In recent decades, the refrigeration and air conditioning industry has undergone significant transformations, especially in terms of refrigerant technology. The complexity of the refrigeration world has intensified due to the wide range of alternative refrigerants introduced to reduce environmental impacts. These refrigerants come with varying properties, necessitating the redesign of compressors to accommodate these changes. One of the pivotal moments in this evolution occurred in 1997 with the adoption of the Kyoto Protocol, which aimed to address the global warming crisis. Since then, there has been a steady reduction in greenhouse gas emissions, driving the air conditioning and refrigeration sectors to focus on reducing both direct emissions and energy consumption.
This drive toward sustainability has led to the development of more efficient refrigeration systems, aiming to decrease CO2 emissions by reducing refrigerant use and improving leak protection. Additionally, as a response to climate change, the industry has witnessed the growing adoption of natural refrigerants, such as CO2 (R744), ammonia (R717), and propane (R290). These refrigerants, with their minimal global warming potential (GWP), are increasingly being integrated into refrigeration systems across various industries. However, transitioning to these natural refrigerants has not been without challenges, especially when it comes to developing compressors capable of withstanding their high-pressure requirements, particularly in CO2-based systems.
Advancing to Natural Refrigerants: A Strategic Shift
The adoption of natural refrigerants like CO2, ammonia, and propane has emerged as a long-term alternative, primarily due to their reduced environmental impact. To facilitate this transition, industry standards needed to be introduced or updated, and components had to be specially designed to meet the high pressure demands of CO2 systems. Initially, these components came at a higher cost, which led many companies to explore potential savings in other areas, maintaining margins while dealing with increased pressure from costs.
As the industry adapted, the availability of natural refrigerants became widespread, driving prices down through economies of scale. Despite these price reductions, the changes in refrigerants and their associated systems caused significant disruption to traditional distribution channels and value chains. The trend of vertical integration became more pronounced, with component manufacturers producing complete systems and wholesalers taking on system production roles. At the same time, plant manufacturers increasingly integrated services, and large end-users began taking control of system specification and planning. This shift towards integration and specialization has led to an emphasis on standardized, modular systems that are factory-guaranteed and often require little to no on-site adjustments.
The transition to natural refrigerants, particularly CO2, is evident in several sectors, notably in supermarkets, where CO2 systems dominate. Moreover, the traditional boundaries between commercial and industrial refrigeration are becoming blurred. CO2 systems are now being used in larger capacity ranges, and compact ammonia systems are increasingly deployed in applications such as water chillers, with capacities ranging from 200 to 800 kW. The rapid progression of standards has compelled former “Freon” system builders and users to continuously upgrade their skills and knowledge to keep pace with these changes.
The Rise of Semi-Hermetic Screw Compressors
Semi-hermetic screw compressors have played a critical role in accommodating the demands of natural refrigerants. These compressors are designed to handle high-pressure environments, making them suitable for ammonia and CO2 systems. Tunel Group, a leader in screw compressor technology, has been at the forefront of developing innovative semi-hermetic screw compressors. Tunel Group’s compressors, launched in 2017, are designed to provide maximum efficiency and long-lasting performance, particularly for ammonia systems.
Tunel Group’s compressors are equipped with the latest i-profile screw rotors, featuring a 5+7 lobe ratio that delivers superior efficiency. The compressors also feature generously dimensioned bearings, ensuring a maintenance-free service life of up to 60,000 operating hours (equivalent to approximately 10 years in standard operation). This design helps to minimize operational downtime and reduce the need for costly maintenance.
One of the key advantages of these compressors is their compact, double-stage design, which makes them ideal for low-temperature applications, such as blast freezers, traditionally served by booster systems. These compact designs are particularly beneficial in space-constrained environments, such as fishing vessels or refrigerated containers. Additionally, the permanent magnet synchronous motor (PM motor) used in Tunel Group’s compressors helps to prevent ammonia-related issues, offering a highly efficient solution with a small design footprint.
The larger compressor series from Tunel Group can be fine-tuned to suit specific operating conditions. These compressors feature a manually adjustable internal volume ratio (Vi), which allows for fine-tuning between suction and discharge gas, offering flexibility for different operational scenarios. Moreover, the compressors can be adapted to varying operational modes, including summer/winter or day/night modes, by simple switch adjustments.
Advanced Features for Enhanced Efficiency
To complement its semi-hermetic screw compressors, Tunel Group offers a series of oil separators optimized for their compressor systems. The oil separators are available in various designs, ensuring that users can select the appropriate option for their required capacity and oil separation rate. These oil separators are essential in ensuring that the compressors operate at optimal efficiency by preventing oil contamination of the refrigerant.
In addition to the oil separators, Tunel Group offers flexible and time-efficient mounting options. Packagers can easily attach brackets to prepared saddle welding plates, allowing for the mounting of up to three compressors along or across the vessel. This design feature eliminates the need for a traditional frame, contributing to space savings and reducing installation costs. The vertical welding plates also allow for the attachment of pressure gauge panels and control/terminal boxes, further reducing the need for additional components and contributing to cost savings.
The SRS-C series of compact semi-hermetic screw compressors is a standout product from Tunel Group. These compressors are equipped with a 3-stage oil separator, making them ideal for compact chillers used in process cooling or air conditioning applications. The SRS-C series offers a wide application window, allowing for evaporating temperatures ranging from -25°C to +15°C and condensing temperatures up to +55°C. This versatility makes them particularly well-suited for systems with air-cooled condensers.
One of the most innovative features of the SRS-C compressors is the patented Vi adjustment system, which automatically adjusts the volume ratio for optimal operating conditions. This system operates independently of external control inputs, ensuring that the compressor operates at peak efficiency under all conditions. Furthermore, the new ActiFlow oil management system ensures that only the necessary amount of oil enters the compression process, optimizing cooling, lubrication, and rotor sealing. This oil reduction enhances efficiency even further, helping users achieve energy savings and improved performance.
Real-World Applications and Successful Projects
Tunel Group’s semi-hermetic screw compressors have been successfully implemented in several notable projects. For example, in July 2017, a SRS14M Duo-Pack compressor system, with a total capacity of 575 kW, was installed at the Braunlage ice rink in Germany. The challenge faced during this installation was the limited space available at the site. Tunel Group’s solution was to arrange the compressors in a linear configuration, making the most efficient use of the available space.
The ice rink application required two compressors that could be operated together for ice buildup at the beginning of the season. The absence of a shaft seal in the design reduced the risk of leakage during the off-season, which is a common problem in seasonal applications such as ice production, wine production, or fish processing.
Another groundbreaking project was completed in Eindhoven, The Netherlands, in 2018. This project involved the world’s first air conditioning system using ammonia as the refrigerant. The system was designed to provide highly efficient cooling in the summer and heating in the winter, utilizing ammonia as a natural refrigerant in a mixed-use commercial and residential complex. The project demonstrated the viability of ammonia-based systems for both cooling and heating applications, further cementing the role of natural refrigerants in the future of the industry.
The Future of Refrigeration and Compression Technology
As the demand for more energy-efficient and environmentally friendly refrigeration systems continues to rise, the role of semi-hermetic screw compressors, particularly those designed for natural refrigerants, will only become more critical. Companies like Tunel Group, with their commitment to innovation and efficiency, are leading the charge in developing compressor technologies that meet the evolving needs of the industry.
With advancements in compressor design, oil management, and system integration, natural refrigerant systems are becoming more accessible, reliable, and cost-effective. As standards continue to evolve, and as more industries adopt sustainable practices, the future of refrigeration will be shaped by energy-efficient, environmentally responsible systems that rely on natural refrigerants and advanced compressor technologies.
In conclusion, the development of semi-hermetic screw compressors has been integral in the evolution of refrigeration systems, particularly in the context of natural refrigerants. With innovations in compressor design, enhanced efficiency, and flexibility, Tunel Group has positioned itself as a key player in this ongoing transformation, helping to drive the industry toward a more sustainable future.
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