A central plant cools glycol, brine or another secondary fluid circulated to room coolers.
In short: this can keep primary refrigerant in a plant area and serve many rooms, but adds pumps, piping and heat-exchange losses.
Fluid concentration, viscosity, flow and pipe insulation require calculation. The architecture does not remove refrigerant safety duties.
How it differs from DX
In a secondary-loop system the primary refrigerant never enters the cold room. A central chiller plant uses the primary refrigerant (commonly ammonia or CO₂) to cool a secondary fluid — glycol, brine, or chilled water — which is then pumped through insulated pipes to heat exchangers inside each cold room.
The evaporator in the room handles only the benign secondary fluid; the hazardous or high-GWP charge stays contained in one plant room.
Pros and cons
| Secondary-loop systems | |
|---|---|
| Pros | Refrigerant charge concentrated and minimised in one location → smaller leak exposure; major safety win with toxic ammonia or high-pressure CO₂; one fluid loop serves many rooms and setpoints (scalable); the plant can be isolated and serviced without disturbing cold-room operation. |
| Cons | High initial cost (central plant + distribution pipework + pumps); an extra heat-exchange step adds a thermodynamic penalty unless carefully designed; pumping power is a parasitic load; multi-zone temperature coordination needs more sophisticated controls. |
Typical application
A large meat-processing plant runs ammonia in a central engine room to chill glycol, which is pumped to each processing line and CAM-LOCK store. This keeps ammonia out of public and production areas — satisfying the machinery-room, ventilation, and leak-detection requirements that apply to larger ammonia charges (per EN 378 / ISO 5149) — while serving very high cooling loads across many rooms.
Note that ammonia (R-717) is classed B2L: toxic and mildly flammable. The secondary loop is precisely the architecture that keeps it out of occupied space.
Related articles
- Cold room refrigeration systems: an overview
- Direct expansion (DX) cold room systems
- Natural refrigerants: CO₂, ammonia, hydrocarbons
- F-gas rules and refrigerant selection
- Choosing the right system for your cold room
Planning a multi-room facility? Contact [email protected].
