The main architectures are direct expansion (DX) and indirect secondary-loop systems. Refrigerant choice is a separate decision.
In short: compare load, number of rooms, piping, safety, service and regulation.
CO₂, ammonia and propane can appear in different arrangements; “natural refrigerant” is not a third piping architecture.
The refrigeration cycle in 60 seconds
Every cold-room system runs the same vapour-compression cycle. Four components move heat "uphill" from the cold interior to the warmer outdoors:
- Compressor — raises refrigerant pressure (and temperature), driving the cycle.
- Condenser — rejects heat outdoors; refrigerant condenses to liquid.
- Expansion device — drops pressure, sharply cooling the liquid.
- Evaporator — absorbs heat from the room; refrigerant boils back to vapour. A fan circulates the chilled air.
What changes between architectures is where the phase change happens and which fluid touches the inside of the cold room. That single distinction drives every trade-off — leak risk, charge size, efficiency, and cost.
What characterises a refrigerant
Four properties decide what regulators and safety codes will allow:
| Property | What it means |
|---|---|
| GWP | Warming effect of 1 kg of the gas vs 1 kg of CO₂ over 100 years (CO₂ = 1 by definition). |
| Flammability | Safety class A1 (none) → A3 (highly flammable); A2L = mildly flammable. |
| Toxicity | B-class refrigerants (e.g. ammonia) are toxic. |
| Operating pressure | Drives pipe, valve, and compressor design (CO₂ runs very high). |
These four properties — not just GWP — govern the architecture and refrigerant you can specify, and they are tightening fast under EU F-gas rules.
The three architectures at a glance
| Architecture | Refrigerant in the room? | Best fit |
|---|---|---|
| Direct expansion (DX) | Yes — evaporates in the room coil | Single small–medium room |
| Secondary loop | No — benign glycol/brine in the room | Multi-room, multi-zone, large |
| Natural refrigerant | Depends — used as DX, primary, or self-contained | Future-proof builds of any size |
Related articles
- Direct expansion (DX) cold room systems
- Secondary-loop (indirect) cold room systems
- Natural refrigerants: CO₂, ammonia, hydrocarbons
- F-gas rules and refrigerant selection
- Choosing the right system for your cold room
Questions about which system suits your project? Contact [email protected].
