What could be easier than buying a fridge or freezer and plugging it in and then start using it? Of course, in the GMP world, things are more complex. There are setpoints, alarm points, validation protocols, maintenance schedules, Operational SOPs, calibrations, oh my! Today I want to talk about just one aspect of all this: setpoints, alarms, and fridge/freezer type.
If we start with setpoints, the most common setpoint for a fridge is 4C. This is mostly because the accepted range is 2-8C. Modern fridges with separate condensers for fridge/freezer (if using a combo unit) or fridge alone can keep the temperature very even–up to +/- 0.5C for controlling, so the setpoint can be lower and the range tighter for temp sensitive products. One could use a setpoint of 2C and a range of 0.5C to 4C for example, as long as products did not freeze. Or a setpoint of 3C and a range of 1-5C may be acceptable. When I say “range” I mean the low and high temp one would use for the alarm setpoints. Freezers are most commonly set at -20C with a range of -30 to -10C, although modern freezers are capable of controlling in a tighter range, say -25 to -15C. The range chosen should be reasonable so as to avoid nuisance alarms. Ultracold freezers are most commonly set at -80C with a range of -65 or -70 to -90C.
Alarm setpoints should be adjusted to have a low and high setpoint that is appropriate for the products and materials stored in the fridge/freezer. The above examples for range are commonly used alarm high and low setpoints. These should be chosen to both cover the desired range and also avoid nuisance alarms. A fridge constantly alarming at 1.5C when nothing is frozen is not helpful; it is just fine. In this case, the fridge temp setpoint can be pushed up slightly, or the alarm low setpoint can be changed to 1C. By the way, probes for the monitoring system should be periodically calibrated, so we can trust the temperature reading.
Modern fridge/freezer combo units are popular in clinical trial phase organizations, and these newer fridge/freezers combo units have very good temperature control capability. Modern units are also available as stand-alone refrigerators or separate freezers. Many are frost-free, which require less maintenance. Newer models don’t heat up as much as older ones during the defrost cycle, so the frost free option is often acceptable now because products and materials don’t heat up when the unit is defrosting. Solid state refrigerators are also now an option, and this can be a good choice for very good temperature control, energy savings, and no vent/dust collectors for cleanrooms. Ultracold freezers (-80C) are now available with WiFi and a monitoring app, so that chart recorders are a thing of the past. These newer units have very good temp control and also save energy.