One of the essential considerations when maintaining a medical freezer is defrosting it regularly. Medical Freezers will build up ice on the cooling elements that support the freezers' low temperature. This ice build-up occurs because the humidity in the air condenses on the cooling parts, producing a layer of ice.
While some ice accumulation does not create much of an effect, as its thickness increases, it will begin to act as an insulator, decreasing the cooling elements' ability to reduce and maintain the freezer's internal compartment. Therefore, the lab freezer must work harder to maintain its target temperature, requiring more energy and leading to possible disruptions in temperature stability and uniformity.
Defrosting Medical Freezers
Defrosting refers to the removal of ice from the cooling elements. The process helps prevent excessive power usage and ensures the viability of medications, vaccines, specimens, or blood products that are perishable and sensitive to temperature instability.
The process of defrosting a medical freezer depends entirely upon the type of cooling unit you have selected. There are two types of medical freezers when considering defrosting; these are auto-defrosting and manual defrosting.
Auto-Defrosting
Auto-defrosting Medical Freezers will defrost automatically. There are two different and complementary strategies used in auto-defrosting freezers. The first strategy is a built-in heater on the cooling elements that briefly and regularly heats the cooling elements to melt any ice build-up. The heating periods are short enough that they may not cause the freezer's internal temperature to move outside the target range but are intense enough to melt any ice build-up that has occurred since the last heating cycle. Typically, these heating cycles are about 15-30 minutes apart.
The second strategy that auto-defrost lab freezers use is to have fans that create continuous air movement within the freezer. Increased airflow reduces much of the condensation that can occur on the cooling elements. When coupled with regular heating cycles, auto-defrosting freezers reduce ice build-up problems.
While very convenient, auto-defrosting medical freezers do have some potential negative considerations. The moving air that reduces condensation can be dehydrating to uncovered specimens. Because there are regular heating cycles, these freezers are also less energy efficient. Further, depending on the quantity and sensitivity of the contents stored close to interior walls, some temperature fluctuation may impact select content.
Manual Defrosting
Manual medical/lab freezer defrosting involves allowing the ice to melt once it builds up to a level that could affect the freezer's ability to function. These freezers are more straightforward and use less energy if maintained correctly, but the process of manually defrosting them requires a planned schedule for defrosting.
When to Defrost Your Medical Freezer
The CDC recommends defrosting anytime ice builds beyond 1/2 inch in thickness or whenever there is any change in the freezer's function due to ice accumulation. Clues that point to decreased function include taking longer to cool after being opened, difficulty maintaining the target temperature, or increasing amounts of energy usage.
How to Defrost a Medical Freezer
Preplanning helps reduce inconvenience. Plan for your lab freezer to be unavailable for up to 48 hours during the manual defrost. Ensure you have sufficient storage space for the content of the lab freezer you are defrosting over that timeframe. While this may seem obvious, there are times when temperature-sensitive deliveries may occur during defrosting, or lack of communication between teams may lead to inadequate storage space. Be sure potential storage issues will be avoided during the manual defrost—plan around school or flu vaccine arrivals, for example.
Once downtime has been planned for, the steps for performing a medical defrost are straightforward:
1. Empty the freezer into your backup storage area. Be sure no temperature-sensitive medications or biological specimens are left, as they may spoil.
2. Turn the freezer off. It is recommended you disconnect the freezer from a power source, as some freezers may appear off but still be active.
3. Allow the ice to melt. Allow it to dissolve by itself. It may be tempting to speed up the procedure, but removing ice build-up mechanically may damage the cooling elements and affect the medical freezer's function.
4. Dry water accumulation. As the ice melts, water will collect. Removing this water ensures that frost build-up will not immediately reoccur.
5. Turn the freezer on. Allow the freezer time to reach its target temperature. Some people make the error of resuming use as soon as the freezer is on, but it will take some time to reach the stable target temperature.
6. Resume use of the freezer. Note that the defrost occurred in a maintenance log. It is good practice to plan for at least one full defrosting procedure each calendar year.
Auto-defrosting freezers don't ordinarily require a manual defrost. In some unusual cases (such as high humidity), it may become necessary to manually defrost an auto-defrosting freezer. In these situations, follow the same actions you would do for a manual defrosting unit.
Maintain Your Medical Freezer's Value
Ensuring your medical freezer is regularly defrosted and maintained correctly can extend your product's life by preventing it from working too hard. Regular maintenance will also ensure that temperature-sensitive medications or specimens are kept viable. You will also avoid inefficient energy use, helping to reduce the cost of maintaining frozen storage while reducing your environmental impact.
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