176 ㎡ GSP Dual-Temperature Pharmaceutical Cold Storage Project of Zhejiang Xianju Pharmaceutical, Hangzhou

Building Envelope and Air Distribution System

The cold storage adopts an assembled structure with all enclosure panels being 150 mm thick polyurethane sandwich panels featuring 0.6 mm steel sheets. Clean stainless steel sheets are used for interior surfaces, and polyurethane caulking agent plus special sealant are applied at joints to form a continuous airtight barrier. The floor adopts a composite thermal insulation structure consisting of extruded XPS boards, reinforced concrete and anti-slip epoxy finish to prevent frost heaving. One anti-condensation electrically heated horizontal sliding door with observation window is installed for the refrigerated room and frozen room respectively, interlocked with air curtains that activate upon door opening to block intrusion of hot and humid air.

Given the limited floor height, ceiling-mounted air coolers with low wind velocity and large heat exchange area are selected to deliver air to all areas of the storage chamber. Smoke testing is conducted to verify uniform airflow in working zones with top air supply and side return air, eliminating dead air zones. The evaporator of the frozen room is equipped with a stainless steel outer frame and electric heating defrost modules, and heat tracing is laid along the entire defrost drain pipeline to avoid ice blockage under -18°C operating conditions.

Dual Redundant Refrigeration System Design

This constitutes the core engineering highlight of the project. Separate sets of dual redundant compressor-condensing units are configured for the refrigerated and frozen rooms, forming a hard standby architecture with two independent systems backing each other up and fully eliminating risks arising from single-unit breakdowns.

Refrigeration Configuration for 2~8°C Refrigerated Zone

2 sets of Copeland scroll air-cooled compressor-condensing units (one operational, one standby)

Electronic expansion valves + 2 sets of high static pressure ceiling air coolers

Designed evaporation temperature: -5°C, maintaining relative humidity at 80%~85%

Unit rotation strategy: automatic switchover of main operating unit every 24 hours for even wear distribution

Refrigeration Configuration for -18°C Frozen Zone

2 sets of medium-low temperature scroll air-cooled compressor units (one operational, one standby)

High-efficiency low-temperature air coolers with 304 stainless steel electric heating defrost function

Designed evaporation temperature: -28°C; PLC dynamically adjusts defrost cycles based on actual frost accumulation

The dual redundant control logic is realized via Siemens PLC. If any shutdown signal including high pressure, low pressure, low oil level or compressor overload is triggered on the main unit, the standby unit will start automatically within 2 seconds to fully restore rated cooling capacity. Actual full-load testing shows temperature fluctuation is controlled within ≤0.8°C during switchover, complying with pharmaceutical storage guidelines.

Main Components of Refrigeration System

Automatic Temperature & Humidity Monitoring and GSP Compliance

8 temperature sensors and 2 humidity sensors are deployed across the storage area, mounted at cold and hot spots determined by thermal distribution validation. Additional monitoring points are arranged at the air return opening of each evaporator and the farthest potential goods stacking areas. The monitoring system operates independently of the refrigeration control system and is calibrated by a provincial metrology institute, satisfying GSP requirements of automatic and tamper-proof data recording. Local audible and visual alarms are integrated with a 4G module for SMS and phone notifications under a three-tier alarm system: warning alarm (1°C deviation), action alarm (1.5°C deviation), and over-limit alarm (out of 2~8°C or below -18°C thresholds). The system supports offline data caching and resume transmission after network recovery. All data is synchronized to the cloud, with audit reports available via regulatory inspection interfaces.

Validation tests are carried out in accordance with GSP appendices, including no-load thermal distribution, full-load thermal distribution, power failure insulation test (refrigerated zone maintains 2~8°C for over 2.5 hours; frozen zone stays above -10°C for over 1.5 hours), and 2-minute door opening test. All indicators pass the inspection on the first attempt.

Construction and Handover

Construction mobilization commenced in late April 2025. After casting and curing of floor thermal insulation layers, enclosure panel assembly, refrigeration pipeline welding, pressure testing, vacuum pumping and pipeline insulation works were conducted in early May. Armaflex closed-cell rubber insulation with thickness ≥30 mm is applied to freezing pipelines to strictly control condensation. Power-on commissioning was launched in mid-May. After 72 hours of stable operation, consecutive 120-hour no-load and full-load tests were performed. All validation reports were completed in mid-June 2025, signed off by the Quality Department of Xianju Pharmaceutical, marking official commissioning. The entire project took 51 days from construction start to handover.

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