Oil-free refrigeration compressor technology offers significant benefits in terms of efficiency and performance. Eliminating oil from the system can yield up to 40% improvement in part-load efficiency compared to fixed speed screw compressors. And, this performance improvement can be sustained over the life of the compressor since oil-free compressors incur no mechanical wear during operation.
While long-term performance is a key advantage, there are additional benefits of oil-free compressor technology in terms of maintenance. Removing oil from the chiller system results in a simplified chiller design that eliminates frequent maintenance tasks required on traditional oiled chiller systems.
A chiller with an oil management adds a significant number of additional components and design complexity to the system. A typical oil management system includes components such as an oil separator, which separates the oil from the refrigerant; oil cooler, which reduces the temperature of the oil because hot oil loses some of its lubrication properties; oil heater, which boils off refrigerant from the oil to prevent dilution; and an oil pump, which circulates the oil through the system.
A chiller using oil-free compressor technology, however, has significantly fewer mechanical components and design complexity since all the components associated with the oil management system are eliminated. This results in reduced maintenance and higher reliability over the life of the chiller.
Shown is a chiller with an oil management system.
An oil-free chiller.
Eliminated Tasks with Oil-free Compressors
The following maintenance tasks are required on traditional oiled chillers but no longer required on oil-free chiller systems:
1. Check the Oil Level
Frequency: Daily. Maintaining the correct oil level is one of the most critical tasks on a traditional oiled chiller system. Similar to a car with an internal combustion engine, improper oil levels can have catastrophic consequences to the reliability of the chiller. Low oil levels can result in damage to the bearings and motor shaft while excess oil can significantly degrade the efficiency of the chiller. In fact, an independent study conducted by ASHRAE Research Project 751-RP found the majority of chillers installed in the field have excess oil beyond the recommended charge levels which further degrades performance.
2. Change the Oil
Frequency: Annually. Changing the oil on a regular basis is needed to ensure the quality and reliability of the oil is maintained. Oil that is contaminated with foreign objects can result in significant damage to the compressor. The typical cost: $1,600 each change (excluding disposal fees).
3. Replacing the Oil Filter
Frequency: Biannually. An oil filter is required on a traditional oiled chiller system to filter contaminants in the oil circulating in the system. A clogged oil filter will prevent oil circulation in the system and can result in foreign objects damaging the compressor. The typical cost: $1,000 per replacement.
4. Inspect and Maintain Key Components on Oil Management System (Oil Pump, Oil Sump Heater)
Frequency: Weekly. There are many critical components in an oil management system needed to ensure proper oil circulation. An oil pump is necessary to ensure oil that collects in the heat exchangers and oil separator is delivered back to the compressor bearings. In addition, as oil mixes with refrigerant, it is important that excess refrigerant is removed from the refrigerant/oil mixture to ensure only oil is sent back to the compressor. This removal of refrigerant from the oil is performed by the sump heater. Any failure by these two components will prevent oil from returning to the compressor and can result in significant damage to the compressor.
5. Conduct an Oil Analysis
Frequency: Annually. An oil analysis is required on traditional oiled chillers to determine the condition of the oil and if any metal objects have contaminated the system. Metal object contamination in oil-free systems are significantly reduced as there is no metal-to-metal contact for any of the internal components of the compressor. The typical cost: $50 each analysis.
Lifetime Savings of Nearly $84,000 Possible
Eliminating oil from the chiller improves performance and reduces maintenance, saving up to $3,650 in annual maintenance costs associated with maintaining the complex oil management system. Considering a chiller can expect to have a life expectancy of 23 years, this can result in $83,950 in lifetime maintenance cost savings, based on 23-year chiller life expectancy, per the ASHRAE Handbook.
When you consider both performance and maintenance, oil-free compressors offer clear advantages over traditional oiled compressors in both areas. The performance improvement and maintenance cost savings for oil-free compressors result in the lowest overall total cost of ownership of any chiller in the industry today.
About the Author
Eddie Rodriguez is Strategic Marketing Manager, Danfoss Turbocor Compressors.
About Danfoss Turbo Compressors
Danfoss is a leading manufacturer of oil-free compressors and the pioneer of the Danfoss Turbocor® compressor — the world’s first oil-free magnetic bearing compressor for the HVAC industry. Today, award-winning Danfoss Turbocor® oil-free centrifugal compressors are used around the world in air-cooled, water-cooled, or evaporative cooled chillers in a wide range of applications, including comfort cooling, low-temperature process, ice storage, and heat recovery. Danfoss manufactures its Danfoss Turbocor® compressors in Tallahassee, Florida.
Danfoss engineers advanced technologies that enable us to build a better, smarter and more efficient tomorrow. In the world’s growing cities, we ensure the supply of fresh food and optimal comfort in our homes and offices, while meeting the need for energy-efficient infrastructure, connected systems and integrated renewable energy. Our solutions are used in areas such as refrigeration, air conditioning, heating, motor control and mobile machinery. Our innovative engineering dates back to 1933 and today Danfoss holds market-leading positions, employing 27,000 and serving customers in more than 100 countries. We are privately held by the founding family. Read more about us at www.danfoss.com.
All photos courtesy of Danfoss.
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