By Dave Holmquist
Are you giving your customers' large tonnage chillers periodic checkups? If not, why not?
I've heard of many reasons. "No money," "Not enough time," or "We can't shut it down," just to name a few. They may be valid reasons at the moment, but over time, the lack of a checkup will cost you. When that happens, money may be least of your worries. Dealing with angry tenants or production managers asking "Why aren't we producing" may be a headache you could have avoided.
Today, the current buzz phrase of "return on investment" (ROI) is louder than ever. Do chiller checkups show a good ROI?
To justify chiller check-ups, you must look at the cost of a failure versus the cost of a check-up. One must take into consideration how much in lost production, equipment and repair personnel costs could be lost versus increased operating time, reduced repair time, reduced energy consumption and increased equipment life.
Preventive vs. Predictive Maintenance
There are two types of checkups for chillers: preventive and predictive maintenance. The two are very similar, however, each has its own specific tasks designed to help you maximize the productivity and reliability of your central chiller plant. By using these services, you prove to all concerned that you have maintained the equipmentto the highest standards. If you delay maintenance, and something does go wrong, you probably know what questions you will be asked. What will your answers be?
Preventive maintenance is the annual, prescheduled service, where all or part of the components of a chiller are tested, inspected, or replaced. Typically, this would include:
- an inspection of the condenser heat exchanger and cleaning if necessary
- changing the oil filter, refrigerant filters and purge filter/driers, for low-pressure chillers
- an oil change, depending on what the oil analysis report indicates
- a thorough refrigerant leak test
- performing diagnostics tests on the control panel and chiller starter
- checking wiring for overheating and tightness at the connections
- testing the compressor motor and oil pump motor windings with a meg ohmeter. This test tells the condition of the motor windings
- lubricating the compressor, compressor motor, related pumps and motors to their manufacturer's specifications.
All of these tests are standard procedures that can be performed by a large machine service technician.
Predictive Maintenance Looks for Trouble
With predictive maintenance, the technician walks around the chiller and looks for anything unusual.
He should be looking at the condition of the:
- vibration eliminators
- worn couplings
- equipment cleanliness
Loose insulation is a major cause of evaporator shells leaking. Water accumulates under the insulation. The water sits there, having no chance to evaporate. This causes rusting of the shell from the outside in. If left unattended the shell will eventually leak. The repair can be costly depending on the severity of the leaks. At Owens Companies, we've had to repair small patches and coat entire evaporator shells.
During a recent inspection, one of our service technicians noticed cracks in welds that held the stator housing to the motor housing. These cracks were taken care of under a scheduled and controlled repair.
Predictive maintenance services are procedures that are meant to avoid more costly repairs. Repair time can be reduced through the information gained by these various predictive maintenance analysis procedures.
Parts are secured and personnel scheduled prior to the repair and a plan for the repair process is developed in advance.
Every Chiller has a 'Heartbeat'
A true preventive maintenance program would also include operating inspections. All of the services mentioned above are performed with the chiller not running, and in my opinion, are the bare minimum for annual service. Operating inspections reveal the chiller's "heartbeat." This is where you find the subtle changes in a chiller's performance. These changes may not be noticeable to the ordinary eye, but to a trained service technician, the problem can be corrected before it becomes a failure.
During an operating inspection, all temperatures, pressures, refrigerant and oil levels, voltages, and amperages are recorded. These readings are then compared to previous readings. The service technician should look at the daily logs filled out by the operating staff. An experienced technician will note what needs to be done to get the chiller operating to top specifications.
It's one thing to take readings, but if the readings aren't interpolated properly, you lose the opportunity to make corrective actions immediately. Dirty condenser tubes or water strainers usually don't cause a real problem until the chiller goes into a surge condition. It can get pretty exciting if you've never heard a chiller in a surge condition. This happens when the compressor's impellor can't over come the lift required to push refrigerant into the condenser, and the refrigerant actually goes backwards through the impellor. The sound is not unlike an elephant blowing his horn in rapid succession. If left unattended, there could be bearing failure, due to the loading and unloading of the compressor.
Surging is the extreme result of fouled condenser tubes or strainers. Operating inspections will detect this condition long before it becomes your problem.
With any good preventive maintenance program, if you d n't document what has been done, you might as well consider it not performed. At Owens Companies, we give our customers the "Owens Blue Book," which lists all of the tasks required for each inspection. This is also where all copies of logs and work tickets are placed for future reference. It's a quick, easy-to-use, invaluable tool for our customers and technicians.
So think about this: what would it would cost if your customers' chiller failed for one day? How about one week of down time?
What would happen if you heard the dreaded phrase, "The parts are three weeks out"?
A good preventive maintenance program is small in cost, compared to a major failure.
Predictive Maintenance Includes Analysis and Testing
The timing of these services varies. Guiding factors should be the age of the equipment: how critical the chiller is to the operation and productivity of the facility, whether the units have a history of unexpected failure, and if they fail, what safety problem could arise?
Oil and lithium bromide analysis should be done annually. The oil analysis would show indicators of wear metals, contaminants, viscosities and inhibitor levels. When performed annually, it's easy to trend by using charts showing the condition of the oil. We had performed oil analysis testing for a customer for many years. In one year the tin and iron increase considerably.
The decision was made to open and inspect the compressor. The thrust bearing had worn to the point where it would not have been long before there would have been damage to the impellor. We replaced the bearings and the chiller has been running fine since.
Lithium bromide analysis shows what the chemical balance is of the solution in the absorber. The analysis would tell you what the inhibitor levels are, whether ammonia is present, solution percentage, octyl alcohol content, alkalinity, copper, and foreign contaminants.
Without knowing the chemical balance, you run the risk of prematurely ending the life of the chiller.
The vibration analysis also should be done annually. This test indicates an imbalance, misalignment, bearing defects, open rotor bar conditions, gear wear, harmonics, and excessive shaft run-out.
Eddy current testing is a non-destructive test of the heat exchangers within the chiller. It can detect inside diameter and outside diameter defects. The test also determines the severity of the defect and whether immediate action should be taken. We recommend this test be done every three to five years.
Ultrasonic, infrared, and motor current analysis are important predictive maintenance tools that should be a part of the customers' maintenance budget. All three help to confirm whether the chillers are operating reliably and efficiently as possible.