Many of our posts on scientific refrigeration equipment focus on selecting correct scientific refrigerator and scientific freezer units, and the importance of temperature control, monitoring and alarming systems that protect valuable vaccines, biological specimens and similar temperature-sensitive materials.
It might be a stretch to liken laboratory, pharmacy and scientific refrigeration equipment purchases with automobile purchases where the savvy buyer is interested in “what’s under the hood?” Nevertheless we post this post on what’s “under the cabinet” of your scientific refrigerator or freezer. Our point is to point out how these units protect your investment in their contents.
Your take-away is a better understanding about how refrigeration works, which type of lab refrigerator or freezer to buy, how to maintain it, and where to set it up to get the best performance.
How Scientific Refrigeration Equipment Makes Cold
When a liquid evaporates it absorbs heat and when a gas condenses to a liquid it releases heat.
We’ll start with the receiver where the liquid refrigerant is stored under high pressure. The liquid passes through a thermal expansion valve causing a sudden reduction in pressure. When the pressure is reduced some of the liquid evaporates and this causes the remaining liquid to cool. The cold refrigerant passes through the evaporator coil absorbing heat from the space inside the refrigerator.
During this cycle the liquid refrigerant completely evaporates inside the evaporator and becomes a low pressure gas. This gas enters the unit’s compressor where it is recompressed to a high pressure. Then it is directed into the condenser to be cooled by a fan. This condenses it back into a liquid directed back to the receiver. The cycle is repeated.
The condenser dissipates heat. Most condensers have a fin and tube design with a motor-driven fan. The fan forces air through the fin and tube assembly to drive heat away from the condenser’s coils. You can sense the warmth coming off the coils. This makes it important to place your refrigerator or freezer in a location that facilitates heat dissipation.
These cycles cause frost to accumulate on the unit’s evaporator coils and, if allowed to build up, will eventually stop heat transfer and cause the system to stop working. The following paragraphs on manual defrost and auto-defrost scientific refrigeration systems will explain how frost is removed from the evaporator coils.
Manual Defrost vs. Auto Defrost Refrigerators
Most folks are familiar with the difference between manual and automatic defrost freezers. Such is not always the case with manual and auto-defrost refrigerators.
An automatic defrost refrigerator is the most popular type of lab refrigerator. More than likely (but not always) it is probably the type of unit you want. During the automatic defrost cycle the compressor shuts off and a fan blows air over the coils to remove frost. Most models also have internal fans that circulate the air keeping the temperature inside the cabinet uniform.
A manual defrost refrigerator has no fan to circulate the cold air and no timed defrost cycle. It has copper tubing with refrigerant inside the sidewalls, back, and top of the unit. Because there’s no fan, samples inside the refrigerator won’t dry out. But moisture that condenses on the inside walls must be wiped down every few days. Manual defrost scientific refrigerators are recommended when it’s important to protect samples from drying.
How Auto Defrost and Manual Defrost Freezers Work
An auto defrost scientific freezer has electric heating elements embedded in the evaporator coil. The heaters turn on during the automatic defrost cycle. Heating cycles are on a timer, but advanced models permit technicians to set how often the freezer defrosts.
It is important to keep in mind that during the defrost cycle temperatures rise inside the freezer. The best way to minimize the temperature increase is keeping the cabinet full with product or ice packs or bottles of frozen water.
In contrast to auto-defrost models, the temperature in a manual defrost freezer is very stable. This is the best type of freezer for samples like enzymes that can’t tolerate even small temperature fluctuations.
BUT a manual defrost freezer has to be turned off on a regular basis to melt the ice. This requires a back up freezer to store contents during primary freezer defrosting. AND care must be taken to assure that the primary freezer has returned to the correct temperature before contents are replaced.
Most manual defrost freezers should be defrosted at least once a month. An accumulation of ¼ to ½ inch of frost tells you the time has come.
So, which to choose? There’s no doubt that automatic defrost scientific freezers are more convenient, but they use more electrical power and you need to decide whether they’re best for the materials you store. Contact the scientists at Tovatech for help selecting the best model for your lab or clinic.
Selecting a Combination Scientific Refrigerator Freezer
Limited space availability and the need to provide both scientific refrigeration and freezing capability suggest a combination scientific refrigerator-freezer unit. Here is a brief description of three design configurations:
The best temperature control is offered by a combination lab refrigerator/freezer where each compartment has its own compressor, thermostat, and external door. This type of combo model is recommended when storing highly temperature sensitive products.
A lower-cost option for storing less temperature-sensitive products is a laboratory refrigerator/freezer with only one compressor for both compartments. In this case the two compartments have separate external doors and may have separate temperature controls.
Cold air from the freezer compartment flows via a vent into the refrigerator compartment. Consequently the temperatures of the two compartments are not completely independent. In addition, cold air entering the refrigerator from the freezer compartment can create spots where refrigerated product may be accidentally frozen. Placement of water bottles in these cold spots can prevent refrigerated samples from being positioned where they may freeze.
When space is tight consider an undercounter or countertop fridge/freezer unit. These are generally configured as a refrigerator compartment that contains an internal freezer compartment with a door. In this case the freezer compartment does not have its own thermostat.
As a general rule, a stand-alone refrigerator and stand-alone freezer will maintain better temperature control than a combination refrigerator/freezer with a single condenser. This should be considered when tight temperature control is important.
Tips on Using Lab Refrigerators and Freezers
Now that you know all about the differences and choices between lab refrigerators and freezers here are some tips on using them.
Scientific laboratory refrigerators and laboratory freezers are substantial investments necessary to insure compliance with storage regulations appropriate to your industry. If these units malfunction due to improper operation and maintenance, your organization is not only subject to being cited for non-compliance by the FDA and/or other regulatory authorities but also the financial loss of the contents.
While lab refrigerator and lab freezer manufacturers provide detailed instructions on the proper setup and use of these units, operating procedures should be detailed in your company’s operations manual to govern their use and maintenance during their service life. As one example, floor plan reconfigurations in your lab or manufacturing facility may change, resulting in the lab refrigerator or lab freezer being moved. Wherever they are relocated, care must be taken to insure the move is done properly.
Ongoing Care and Maintenance
Lab refrigerators and freezers with top-mounted scientific refrigeration systems require free air access. Avoid the temptation to use this area for storing files or other materials, and do not crowd the units by placing file cabinets or other equipment in close proximity. Some manufacturers call for a minimum of 4 inches at the top, rear and sides of the units.
Models with bottom-mounted scientific refrigeration systems should also be positioned to allow free air access.
Clean the interior of the cabinets on a regular basis to remove odors from spillage that may occur. Use a solution of baking soda in warm water. A commercial glass cleaner will maintain the exterior of your units.
Remove accumulations of dirt, dust and lint on condenser fins to maintain efficient operation. Use a stiff-bristled brush, and then remove the particles with a vacuum cleaner. Ignoring this simple cleaning operation could lead to temperature fluctuations, loss of contents and compressor damage.
Moving Lab Refrigerators or Freezers
Disconnect the power source and confirm that the power source at the new location is sufficient to run the equipment. Do not use extension cords. Equipment connected directly to the building power supply must be reinstalled according to all applicable codes.
If your equipment was shipped with the compressor secured by mounting bolts and spring clips re-secure compressor before moving the unit.
If the unit has a condensate vaporizer bracket, disconnect and remove it if there is a chance it could be damaged during the move.
Carefully place the unit on a dolly or handcart, keeping it as vertical as possible. Under no circumstances should top-mounted condenser units be subjected to weight or strain as they are surrounded by thin-gauge steel.
If it is necessary to tilt the unit to move it through a doorway, do not operate it immediately. Allow it to remain in a vertical position for 36-48 hours at the new location before turning it on.
When relocation is complete, turn the unit on and allow it to reach the correct temperature before restocking it.
These simple steps go a long way toward maintaining your investment in a lab refrigerator or lab freezer and help avoid loss of product.
For additional information and recommendations on selecting scientific refrigerators and freezers please visit our learning center on this topic or call the scientists at Tovatech at for expert advice.