SRT Series Screw Refrigerant Compressors

When a refrigeration system has to span a very large temperature difference — for instance, -60°C low-temperature freezing on one side and a heat pump application needing a higher leaving-water temperature on the other — the pressure difference the compressor must withstand rises significantly. Under such high-pressure-difference duty, single-stage compression often faces excessive discharge temperature, falling efficiency and poorer reliability. Single-unit two-stage compression then becomes the more reasonable technical route.

The Fusheng SRT Series screw refrigerant compressor is exactly such a single-unit two-stage heat pump compressor. It uses a pair of rotors for each of the high- and low-pressure stages, driven synchronously by the motor through a direct coupling, and is matched with a high-precision curved-tooth coupling so the whole unit reaches an ideal state of balance. The product covers two lines, high-temperature heat pump and low-temperature freezing: the heat pump series uses the environmentally friendly R134a refrigerant, and the freezing series is compatible with R22 and R404A (R507), with a displacement of about 144/60-759/300 m³/hr.

Single-Unit Two-Stage: A Solution for High Pressure Difference

Single-unit two-stage means integrating a low-pressure stage and a high-pressure stage in one compressor, driven directly by a single motor. Gas is first compressed by the low-pressure stage, cooled in between, then enters the high-pressure stage to reach the required pressure. Compared with single-stage compression, splitting the pressure ratio between two stages gives each stage a lower discharge temperature and a compression process closer to ideal; compared with two compressors in series, the single-unit two-stage design is more compact and does away with a separate drive and control system. The SRT uses a pair of rotors for each of the high- and low-pressure stages, driven synchronously by the motor through a direct coupling and matched with a high-precision curved-tooth coupling, so the unit runs in ideal balance.

Freezing and Heat Pump: One Technical Route, Two Applications

The SRT series includes two product lines. The high-temperature heat pump line, represented by SRT314HA to SRT413HA, has a capacity range of 200-500 kW and a heating capacity of 120-300 kW, suiting heat pump applications that need a higher leaving-water temperature; the low-temperature freezing line, represented by SRT218 to SRT415, covers an evaporating temperature of -25°C to -60°C with R22 and -25°C to -65°C with R404A (R507), aimed at deep-freezing needs such as quick freezing and low-temperature cold storage. Deriving two product lines from one technical platform also gives system integrators a consistent technical basis when designing different projects.

Eco-Friendly Refrigerants and Energy Efficiency

The heat pump line uses the environmentally friendly R134a refrigerant, while the freezing line is compatible with R22 and R404A (R507). At an evaporating temperature of -35°C the series reaches a COP of 1.68 — for deep-freezing equipment this figure bears directly on long-term electricity cost. Heat pump applications recover heat to work alongside or replace a boiler, a common route for industrial waste-heat utilisation and clean heating.

Specifications at a Glance

Industries and Applications

• High-temperature heat pumps: industrial waste-heat recovery, clean heating, process heating that needs a higher leaving-water temperature;
• Low-temperature freezing: quick-freezing equipment, low-temperature cold storage, food processing;
• Chemical and pharmaceutical: deep-refrigeration processes such as low-temperature reaction and low-temperature crystallisation;
• Central cooling and heating systems: integrated solutions that must cover both freezing and heating.

Selection Advice

1. First decide whether the application is freezing or heat pump: the two lines use different refrigerants and duties and are not interchangeable;
2. Determine the model by evaporating and condensing temperature: for low-temperature freezing, check that the actual evaporating temperature falls within the R22 or R404A (R507) range;
3. Look at reliability under high pressure difference: the two-stage design is built for high pressure difference, but the full operating range of the system should still be confirmed during selection;
4. Include life-cycle energy efficiency in the evaluation: deep freezing and high-temperature heat pumps both run continuously over the long term, so the effect of COP and maintenance cost keeps growing during operation.

Conclusion

Single-unit two-stage is essentially an engineering answer to the problem of high pressure difference. Using high- and low-pressure two-stage rotors and a synchronised direct-coupled structure, the Fusheng SRT Series brings low-temperature freezing and high-temperature heat pump needs onto one technical platform, and answers today's energy-saving requirements with eco-friendly refrigerants and optimised efficiency. When a system needs deep refrigeration and higher-temperature heating at the same time, it deserves to be considered first.