How to Choose Manual or Auto-Defrost Cold Storage Units for the Lab

Lab refrigerators and lab freezers come in various sizes and temperature capabilities, many of which are designed for specific storage functions.  What you store in these units has a large part in determining the type of unit you purchase.  This post will cover decision-making factors such as storage temperature capability and whether manual or auto-defrost equipment should be specified when you choose manual or auto-defrost cold storage units for the lab.

We’ll separately take a look at scientific refrigerators and scientific freezers, then provide suggestions on how to manage defrosting operations.

Always keep in mind that temperature monitoring and alarming is a subject onto itself in laboratory refrigerators and freezers.  The defrosting operation by definition signals a change in storage temperature within these units, whether a scientific freezer or scientific refrigerator.  We’ll touch on this briefly at the end of our post.

In addition, two important points to include in your company’s operations manual are recommended storage temperatures as provided by the contents’ manufacturers and how your personnel deal with this during the defrosting operations.

What are the Differences Between Manual and Auto-Defrost Scientific Refrigerators?

What are the Differences Between Manual and Auto-Defrost Scientific Refrigerators?There are a lot of differences.  We’ll look at them separately.

A manual-defrost scientific refrigerator cools by circulating refrigerant through tubing in the walls. There are no fans as used on auto-defrost units to circulate air.

Instead the internal temperature differential causes the cold air to circulate.

This means that product placed adjacent to the walls and toward the bottom will be colder than elsewhere in the unit.

If this is a cause for concern it must be addressed.  Also keep in mind that condensate will pool at the bottom of the unit.  It can be removed by a condensate drain if the refrigerator is so equipped.

As a typical application, because there is no fan-forced air circulation in manual-defrost units they are favored for experiments in open containers where it is not permissible for product to dry out due to moving air.

When the unit is turned off for defrosting and cleaning, it may be necessary to store the contents in another refrigerator until defrosting is completed.  Do not replace the contents until the refrigerator returns to its set operating temperature.

Auto-defrost scientific refrigerators, in contrast, have fans that circulate chilled air throughout the unit.

This has the advantage of creating a more uniform temperature but does not completely eliminate slight fluctuations that occur when the compressor cycles on and off.  Air circulation could cause contents to dry out unless they are fully protected.

During the defrost cycle the compressor shuts down but the fans continue to run to remove any frost accumulation on the condenser.  With this there will also be slight temperature fluctuations that may have to be addressed depending on the contents of the refrigerator.

The fluctuation is less if the unit is filled, either with product or water bottles. Another caution is to minimize or eliminate opening the door during the defrost cycle as the compressor will not come on and the cabinet cool down until the cycle ends.

Certain models of auto-defrost lab refrigerators allow users to control the frequency and duration of the cycle or even turn it off if there is a need to maintain a constant temperature.  Your organization should have specific instructions to manage this operation.

Manual and Auto-Defrost Scientific Freezers

Manual-defrost scientific freezers work on the same principal as manual-defrost refrigerators.

But in this case ice buildup on interior walls must be removed on a planned basis that includes providing alternative freezer space for the contents during the defrosting operations.  Be certain that the lab freezer reaches its set temperature before replacing the contents after the defrosting operation.

Auto-defrost scientific freezers use a heater to defrost the condenser coils, which will cause a temperature spike within the unit.

This can be minimized by keeping the freezer compartment full, whether with product or with ice packs.  Nevertheless you will have to make sure the contents can accommodate the temperature spike or make alterative storage arrangements.

As with auto-defrost refrigerators some auto-defrost freezers are equipped to provide user control over the defrost cycle.  Be certain there are procedures in place to avoid potential product loss or damage to the unit.

Summarizing Manual and Auto-Defrost Lab Refrigerators and Freezers

Manual and Auto-Defrost Lab Refrigerators and FreezersWhat you store in your lab refrigerators and lab freezers has a major bearing on deciding between manual and auto-defrost units.

Some products can withstand the temperature fluctuations of auto-defrost, others can’t.  That’s why it is so critical to be aware of and accommodate manufacturers’ storage recommendations.

Manual-defrost freezers must be emptied and contents accommodated while ice buildup is removed and the unit allowed to return to its set temperature.

In a nutshell:

  • Auto-defrost advantages include less maintenance, more uniform internal temperatures.
  • Auto-defrost disadvantages include more power consumption, less/no control over the defrost cycle and the potential for contents drying out.
  • Manual-defrost advantages include full control over the defrost cycle, less power consumption and a more constant internal temperature.
  • Manual-defrost disadvantages include the work of defrosting and relocating contents during defrosting.
  • Full cold storage equipment, whether with product, water bottles or freezer packs, retains temperature longer than partially filled units.

A Word on Temperature Monitoring and Alarming

Temperature monitoring and alarming systems are key points to CDC vaccine storage compliance and should be carefully considered when you select your scientific refrigerator or freezer.  Here are some things to look at.

Following is a description of what is required.  Depending on models some of these features are standard; others can be added to bring scientific freezers and refrigerators into compliance.

The temperature inside the unit is best monitored with product temperature sensors which are typically inserted in a bottle of glycerin or glycol to mimic the temperature of refrigerated products.

This is due to the fact that internal air temperature changes faster than the product temperature when storage unit doors are opened.

Since the variation in product temperature is the important factor, the product sensors avoid unnecessary temperature alarms set off by routine door openings.  Sensors may be used to record product temperature in two areas of the unit as well as air temperature.

Temperature control options range from simple dial-type thermostats with letters or numbers (cold, colder, coldest) to highly sophisticated digital LED display microprocessor temperature controllers.  The internal temperature display may be located at the bottom or near the top of refrigerator units.

Premium refrigeration systems use the more precise programmable logic controls, which is the best choice to maintain the absolute minimum temperature drift.   High-end models also allow setting temperatures to one decimal place.

Temperature alarming is an absolutely critical feature when storing vaccines and other highly temperature sensitive contents.  Alarm systems are standard on many models.  They take the form of built-in digital audio and visual high/low temperature alarm, some with remote alarm contacts that can be connected to alert personnel elsewhere in the facility.

Otherwise compliant equipment can be fitted with optional digital temperature alarms.  These consist of internal sensors placed in bottles as described above.  They are connected by wire passing over the hinge-side door gasket or through optional sensor access ports to an external control and display module.

Important Note: Have an Emergency Plan to Protect Valuable Contents

Power failures have resulted in substantial losses when vaccines, pharmaceuticals, biological samples and irreplaceable items are stored in scientific refrigerators and freezers.  Back-up storage plans should be made in advance and quickly carried out in the event of outages.  See our post on power failure planning for suggestions.

The scientists at Tovatech are available to help you make your decision on manual or auto-defrost cold storage units and select temperature control, monitoring and alarming systems. Contact us for help choosing equipment or products that fit your needs.

About Rachel Kohn

So how did an MIT Ph.D. end up selling refrigerators? When I figured out that a lot more scientists buy lab refrigerators than innovative leading-edge instruments. I hope that my many years of lab experience will help you find the right equipment for your work. Before co-founding Tovatech I worked in business development and project management at Smiths Detection, Photon-X, Cardinal Health, and Hoechst Celanese. And before that I spent 12 years as an R&D chemist at Hoechst Celanese and Aventis working on advanced drug delivery systems, polymer films and membranes, optical disks, and polysaccharides. Some day, eventually, I’ll make enough money to develop an innovative technology that will change the world. Read More