Ultralow-temperature freezers, or ULTs, are integral to any lab in which cold storage is necessary for sample security. While a small-capacity, general-purpose freezer can cost a few thousand dollars, ULT models can reach or exceed $10,000. Because the samples they hold can be worth considerably more than that, and are sometimes irreplaceable, performance is more important than price. But performance is not solely up to the manufacturer—how scientists manage their inventory and utilize their freezer can impact performance factors such as sample preservation, economics and sustainability. While on the topic of costs, it is worth noting that laboratories can use as much as five times more energy than standard office space and that ULTs in particular contribute an outsize share to this number.

ULTs provide temperatures as low as –86 °C, and sometimes lower. They are typically used in the –70 to –80 °C range, a temperature that protects samples, saves energy and reduces compressor run time. Due to their smaller footprint, considerably more uprights are purchased than chest freezers. Chest freezers last longer, and their efficient design (cold air falls) means that setpoints are reached and maintained more readily and thus compressors run less. (Freezer life and performance over time are very much related to compressor life.) Some manufacturers offer twin-compressor models, which can provide added sample security and operating efficiencies. The redundancy in dual-compressor units can help maintain valuable samples at the desired temperature should one of the compressors fail.

There is a trade-off between sample security and costs and environmental concerns related to storage temperatures: a colder setpoint will offer longer protection during a power outage, but will mean higher energy costs. Roughly speaking, raising the setpoint on a ULT from –80 to –70 °C can save $4–11 per month (mygreenlab.org). Any savings must be weighed against sample needs and the extra time that samples are preserved during a power outage. In regions that experience more frequent power interruptions, uninterruptible power supplies and/or back-up generators may be required. Compressors will cycle less frequently when units are full—there is an internal mass holding cold temperature—but out-of-date or unneeded samples should be disposed of on a regular basis.

Most ULTs run on 220 V at 60 Hz, 15-amp single-phase circuits. Smaller units may provide sufficient temperatures on 115-V, 20-amp circuits. Some 220-V models include voltage boosters, useful in buildings that provide less than the rated 220 V in the U.S.A. or 230 V in Europe. (In the United States, it is not uncommon to have 208-V service; a freezer compressor will fail in a shorter period of time if run on an incorrect voltage.)

Also important are the type and number of samples that will be stored in a ULT and the number of users who will have access. Consider whether the requirements for a particular unit may grow in the future. Freezer inventory management is critical as well. Ideally, each user will have a designated storage section, each clearly mapped out so that the user spends as little time as possible looking for a sample. In this way, setpoint will be more quickly reestablished and the compressor will run less. Some freezers offer proprietary inventory software accessible via an integrated display. Other software is available for use on a scientist’s desktop or laptop computer. When practical, co-workers should access their samples simultaneously. To determine overall capacity needs, note the number of boxes and tubes that can be accommodated by the racks and shelves. Footprint should be compared to capacity to see how well the unit is designed.

Freezers should be located near vents to remove the heat they generate from conditioned room air.

Some things to look at:

  • Insulation performance/rating (some less bulky insulations provide comparable performance and increase usable space as a percentage of overall footprint)
  • Door and gasket design
  • Defrosting methods
  • Type of refrigerant (there are currently more options in Europe than in the U.S.)
  • Specifications (i.e., pull-down time, capacity, energy usage, layout and shelving)
  • Number and type of compressors
  • Recovery time after power failure
  • Door lock and access
  • Data storage and alarms
  • Energy-consumption charts
  • Temperature uniformity (throughout the chamber, with and without inventory)
  • Capacity/types of shelving
  • Maintenance requirements
  • Decibel rating (particularly if located near busy work areas)
  • Design elements that reduce frost buildup
  • Installed software/compatibility
  • Networking and data-output options.

ULT freezers require chilled process water, reliable power and vacuum. Units should be located with some clearance (approx. 6 inches, sides, top and back), preferably in a climate-controlled room. Users should consult with manufacturers well ahead of purchase to discuss optimal location.

ULTs are intended to store and conserve product that is already frozen. Lifetimes may be reduced if the units are used frequently to freeze large volumes of room-temperature samples. At start-up, it is best to load the chamber to a quarter-full, at most, with frozen product, and avoid placing warm samples into the chamber.

Technology advancements, industrial design, very sensitive and sometimes rare samples and concerns about sustainability have led to incredibly nuanced performance and design. For all they have in common with the units in a typical kitchen, ULTs offer a host of other features. Fortunately, many resources are available (see below). A thorough investigation will likely result in performance, sustainability and economic benefits during the lifetime of the ULT.

Resources

Information on ULT performance, design and use is provided by many manufacturers and university sustainability programs. The following is a short list of primary resources:

1. mygreenlab.org
2. labconscious.com
3. https://nems.nih.gov/programs/Pages/NIH-Ultra-Low-Temperature-Freezer-Policy.aspx