Thermal Analysis of Refrigeration Systems Used for Vaccine Storage

Background: Each year, billions of dollars of vaccines are stored in refrigerators at the facilities of a variety of medical providers. Many vaccines must be maintained in the range from 2 °C to 8 °C to retain product potency.

Objectives: We have tested the performance of two type of household refrigerators to determine if these refrigerators are suitable to this task, and to identify proper storage and temperature monitoring methods. Additionally, we tested four electronic data loggers as a means of continuously logging refrigerator temperatures.

Methods: Nineteen calibrated Type T thermocouples, distributed through the refrigerator interior, served as reference thermometers. Attachment of thermocouples directly to vaccine vials gave accurate measurements of the vaccine temperature, which often differed from the air or interior wall temperatures during door openings or defrost cycles. Tests of intermittent and continuous door opening and of simulated power outages demonstrated the value of adding water bottles to the door as a thermal ballast.

Results: A household, full-size freezerless refrigerator [capacity = 0.47 m³ (16.7 ft³)] proved fully adequate at maintaining vial temperatures within the desired 2 °C to 8 °C range, independent of how the refrigerator was loaded. The performance of compact dormitory-style refrigerators suffered from drift of the refrigerator set point, sensitivity to load density, and temperature non-uniformity. These problems make the dormitory-style refrigerator [capacity = 0.08 m³ (2.7 ft³)] unsuitable for vaccine storage.

Conclusions: Properly located, data loggers accurately monitored vial temperatures for extend periods of time.