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This Expert Opinion column has been written by Ritesh Raj, a Growth Engineer at Mindlabs Cloud, which deploys IoT (internet of things)-based environmental monitoring systems across pharmaceutical cold chains, GMP (good manufacturing practice) manufacturing facilities and regulated cold storage operations around the world. Here, Raj writes about the need for cold storage operators to revisit their temperature monitoring sensor placement and calibration assumptions after transitioning from HFCs to naturals.
Ritesh Raj: Cold storage operators across the food and pharmaceutical sectors are transitioning to natural refrigerants at a rapid pace. The technical conversations around these transitions tend to focus on the refrigerant itself: system pressure profiles, compressor selection, defrost strategies and ammonia (R717) charge reduction, for example. What gets considerably less attention is what happens to the temperature monitoring layer inside the cold space. That oversight matters more than most operators realize, and it’s showing up in compliance records.
Why the thermal environment changes – not just the refrigerant
Transcritical CO2 (R744) refrigeration systems operate at significantly higher pressures than the HFC systems they typically replace, and they run more frequent and aggressive defrost cycles. Where an HFC system might defrost every 12 to 24 hours, a CO2 booster system commonly defrosts every four to six hours using hot gas. Each defrost event introduces a controlled thermal pulse into the cold space. Those pulses have a different timing profile, a different peak temperature and a different recovery curve than what the previous system produced.
This matters for temperature monitoring because the sensors and alert thresholds in a cold room were calibrated against the old system’s cycling behavior. A monitoring sensor placed to avoid triggering false alarms from HFC defrost pulses – positioned and threshold-set for that timing – may now sit in entirely the wrong relationship to a CO2 system’s defrost pattern. It might be absorbing more thermal pulse than it was designed to flag, or it might be in a location where the new evaporator configuration produces a dead zone in the airflow pattern.
Ammonia systems introduce a different set of monitoring considerations. In facilities transitioning to low-charge ammonia designs where secondary CO2 loops are used to reduce ammonia inventory in the cold space, the evaporator configuration and airflow distribution within the storage area often changes substantially from the legacy HFC layout. Temperature sensors positioned for the legacy system’s airflow are not automatically positioned correctly for the new one.
The calibration assumption that needs to be revisited
Most cold storage operators treat sensor calibration as a commissioning-stage event. A calibration certificate is issued, the monitoring system is commissioned, and the reading is assumed to be accurate unless there is a visible problem. This assumption is fragile under any system because sensors drift due to thermal cycling, humidity exposure and vibration regardless of the refrigerant. It becomes particularly problematic in the period immediately following a refrigerant transition.
Transcritical CO2 refrigeration systems run at higher operating pressures and produce different vibration signatures than legacy HFC equipment. Mechanical vibration accelerates drift in capacitive humidity and temperature sensors. If a facility commissions a CO2 system in January and runs its monitoring under HFC-era calibration baselines through June, the compliance record for that period reflects an assumption of sensor accuracy that was never verified against the new system’s operating profile.
For pharmaceutical cold storage operators, this isn’t an abstract compliance concern. GDP (good distribution practice) guidelines require documented, continuous evidence that temperature ranges were maintained throughout storage. If a sensor that was accurate under an HFC system has drifted under a CO2 system’s operating conditions, the compliance record doesn’t reflect that drift. It reflects a reading that looked plausible but was no longer accurately measuring the storage environment. For food producers, the same principle applies under HACCP (hazard analysis and critical control points) and the traceability requirements from the U.S. FDA’s Food Safety Modernization Act (FSMA).
“The monitoring infrastructure that ensures product quality and compliance integrity doesn’t upgrade itself when the refrigerant does.”
Ritesh Raj,
Growth Engineer at Mindlabs Cloud
What a transition verification protocol should include
A refrigerant transition provides a natural trigger point for an environmental monitoring reset that most operators currently skip. First, re-survey sensor placement before declaring the system commissioned. Map the new airflow patterns from the natural refrigerant evaporator configuration and confirm that existing sensor positions remain in the representative sample zone — mid-shelf, clear of the evaporator coil, clear of door proximity and clear of HVAC return paths.
Second, establish new baseline readings against a NIST (National Institute of Standards and Technology)-traceable reference immediately after commissioning and again at 30 days post-commissioning. The 30-day check catches early drift introduced by the new system’s operating profile before it compounds. Document both readings with the reference probe model, certificate number and delta.
Third, revise alert thresholds to account for the new system’s defrost cycle timing. If CO2 defrost events occur every six hours, thresholds need to be validated against the actual thermal recovery curve of the new system and not inherited from the HFC system’s slower defrost profile.
Fourth, for facilities transitioning to ammonia systems, treat ammonia gas monitoring as part of the environmental monitoring scope, not just a safety compliance item. Standard electrochemical ammonia sensors struggle in sub-zero environments due to electrolyte freezing, and sensor selection needs to be validated against the actual temperature range of the storage area.
The broader principle
The transition to natural refrigerants is a meaningful step for cold storage operators managing their environmental footprint and regulatory posture. But the monitoring infrastructure that ensures product quality and compliance integrity doesn’t upgrade itself when the refrigerant does. A CO2 or ammonia system installed on top of an HFC-era monitoring setup – the same sensors, same placements and same calibration assumptions – creates a gap between the refrigerant’s improved environmental profile and the accuracy of the compliance record it’s meant to support.
The refrigerant transition is the right time to close that gap as the system is already being re-engineered and the operational disruption is built into the project plan.
