Controlled Atmosphere (CA) Storage: Cold storage installers

Controlled atmosphere (CA) storage is refrigeration plus a managed gas mixture, and it is what lets a British apple or pear picked in autumn reach the shelf the following spring or summer in near-fresh condition. By holding fruit cold and lowering the oxygen while controlling carbon dioxide, a CA store slows the fruit’s respiration almost to a standstill, extending marketable storage by six to twelve months. This page explains what CA storage is, who needs it, how the atmosphere and refrigeration are sized and controlled, how a gas-tight store is built, what it costs, and the critical safety regime that governs a sealed low-oxygen room.

What controlled atmosphere storage is, and who needs it

A CA store is a refrigerated room, typically held at 0 to +4°C, that is also gas-tight, so its internal atmosphere can be deliberately altered and held. Fruit and vegetables are living tissue that continues to respire after harvest, consuming oxygen, producing carbon dioxide and ripening toward the point of spoilage. By lowering the oxygen (often to a few per cent) and controlling the carbon dioxide, a CA store slows that respiration dramatically, so the produce ages far more slowly than it would in ordinary chilled storage. The result is that top fruit stored in the autumn can be sold in good condition many months later.

The buyers are almost entirely in produce. Apple and pear growers and packers are the core market, using CA to hold their crop across the season and market it steadily rather than dumping it all at harvest. Long-season produce operations and produce marketing groups use CA to smooth supply and stabilise price. This is a specialist capital investment made by a grower or packer whose whole commercial model depends on being able to sell fruit out of season, so the store has to hold the atmosphere reliably for months on end, and it has to be safe to work around, because a sealed low-oxygen room is lethal to anyone who enters it under atmosphere without controls.

How a CA store is sized and specified

CA storage adds a second engineering problem on top of refrigeration: holding a target gas mixture in a large sealed room for months.

• Pallet spaces and room count. Capacity runs up to 5,000 or more pallet spaces per sealed room, and growers typically operate several rooms so they can open one to market while the others stay sealed. Room size is a balance between storage volume and the practicality of pulling a room down and sealing it.
• Refrigeration duty. The store is sized on the usual cold-store heat load, product respiration heat, envelope ingress and infiltration, at a chilled setpoint. Because CA rooms stay sealed for long periods with little door traffic, infiltration is low once sealed, but the initial pull-down of a freshly filled room is a significant load.
• Atmosphere generation and scrubbing. The gas system is sized to pull the room down to the target atmosphere within an acceptable time and to hold it against the fruit’s continuing respiration. Nitrogen generators displace oxygen, and CO2 scrubbers remove the carbon dioxide the fruit produces so it does not rise above the target. The generation and scrubbing capacity is matched to the room volume and the crop’s respiration rate.
• Gas-tightness. The whole system depends on the room being genuinely sealed; a leaky room cannot hold its atmosphere and wastes generation and scrubbing capacity chasing a moving target. Gas-tightness is designed in and verified by pressure testing.

We size both the refrigeration and the atmosphere control together, because the two must work as one system to hold fruit for the full storage season.

How a CA store is built

The gas-tight envelope

The defining build challenge is gas-tightness. A CA room is constructed from insulated panel like any cold store, but every joint, penetration and door is sealed to hold gas, not just to insulate. Gas-tight doors, sealed cable and pipe penetrations, and continuous vapour and gas barriers are detailed throughout, and the completed room is pressure-tested to verify it holds its atmosphere before it is commissioned. This testing is not optional: a room that fails the pressure test cannot do its job and cannot be operated safely.

Refrigeration plant

The refrigeration is a chilled-duty cold store system, sized and installed to the same standards as any refrigerated warehouse, holding 0 to +4°C evenly across the room. Plant is sited outside with free airflow, pipe runs kept short, and controls integrated with the atmosphere system.

Atmosphere control and monitoring

Nitrogen generators and CO2 scrubbers are installed and integrated with continuous monitoring that reads oxygen and carbon dioxide levels and adjusts to hold the target. The atmosphere and temperature are logged continuously, both to prove storage conditions for traceability and to catch any drift. Because the store is sealed for months, reliable monitoring and alarming are central, not an afterthought.

Commissioning and mapping

The store is commissioned by proving the seal, verifying the refrigeration holds setpoint evenly through temperature mapping, and confirming the atmosphere system can pull down and hold the target gas mixture. Handover includes pressure-test records, calibration certificates, F-gas documentation and the safety systems described below.

What a CA store costs to install and run

Real UK costs, 2025-26, run from £150,000 to £2m per CA store, driven by pallet capacity, the number of sealed rooms, and the atmosphere generation and scrubbing specification. The gas-tight construction, nitrogen generation and CO2 scrubbing are what carry the cost above an ordinary chilled store of the same size.

Running cost combines refrigeration with atmosphere control: the chilled plant plus the energy for nitrogen generation and CO2 scrubbing. But the economics of CA are not really about the running cost; they are about the revenue the store unlocks. Extending marketable storage of top fruit by six to twelve months lets a grower sell across the whole season at a steadier, often higher, price rather than clearing the crop at harvest when the market is flooded. That revenue smoothing is what pays for a CA store, and it is why growers invest in it despite the capital and running cost. Our cold storage cost guide covers the numbers, and the plant qualifies for the capital allowances set out on the grants and funding page. Simple payback is typically around six years, driven by the marketing value of out-of-season fruit.

Refrigerant choice and the F-gas phase-down

The refrigeration side of a CA store is subject to the same GB F-gas rules and the same phase-down toward an 80 per cent HFC cut by 2036 as any cold store. Because a CA store is a long-lived capital asset that a grower expects to run for decades, installing it on a natural refrigerant that sits outside the phase-down, CO2 (R744), R290 (propane) or ammonia (R717) at scale, is the sensible choice, avoiding a system that becomes expensive to service as HFC supply is squeezed. The government’s gov.uk F-gas guidance sets out the timetable behind that decision.

Compliance and the CA safety regime

CA storage carries a compliance obligation that other cold stores do not: the atmosphere itself is dangerous.

• Confined-space and oxygen-depletion safety. A sealed CA room under atmosphere holds a low-oxygen mixture that is immediately life-threatening to anyone who enters it. Rigorous confined-space controls, oxygen monitoring, interlocks, entry procedures and signage are mandatory and are designed into the store. This is the single most important safety consideration in CA storage and it is treated as such.
• Gas-tight construction verified by pressure testing. The seal is both an operational and a safety requirement and is proven before use.
• BRCGS and food-safety traceability. Continuous logging of temperature and atmosphere provides the traceability the produce trade expects.
• GB F-gas Regulation. The refrigeration circuit is installed and serviced by an F-gas certified (REFCOM registered) company, working to the engineering standards upheld by the Institute of Refrigeration.
• PSSR and PUWER. The refrigeration plant and pressure system fall under the usual regulations.

We build the safety regime in from design, because a CA store that is not safe to operate is not fit for purpose regardless of how well it holds fruit.

Redundancy: protecting a whole season of fruit

A CA store often holds an entire season’s crop, so a failure is not a matter of one day’s stock but of the grower’s year. Refrigeration is designed with resilience in mind, and N+1 compressor redundancy protects against a single plant failure spoiling a sealed room that represents months of holding. Equally important is the resilience of the atmosphere and monitoring systems, since a store that loses its atmosphere control also loses the storage extension that justifies it. We design both refrigeration and atmosphere control for reliability across a long sealed season.

Cutting the running cost with solar

A CA store runs its refrigeration around the clock and its atmosphere control continuously, and many top-fruit operations have the roof and land area to host solar. Because the refrigeration load is constant, on-site generation is largely self-consumed, offsetting a slice of the store’s electricity. The seasonality of a grower’s wider operation makes the load modelling worth doing properly, which is the job of our sister service specialising in solar for cold storage and produce sites.

Frequently asked questions

How much longer will fruit keep in CA storage?

Controlled atmosphere storage typically extends the marketable life of top fruit such as apples and pears by six to twelve months compared with ordinary chilled storage, by lowering the oxygen and controlling the carbon dioxide to slow the fruit’s respiration almost to a standstill. The exact gain depends on the crop, variety and target atmosphere.

Why does a CA room have to be gas-tight?

Because the whole point is to hold a deliberately altered atmosphere for months. A leaky room lets oxygen back in and lets the controlled gases escape, so the atmosphere system cannot hold the target and the storage benefit is lost. Gas-tightness is designed in and verified by pressure testing before the store is used.

Is it safe to enter a CA store?

Not while it is under atmosphere. A sealed CA room holds a low-oxygen mixture that is immediately life-threatening, so entry is strictly controlled with confined-space procedures, oxygen monitoring and interlocks. The room must be flushed back to a safe atmosphere and verified before anyone enters. These controls are built into every store we install.

What refrigeration temperature does a CA store hold?

CA stores for top fruit typically hold 0 to +4°C, the chilled range, alongside the controlled gas atmosphere. The combination of cold and altered atmosphere is what delivers the long storage extension; neither alone achieves it.

How many CA rooms should a grower have?

Most top-fruit operations run several CA rooms rather than one large one, and the reasoning is commercial as much as technical. A sealed CA room has to stay closed to hold its atmosphere, so once you open a room to market its fruit, that room is effectively out of controlled-atmosphere storage. Splitting the crop across several rooms lets a grower open one at a time and market it steadily while the others stay sealed and protected, which is exactly the supply-smoothing that justifies CA in the first place. The right number of rooms balances storage volume, the practicality of filling and sealing each room at harvest, and how finely the grower wants to stage the season’s sales. We size the room count and volume around the crop and the marketing plan, not just the pallet total.

Related cold storage services

CA storage is the specialist end of chilled storage. Growers and packers often also run conventional refrigerated warehousing and cold stores for shorter-term holding, and use modular and containerised cold storage to absorb a harvest peak. To scope a CA store from your crop, pallet requirement and storage season, request a quote and we will size the refrigeration and atmosphere control together.