Don’t Open the Freezer Door: Stability vs. Efficiency in ULT Freezers

One day, hopefully sooner rather than later, a truly energy-efficient, ultra-low-temperature (ULT) freezer will reach the market. Unfortunately, for now, no technology exists that provides significant gains in efficiency, without compromising unit stability. Power savings can be achieved, but is the trade-off in reliability and temperature uniformity worth the risk of damaging laboratory samples?

Those interested in purchasing an ultra-low temperature freezer, need to assess how fragile specimens are and if they need to be accessed multiple times a day. Fragile biological samples may not survive a freezer that lacks high standards for reliability and temperature uniformity.

Determining your freezer needs

How many times do you plan on opening the ULT freezer door? If the freezer is frequently trafficked, you‘ll need a freezer that can quickly recover temperature. Without a stable freezer to buffer the constant loss of cold, an oft-open freezer door might endanger a samples’ viability. Known as the “pull-down” time, ULT freezers need to have the capacity to quickly return to set-point temperature after exposure to ambient air. Unfortunately, rapid cooling requires substantial levels of circulating refrigerants, a feature that is often sacrificed in pursuit of energy efficiency.

Reliability comes in many flavors, however. To make sure your freezer is trustworthy, look for temperature-mapping data from a reliable secondary source. Manufacturers often place internal temperature probes in the coldest part of the freezer, biasing the information it displays.

Selecting the right brand

Freezer failure happens more often than you think, to all types of laboratories and companies. Part of this is due to scale; ULT freezers are not mass-produced, which limits the amount of testing that can be done. Look for freezers built by trusted and established manufacturers, these have proven rapid recovery capabilities.

New companies and new models may not be the best choice for a  ULT freezer that holds precious specimens— clearly not a good site for experimental technology. Experienced engineering teams, on the other hand, have learned with practice the intricacies and nuances of any equipment’s design. Technicians will be familiar with the mechanisms of these long-standing brands, but perhaps not newer, less widely distributed devices. Should an issue arise, a technician will find it easier to quickly and economically fix problems with the machines that are the most familiar.

Which freezers can offer stability and uniformity?

As with temperature, uniformity mapping has become a common practice in the pharmaceutical industry, and this data should be readily available. Measurements show how evenly different areas of the freezer are cooled. It is surprisingly common for upright ULT freezers to have temperature variances of up to 30 degrees from top to bottom.

If the freezer is not achieving uniformity it may mean the compressor system is too weak, or the design does not facilitate air circulation. Regardless of the cause, both long-term and frequent-use samples need reliable, ultra-low temperatures to ensure biological clocks are stopped. This cannot be controlled if different sites in the freezer vary widely from set point. Once again, common measures to save power, such as reducing the capacity of the compressors, place your samples in a vulnerable position.

Ensuring safety for your samples

Finally, when purchasing a ULT freezer, consider what safety provisions your facility has installed. Does it run multiple units and have emergency back-up systems in place? If you deal with high-value biologicals, you may want to consider a product like the Panasonic Twin Guard, which has dual refrigeration systems. Should one of the compressors fail, the other automatically takes over, holding temperatures at or below -65 degrees Celsius for an indefinite period of time. In emergency circumstances, this can save the integrity and usefulness of high-value biological samples. During normal operations, the compressors run efficiently in sync, ensuring the added safety does not lead to higher energy bills.

Where does that leave energy efficiency?

Power usage factors strongly into a purchasing decision for facilities that are large and carry high utility costs, or for a review board concerned with environmental impact. But cutting costs may lead to frustrations down the road if you have sacrificed power and function for energy efficiency. Without powerful refrigerants circulating a freezer, temperatures may remain elevated for hours after the door is opened. Even worse, if a single compressor freezer malfunctions and stops, an entire store of samples could be lost. Energy efficiency is appealing, but choosing energy consumption as a key decision point can ignore other, more important, long-term considerations.