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How Do Ultra-Low Temp Freezers Work?

The global ultra-low temperature freezer market is expected to see a compound annual growth rate of 5.67% from 2020 through 2027, bringing it to a $989.44 million market. 

The reason for this growth? Demand has increased over the years due to the need for temperature-sensitive biological product storage. 

This has become especially true in times of rapid vaccine production and research. In this article, we’ll cover the basics of ultra-low temp freezers, how they’re most commonly used, and how they work.

What Are Ultra-Low Temp Freezers?

Ultra-low temp freezers, or ULT freezers, are freezers that store samples below -40℃ (-40℉). They are available in multiple styles and sizes to accommodate your lab space and individual needs.

When looking for high-quality laboratory freezers for your cold storage needs, go beyond just looking at the price.

Ultra-low temp freezers are a big investment, so it’s important to review all aspects before finally deciding to purchase one. Here a few things to consider when in the market for a ULT freezer:

Orientation

  • Upright Freezers/Vertical: These look much like a traditional kitchen refrigerator and feature a door that opens outward to access what’s inside. These are the most common choices for many labs since they don’t take up as much floor space and they are often easier to move around.
  • Chest Freezers: These are box-like freezers with a lid that opens from the top for access. Chest freezers are generally more efficient and last longer than upright models, and temperature setpoints are reached faster than uprights. Even with this in mind, chest freezers represent less than 5% of ULT freezers sold, according to Nuaire, usually because space-constrained labs make chest style freezers harder to accommodate.
  • Table-top: These are typically much smaller than upright or chest freezers since they are meant to sit on top of a counter or table in the lab.
  • Under-counter: Like the table-top models, these are smaller because they are meant to be mounted under the counter, much the same way a dishwasher is installed in most home kitchens.

Location

Where the ULT freezer will be placed in your lab is a crucial part of your buying decision. Location determines how easy the unit will be to access and may even determine the configuration you have to purchase. Your ULT freezer location determines the flow of the lab, and every lab owner should consider completely optimizing the space they have to work with first.

Here are some questions to ask yourself about the location of your ULT freezer:

  • Will it be the only freezer in the lab or part of a group of freezers?
  • Is the lab climate controlled? If not, the ambient temperature and other regional considerations are important. 
  • Is there adequate ventilation around the freezer for the warm air to make it into the return register? Without appropriate airflow, energy consumption will be higher. The lab freezer may also have a shorter lifespan overall.
  • How big is your workspace? Can you utilize your space to optimize your workflow?

Insulation

The type of insulation is important because it helps the freezer stay colder longer, without using as much energy. Cracks can develop in the insulation, which can lead to failure. 

Try to reduce the amount of ice buildup and consider adding extra inner doors to minimize the loss of temperature whenever opening the main freezer door.

Volume Storage

This refers to the amount of internal storage space that’s available in the unit. Internal capacity ranges from 200 to 800 liters. Certain manufacturers offer customized volumes on request. Within that volume, it’s also essential to consider the structure or the shelving units inside. Shelves may have internal doors to maintain a uniform temperature throughout the unit.

To ensure you get high performance and strong energy efficiency from your unit, make sure that all the gaskets are in good shape, the door openings are free of debris, and that the inner doors seal shut as intended. If the door gaskets are damaged or have a significant layer of dirt buildup, the freezer door may not close properly, leading to a warm-up and potentially ruined samples.

Common Uses for ULT Freezers

ULT freezers are common for pharmaceuticals, biological uses, and (sometimes) typical food uses. The pharmaceutical industry often uses them to preserve drug compounds and biological samples. The biological samples play a vital role in research and development for therapeutics around rare and chronic diseases. They also are used to store vaccines, where temperature uniformity is critical.

ULT freezers also preserve DNA from a variety of sources, including:

  • Blood (specifically white blood cells)
  • Semen
  • Human, animal, and microbial cells
  • Urine
  • Plasma
  • Organ tissue

ULT freezers are also used for food storage and assist agriculture industries, though this is not as common. Freshly caught fish is often stored in ULT freezers because it helps preserve the fish’s texture once thawed. If frozen at ultra-low temperatures, fish can be stored for two years, but fish frozen at conventional freezing temperatures can only be stored for about nine months.

How Do ULT Freezers Work?

There’s one thing all ULT freezers have in common—the ability to freeze material at incredibly low temperatures. Just how cold they get and how they do it, though, depends on the compressors, condensers, and a few other factors.

The refrigeration system may either be a single high-powered compressor that’s been hermetically sealed or use two cascade compressors. With the two-cascade approach, two refrigeration circuits are connected. The evaporator on one circuit cools the condenser on the other, making it easier for the compressed gas in the first circuit to condense.

Air-cooled condenser models are typically part of laboratory refrigeration systems. They are made of tubular batteries that are either copper or copper-aluminum. The batteries are arranged to provide as much surface heat transfer as possible. An engine-driven fan forces the cool air circulation. The refrigerant expands through capillary tubes.

Steel plate heat exchangers or coils facilitate evaporation. These freezers can use a few different types of refrigerant fluids. These are made with gaseous chemical compounds that can be liquified easily. The refrigerants are characterized by properties such as high critical temperature and low critical pressure.

Refrigeration Cycles

There are three types of refrigeration cycles ULT freezers can use. Hydrocarbon refrigerants (HFC) are the industry standard and provide more energy savings since the banning of Chlorofluorocarbons (CFCs).

  • Heat Pump and Refrigeration Cycle – With a heat pump and refrigeration cycle, heat is taken from one source and transferred to the heat sink, where it is cooled. The heat source is inside the freezer unit, and the heat sink, in the case of commercial freezers, is the room the freezer is in. 
  • Vapor-Compression Cycle – With this cycle, the actual transfer of heat from one location to another is done with a working fluid. The fluid cycles through a series of tubes and changes phases to absorb heat from inside the freezer. The fluid, known as a refrigerant, expands and rapidly drops in temperature. The refrigerant will then ideally enter the condenser in a liquid state. Afterwards, the warmer fluid passes into a compressor to superheat it and increase its pressure before the cycle starts again. Common ULT refrigerants include nitrogen and methane. Ethane and propane are highly energy efficient as refrigerants, but because they are potentially flammable, their use is often limited.
  • The Carnot Cycle – Named after Nicholas Leonard Sadi Carnot, the father of thermodynamics, this cycle is the scientific explanation behind why steam engines worked. The Carnot Cycle starts with a gas, which undergoes isothermal expansion to reduce its weight and pressure. The temperature remains constant, but it increases in volume and transfers from the source to maintain the temperature. Then comes the adiabatic expansion, where no heat is transferred, but the pressure is lowered. The gas cools and volume increases. Then, in the process of isothermal compression, the pressure is raised with a constant temperature, but decreases in volume. In adiabatic compression, weight is added to increase the gas pressure, while temperature increases and volume decreases. At the end of this process, the gas has returned to its original state and the entire process starts again.

No matter which cycle your freezer uses, make sure you have a backup power source available at all times. This way, in the event of a power failure or long-term power outage, your materials and samples can stay cold.

Ultra low-temperature freezers are a crucial part of many lab spaces, but adding one to your lab doesn’t need to cost as much money or concern. Find one at your local manufacturer, or look into a lab equipment auction. If neither of those options sounds right for you, our ULT freezer leases give you a financially sustainable way to get your equipment without the major expense of an outright purchase.

Looking for support in procuring your next ultra-low temp freezer? Contact us today and our experts will help you every step of the way.