Chillers represent a substantial capital investment and are a major contributor to operating costs in institutional and commercial facilities. For many organizations, chillers are the largest single energy users, and comprehensive maintenance is critical to ensure their reliability and efficient operation.
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While some organizations use predictive maintenance — including vibration analysis, infrared thermography, and rotor bar testing — to diagnose problems in advance, a comprehensive preventive maintenance (PM) plan remains the key to ensuring the best performance and efficiency of a chiller.
Chiller efficiencies have improved steadily over the past decade due to advances in controls, refrigerants and equipment design. As a result, chillers now have tighter operational tolerances, and regular service and maintenance are more crucial than ever. When developing a PM plan for chilling equipment, maintenance and engineering managers should consider five essential areas.
Chiller operators should document chiller performance daily with an accurate and detailed log, comparing this performance with design and start-up data to detect problems or inefficient control setpoints. This process allows the operator to assemble a history of operating conditions, which can be reviewed and analyzed to determine trends and provide advanced warning of potential problems.
For example, if machine operators notice a gradual increase in condensing pressure during a month’s time, they can consult the daily operating log and systematically check and correct the possible cause of this condition, such as fouled condenser tubes or non-condensables.
Chiller manufacturers can provide a list of recommended data points specific to equipment upon request. Operators can take data readings daily, once per shift at about the same time. Today’s chillers are controlled via microprocessor controls, so managers can automate this process using microprocessor-controlled building automation systems.
One large potential hindrance to desired chiller performance is heat-transfer efficiency. Chiller performance and efficiency relate directly to its ability to transfer heat, which begins with clean evaporator and condenser tubes. Large chillers contain several miles of tubing in their heat exchangers, so keeping these large surfaces clean is essential for maintaining high-efficiency performance.
Chiller efficiency deteriorates as tubes become fouled, when mud, algae, sludge, scale or contaminants accumulate on the waterside of heat-transfer surfaces. The rate of fouling depends on the system type — open or closed — as well as on water quality, cleanliness and temperature.
Most chiller manufacturers recommend cleaning condenser tubes annually, since they typically are part of an open system, and they recommend cleaning evaporator tubes once every three years for closed systems. But if the evaporator is part of an open system, they recommend periodic inspection and cleaning.
Managers can consider two primary methods for cleaning tubes:
New chillers feature automatic tube-brushing systems, which can be retrofit onto existing chillers. These systems use small, nylon-bristled brushes that flow through the tubes for cleaning. A custom-manufactured, four-way reversing valve is installed in condenser water-piping system, and every six hours, the system automatically reverses the flow through the condenser tubes for about 30 seconds.
Coupled with proper water treatment, these systems virtually eliminate fouling within the chiller and maintain design-approach temperatures. These systems typically show payback periods of less than two years.
Manufacturers recommend quarterly tests of compressors for leaks. Low-pressure chillers using either CFC-11, which has been phased out, or HCFC-123 have sections of their refrigeration systems that operate at subatmospheric pressure. Although these chillers are the most common in today’s facilities, it is difficult to create a perfectly sealed machine, and leaks allow air and moisture, commonly referred to as non-condensables, to enter the unit.
Once in the chiller, non-condensables become trapped in the condenser, increasing condensing pressure and compressor-power requirements and reducing efficiency and overall cooling capacity. Low-pressure chillers have high-efficiency purge units that remove non-condensables to maintain design-condensing pressure and promote efficient operation. One chiller manufacturer estimates that 1 psi of air in a condenser equates to a 3 percent loss in chiller efficiency.
Moisture in a chiller also can create acids that corrode motor windings and bearings and create rust inside the shell. Small rust particles called fines float in the vessels and get trapped inside heat-exchanger tubes. Fines on tubes decrease the unit’s heat-transfer effectiveness and overall efficiency. Left unchecked, they can lead to costly tube repairs.
The best way to monitor leaks in a low-pressure chiller is to track purge-unit runtime and the amount of moisture accumulation at the purge unit. If either of these figures is too high, the unit has leaks. Other indications of air in the system include increased head pressure and condensing temperature.
High-pressure chillers using CFC-12, HFC-134a, or HCFC-22 operate at pressures well above atmospheric pressure, and leaks in these types of chillers release potentially hazardous refrigerants into the environment. Environmental regulations limit the amount of annual refrigerant leaks.
Leaks also results in a lower refrigerant charge and other operational problems, such as lower evaporator pressure, which can cause the compressor to work harder to produce a lower cooling capacity. For positive-pressure chillers, technicians should monitor the refrigerant charge level and evaporator pressure to detect leaks.
Most chillers use water for heat transfer, so the water must be properly treated to prevent scale, corrosion and biological growth. A one-time chemical treatment is required for closed-water systems, which are typical of chilled-water systems connected to the chiller evaporator.
Open systems typically are used for condenser-water systems connected to the chiller condenser. Condenser systems that use sources such as cooling towers require continuous chemical water treatment. Managers should work with a chemical-treatment vendor familiar with local water supplies and can provide full-service maintenance for all facility water systems.
Scale should not be a problem if the vendor maintains proper chemical treatment of the evaporator and condenser-water systems. The presence of scale in the condenser or evaporator tubes indicates improperly treated water. The vendor needs to test water quality every three months and correct the water treatment program, which should aid in cleaning the chiller tubes.
Also, all systems strainers should be cleaned every three months. Sand filters and side-stream filters for condenser-water systems are very effective at maintaining clean water, if properly maintained. To determine when cleaning is required, technicians should monitor pressure drop at the filters and refer to manufacturer recommendations on cleaning. Filters should be cleaned quarterly, regardless of pressure drop.
Maintenance of strainers and filters limits chiller-tube erosion caused by sand or other small particles moving at high velocities. Erosion and tube pitting decreases overall heat-transfer effectiveness and decreases efficiency. If uncorrected, these conditions can lead to plugged tubes or catastrophic tube failure.
Technicians should inspect chilled-water and condenser-water piping systems annually for evidence of corrosion and erosion. Most manufacturers recommend eddy-current inspection of heat-exchanger tubes, including an electromagnetic procedure for evaluating tube-wall thickness, every three-five years.
Annual chemical analysis of oil and refrigerant can aid in detect chiller-contamination problems before they become serious. Testing consists of spectrometric chemical analysis to determine contaminants, including moisture, acids and metals, which hamper performance and efficiency. A qualified chemical laboratory specializing in HVAC equipment must perform the analysis. Most manufacturers provide annual oil and refrigerant analysis services.
Technicians should take an oil sample while the chiller is operating. The oil should be changed only if indicated by oil analysis. Technicians also should monitor oil filters for pressure drop and change them during a recommended oil change or if pressure drop is outside of tolerance.
Oil analysis can help detect other chiller problems. For example, high moisture content in the oil can signal problems with the purge unit, and changes in oil characteristics can signal the development of unacceptable compressor wear.
Managers use refrigerant testing to determine contaminants that might lead to reliability and efficiency problems. One main contaminant is oil that migrates into the refrigerant. One chiller manufacturer estimates there is a 2 percent loss in chiller efficiency for every 1 percent oil found in the refrigerant, and it is not uncommon to find 10 percent oil in older chillers’ refrigerant. Based on this estimate, such contamination can lead to a substantial 20 percent decrease in efficiency. The bottom line — testing can pay large dividends.
Want more information on oil chiller manufacturers? Feel free to contact us.
Kevin M. Graham, P.E., is a project manager with 10 years’ experience for Smith Seckman Reid Inc. an engineering and facility consulting firm.
Many industrial processes generate significant quantities of heat, which must be dissipated as quickly as possible to prevent damage to sensitive equipment as well as prevent defects in the quality of finished products.
Industrial chillers are heat exchange machines that exert a cooling effect that helps to rid a process or machine of unwanted heat. An industrial chiller can be a significant purchase, so it is vital to understand how to maintain it to keep it operational for as long as possible.
Depending on the chiller types you are considering, the key features of this list may vary slightly. For example, the points on a water-cooled chiller maintenance checklist won’t necessarily apply to air-cooled chillers.
Below is a general checklist for chiller machine maintenance with items that apply air-cooled chillers and/or water-cooled chillers.
Here are a few tips for maintaining your industrial chillers below:
As basic as this may seem, maintaining a daily record of operating conditions, including pressure and temperature in the chiller unit, as well as fluid levels and flow rates, can help quickly predict the likelihood of future damage to the chiller machine. Keeping a chiller log sheet is advantageous as a pre-emptive chiller maintenance schedule can be structured before the onset of actual damage.
Make chiller preventive maintenance tasks easy with the Cold Shot Guardian™ predictive maintenance app. This tool helps eliminate unscheduled downtime by providing “real-time” chiller guardian app screenshot operational information through your WIFI, LAN, or even LTE connections.
The industrial chiller working principle is reliant on heat transfer to exert a cooling effect. In shell-and-tube and brazed-plate heat exchangers, an obstruction to the flow of cooling fluid through condenser tubes will significantly diminish the efficiency with which a chiller transfers heat.
Over time, corrosion can accumulate inside the chiller tubing and impede the removal of generated heat. Therefore, it is necessary to schedule and carry out regular quarterly or at least yearly cleaning of the chiller tubes.
Reducing the temperature of the water entering the condenser of an industrial chiller, significantly improves efficiency as it has to work less to exert its overall cooling effect. Although not recommended as standard practice, reducing the water temperature passing through the chiller’s condenser unit may serve as a temporary measure to overcome coil problems.
Although all units Cold Shot Chillers manufactures are closed-loop chillers, some chiller condensers have water loops that utilize open cooling sources such as air-cooling towers. As a result of this environmental exposure, there is a tendency for the water to become contaminated with biological growths, corrosion, and scale, which could affect overall heat transfer and chiller efficiency.
Chilled water loops should be inspected at least yearly and treated to remove contaminants. Regularly inspect your chiller’s “Y” strainer and use an inline cartridge filter for additional protection.
Light should be visible through the condenser coil for dirt or airborne particle build-up. Check deep into the coils with a flashlight and, if dirty, clean as needed.
Always disconnect the power before cleaning and protect all electrical components from water and from water entering electrical conduit lines. Remove the covers of the chiller and use water or compressed air to blow back through the coil in the opposite direction of airflow. Avoid any damage to coil fins such as bending fins flat.
The rate of cooling of a chiller is dependent on the amount of refrigerant circulating through its compressor. Valve stems sometimes vibrate loose and will result in leaks. Refrigerant leaks from the compressor or the introduction of moisture into the system can also impact the cooling capacity of the chiller.
Checking for leaks and maintaining a proper level of refrigerant in the chiller’s compressor will ensure optimal performance.
Protection of system components from freezing is critical, as freezing can occur from the external ambient or internal system temperatures.
The evaporator (or other heat exchanger) is the most susceptible component to freezing, even during normal operation. The fluid entering the evaporator must be capable of passing through without forming ice. Ice formation quickly restricts the flow, causing further freezing and eventual rupture.
The chilled fluid needs to have a freeze point that is well below any temperature that the chiller is capable of cooling.
The rate of flow of chilled water must be maintained to ensure satisfactory industrial cooling performance. Chillers need between 2.5 and 3 gallons per minute (GPM) per ton to provide efficient heat exchange. You will typically see a 10°F temperature exchange at 2.5 GPM per ton, and an 8°F temperature exchange at 3 GPM per ton.
Another significant aspect of chiller maintenance is keeping air and moisture out of your chiller system. As these elements can diminish chiller efficiency and increase energy consumption, it is vitally important that they are quickly purged from the condenser circulation.
Laboratory analysis of the oil from the compressor unit of a chiller should be done every year and changed according to recommendations from the analyzing lab. When oil changes are made, it is necessary for filters to be tested and replaced if faulty. However, oil analysis is limited to only centrifugal chiller operation and maintenance. Newer magnetic bearing frictionless chillers do not utilize oil.
Routine sensor calibration, microprocessor control inspection, safety checks for electrical connections, wiring, and switchgear, are all recommended. Additionally, regular drive motor checks are required to keep chillers fully functional.
Chiller motors consume significant amounts of electricity when in use, which increases operation costs. Installation of variable frequency drives (VFDs) will offer energy savings as varying the motor speed matches motor efficiency to load, minimizing energy waste. These VSDs can allow chillers to operate normally even on emergency power generators.
Preventive maintenance not only reduces these costs but ensures longer equipment life and fewer production disruptions.
Cold Shot Chillers has been at the forefront of industrial chiller manufacturing and maintenance for over three decades. Our experienced and dedicated staff are always on hand to assist you with all industrial chiller needs.
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