REFRIGERATION SYSTEM制冷系统

制冷系统的设计和组装都是基于保证工艺操作稳定性，整个制冷系统组装于同一个机架上，位于箱体/冷阱的后部。采用双级半封闭螺杆式压缩机，实现低温并减少了泄漏的风险，特别是在当吸气压力低于常压的低温阶段。

每一台双级压缩机都有一个D立的循环系统，既可使用R404A制冷剂，也可以采用R507制冷剂

（本方案采用R404A）。每个压缩机循环系统都安装有必要的控制阀门、安全阀门、过滤器、湿度指示器、仪表、油分离器、冷凝器、视镜、热气旁通阀和温度调节装置等以保证系统操作的稳定性，并能保证足够的制冷能力。制冷系统同时配有聚合发泡材料的保温。

尽可能采用铜焊以防止泄漏，系统的泄漏率检测是以氮气打压方式进行的，如有必要使用低浓度的HFC 制冷剂。在安装前系统内部进行彻底清洗，并在使用前进行干燥处理。

所有制冷循环的配置均保证在各个不同的工艺阶段能够满足冷阱或搁板的冷量供应。这种配置也可以保证当一套系统故障，冻干程序仍然可以以较低的效率继续进行。通过制冷剂冷却器可以确保制冷效果，在一定条件下冷却水温可到32°C。水冷压缩机上的热量控制阀（水量调节阀）安装在制冷剂冷凝器的入口处， 用于优化效率及减少冷却水用量。

The refrigeration system is designed and assembled to ensure the specified process performance is achieved reliably. The entire refrigeration group is mounted on a frame that is positioned to the rear of the chamber/condenser. The compressors are of screw type (see item 22) of two stage, semi-hermetic compressors, providing low temperature performance and minimising the risk of leakage, especially at low temperature when the suction pressure is below atmospheric pressure.

Each compressor has a discrete circuit employing either R404 or R507HFC refrigerants (R404 used as default). Each compressor circuit is equipped with the necessary control valves, safety valves, filters, moisture indicators, gauges, oil separator, suction accumulator, condenser/liquid receiver, sight glasses, hot gas bypass valve and thermostats to enable the system to operate reliably and deliver the required refrigeration performance. Where appropriate the refrigeration circuits are insulated with polymer foam.

As far as possible brazed connections are employed and fittings such as elbows are minimised to reduce the possibility for leakage. Systems are leak checked using Nitrogen at positive pressure and low concentrations of HFC refrigerants if necessary. The systems are Nitrogen purged during brazing and dehydrated prior to operation.

To ensure the most efficient use of the installed refrigeration capacity all refrigeration circuits are configured to be able to serve either condenser or shelf cooling duties. This configuration also ensures the freeze drying process can continue, albeit at a lower The refrigerant condensers are selected to ensure refrigeration performance can be maintained with a cooling water supply up to 32°C at the specified supply rate.  Thermostatically controlled valves (water regulating valves) on the water cooled refrigerant compressors are provided at the inlet of the refrigerant condensers to optimise efficiency and minimise water usage.