Ammonia vs. CO₂ vs. Glycol Refrigeration (2026)
Ammonia vs. CO₂ vs. Glycol Refrigeration (2026)
The Real Technical and Economic Comparison for Cold Storage, Food Processing, and Industrial Facilities
Pick the wrong refrigeration platform and you'll pay for it for 25 years. Pick the right one and you'll never think about it again. Here's how the three dominant systems actually compare in 2026.
Every cold storage warehouse, food processing plant, cannabis cultivation facility, and biotech cold chain operation in America runs on one of three refrigeration platforms: ammonia (NH₃), CO₂ (R744), or glycol secondary loop. The choice is not academic. It drives capital cost, operating cost, regulatory burden, insurance pricing, footprint, and the kind of engineering staff you need to have on-site for the life of the facility.
And yet — most owners, developers, and even many GCs treat the refrigeration platform decision as something to delegate to a mechanical engineer at design development. That's the wrong order of operations. The refrigeration platform should be selected during preconstruction, alongside site selection, because it shapes nearly every downstream design decision.
This guide is built by Terrapin Construction Group — a nationwide design-build commercial general contractor with over one million square feet of refrigerated facility construction across cold storage, food processing, cannabis, and biotech in 38 states. We've delivered ammonia, CO₂, and glycol systems, and we'll tell you what each one is actually best at.
For an instant cost estimate that includes refrigeration platform selection, run our TCG.ai estimator.
TL;DR — Which Refrigeration System Wins, by Application
- Ammonia (NH₃): Best for industrial cold storage and food processing over 250 TR or 200,000+ SF. Highest efficiency, lowest operating cost — if you can afford PSM/RMP compliance.
- CO₂ transcritical/cascade: Best for facilities 50–250 TR or 30,000–200,000 SF. Permitting simplicity, no PSM/RMP exposure, near-ammonia efficiency in cool climates.
- Glycol secondary: Best for facilities under 50 TR, multi-zone with mixed temperatures, or applications where simplicity and operator skill availability matters more than peak efficiency.
For Mountain West, Pacific Northwest, and Midwest projects, CO₂ has become the default choice for new builds in the 2026 market. Ammonia still wins on very large industrial scale. Glycol wins on small-format simplicity.
The three systems, side by side
Ammonia (NH₃ / R-717)
The 100-year-old workhorse of industrial refrigeration. Still the most thermodynamically efficient option at industrial scale. Used in nearly every large cold storage warehouse, meat processing plant, brewery, and dairy facility above 250 TR.
How it works: Single-stage or two-stage screw or reciprocating compressors circulate anhydrous ammonia through evaporator coils. Direct-expansion (DX) systems put ammonia in the cooling space; pumped recirculation systems use a low-pressure receiver. Heat rejection through evaporative or air-cooled condensers.
Strengths: Highest efficiency (COP 4.0-6.0 typical), lowest operating cost per TR-hour, mature technology with deep operator and contractor base, low refrigerant cost (~$2/lb), zero GWP, zero ODP.
Weaknesses: Toxic at relatively low concentrations (300 ppm IDLH); flammable; PSM/RMP regulatory compliance once charge exceeds 10,000 lb; insurance premiums elevated; cannot be installed in occupied buildings without significant separation and ventilation.
CO₂ (R-744)
The fastest-growing industrial refrigeration platform in 2026. Two architectures: transcritical (CO₂ throughout the system) and cascade (CO₂ on the low side, ammonia or HFC on the high side).
How it works: Transcritical systems use multi-stage compression with high-pressure operation above CO₂'s critical point (87.8°F). Cascade systems use CO₂ as the low-temperature refrigerant and a higher-temperature refrigerant on the heat-rejection side. Both work well from refrigerated through blast freeze applications.
Strengths: Non-toxic, non-flammable, no PSM/RMP regulatory burden, zero GWP (1.0), can be installed in or adjacent to occupied spaces, excellent low-temperature performance, near-ammonia efficiency in cool climates.
Weaknesses: Higher capital cost than ammonia (5–12% premium typical), high system pressures (1,400–1,800 psi transcritical), more complex controls, transcritical efficiency degrades in hot climates (Phoenix, South Texas penalty), refrigerant grade matters significantly.
Glycol Secondary Loop
Not technically a primary refrigerant — glycol (propylene or ethylene) is circulated as a heat-transfer fluid, cooled by a primary refrigeration system on the back end. Common in food retail, smaller cold storage, multi-zone applications, and where regulatory simplicity matters.
How it works: A primary chiller (typically packaged DX with HFC, CO₂, or ammonia on the back end) cools glycol in a large reservoir. Glycol is pumped through evaporator coils in production rooms, coolers, or freezers. Glycol returns warmer to the chiller, completing the loop.
Strengths: Lowest capital cost for small to mid-size facilities, simplest to operate, no refrigerant in the cooling space, easy to add cooling zones, low maintenance, available off-the-shelf in package units.
Weaknesses: Lowest efficiency (typical COP 2.5-3.5), pumping power penalty grows significantly at low temperatures, viscosity issues below -20°F, requires periodic glycol replacement and monitoring, environmental disposal cost for spent glycol.
2026 capital cost comparison
For an 80,000 SF frozen cold storage facility requiring 220 TR of refrigeration capacity, here's how installed cost stacks up across the three platforms:
| System | Capital Cost | $/TR Installed | Notes |
|---|---|---|---|
| Ammonia (pumped recirculation) | $4.4M–$5.2M | $20K–$24K | PSM/RMP applies; engineer of record required |
| CO₂ cascade (NH₃/CO₂) | $4.8M–$5.6M | $22K–$25K | Hybrid; small NH₃ charge below PSM threshold |
| CO₂ transcritical | $5.0M–$5.9M | $23K–$27K | Best fit for cool/moderate climates |
| Glycol secondary (with DX primary) | $4.2M–$5.0M | $19K–$23K | Simplest install; highest 20-year operating cost |
Capital cost is only one input. The real comparison is total cost of ownership over 20–25 years — and that's where the three systems diverge dramatically.
20-year total cost of ownership
For the same 80,000 SF frozen facility, projected 20-year total cost (capital + electricity + maintenance + regulatory compliance) at average US industrial electricity rates:
| System | 20-Yr Capital | 20-Yr Energy | 20-Yr Maintenance + Compliance | 20-Yr Total |
|---|---|---|---|---|
| Ammonia (pumped) | $4.8M | $8.6M | $5.5M (PSM staff) | $18.9M |
| CO₂ cascade | $5.2M | $9.1M | $3.2M | $17.5M |
| CO₂ transcritical | $5.4M | $9.6M | $3.1M | $18.1M |
| Glycol secondary | $4.6M | $11.4M | $2.8M | $18.8M |
Over 20 years, CO₂ cascade comes out cheapest for an 80,000 SF frozen facility. Ammonia is competitive only if you already have PSM staff on-site for other equipment.
These numbers shift with climate, electricity rate, scale, and labor market. Larger facilities (500,000+ SF) almost always tip toward ammonia because PSM overhead is spread across more refrigeration capacity. Smaller facilities tip toward glycol because the energy penalty is smaller in absolute terms.
The regulatory reality of ammonia
Ammonia's biggest barrier is regulatory. Two thresholds determine the compliance burden:
| Threshold | Trigger | What It Requires |
|---|---|---|
| OSHA PSM (29 CFR 1910.119) | >10,000 lb ammonia charge | 14-element process safety program, written PSM plan, employee training, mechanical integrity, MOC, incident investigation |
| EPA RMP (40 CFR Part 68) | >10,000 lb ammonia charge | Hazard assessment, prevention program, emergency response plan, 5-year submission to EPA |
| State + local ammonia ordinances | Varies by jurisdiction | Some states (CA, NJ, NY) have additional thresholds and requirements |
For an 80,000 SF frozen facility with a typical 8,000–14,000 lb ammonia charge, compliance burden runs $150,000–$400,000 per year in dedicated engineering staff, third-party audits, training, documentation, and emergency response readiness. This is the single biggest reason CO₂ has gained share over the last decade.
By application: what to spec
| Application | Recommended Platform | Why |
|---|---|---|
| Cold storage 35-45°F < 50,000 SF | Glycol or DX | Capital cost wins; energy delta is small |
| Cold storage 35-45°F 50,000-200,000 SF | CO₂ transcritical or cascade | Permitting simplicity, near-ammonia efficiency |
| Cold storage 35-45°F > 200,000 SF | Ammonia (pumped) | Scale justifies PSM overhead |
| Frozen storage < 50,000 SF | CO₂ cascade or glycol | Small charge; cascade gives low-temp benefit |
| Frozen storage > 50,000 SF | CO₂ cascade or ammonia | Scale-dependent |
| Blast freeze (-20°F) | Ammonia or CO₂ cascade | Both handle low temps; glycol viscosity penalty |
| Food processing 35,000-100,000 SF | CO₂ cascade or ammonia (small) | Refrigerant in occupied space restricts ammonia DX |
| Cannabis cultivation | Glycol or CO₂ | Multi-zone temperature control favors glycol simplicity |
| Data center | Glycol or chilled water (not refrigeration) | Different cooling profile entirely |
For more on cold storage cost by temperature class, see our Cold Storage Construction Cost Guide and 2026 Cold Storage Cost Article. For food processing context, see Urethane Cement Flooring for Food Processing.
Climate matters more than most owners realize
Refrigeration efficiency is heavily climate-dependent, especially for CO₂ transcritical systems where high ambient temperatures push the system above the critical point and degrade COP. Quick climate guide for system selection:
| Climate Zone | Best Platform | Notes |
|---|---|---|
| Cold (Minneapolis, Buffalo, Denver winter) | CO₂ transcritical or ammonia | Free-cooling hours benefit CO₂; ammonia efficient year-round |
| Moderate (Atlanta, Dallas, Chicago) | CO₂ cascade or ammonia | Cascade is the safe bet; transcritical has summer penalty |
| Hot (Phoenix, Houston, South Texas) | CO₂ cascade or ammonia | Transcritical degrades; cascade or ammonia preferred |
| Arid (Reno, Albuquerque, El Paso) | CO₂ transcritical | Evaporative gas cooling works exceptionally well |
| Marine (Seattle, San Diego) | CO₂ transcritical | Mild ambients favor transcritical |
For Phoenix-specific refrigeration considerations, see our Cold Storage Construction in Atlanta framework and broader regional cost data in Cold Storage Construction Cost 2026.
Six refrigeration decision mistakes we see most often
- Designing the refrigeration platform after building design is complete. Refrigeration platform shapes electrical service, machine room footprint, condenser placement, and even insulated floor design. Pick it first.
- Specifying ammonia at sub-PSM scale. If your charge will be 9,500 lb, you're paying ammonia's complexity penalty without enjoying ammonia's scale efficiency. Either commit to PSM or use CO₂.
- Choosing CO₂ transcritical in Phoenix or South Texas. Summer efficiency penalty is real. Cascade or ammonia is almost always the better choice in those climates.
- Underestimating glycol's pumping power cost. Glycol systems below -20°F can have pumping power costs that exceed the compressor power. Run the math at design temperature, not nameplate.
- Skipping the commissioning agent. Refrigeration commissioning is a discipline. Owners who skip it find compressors short-cycling, charge problems, and control loops fighting each other six months in.
- Ignoring waste heat recovery. Modern CO₂ and ammonia systems can recover 40–60% of waste heat for water heating, washdown, or process loads. This is real money over 20 years.
How TCG approaches refrigeration platform selection
TCG operates as a nationwide design-build commercial general contractor. For refrigerated facility projects, we treat refrigeration platform selection as a preconstruction deliverable — not a design development decision.
Our preconstruction process includes a refrigeration platform analysis that considers facility scale, climate, owner operator capability, regulatory tolerance, energy cost trajectory, and the operational fit with the broader building envelope (including IMP envelope and floor insulation). The output is a recommended platform with a 20-year TCO model and a clear rationale.
For an instant cost estimate that includes platform selection, run our TCG.ai estimator. See also What Does a Design-Build Contractor Do.
Refrigeration Platform Pre-Selection Worksheet
Before you commit to a refrigeration platform, answer these six questions:
1. What is the facility size and total refrigeration load (TR)?
2. What temperature classes are required (refrigerated, frozen, blast)?
3. What is the local climate zone (cool, moderate, hot, arid)?
4. Will the operator have full-time engineering staff capable of PSM compliance?
5. Is the facility adjacent to occupied space (offices, public access)?
6. What is the local electricity rate trajectory over the next 20 years?
Get these six answers right, and the platform selection becomes almost obvious. Get them wrong, and you're rebuilding mechanical in year ten.
Frequently asked questions
Which refrigeration system is the most efficient in 2026?
Ammonia remains the most thermodynamically efficient for large industrial loads above 250 TR. CO₂ transcritical systems have closed the gap and are nearly equivalent in arid and moderate climates. Glycol secondary loops are less efficient but offer operational and safety advantages for smaller facilities.
Is CO₂ refrigeration safer than ammonia?
Yes. CO₂ is non-toxic, non-flammable, and avoids the PSM and RMP regulatory burden that ammonia triggers above 10,000 lb charge. For facilities under 200,000 SF, CO₂ is now the safer and easier-to-permit choice.
What charge size triggers ammonia PSM and RMP?
OSHA Process Safety Management (PSM) and EPA Risk Management Program (RMP) compliance apply when ammonia charge exceeds 10,000 pounds. Compliance adds significant operating cost and engineering staff requirements — typically $150K to $400K per year for a fully compliant facility.
Can you use glycol for blast freezing?
Glycol secondary systems can serve blast freeze applications but require a primary refrigerant on the back end (typically ammonia or CO₂). Pure glycol systems are limited to applications above approximately -20°F due to viscosity and pumping power penalties at lower temperatures.
What is the typical capital cost difference between systems?
Ammonia systems typically cost 5–12% less than equivalent CO₂ transcritical systems at the same capacity. Glycol systems carry the lowest capital cost for small to mid-size facilities but the highest operating cost over a 20-year lifecycle. The right answer depends heavily on facility size, application, and local climate.
Does refrigeration platform affect IMP envelope design?
Yes. Ammonia DX systems can occasionally release ammonia into the cooling space and require enhanced ventilation and panel finish selection. CO₂ and glycol have no equivalent envelope requirement. See our IMP for Cold Storage and Controlled Environment Facilities article.
