In the medical field, refrigeration is much more than a convenience—it's a guarantee of safety. Production units, warehouses, and research laboratories depend on stable and validated temperature conditions to ensure the integrity of medicines, samples, and research materials. Small variations in the set point can have serious consequences.

To minimize risks, installations are often built with 100% redundancy: two completely independent refrigeration systems, designed to ensure continuous operation. But this very redundancy raises important design questions. Should both systems operate simultaneously? Or should one remain on standby, only coming into operation when an alarm occurs?

Regardless of the configuration, one requirement remains unchanged: the temperature must always stay within the validated limits.

The transition from HFCs to natural refrigerants.

Historically, medical refrigeration systems used HFC (hydrofluorocarbon) refrigerants, such as R404A. These synthetic gases offered reliable performance but had a high global warming potential. With stricter environmental regulations worldwide, the industry is rapidly moving towards natural refrigerants, which provide equivalent performance with a much lower environmental impact.

The shift to CO₂ systems represents more than just a compliance issue—it's an opportunity to rethink the entire system design, improving energy efficiency, control, and long-term sustainability.

A case in Copenhagen

Pharmacold A/S, a Danish refrigeration specialist with decades of experience in the medical sector, was challenged to refurbish a freezer chamber for a local pharmaceutical company. The original installation, using R404A, included two independent condensing units in a technical room, each with its own control panel.

The design was typical of previous generation systems: pump-down circuit, thermostatic expansion valves, solenoid valves, and simple on/off temperature control. Ventilation was necessary to remove heat from the condensers. Energy optimization was practically nonexistent, and suction pressure control depended solely on a low-pressure switch. In short, there was much room for improvement.

The project objectives were defined as follows:

• Replace the HFC system with an alternative using natural refrigerant;

• Maintain full redundancy with two independent units;

• Introduce electronic expansion valves for more precise control;

• To improve energy efficiency by maintaining the temperature within ±3°C of the setpoint. In practice, the current result is ±2.5°C.

A new design philosophy

The new installation replaced the HFC system with two high-efficiency CO₂ units. Each unit operates independently, but together they ensure precise temperature control.

One of the key innovations was the redundancy strategy. Instead of using a traditional standby system, triggered by remote on/off signals, Pharmacold implemented a configuration with both units active:

• Both remain in operation, but one operates with a slightly shifted set point (approximately +2°C);

• The evaporator fans in the standby unit continue to operate, ensuring even air distribution and thermal stability.

• A weekly automatic switch alternates between lead and lag functions, balancing operating hours and wear;

• In case of a change failure, both units automatically return to the same set point, ensuring complete continuity.

This simple yet robust control logic ensures constant redundancy without the need for complex supervisory systems, achieving thermal stability through straightforward design.

Smarter monitoring and validation

In the medical industry, compliance and traceability are as important as performance. Therefore, the system was equipped with dual monitoring:

• an independent temperature recording system, with high/low alarm management and regulatory validation;

• A central monitoring platform with real-time data on compressor operation, defrost cycles, and energy performance.

The monitoring system communicates directly with the client's BMS via TCP/IP, integrating alarms, operational data, and system status. This dual structure ensures regulatory compliance and provides useful information for optimization and validation, both during normal operation and during defrosting.

Measurable results

The update brought immediate and clear improvements:

• Greater temperature stability, both in steady-state conditions and during defrosting;

• Reduced compressor operating time thanks to inverter modulation;

• Reducing energy consumption and operating costs;

• Reliable redundancy, with smooth switching between the two units.

The result is an efficient, sustainable, and future-proof cooling system that meets the high reliability requirements of the medical industry.

A model for the future

This case demonstrates how transitioning from HFC to CO₂ systems can generate real benefits in one of the most demanding sectors. Beyond the environmental advantages of natural refrigerants, the combination of modern control logic, data-driven monitoring, and intelligent redundancy offers clear improvements in efficiency and reliability.

For Pharmacold A/S and its client, the conclusion was simple: keep things simple. With intelligent yet straightforward design principles, it's possible to achieve validated thermal stability, improved energy performance, and long-term sustainability—essential elements for the next generation of medical refrigeration.