Tuesday, August 15, 2017

Keeping the Cool in Your Laboratory Refrigerator

sliding glass door laboratory refrigerator
A small amount of regular maintenance can
assure sustained performance of your lab refrigeration equipment
Image courtesy Powers Scientific
Hardly the highest tech piece of equipment in your lab, that refrigerator or freezer is nonetheless important to much of what goes on in the lab. The supplies or work in process stored in those refrigerated spaces represents precious time and budgeted funds. Knowing and doing a few simple things can keep refrigeration equipment operating smoothly, save energy, and head off costly repairs.

There are a number of different refrigerator configurations, so let me limit this brief explanation to something of a generic lab refrigerator, like that pictured above from Powers Scientific. Here are some basics.

  • Double sliding glass doors
  • Bottom mounted air cooled refrigeration system
  • +4 degree Celsius operating temperature

How does a refrigerator really work?

The refrigerator essentially consists of three things:

  • Insulated Cabinet - The cabinet is what you see, what you refer to as the refrigerator. It contains the stored materials. The cabinet also keeps the cold air from leaking out to the surrounding space and keeps the surrounding air from entering the contained area. The cabinet structure also provides a barrier of thermal resistance to heat transfer, or insulation.
  • Heat Transfer System - Also called the refrigeration system or cooling system, the heat transfer system takes heat from the air within the cabinet and expels, or transfers, it to some medium outside the cabinet. Most often, the medium outside the cabinet is the air in the lab, although it is possible to have a system that employs a liquid, such as water, in place of air. It is important to understand that an air cooled system delivers a net heat gain to the surrounding space. That rejected heat must be removed or otherwise dissipated to keep the space from overheating.
  • Controls - Unbridled operation of the cooling system will not deliver the predictable temperature performance needed for laboratory settings. A controller, in its most basic configuration, must be able to accurately measure the chamber temperature and regulate the operation of the cooling system in response to changes in that temperature.

What are some things to do, or be aware of, with refrigerator operation?

  • Doors - Doors are part of the cabinet containment that keeps cold air from escaping and warm air from entering. They should operate smoothly, without requiring undo force to open or close. When closed, the doors should set firmly against their sealing surfaces and any gaskets should be kept clean and free of dirt and grit that can inhibit sealing and lead to premature deterioration. A simple periodic inspection and wipe down with a wet cloth will go a long way toward maintaining good performance. Doors that creak or squeak when operated should be further examined for excessive hinge or bearing wear, possibly in need of lubrication.
  • Condenser - This is the device that ejects heat to the surrounding space on the example air cooled unit. On most refrigerators, the condenser will be located either on the top of the cabinet or in a compartment below the cabinet. To locate the condenser, look for louvers or a grille that permits air to flow to the condenser. It is important that air be able to flow freely across and through the condenser. If the fins on the condenser become clogged or blocked with dust, pieces of paper, tape, bags, plastic, or anything else that inhibits free air flow, the cooling capacity of the system will be reduced. Excessive blockage can cause the equipment to fail. A simple cleaning can be accomplished with a vacuum cleaner or a flow of compressed air. Even if you are not the person who will ultimately clean the condenser, it is important to know when to schedule the maintenance to be done.
  • Evaporator - Inside the refrigerator there will be a fan unit that also houses a finned evaporator. The chamber air flows across the evaporator surface and is cooled by evaporating refrigerant. Keep the air flow passage free of accumulated dust and debris that may block air movement through the fan housing and across the evaporator. Sometimes pieces of plastic film or paper can get loose in the refrigerator and be drawn into the inlet side of the evaporator, blocking some of the air flow. In most cases, it is just useful to inspect and recognize when service might be needed. 
  • Temperature - Over time, you will grow accustomed to normal refrigerator performance. Any long term excursion of chamber temperature outside of the expected performance range is cause for a service call. There is only one way that operation will be right, but a vast number of ways that it can go wrong. A short term, probably no more than one hour, temperature excursion out of range likely is the result of excessive heat load. The most common causes of this are large additions of warm mass to the chamber or excessive door opening time or frequency. Any temperature anomaly that lasts longer than about one hour is cause for diagnosis by a qualified technician.
A lab refrigerator is not a piece of equipment that garners close scrutiny by lab occupants. The best plan may be to have a qualified technician inspect the equipment on a regular basis. Inspections are generally inexpensive and can often be scheduled along with regular maintenance of other equipment in the lab. Share your questions and concerns about laboratory refrigeration applications for all temperatures and sizes with application experts. Combining your own on site knowledge and experience with their product application expertise will result in an effective solution.

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