12,000 m³ Agricultural Cold Chain Logistics Center in Pishan County, Hotan

As the EPC general contractor, we have developed a full turnkey delivery solution covering three dimensions: thermal design of building envelopes, refrigeration system architecture, and intelligent IoT control platform.

1. Thermal Design and Installation of Building Envelopes

Thermal Insulation System

150 mm-thick rigid PIR foam sandwich panels are adopted for cold storage walls, with a core density of 42±2 kg/m³ and closed-cell ratio ≥95%. The factory-certified R-value reaches 6.8 per inch in compliance with ASTM C518.

To accommodate the wide temperature swing, panel tongue-and-groove joints adopt a dual-seal structure: an inner EPDM foam sealing strip plus an outer weather-resistant silicone sealant to block infiltration of hot and humid air.

Thermal Interruption for Floors

A three-layer floor structure is implemented: staggered-laid XPS boards + cement mortar leveling layer + PE vapor barrier membrane.

100 mm XPS boards are laid in two staggered layers with compressive strength ≥300 kPa to balance thermal insulation and load resistance. DN150 PVC floor ventilation pipes are arranged at a spacing of 2.5 m and connected to natural ventilation shafts, creating passive convection by leveraging the large day-night temperature difference typical of desert regions.

Modular Installation

All cold storage panels, refrigeration unit bases, and pipe supports are prefabricated in the factory. On-site assembly uses bolted connections instead of conventional welding, with a maximum daily panel installation area of 380 m². The overall construction period from foundation pouring to enclosure water tightness test is shortened by 25% compared with traditional construction methods.

2. Design of Refrigeration and Defrost Systems

Based on the total volume of 12,000 m³ and multi-temperature-zone requirements, the refrigeration system configuration is specified as follows:

Key Design Points for Hot Gas Defrost Piping

A bypass loop is added from the oil separator to evaporators. During defrosting, high-pressure discharge gas flows through bypass valves into evaporators, delivering sensible and latent heat for rapid frost removal. A suction pressure regulating valve (KVP valve) maintains evaporating pressure within a preset range throughout defrosting to eliminate risk of compressor liquid slugging.

3. IoT Intelligent Control and O&M System

To address the local shortage of professional maintenance staff, a three-tier intelligent control architecture is deployed:

Local Control Tier: Siemens S7-1200 PLCs execute real-time refrigeration cycle control, defrost sequence management, and condenser fan speed regulation.

Edge Computing Tier: Industrial gateways aggregate data and convert communication protocols, with on-site 72-hour data cache to prevent data loss during network outages.

Cloud Platform Tier: Operating data uploaded via MQTT protocol with response latency below 2 seconds. The platform embeds a digital twin model of the refrigeration system, which continuously compares theoretical COP against actual COP and triggers automatic alerts once deviation exceeds 15%.

Core IoT Functions

Remote start/stop control, setpoint remote issuance, historical curve retrieval, fault code diagnosis, and spare part lifespan prediction based on cumulative operating hour statistics.

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