Cutting lifetime costs on industrial refrigeration systems

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Published: 20 October 2017


Thomas Lergenmüller, Product Manager Screw Compressor Packages at GEA Grasso, looks at bringing down the all-important total cost of ownership.

Cost and competitive pressure on companies keeps growing in almost every industry where industrial refrigeration or air conditioning cooling is concerned. Efficient refrigeration systems are vital for economic, safe and sustainable production and storage in this area.

The focus of planners and investors aiming at modernisation or new construction of systems has long changed to encompass more than just low investment costs. The total cost of ownership (TCO) for the entire service life of a facility has become decisive instead.
Special attention must be paid to the energy costs at full and partial load, which are usually a multiple of the investment costs when viewed across the service life. Life-cycle costs are adjusted by reducing operating, service and spare parts costs through optimisation of components such as screw compressors, variable-speed drives, oil separators and control units.
Engineering motto: redefine your TCO
Machine manufacturers like GEA have reacted to market needs, developing redesigned and new models in the area of industrial refrigeration and air conditioning: The GEA Grasso M series (types H, L, M, N) for screw compressors and screw compressor units was revised completely in the scope of the "Redefine your total cost of ownership" project in 2015. Users can enjoy optimised compressor technology at high availability to considerably lower costs, among others by significantly improving energy and working efficiencies under full and partial load and by reducing the complexity of parts and, as a result, the effort needed for maintenance and wear. Frequency inverters can be added to the units, and new motors with a larger speed range of up to 4,500 rpm increase peak capacities by up to 35% (max. 879 kW, ammonia [R717], -10/+35 °C). The compressor units were redesigned to make them even smaller, which helps planners working on facility modernisation within existing premises.

Model expansion: four smaller output levels for the GEA Grasso M series 
GEA recently supplemented this compressor family downwards with four smaller output levels (types C, D, E, G) based on the re-designed GEA Grasso M series for screw compressors and screw-compressor units. The performance range of the screw compressors now starts at a displacement of 231 m³/h at 2,940 rpm, instead of the previous 471 m³/h at 2,940 rpm. The upper end of the range is at 870 m³/h at 2,940 rpm and 1,332 m³/h at 4,500 rpm respectively in the largest models of type N. Planners and investors now have additional options if they wish to implement customized but cost-efficient refrigeration system concepts where lower and medium output levels are needed. The unit solutions of the GEA Grasso M series clearly reduce the TCO across the entire life-cycle of the system as compared to conventional screw compressors.

GEA Grasso M screw compressor
The eight screw compressors of the GEA Grasso M series offer a number of technical innovations and special characteristics that have a positive effect on the overall operating costs of the refrigeration system. The first among these is their very good energy efficiency under full or partial load. GEA engineers ensure this by providing a variable speed range of 1,000 to 6,000 rpm (compressor type C, D, E, G) and 1,000 to 4,500 rpm (type H, L, M, N) respectively, as well as by integrating a number of other features. A tandem slider smoothly adjusts the output between 10 and 100 percent and just as smoothly adjusts the internal volume ratio (Vi) in an expanded range, automatically implementing energy-optimized system operation even at fluctuations of the evaporation and liquefaction temperatures. The screw compressors of the GEA Grasso M series also are the first industrial compressors with a gas-pressure-activated check valve that minimizes expensive pressure loss on the intake side.
 
Less maintenance, lower costs
Maintenance and wear also raise the costs in system operation. An economically working refrigeration system must not fail. Efficiency is guaranteed decisively by long service lives at the least possible maintenance and spare parts effort. GEA has consistently implemented these system requirements in redesigning the GEA Grasso M series: The screw compressors have been made less complex, e.g. by integrating a central oil connection to avoid use of an oil pump in most cases. Axial bearings and shaft seals are built to be replaceable without removing the motor when maintenance is required on site. Simple and quick integration in a refrigeration system are ensured by an integrated compact suction filter and adaptive clutch housing with easy access to the clutch. High operating safety and a long service life have been ensured, among others, by a gas oscillation protection for small output ranges and a compensation piston for the axial bearing.
The GEA Grasso M series screw compressors also stand out with their compact build and space-savingly constructed components: The smallest model of type C weighs 392 kg and is only 852 mm long, 660 mm wide and 660 mm high (including the clutch housing).
 
GEA Grasso M screw compressor units
In addition to the eight screw compressors, the GEA Grasso M series also contains eight single-stage screw-compressor units that are delivered as installed and wired ready for connection as complete plug-and-play solutions. Components include a screw compressor of the GEA Grasso M series, a drive motor and oil management with oil separator, cooler and filter, as well as the GEA Omni™ control with sensors and safety devices each. The refrigeration output of the different types covers the area from 140 to 879 kW (R717, −10/+35 °C).

Clear reduction of life-cycle costs
Like the screw compressors, the compressor units from the GEA Grasso M series stand out by bringing down operating costs. Optimizing plant performance and design, they permit significant savings in energy consumption as well as in the costs for service, maintenance and equipment.

Using saving potentials
The engineering team consistently used any remaining savings potentials when redesigning its compressor units: the drive power required has again been reduced by three to five per cent as compared to previous models. Optional variable-speed drive motors have a speed range of 1,000 to 4,500 rpm. Energy-saving operation at improved efficiency is possible even in the smallest partial-load areas by gradual adjustment of revolutions with frequency inverter, combined with an automatic control of the optimal Vi.

The efficient oil circuit with filtration, automatic pressure control and minimized leakage risk to reduce oil consumption is another cost-saving component of the GEA Grasso M units. Its horizontal 3-level oil separator with level display, oil heating and micro-separation stage only needs a small oil volume and minimizes the oil discharge rate to 5 ppm at most. Costs are further reduced because the screw compressor units usually do not even need an oil pump (unless they operate at very low differential pressures), saving additional drive output, maintenance and spare parts, while increasing availability. Optional economizer operation can increase efficiency in applications with high temperature increases and pressure differences by interim cooling.
 
Optimised system control with GEA Omni
A demand-oriented, safe and economically efficient system process needs more than state-of-the-art components. They also must interact optimally. GEA Omni gives the screw compressor units an industry-leading open control and regulation system to ensure power-saving, stable plant operation at high availability. It integrates and coordinates all the relevant system components, ensures simple commissioning and efficient system management. The operating interface is a high-resolution 15.6" HD colour display (1,366 x 768 pixels) to support simple, intuitive work including single- and multiple-finger gestures. The integrated GEA OmniLink and GEA OmniHistorian programs permit quick remote access with a view and analysis of the entire recorded data history. System communication can be configured by Modbus/TCP and Ethernet, as well as optionally by Profibus DP or Profinet.
 
Long service intervals, high system availability 
Just like their screw compressors, the GEA Grasso M units are charactersied by their high reliability and low maintenance requirements. All relevant components, such as motors with flange connections, drive shafts, bearings, seals, oil circuits and tubing, are designed for the highest stress and work reliably in permanent operation as well. This ensures high plant availability thanks to long service intervals. All parts are easily accessible for maintenance and can usually be replaced on site. The units are compact with a very small footprint: even the largest model of type N is only 2,300 mm long, 1,250 mm wide and 1,950 mm high in the standard configuration, at a weight of 1,550 kg (drive motor not included).