Controlled Atmosphere (CA) Cold Storage: Full Guide
CA cold storage = mechanical refrigeration + gas composition control. Built upon fresh-keeping cold storage, it regulates O₂, CO₂, ethylene, temperature, and humidity to put produce into a "near-dormant" state.
🔬 Core Principle: Three Words — Reduce, Regulate, Remove
ParameterTarget ValueFunction
O₂ (Oxygen)21% → 3%~5%Suppresses respiration, slows metabolism
CO₂ (Carbon Dioxide)0.04% → 2%~5%Synergistically suppresses respiration, delays ripening
Ethylene (C₂H₄)→ <1μL/LEthylene is a ripening hormone and must be removed
Temperature0~8℃ (produce)Combined with gas control for compounded effect
Humidity90%~95%Reduces moisture loss, maintains freshness and crispness
Result: Extends shelf life by 0.5 to 1 times compared to ordinary cold storage; post-storage shelf life is 4 to 5 times longer. A key tool for off-season sales.
🏗️ Storage Room Requirements: Airtightness is Critical
ParameterStandard
AirtightnessAt 300Pa, half-pressure decay time ≤20~30 minutes
Room Structure370mm masonry wall + internal double-sided color steel PU panels (for both airtightness and insulation)
CA DoorSpecial airtight door; kept closed for long periods
Safety Valve/Buffer BagMandatory; pressure differential during gas adjustment can impact the room structure
❄️ Refrigerant Selection (Following Your Previous Inquiry)
The refrigeration system for CA storage is essentially the same as for ordinary cold storage, but requires higher reliability and greater automation:
ScaleRecommended RefrigerantRationale
Large (>500㎡)Ammonia (R717)High efficiency, low operating cost, ODP=0, GWP=0, industry standard
Medium (100~500㎡)R404A / R448ANon-flammable, low toxicity, ODP=0, stable at medium temperatures, easy maintenance
Small (<100㎡)R290 (Propane)Natural refrigerant, GWP≈3, but requires explosion-proof design
Household/Commercial Display CabinetsR600a (Isobutane)Very environmentally friendly, but flammable; restricted to professional equipment
⚠️ R22 is in its phase-out countdown, fully banned by 2030. Replace it as soon as possible if still in use.
💧 Secondary Coolant (Essential for Food Storage)
CA storage is mostly for produce and food; a secondary coolant must isolate the refrigerant from the food:
Secondary CoolantApplicable TemperatureFood SafetyRecommendation
Propylene Glycol Solution (40%~50%)Below -30℃✅ Food-grade, non-toxic⭐⭐⭐⭐⭐ First choice
Ethylene Glycol Solution (20%~30%)Around -15℃⚠️ Low toxicity, must not contact food⭐⭐
Brine (NaCl/CaCl₂)Around -20℃⚠️ Corrosive to pipes⭐
Conclusion: Food-grade CA storage must use propylene glycol. Don't cut corners here.
🔧 Four Key Components of the CA System
SystemFunctionMainstream Solutions
Nitrogen Generation/Deoxygenation SystemReduce O₂ to 3%~5%Carbon molecular sieve adsorption (common), hollow fiber membrane, VSA vacuum swing adsorption deoxygenation
CO₂ Removal SystemScrub excess CO₂, stabilize at 2%~5%Activated carbon scrubber (common); hydrated lime or water scrubbing also viable
Ethylene Removal SystemRemove ripening gasOzone-based ethylene removal (new trend; operates at low temperature, consumes only 500W, 1/10 of high-temperature catalytic units)
Automatic Monitoring & ControlReal-time monitoring of O₂/CO₂/temperature/humidityCentral computer remote monitoring, automatic adjustment
💰 2026 Budget Reference
ItemPrice Range
Room Construction (incl. airtightness + insulation)RMB 800~1,200/㎡
Refrigeration System (Ammonia)RMB 150,000~250,000 (for 500㎡ scale)
CA System (Four Key Components)RMB 80,000~150,000
Secondary Coolant (Initial Propylene Glycol Charge)RMB 30,000~50,000
Total (500㎡ Produce Storage)Approx. RMB 600,000~900,000
Small (100㎡)Approx. RMB 150,000~250,000
Operating Cost: CA storage is about 20%~30% higher than ordinary cold storage (due to CA equipment electricity), but produce can sell for 50%~100% more after storage, more than covering the off-season profit margin.
🍎 What to Store?
ProduceO₂CO₂Shelf Life Comparison
Apples2%~3%1%~3%Ordinary cold storage: 6 months → CA: 10~12 months
Kiwifruit2%~3%2%~5%3 months → 6~8 months
Pears1%~2%0.5%~1%4 months → 8~10 months
Bananas11%~13%2%~5%Special; requires high O₂
