|
— By James Piper
Building chillers are the single largest energy-using component in facilities. So proper
chiller operation and maintenance is critical to an organization’s energy efficiency.
Issues such as routine and preventive maintenance tasks to be performed, chiller overhauls,
and chiller replacement are critical, given the chiller’s impact on the bottom line. Bad
choices will result in high operating costs, low system reliability and dissatisfied
customers.
How effective can chiller maintenance programs be? A typical centrifugal chiller that has
been in operation for five years without a comprehensive maintenance program that is designed
to maintain the design efficiency of the chiller probably will have a full-load operating
efficiency in the range of about 1.0 kW per ton.
Had that same chiller been maintained by a program that monitored its operation for leaks,
cleaned its tubes once every two years, and provided proper water treatment, it would have a
full load operating efficiency close to about 0.70 kW per ton. On an annual basis, the
chiller that had been properly maintained would use 20-25 percent less energy each year.
Although it costs money to perform maintenance tasks, energy savings produced by the properly
maintained chiller would recover those costs in weeks.
Maintenance and engineering managers can take seven time-tested steps that can help ensure
that their facilities’ chiller systems operate as efficiently and effectively as possible.
While these steps are often straightforward, many are too often overlooked, resulting in
chiller systems that use more energy, break down more frequently, and need to be replaced
sooner than chillers that are properly operated and maintained.
Training
One important step in managing chiller system operation is seeing that maintenance personnel
are properly trained in maintenance and operating practices. Too often, chillers may appear
to be running well but may not have been properly set up for efficient operation, due to lack
of operator training.
For example, chilled-water-supply temperatures may be incorrect for the space conditions, or
condenser water temperatures may be out of the manufacturer’s recommended range. Such
problems may seem minor, but they are major when it comes to efficiency. Proper training can
help maintenance personnel recognize and correct poor operating practices, and developing
maintenance problems.
Chiller logs
An essential diagnostic tool for chiller systems is the operating log. Most chiller problems
develop so slowly over time that unless someone is specifically looking for them, they will
go unnoticed.
By recording and reviewing operating data on a regular basis, technicians can establish
chiller performance trends that reveal the chiller’s health and efficiency. Many facilities
maintain logs, but too few review data in the logs regularly.
For example, trend data may clearly show that air is entering the system, refrigerant is
leaking out, or bearings are wearing, but unless someone reviews the log’s data, the first
indication of a problem either will be the chiller’s inability to meet the building’s
cooling load on a hot day or the outright failure of the chiller.
Scheduled inspections
An inspection schedule is important to ensure a chiller’s health and operating efficiency.
Inspections that are performed daily, weekly, monthly and annually will identify minor
problems long before they develop into larger, more costly ones. They also will help identify
specific maintenance activities that must be performed to ensure the chiller is operating
efficiently.
Some tasks, such looking for leaking oil, water, or refrigerant can be performed while the
chiller is operating. Other tasks, such as annual or semi-annual inspections of the tubes for
corrosion and scale, require that the chiller be taken out of service and torn down.
Cooling tower inspection
Too often, managers view chillers with tunnel vision but overlook the supporting equipment,
even though the condition of this equipment to a great extent impacts the operating
efficiency of the chiller.
Of particular concern is the cooling tower. A chiller is only as efficient as its cooling
tower, yet cooling towers too often are treated as out of sight and out of mind.
While regular maintenance and inspections are important for the efficient, reliable operation
of chillers, they are critical to the operation of cooling towers. Conditions such as
biological growth, physical damage and clogging of spray nozzles all can significantly impact
the ability of the tower to reject heat, reducing the chiller’s operating efficiency and
leading to long-term damage.
The efficiency of the chiller falls by 2 percent for each degree of Fahrenheit temperature
rise in condenser water supplied by the tower to the chiller. Managers should make sure
technicians evaluate the condition of the cooling tower before making a chiller-replacement
decision.
Chiller replacements
No matter how well the chillers are operated and maintained, they eventually reach the point
where it is no longer economical to keep them running, and they must be replaced. Selecting a
replacement chiller is one of the most important purchases a engineering maintenance manager
can make, not only because of the chiller’s cost but also because of the its impact on the
facility’s operating budget. With equipment life expectancies of 15-25 years, that impact is
going to be felt for a long period of time.
Traditionally, worn-out chillers were replaced with similar models of the same size. Today,
thanks to new technologies, managers have a wider range of options available to them, options
that must be carefully considered in order to gain the most out of the replacement project.
Fuel source
Historically, the fuel choices for building chillers have been ignored. Electric chillers
were replaced with electric chillers. Deregulation, however, has put an end to this practice
by providing engineering and maintenance managers with an incentive to better manage their
electrical loads. With the advent of real-time pricing for electricity, managers are looking
for ways to flatten their facilities’ electrical load profile. And the electric chiller, with
its high electrical load, is a very big target.
With alternatives available, including natural-gas-driven centrifugal chillers, as well as
steam- and gas-fired absorption units, managers can install an alternative-fuel-source
chiller for use during periods of peak electrical demand, thus reducing their electricity
costs.
Sizing
When making chiller-replacement decisions, managers need to pay careful attention to the
capacity of the replacement unit. Chances are, the cooling loads have changed considerably in
the building since the original chiller was installed.
Factors such as changes in building use, upgrades to other energy-using systems and original
system oversizing all can combine to produce situations were the existing chiller is
oversized for the current building needs.
Oversized chillers cost facilities money in two ways. First, excess installed capacity wastes
money. At roughly $600 per ton of installed capacity, an oversizing of only 10 tons costs an
additional $6,000.
Second, oversized chillers cost more to operate. Operating a chiller at less than full load
reduces its operating efficiency. The lower the load, the lower its efficiency. Oversized
chillers spend more of their time operating in lower efficiency ranges than properly sized
chillers.
James Piper is a consultant with more than 25 years’ experience in facilities management.
Efficiency Matters
In the past, specifiers made comparisons between chillers using full-load efficiency ratings.
But while full-load efficiency is a relative measure of a chiller’s efficiency, it is not
very realistic.
A chiller typically operates at full load less than 1 percent of the time. Comparisons
between chiller full-load efficiency ratings will not produce an accurate indication of a
chiller’s actual performance.
A more reasonable estimate of a chiller’s performance is its integrated part-load
value/application part-load value (IPLV/APLV).
Developed by ARI, this rating uses a weighted average, based on a wide range of factors,
including geography, type of building, hours of operation and part-load operation. Managers
can consider using the IPLV/APLV to evaluate replacement chiller options.
Maintenance Solutions Online
|
