Category: Technology Comparison

For most of the past century, industrial ammonia refrigeration meant large central plants holding thousands of pounds of refrigerant in flooded or liquid-overfeed systems. Low-charge ammonia turns that model on its head, delivering comparable cooling with a small fraction of the ammonia inventory. The approach has moved from novel to mainstream, and it is reshaping how plants are designed and which equipment buyers should be sourcing. This article explains what low-charge ammonia is, why operators are adopting it, and how surplus components fit into a low-charge build.

What “Low-Charge” Actually Means

Traditional ammonia plants use liquid overfeed or flooded evaporators, which require a large refrigerant charge circulating through the system and held in vessels. A low-charge system minimizes the ammonia inventory, often by an order of magnitude, by using direct-expansion evaporators and packaged designs that keep the refrigerant confined to a compact, factory-built unit. Instead of a sprawling machine room piped throughout a facility, a low-charge plant is frequently a skid-mounted or rooftop package with the charge contained on board.

The defining metric is pounds of ammonia per ton of refrigeration. Where a traditional plant might carry several pounds per ton across the whole system, a well-designed low-charge package can bring that down dramatically, which is the source of most of its safety and regulatory advantages.

The Configurations

Low-charge ammonia shows up in a few common forms:

• Packaged DX units: Self-contained skids or rooftop packages with compressor, condenser, and DX evaporator integrated, holding the ammonia charge on board.
• Central low-charge systems: Larger plants engineered to minimize charge through DX evaporators and tighter system design while still serving multiple loads.
• Distributed packages: Multiple smaller units placed near the loads they serve, reducing long refrigerant runs and the inventory they require.

The right configuration depends on load size, layout, and how much the operator wants to reduce on-site ammonia inventory.

Why Plants Are Switching

The driving force is risk and regulatory burden. A smaller ammonia inventory reduces the consequences of a release and can keep a facility below key regulatory quantity thresholds. In the United States, OSHA’s Process Safety Management (PSM) standard and the EPA’s Risk Management Program (RMP) impose extensive requirements on facilities holding ammonia above a threshold quantity. Staying under that threshold by minimizing charge can materially reduce a facility’s compliance and administrative load.

Beyond regulation, a smaller charge means a smaller potential release, simpler emergency planning, and often easier siting near occupied areas. For many operators, those benefits justify the move even where capacity needs are modest.

Energy and Performance

Low-charge does not mean low performance. Well-designed DX systems can match or improve on the efficiency of older plants, particularly when they replace aging liquid-overfeed equipment. Reported results from facilities that have made the switch include substantial energy reductions; in one set of cold storage cases, replacing ammonia liquid-overfeed systems with dual-stage dry-expansion plants cut energy use by a large margin. Results vary with climate, load profile, and design, but the headline is that minimizing charge and modernizing the system can deliver efficiency gains alongside the safety benefits.

The Adoption Trend in Numbers

Low-charge ammonia is one of the fastest-growing configurations in industrial refrigeration. Roughly 1,480 North American industrial sites had adopted low-charge ammonia systems by 2025, reflecting about 20 percent year-over-year growth and a 1.4-fold increase since 2023. That growth is occurring alongside the rise of transcritical CO2, with both natural-refrigerant approaches expanding as operators move away from high-GWP HFCs.

Which Surplus Components Fit a Low-Charge Build

A low-charge project does not require everything to be new. Several categories of surplus equipment fit well:

• Packaged and screw compressors: Well-maintained units sized to the load are a natural fit, particularly where a packaged skid is being assembled or refurbished.
• DX evaporators and unit coolers: Direct-expansion coils suited to ammonia service are central to a low-charge design; surplus coils in good condition can serve here.
• Condensers: Evaporative and air-cooled condensers matched to the system’s heat rejection needs.
• Controls and valves: Control panels, valves, and instrumentation appropriate to ammonia DX service.

What to verify when sourcing used components for a low-charge build: confirm the equipment was rated for ammonia service, check operating hours and overhaul history on compressors, verify coil and vessel condition and any ASME documentation, and make sure controls and valves match the intended DX duty and pressures. Refrigeration Equipment Pros stocks compressors, evaporators, condensers, and auxiliary equipment suited to ammonia systems, and can help match surplus components to a low-charge design.

Planning a low-charge ammonia project? Browse compressors, evaporators, and condensers at refrigerationequipment.net, list equipment through our Sell To Us page, or call 201-805-1441 to match surplus components to your design.

The choice between ammonia and CO2 is no longer a settled question with one default answer. Over the past two years, transcritical CO2 has moved from a niche option that most industrial contractors would not quote into a mainstream alternative that is regularly priced alongside ammonia. That shift changes the calculus for anyone sourcing equipment on the used market, because it influences both what becomes available and how long a given technology will hold its resale value. This article compares the two refrigerants on the factors that actually matter to a procurement decision, then looks at what the trend means for surplus buyers specifically.

The Numbers Behind the Shift

Industry data tells a clear story. In North America in 2025, there were more industrial sites using low-charge ammonia (around 1,480) than transcritical CO2 (around 1,240), but the CO2 count grew roughly 42 percent year over year, a 2.5-fold increase since 2023. Low-charge ammonia also grew, at about 20 percent year over year. Both natural refrigerants are expanding; CO2 is simply expanding from a smaller base at a steeper rate.

Contractor behavior reflects this. As recently as two years ago, most industrial contractors that did ammonia work were not interested in exploring CO2. That has flipped: many now quote CO2 alongside ammonia, or at least price it as an option. For a buyer, that means the population of CO2 equipment in service, and eventually on the used market, is growing quickly.

How the Two Refrigerants Differ Operationally

Ammonia and CO2 are both natural refrigerants with negligible global warming potential, but they behave very differently in a system.

• Charge and toxicity: Ammonia is toxic and flammable at certain concentrations, which drives safety systems, setback distances, and regulatory thresholds. CO2 is non-toxic and non-flammable, which simplifies siting in occupied or retail-adjacent spaces.
• Operating pressure: CO2 systems run at much higher pressures than ammonia, which dictates heavier-rated components, valves, and vessels. Ammonia operates at comparatively modest pressures.
• Efficiency by climate: Ammonia tends to hold its efficiency advantage in large, low-temperature applications. Transcritical CO2 efficiency is more sensitive to ambient temperature, which historically favored cooler climates, though gas cooler and parallel-compression improvements have narrowed that gap.
• Footprint: Low-charge ammonia and packaged CO2 systems both reduce the central machine-room footprint compared with traditional flooded ammonia plants, but they get there in different ways.

Where Ammonia Wins

Ammonia remains the default for large-capacity industrial refrigeration, particularly cold storage warehouses and food processing plants with substantial low-temperature loads. Its efficiency at scale, mature contractor base, deep parts ecosystem, and decades of operating history make it hard to displace where the load is big and the plant is purpose-built. The used market for ammonia compressors, vessels, and evaporative condensers reflects that durability; well-maintained ammonia equipment has a long service life and a steady resale demand.

Where CO2 Wins

CO2 has the edge where charge size, siting, and regulatory simplicity matter more than peak efficiency at scale. It is well suited to smaller industrial loads, facilities near occupied spaces, and applications where minimizing refrigerant toxicity is a priority. The new-build skew is telling: in 2025, new builds made up roughly 74 percent of industrial transcritical CO2 rack installations in North America, versus about 26 percent for retrofits. CO2 is largely being designed into new facilities rather than retrofitted into old ones, which shapes the kind of equipment that will eventually cycle into the used market.

The Surplus-Market Angle

Two dynamics matter for surplus buyers. First, as facilities modernize and some operators shift loads toward CO2 in new builds, well-maintained ammonia equipment is displaced and becomes available on the secondary market, often at attractive value relative to its remaining service life. Second, because CO2 adoption is recent and concentrated in new construction, the used CO2 equipment pool is still relatively thin and the components are higher-pressure-rated, which affects both availability and price.

The practical implication: ammonia equipment offers depth, proven longevity, and value on the used market today. CO2 equipment is a growing but younger segment where supply is tighter. A buyer’s choice should follow the application, not the trend headline.

Buying Considerations for Each

If you are sourcing ammonia equipment, focus on operating hours, overhaul history, oil analysis where available, motor and starter condition, and ASME documentation on vessels. The contractor and parts ecosystem is broad, so service support is rarely a constraint.

If you are sourcing CO2 equipment, verify pressure ratings carefully, since transcritical components are built for higher pressures and mismatches are dangerous. Confirm that controls, valves, and gas coolers are matched to the intended duty, and weigh the smaller installed base when planning for parts and service.

Refrigeration Equipment Pros stocks ammonia and freon-sector equipment and works with buyers to match refrigerant strategy to the application. If you are weighing an ammonia plant against a CO2 design, or sourcing displaced ammonia equipment as facilities modernize, our team can help you evaluate condition, documentation, and fit before you commit.

Comparing an ammonia plant against a CO2 design, or looking to source displaced ammonia equipment? Browse the inventory at refrigerationequipment.net, list equipment through our Sell To Us page, or call 201-805-1441 to talk it through with our team.