Environmental regulations are prompting many companies to switch to non-CFC refrigerants. Simply substituting a new refrigerant in an existing unit will typically result in a 5% to 30% loss in cooling capacity and up to a 20% increase in power consumption. The only practical solutions to this problem are to modify or replace these chiller units. For most installations, modifying a chiller to use alternative refrigerants is far less expensive than replacing the machine.
High-Efficiency Replacement ImpellersConcepts NREC offers cost-effective chiller conversions with high-efficiency replacement impellers that maintain cooling capacity with little or no increase in power consumption. These advanced compressor impellers achieve a significant increase in efficiency. Combined with the newly optimized compressor operating point, improved efficiency offsets the losses inherent in a change from CFCs to new refrigerants. Depending on the operating conditions of the machine, performance can be substantially improved to be equal to or better than the original capacity without a sacrifice in power consumption.
Many existing chillers must be converted or replaced to meet federal regulations. Scheduling conversions to accommodate changeover strategies requires action now. A complete facility changeover can take several years, depending on the number and types of chillers. By planning ahead, disruption in facility operations can be minimized or avoided.
Performance ImpactThe CFC refrigerant in present equipment often cannot simply be replaced with new fluids. Only certain classes of materials can provide the thermodynamic and physical properties required of a refrigerant, and the current substitutes present several new problems. Because the thermodynamic and fluid-dynamic properties of the new refrigerants differ from those of existing fluids, they are not "aerodynamic drop-in" equivalents.
Retain Original Chiller Capacity
To retain original chiller capacity, the compressor must
be able to effectively drive the new refrigerant at the flow and
pressures required by the system. Chiller performance is established
by the heat load added to the system through the evaporator and
compressor, as well as the heat extracted by the condenser. The
working temperatures of the evaporator and condenser directly
translate into operating pressures according to the vapor pressure-temperature
relationship of the selected refrigerant. Since this differs for
each refrigerant type, changing refrigerants alters the operating
pressures and therefore the pressure ratio that must be developed
by the compressor. In a similar manner, the heat load that must
be absorbed by the refrigerant translates to a particular flow
rate according to the heat capacity of the substitute refrigerant.
System Design Point Alignment
with Compressor Capability
Changing refrigerants causes the system design point to shift as shown on a typical compressor performance map. The ability of a compressor to meet these new system requirements depends on its available range of performance and how the compressor was matched to the original system. A poor fit between the system design point and the compressor's capabilities forces the chiller to run less efficiently, thereby reducing capacity and increasing power consumption.
Typical Conversion Options Available
Chiller owners using CFC refrigerants have several options available for conversion. Only impeller replacement can provide the full capacity of the original chiller with minimal impact on operating costs, while economically using existing equipment. A machine can be returned to its original capacity with a minimum of downtime by retaining all major components except the impellers. Conversion options include the following alternatives:
- Stockpile CFCs and prevent leakage. Users can continue operating with CFCs knowing that refrigerant purchases will become increasingly expensive and difficult to acquire. There are also severe federal penalties for releasing CFCs into the atmosphere, so leakage prevention is critical.
- Use a substitute refrigerant. CFC refrigerants can be replaced with HCFCs or HFCs. However, the new refrigerants can react destructively with the elastomers and lubricants commonly used in present equipment. Substitution must also include the replacement of original gaskets, seals, and other vulnerable components using ones compatible with HCFCs or HFCs. Direct substitution also generally results in substantial performance penalties.
- Increase compressor operating speed. Increasing operating speed will often regain original chiller capacity. Electric drives almost always require physical modifications to increase speed, including gearing changes, motor rewinding, or motor replacement. Steam turbine drives may require refurbishment or even replacement to handle the required speed and power levels. However, speed increases generally force the compressor to operate in a lower efficiency region. Because overall power consumption goes up significantly, increased energy costs should be considered when evaluating this alternative.
- Replace chiller equipment. Original performance can be returned by completely replacing all or part of the chiller system with new equipment designed to operate with new refrigerants. Equipment manufacturers argue that older chillers are inefficient and should be replaced simply due to age. However, chiller compressors operate in a relatively benign environment and an extended life cycle can be expected of older machines that are well maintained. The parts that do ordinarily wear must be replaced in any case as part of a CFC conversion. To accommodate new equipment, extensive and costly facility modifications are often required. It can be far less expensive to bring an older unit up to current specifications than to completely replace it.
- Concepts NREC solution: Replace compressor impellers. Replacing the original impellers with a more efficient, modern design returns original performance. Most of the original components and operating conditions, including drive speed, are retained. The impellers are removed and new, high-performance impellers are designed, precision manufactured, and assembled onto the original shafts.
Replacement Impellers
Concepts NREC is internationally recognized for innovation in aerodynamic design and is a world leader in turbomachinery development. Using proprietary, state-of-the-art analysis and design technology, Concepts NREC can produce a precision-machined, high-performance replacement impeller that substantially improves compressor performance.
Comprehensive Chiller Conversion Services
Concepts NREC impeller replacement services include systems evaluation, inspection, design, performance prediction, manufacturing, assembly, balancing, QC inspection, and acceptance testing. Advanced engineering expertise and proprietary software are used to determine if impeller replacement is the best and most economical option available. Concepts NREC's cycle analysis capability ranges from simple assessments to detailed performance mapping.
Concepts NREC Offers Critical Technology
and Minimum Turnaround Time
Concepts NREC proprietary technology is also critical to
producing a machined impeller with a minimum turnaround time.
Starting with forged blanks to ensure material strength and integrity,
Concepts NREC uses advanced 5-axis milling machines to manufacture
the new impellers. The new impellers are machined to fit the original
shafts, overspeed spin tested, attached, and balanced.
Concepts NREC Provides Conversion Service Solutions
Concepts NREC offers complete CFC replacement solutions. Conversion services range from supplying new impellers to a complete kit, including new compatible parts (seals, gaskets, lubricants, etc.), new impellers, refurbished older components, reassembly, and acceptance testing of the newly converted machine. Concepts NREC can manage the entire conversion project while working with the on-site maintenance staff, chiller service providers, or nationally recognized product support organizations.
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