In December 2011, Gree CVE Series Permanent Magnet Synchronous Inverter Centrifugal Chiller was accredited by Chinese Academy of Science, Tsinghua University, Xi’an Jiaotong University, Chinese Association of Refrigeration and China Refrigeration and Air-Conditioning Industry Association as: the world’s first high-speed and high-power permanent magnet synchronous inverter centrifugal chiller that reaches world leading standard. In 2015, it won the bidding for the centrifugal chiller project of the Great Hall of the People, which was the first time for a Chinese brand of air conditioning that had entered the Great Hall of the People.
High-speed motor direct-driven two-stage impeller
Unit adopts high-speed motor direct-driven two-stage impeller. Speed-up gears and 2 radial bearings are canceled, which will improve efficiency and reduce mechanical loss by at least 70%. With direct drive and simple structure, compressor works reliably in smaller size. Volume and weight of the compressor is only 40% of the same capacity conventional compressor. Without the high-frequency noise of speed-up gears, compressor’s operating sound is much lower. That is 8dBA lower than a conventional unit.
All-condition “wideband” pneumatic design
Impeller and diffuser are optimized to realize high-efficiency operation of compressor under 25-100% load. Compared with conventional design that is based on full load operation, this design can reduce compressor’s efficiency attenuation. Conventional inverter centrifugal chiller realizes capacity control by the variable speed of compressor and the variable opening angle of guide vane which begins to turn down under 50~60% load. However, Gree CVE series centrifugal chiller can directly change the speed of compressor under 25~100% load to reduce throttling loss of guide vane and improve working performance under all conditions.
Installed sine-wave inverter
By adopting position-sensorless control technology, motor’s rotor can be positioned without probe. With PWM controllable rectifying technology, inverter can output smooth sine wave to improve motor efficiency. Inverter is directly installed on the unit, saving floor space for customers. In addition, all communication wires are connected in factory to improve unit’s reliability.
Low viscosity vane diffuser
Unique low viscosity vane diffuser design and airfoil guide vane can turn high-speed gas into high static pressure gas effectively to realize pressure recovery. Under partial load, vane diversion reduces backflow loss, improves partial load performance, and expands unit’s operating range.
High-efficiency heat exchanger
Heat exchange surface is designed based on heat-transfer mechanism. It is optimized to reduce flowing pressure loss and energy consumption. Sub-cooler is equipped at the bottom of condenser. With multiple flow restraints, sub-cooling degree can be up to 5℃. Middle isolating board adopts light pipe that is twice as thick as threaded pipe to be joined with supporting board, therefore, copper pipe won’t be damaged under the impact of high-speed refrigerant. 3-V grooved tube plate design is adopted to guarantee sealing effect.
High-efficiency hermetic impeller
Compressor impeller is a ternary hermetic impeller, which is more efficient and reliable than an unshrouded impeller. It adopts airfoil 3-dimensional structure so that it is more adaptive. Through finite element analysis, 3-coordinate inspecting machine, dynamic balance test, over-speed test and actual test under actual working condition, it is made sure that impeller meets design requirement and is capable of stable operation. Impeller and basic shaft adopt keyless connection, which can avoid partial stress concentration and rotor’s additive off-balance that is caused by key connection, thus improving compressor’s operation stability.
Two-stage compression technology
Compared with single-stage refrigeration system, two-stage compression improves the circulation efficiency by 5%～6%. Compressor rotational speed is lowered so that compressor is more reliable and durable.
Advanced control platform
High-performance 32-bit CPU and DSP digital signal processor is used. The high data collection accuracy and data processing capacity ensure the real-time feature and accuracy of system control. Together with the colorful LCD touch screen, user can easily realize auto control and manual control in debugging. It also adopts intelligent Fuzzy-PID compound control algorithm, which is integrated with intelligent technology, fuzziness technology and normal PID control algorithm, so that system is capable of quick response speed and stable performance.
High-speed permanent magnetic synchronous inverter motor
The world’s first high-power and high-speed PMSM is used for this centrifugal chiller. Its power is higher than 400 kW and its rotational speed is above 18000 rpm. Motor efficiency is above 96% and 97.5% to the maximum, higher than national grade 1 standard on motor performance. It is compact and lightweight. A 400kW high-speed PMSM weighs the same as a 75kW AC induction motor. By adopting spiral refrigerant spray cooling technology to cool down stator and rotor, motor temperature can be controlled at around 40℃, ensuring efficient operation.