce quieter operation compared to a standard motor, and they
reduce maintenance costs by decreasing the stress on the impeller and bearings.
lag – Lead lag sequences the operation of multiple boilers,
matching system load. Lead lag enables
the boilers to operate at peak efficiency, reduces cycling and decreases maintenance
Facility Increases Efficiency by
Troy Jensen, controls systems specialist for 23-unit Intermountain
Healthcare, knew he could cut operating costs at Utah-based Logan Hospital by
optimizing the boiler system at the 400,000-square-foot, 225-bed facility. In 2010, he received funds to install advanced
Hawk integrated controls systems on the hospital’s three 300-horsepower CBLE
boilers. This gave Jensen the ability to
continuously monitor and control the boilers’ 02 level, stack
temperature, lead/lag sequencing and water level to increase efficiencies and
reduce operating costs.
Because he is not always on site,
and an emergency in the middle of the night could necessitate a quick increase
in the amount of steam required, Jensen integrated the controls into the hospital’s
building automation system. He then created
a schedule to reduce boiler operating pressure in accordance with the hospital’s
needs. Jensen also gave the Central
Sterile Supply Department access to the controls at their workstations so when
emergencies arise they can override the system.
Through his analysis of 24-hour
trend reports, generated by his newly automated systems, Jensen learned that the
boilers were inordinately oversized and cycling during low-load conditions,
even with a 6:1 turndown capability on their integrated burners.
Knowing that excessive cycling
was substantially increasing fuel costs due to repeated pre- and post-purge
losses, Jensen decided to explore his options.
Instead of starting with the current 300-horsepower boilers that turn
down to 60 horsepower, Jensen wanted to start with a boiler of about 60
horsepower and go down from there.
Jensen contacted Servco
Industrial Equipment Representative Jason Hansen in Salt Lake City to discuss the
best options. In June 2011, Jensen had a
ClearFire-V boiler installed at Logan Hospital.
The highly efficient boiler can modulate from 60 horsepower down to 12
horsepower. The flexibility of pairing the smaller ClearFire-V with the
existing boiler eliminated the issue of the boilers cycling off and on at night,
and shared the majority of summer load conditions.
Even if a boiler performs
well throughout an efficiency analysis, incremental savings may be attainable because
of the boiler's original sizing to its load. Inefficiency often occurs during
summer, when an oversized boiler remains mostly in low fire, cycling several
times an hour. This drives up radiation and convection losses as a percent of
input while increasing excess-air levels and reducing combustion efficiency.
Excessive cycling and poor combustion efficiency can reduce a boiler's
efficiency from a normal full-capacity rating of 83 percent to a percentage in
the low 70s.
Purchasing a small
“summer boiler” properly sized for reduced-load conditions is one recommended solution.
Taking into account the hourly cost of plant downtime per unit, annual savings
can be substantial with this strategy, especially during times of fuel-price
volatility. This solution can be applied to any efficient boiler with
“shoulder” operating months. Even on new projects, this can be an effective
“With the Hawk controls and ClearFire integrated into my building
automation system, I run on 56 percent of the gas that I used to run on,” said
Jensen. “That’s a 44 percent reduction
in natural gas.” Jensen said he recouped his expenses in less
than one year. He adds that an optimized
boiler system with Hawk controls can easily be replicated in other facilities, resulting
in a 30 percent to 40 percent decrease in operating costs, which in his
facility amounts to an annual savings of $700,000 to $1.3 million.
In addition, the new system has
environmental benefits as well. Jensen
compared CO samples from July 2009 and July 2011. “The savings was equivalent to taking 2,000
cars off the road,” he declared. “When
you hit numbers like this -- talk about environmental impact. Natural gas isn’t always going to be
around. It’s a finite resource. Wouldn’t it be responsible for us to use less
if we can?”
Jensen is eager to share his
knowledge with industry colleagues. He added, “The healthcare industry is
unique because we always have to be prepared for the worst-case scenario, which
would be a major emergency in the middle of a blizzard. Many facilities purchase equipment based on
this kind of scenario, and the boilers are left at the same set point all the
time, even during the summer. This is inefficient
and is wasting our natural resources.”
Many facility managers today are
looking at how to cut costs, and Jensen explains that if they try to reduce the
pressure on an oversized boiler, it cycles a lot, which results in excess fuel
losses and maintenance issues. In
addition to controls solutions such as parallel positioning, Jensen said there
is still room for improvement. Another retrofit solution to consider is heat recovery,
which further increases efficiency and reduces operating costs. Here are some options to consider:
Economizers transfer energy from the boiler exhaust gas to the boiler feed
water in the form of “sensible heat.” Sensible heat is created by the transfer
of the heat energy of one body, in this case exhaust gas, to another, cooler
body -- the boiler feed water. This reduces the boiler exhaust temperature
while preheating the boiler feed water, increasing overall efficiency. Economizers typically increase energy savings
by 2.5 to 4 percent.
Two-stage condensing economizers -- This
type of economizer combines the functions of both a standard non-condensing
economizer and a condensing economizer.
The first section of the economizer recovers energy by preheating boiler
feed water. The second section recovers
energy by preheating a cool liquid stream such as make-up water. Sensible and latent energy is captured from
the flue gases that leave the boiler.
Condensing economizers can increase energy savings by up to 10 percent,
depending on design and operating conditions.
High turndown burner --
Increasing burner turndown rate will increase energy savings and reduce
maintenance. Energy savings is realized
due to a reduction in on-off cycles.
Each on-off cycle is followed by purge cycles. During a purge cycle, large volumes of room
air pass through boiler, resulting in heat being blown out the stack.
Blowdown heat recovery -- All
boilers must remove dissolved solids from the boiler to maintain water purity
and ensure a long boiler life. Many
boiler rooms route blowdown to a flash tank that allows safe discharge of the
steam by reducing (flashing) the steam pressure in an enclosed tank.
Low-pressure steam is vented from the tank and condensate is discharged to the
drain. In many cases, these tanks are not insulated nor do they allow recovery
of the lost heat. A blowdown heat recovery system transfers the blowdown steam
energy to the boiler feed water, recuperating about 90 percent of this energy.
Proper Maintenance is Mandatory
Installing the proper equipment is the first step to achieving fuel
savings over a long period of time. To
keep the boiler operating at peak performance, it must be regularly maintained
and tuned. Technicians should keep
boiler logs of operating parameters and evaluate the findings regularly to
detect any issues or trends. On an
annual basis, a technician should test all controls for proper operation and
calibration as well as inspect, clean and lubricate mechanical linkages
according to the manufacturer’s instructions.
In addition to prolonging equipment life, regular boiler tune-ups are
required under the EPA’s new Area Source Rule.
To learn more about the new EPA rules for boilers, visit www.cleaverbrooks.com/epa.
Featured in the January issue of HPAC Magazine.