Transcritical CO2 vs HFC refrigeration for cold storage: which and why

If you are specifying a new cold store or replacing ageing plant, the refrigerant is one of the most consequential decisions you will make, because it determines both your running cost and whether you are buying an asset with a future or a liability with a countdown on it. The short version: for most new UK cold storage, transcritical CO2 (R744) beats a legacy HFC such as R404A. This guide explains why, in plain terms, and where ammonia and R290 fit in.

The two contenders

HFC refrigerants such as R404A and R410A dominated cold storage for years. They work, engineers know them, and there is a large installed base. But they have a high global warming potential (GWP), and that is now the problem: the GB F-gas Regulation is deliberately reducing the supply of high-GWP HFCs, which makes them progressively scarcer and more expensive.

Transcritical CO2 (R744) uses carbon dioxide as the refrigerant. CO2 has a GWP of 1, so it sits entirely outside the phase-down. “Transcritical” refers to how the system operates: because of CO2’s properties, the high side of the cycle runs above the critical point, which is why the plant is engineered differently from a conventional HFC system. Modern transcritical CO2 plant is efficient, well-proven at cold-storage scale, and increasingly the default for new UK stores.

Why CO2 wins on the phase-down

The GB F-gas quota is cutting HFC supply, measured in CO2-equivalent tonnes, toward an 80 per cent reduction by 2036 against the 2015 baseline. R410A is already excluded from most new equipment, and R404A, with one of the highest GWPs in common use, is being squeezed hardest. The practical consequences for an operator on legacy HFC plant are:

• Rising service and top-up costs as the gas becomes scarcer.
• A likely early replacement before the plant’s mechanical end of life, because the refrigerant becomes uneconomic to maintain.
• Exposure to supply risk if you need a significant recharge after a leak.

A store built on CO2 avoids all of this. The refrigerant is cheap, abundant and unaffected by the quota, so the plant can run to its full mechanical life without a refrigerant-driven forced replacement. For a capital asset expected to operate for well over a decade, that certainty is worth a great deal. The official position on the phase-down is set out in the government’s F-gas guidance.

Why CO2 wins on running cost

Refrigeration is 70 to 80 per cent of the electricity bill on a cold store, so efficiency is not a footnote, it is the dominant operating cost. Modern transcritical CO2 plant has been shown to cut energy against legacy R404A by around 19 per cent. On a large frozen store where refrigeration runs into the hundreds of thousands of pounds a year, a saving of that order is substantial, and it compounds every year the plant runs.

CO2 systems are particularly well suited to the UK climate. Transcritical efficiency improves in cooler ambient conditions, and the UK spends much of the year in exactly the range where CO2 plant performs well, which is one reason it has become the natural-refrigerant default here rather than in hotter climates where the efficiency picture is more nuanced.

Where ammonia fits

Ammonia (R717) is the other major natural refrigerant, and at the largest industrial scale it is more efficient still than CO2. Big cold stores and industrial refrigeration have used low-charge ammonia for years because it is thermodynamically excellent and, like CO2, sits outside the F-gas phase-down. The trade-off is safety engineering: ammonia is toxic, so a system needs additional detection, ventilation and safety design, and it is generally reserved for larger stores where that engineering is justified and where competent operators are on hand. For a very large refrigerated warehouse, low-charge ammonia is often the efficiency leader; for most other duties CO2 is the more practical natural choice.

Where R290 fits

R290 (propane) is a natural refrigerant with a very low GWP that suits smaller, packaged plant, the kind used in walk-in cold rooms and self-contained units. It is efficient and outside the phase-down, and it is often the right natural refrigerant where the duty is modest and a packaged system makes sense. The consideration with R290 is flammability, which caps the charge size and drives the safety design, so it is applied where the charge stays within safe limits.

A simple decision framework

• New walk-in room or small packaged plant → R290 (propane) is usually the natural-refrigerant choice, efficient and outside the phase-down.
• New chilled or frozen cold store, most duties → transcritical CO2 (R744): efficient in the UK climate, proven, and future-proof against the quota.
• Very large industrial store → low-charge ammonia (R717) for the best efficiency, where the safety engineering is justified, or CO2 where it is not.
• Existing HFC plant → plan the transition. You do not have to rip it out tomorrow, but budget for replacement on a natural refrigerant before servicing costs and supply risk force your hand, and claim the new plant under capital allowances.

What about keeping the HFC plant you have?

If you run R404A or R410A plant today, the question is when to replace, not whether. The case for acting sooner rather than later is that the servicing cost is only going one way, the efficiency gap against modern plant is real money on a bill that is 70 to 80 per cent refrigeration, and the new plant qualifies as plant and machinery for capital allowances, which softens the capital cost. Set against that, if the plant is near the end of its mechanical life anyway, waiting a short while to align replacement with a broader upgrade can make sense. The trap to avoid is drifting: an unplanned failure of scarce R404A plant, with a costly emergency recharge or replacement, is the worst outcome. We cover the numbers behind that decision in our guide to cold storage running costs.

What CO2 plant costs to install

A fair question is whether the efficiency and future-proofing of transcritical CO2 come at a capital premium. Historically CO2 plant carried a higher install cost than an equivalent HFC system, because the components run at higher pressures and the engineering is more specialised. That gap has narrowed as CO2 has become the mainstream choice for new UK cold stores and the supply chain has matured. More importantly, the whole-life comparison favours CO2 once you account for the lower running cost on a bill that is 70 to 80 per cent refrigeration, the avoided cost of servicing and eventually replacing scarce HFC plant, and the capital allowances available on the new plant. Judging CO2 on install price alone misses where the money is actually made or lost, which is over the years the plant runs, not on the day it is fitted.

The bottom line

For most new UK cold storage, transcritical CO2 is the right refrigerant: it sits outside the F-gas phase-down, cuts energy against R404A by around 19 per cent, and removes the supply and service risk that comes with a legacy HFC. Ammonia leads on efficiency at the largest scale, R290 suits smaller packaged plant, and legacy HFCs are a managed retreat rather than a place to invest. If you are specifying a new store or planning to replace ageing plant, request a quote and we will recommend the refrigerant that fits your duty, your site and your timeframe.