R-744 (CO2) vs R-23 for Ultra-Low-Temperature Freezing — Choosing Cascade Refrigerants for Food/Pharma in Thailand

Ultra-low-temperature (ULT) refrigeration — from -40°C food blast freezing to -80°C biological sample/vaccine cabinets — is beyond ordinary refrigerants (R-410A, R-134a). It requires specialized refrigerants in a cascade system.

The core question: choose the environmentally friendly R-744 (CO2), or R-23, which reaches deeper cold? This article compares them clearly by the actual working temperature range.

1. Why Deep-Freeze Work Needs Special Refrigerants

Ordinary refrigerants are designed for 0°C to -30°C. Below that, problems arise:

• Suction-side pressure gets so low the compressor can't draw enough (efficiency drops)
• Some refrigerants approach their own freezing point
• The compression ratio gets too high for a single compressor

The solution is a cascade system — split into two stages, each using a refrigerant suited to its temperature range.

2. How a Cascade System Works

flowchart LR
    A[High-stage
R-744 or R-449A] -->|rejects heat| B[Cascade Heat Exchanger]
    B -->|condenses low-stage| C[Low-stage
R-23 / R-508B / CO2]
    C -->|draws cold from room| D[Cold room -40 to -80°C]

• The high-stage uses a mid-temperature refrigerant to "reject heat" from the lower stage
• The low-stage uses a deep-cold refrigerant in direct contact with the cold room
• The two are linked through a cascade heat exchanger (refrigerants do not mix)

The key selection is the low-stage refrigerant, because it sets the lowest temperature the system can reach.

3. R-744 (CO2) — The Triple-Point Limit

Key limit: CO2's triple point is -56.6°C — below this in a normal cycle, CO2 solidifies into dry ice and blocks the system. In practice, CO2 in a low-stage safely reaches about -50°C to -54°C.

Best for: food blast freezing (-40°C), frozen-food cold rooms, supermarkets — the range where CO2 performs well and GWP = 1.

4. R-23 (HFC-23) — Reaches -80°C but Enormous GWP

R-23 reaches the deep cold that CO2 cannot, so it is still needed in genuine ULT work, such as:

• -80°C biological sample/vaccine freezers
• environmental test chambers
• research/pharma needing -70°C and below

Major downside: GWP ~14,800 (1 kg ≈ nearly 15 tonnes of CO2!) consumes a huge slice of the HFC quota and is aggressively phased down → steadily rising price and scarcity. R-23 is also a by-product of HCFC-22 production, which is declining.

5. Comparison Table — Choose by Temperature Range

Rule of thumb: if the job is ≥ -54°C → choose CO2 (green + cheap). If you truly need < -56°C → R-23/R-508B is necessary (accepting the high GWP).

6. Other Options and Trends

• R-508B — an azeotrope (R-23 + R-116), boiling point -87°C, also high GWP (~13,400), used in place of R-23 in some ULT systems
• R-170 (ethane) — natural, GWP ~6, reaches deep cold, but flammable (A3), requiring strict safety design; popular in sealed, low-charge ULT units
• R-1150 (ethylene) — another natural ULT option, also A3
• Trend: new systems try to avoid high-GWP R-23/R-508B → moving to CO2 (as low as the triple point allows) + natural low-GWP in the low-stage where safety permits

7. Safety + Requirements in Thailand

• CO2: non-flammable but heavier than air + odorless → oxygen depletion in confined spaces. Requires a CO2 sensor (NDIR) near the floor + ventilation (see Refrigerant Leak Detection ASHRAE 15/EN 378/ISO 5149)
• High pressure: CO2 systems run at very high pressure, requiring purpose-designed pipes/components/valves
• R-23/R-508B: hazardous substances (license) + under the HFC quota (DIW) — demand AHRI 700 every lot
• Food/pharma TOR work typically specifies cold-chain standards + refrigerant documentation + a leak-detection plan

Summary Table

Frequently Asked Questions

Q: How do CO2 transcritical and cascade systems differ?

A: Transcritical = CO2 as the single refrigerant for the whole system, operating above its critical point; popular in cold/mild-climate supermarkets. Cascade = CO2 as the low-stage paired with another high-stage refrigerant; better suited to hot climates like Thailand and deep-freeze work, because transcritical efficiency drops in hot weather.

Q: Can I just switch from R-23 to CO2?

A: It's not a simple refrigerant swap — it's a system change, because CO2 runs at much higher pressure and has the triple-point limit. It's only feasible when designing a new system and the working temperature is within CO2's range (≥ -54°C).

Q: What does dry ice have to do with CO2 in the system?

A: Dry ice is solid CO2 — exactly what we must "avoid" in the refrigeration cycle. If system CO2 drops below the triple point (-56.6°C), it solidifies and blocks the expansion valve/pipes, crashing the system.

Q: What refrigerant do -80°C vaccine freezers use in Thailand?

A: Most -80°C ULT cabinets use a cascade with R-23 or R-508B in the low-stage (or natural R-170 in some sealed units). CO2 cannot reach -80°C because of the triple point. Choose per the unit model and cold-chain requirements.

Request a Quote

Sahawatthanakit supplies refrigerants across the full temperature range — R-744 (CO2), R-23, R-508B, and high-stage refrigerants (R-449A/R-513A) — AHRI 700 (2019) certified with full hazardous-substance licensing, and we help match the refrigerant to your temperature range and safety requirements.

• Phone: 02-096-2118
• LINE: @sahawatt1988
• Email: info@sahawatthanakit1988.com
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