Fresh Cold Storage Air Conditioning

In fresh produce warehouses, the core objective of the air conditioning system is to delay the respiration of vegetables and meats, microbial growth, and moisture loss through precise control of temperature, humidity, airflow organization, and environmental parameters. Below are the key strategies and technical points to ensure freshness preservation:
I. Customizing Temperature and Humidity Standards by Category
1. Temperature and Humidity Requirements for Different Fresh Products
Category Suitable Temperature Range Relative Humidity Requirement Recommended Storage Period Key Preservation Goal
Leafy Greens 0~5°C (avoid freezing) 90%~95% 3~5 days Reduce water transpiration, prevent wilting
Root Vegetables 0~8°C 85%~90% 7~15 days Inhibit sprouting, maintain cell activity
Fruits 2~10°C (tropical fruits above 5°C) 80%~90% 7~30 days Delay respiratory peak, reduce ethylene release
Fresh Meat -1~1°C (refrigerated) 85%~90% 3~7 days Inhibit bacterial growth, avoid meat oxidation
Frozen Meat -18~-25°C 80%~85% 3~12 months Prevent ice crystal growth causing cell rupture
Seafood -1~0°C (chilled) 90%~95% 1~3 days Reduce enzyme activity, minimize protein breakdown
2. Precision Requirements for Temperature and Humidity Control
Temperature fluctuation: Refrigerated areas ≤±0.5°C (fresh meat, seafood), frozen areas ≤±1°C, avoiding temperature fluctuations that cause repeated ice crystal melting-freezing ("recrystallization") damaging cell structures.
Humidity stability: Leafy green warehouses require humidifiers to ensure humidity does not drop below 90%; fruit areas need to prevent excessive humidity causing mold, possibly paired with dehumidifiers (automatically activated when humidity exceeds 90%).
II. Core Technical Solutions for Air Conditioning Systems
1. Refrigeration Method Selection
Small warehouses (<500㎡):
Use split-type air coolers (with electric heating humidifiers), single unit cooling capacity calculated at 200-250W/㎡ (e.g., 300㎡ warehouse selects a 75kW air cooler), advantage being flexible installation and zonal control.
Medium warehouses (500-2000㎡):
Choose screw-type chilled water units + ceiling-mounted air handling units (AHU), delivering air via ducts, cooling capacity designed at 180-220W/㎡, paired with electrode humidifiers (humidification capacity 5-10kg/h/100㎡).
Large cold chain warehouses (>2000㎡):
Use ammonia refrigeration systems or CO₂ cascade refrigeration (eco-friendly refrigerants), combined with ceiling-mounted air coolers, achieving 15%-20% higher cooling efficiency than traditional fluorocarbon systems, suitable for low-temperature freezing scenarios.
2. Airflow Organization Optimization
Air delivery methods:
Leafy greens and fresh meat areas use "top-side delivery + bottom return," airspeed controlled at 0.3-0.5m/s, avoiding strong direct airflow causing moisture loss;
Frozen meat areas use "top uniform delivery + wall return," airspeed 0.5-0.8m/s, ensuring warehouse temperature uniformity ≤±1°C.
Air curtain configuration:
Install air curtains with 1.5-2m/s airspeed at warehouse entrances/exits to block external hot air intrusion, reducing cold loss during door openings (each opening can reduce cold loss by over 70%).
3. Special Function Modules
Dehumidification and humidification linkage:
Configure rotary dehumidifiers (dehumidification capacity at 1L/h/100㎡), automatically dehumidifying when humidity >95%; simultaneously install ultrasonic humidifiers (humidification capacity 0.5kg/h/100㎡), activating when humidity <85% to maintain stability.
Ethylene purification devices:
Fruit storage areas require ethylene catalytic decomposers (processing capacity 50-100m³/h), removing ethylene gas released by fruits via catalytic oxidation (activated when concentration >0.1ppm), delaying fruit ripening.
Air sterilization systems:
Built-in UV lamps (wavelength 254nm, irradiation intensity ≥40μW/cm²) or ozone generators (concentration 0.1-0.3ppm), disinfecting for 30 minutes before daily startup, inhibiting microbial growth.
III. Energy Consumption Control and Energy-Saving Design
1. High-Efficiency Equipment Selection
Refrigeration unit energy efficiency ratio:
Refrigerated areas choose variable frequency air coolers with EER≥3.5, frozen areas use screw machines with COP≥4.0, saving over 30% energy compared to fixed-frequency equipment.
Heat recovery technology:
Large warehouses can utilize compressor waste heat for domestic hot water or defrosting, recovering approximately 30kW heat per 100kW cooling capacity, reducing overall energy consumption.
2. Intelligent Control Strategies
Zonal independent temperature control:
Divide warehouse into independent compartments like leafy greens (0-5°C), fruits (5-10°C), fresh meat (-1-1°C), each equipped with independent temperature and humidity sensors (accuracy ±0.5°C/±3% RH) and electric air dampers.
Time-based start-stop logic:
During nighttime (22:00-6:00) when outdoor temperatures are low, activate fresh air systems to introduce cold air (requires filtration and dehumidification), reducing refrigeration operation time (saving about 20% energy).
Load prediction control:
Use Warehouse Management System (WMS) to obtain incoming plans, increase cooling capacity 2 hours in advance to avoid temperature fluctuations during goods intake (e.g., before 10 tons of fresh meat intake, air cooler power increases to 120% operation).
IV. Installation and Maintenance Key Points
1. Insulation and Sealing Treatment
Walls and roof:
Use 150-200mm thick polyurethane sandwich panels (thermal conductivity ≤0.024W/m·K), fill joints with silicone sealant to avoid cold bridge condensation.
Floor treatment:
Lay 30-50mm thick extruded polystyrene board + electric heating wires (power 10-15W/㎡) on freezer floors to prevent ground freezing and heaving.
2. Daily Maintenance Essentials
Equipment inspection:
Daily check air cooler frosting (defrost when frost layer >5mm), monthly clean air filters (replace when resistance >150Pa).
Temperature and humidity calibration:
Quarterly calibrate warehouse sensors with high-precision standard thermometers (accuracy ±0.1°C), annually commission third-party testing for warehouse temperature and humidity uniformity.
Emergency plan:
Equip diesel generators (capacity ≥120% of total refrigeration system power) and backup air coolers, activate within 15 minutes if main equipment fails, ensuring warehouse temperature fluctuation ≤2°C within 1 hour.
V. Typical Cases and Cost Reference
1. Case: 500㎡ Fresh Refrigerated Warehouse
Configuration:
2 units of 30kW variable frequency air coolers (total cooling capacity 60kW), 1 unit of 10kg/h electrode humidifier, 1 set ethylene purification device (processing capacity 100m³/h), total investment approx. 250,000 CNY.
Operation effect:
Temperature controlled at 2±0.5°C, humidity 85%-90%, leafy greens preservation period extended to 5-7 days, 15% lower loss rate than traditional warehouses.
2. Case: 1000㎡ Freezer Warehouse (-18°C)
Configuration:
1 unit of 120kW screw-type chilled water unit, 8 ceiling-mounted air coolers, electric heating defrost system, total investment approx. 600,000 CNY, annual electricity consumption approx. 180,000 kWh.
Energy-saving highlight:
Use off-peak electricity ice storage mode (making ice during low nighttime rates), saving about 300 CNY daily electricity costs, payback period approx. 3 years.
VI. Cutting-Edge Technology Applications
IoT monitoring:
Real-time upload data via wireless temperature and humidity sensors (e.g., LoRa/WiFi dual-mode) to cloud platform, mobile APP views historical curves (10-minute resolution), automatic alerts when temperature exceeds limits (response time <5 minutes).
AI intelligent temperature control:
Use machine learning algorithms to analyze warehouse cargo volume, door opening frequency, outdoor temperature, predict load changes and automatically adjust cooling capacity (±5% adjustment accuracy), improving energy savings by 10%-15%.
Phase change energy storage materials:
Lay phase change cold storage panels (melting point -5°C) near air coolers, releasing cold energy when refrigeration stops, extending stable temperature maintenance by 2-3 hours, suitable for short power outage scenarios.
Through these systematic solutions, the freshness of vegetables and meats in warehouses can be ensured while balancing energy consumption and operational costs. For high-value fresh products (e.g., imported seafood, organic vegetables), adding O2/CO2 gas monitoring modules is recommended, further extending preservation by adjusting gas ratios (e.g., O2 3%-5%, CO2 5%-8%).