Freezer Best Management Practices
Ultra Low Temperature (ULT) freezers are essential in laboratories and research institutions for preserving biological samples. However, they require considerable energy to operate and can easily be overlooked as a significant opportunity for energy efficiency cost savings. Most ULT freezers consume as much power as a typical household, and can cost anywhere between $300 – $800 annually in energy depending on age, model, and condition.1 Considering the fact that many organizations such as universities and hospitals can have dozens or even hundreds of freezers, improving energy efficiency by 10-20% can lead to thousands of dollars in energy savings each year. There are a variety of simple measures that can be taken in order to boost freezer performance, reduce energy use, and save money.
Plan Ahead Before Purchasing
Purchasing a freezer is a significant investment for any laboratory. There are a number of important factors to consider, including initial capital cost, energy consumption and efficiency, footprint, and cost per volume of storage space. It is essential to realize that the initial purchase price accounts for only 28% of the total cost of ownership of a ULT freezer over its lifetime, on average. The operational costs of energy, maintenance and repair, HVAC impact, and floor space account for the remaining 72%.2 Therefore, it is most cost-effective to plan ahead by determining what your laboratory’s storage space needs will be, as well as choosing a freezer with high energy efficiency.
Conserve storage costs by considering these operational expenses. For example, while the purchase price of a high-efficiency ultra-low freezer may be greater than standard ULT freezers, the increased energy efficiency of these models will payback this initial investment several times over across the freezer’s lifetime.
Before purchasing, it may be worthwhile to notify the building manager about the additional freezer, since it will be impacting HVAC systems. Sometimes it is beneficial to consolidate freezers into a single room; other times it is better to distribute them throughout the floor, or even into another building. Cleaning out older freezers may free up enough space to avert the need for purchase entirely.
Size is an especially important factor to consider in long term budgeting for freezers. Smaller freezers have higher energy intensity; that is, they are less energy efficient than larger freezers on a per volume basis. This is due to their larger surface area to volume ratio and smaller, less efficient compressors and motors. It is recommended to purchase freezers of 23 ft3 capacity or greater for optimal energy intensity.3
Clean and/or Defrost Components
Frost and dust buildup are important issues to keep an eye on as basic preventative maintenance on your freezer. This improves overall performance of the freezer and minimizes its energy consumption. A poorly maintained freezer can consume 12-25% more energy, shortens its life expectancy, and increases the frequency and costs of labor, maintenance, and replacement of damaged parts.
Frost accumulates naturally within the freezer. If it is easy to remove, brush or scoop it out of the freezer. Ice layers will build up within the freezer, which both restricts proper air circulation and causes the freezer to use more energy to cool. Annual defrosts are recommended.4
Frost buildup on the freezer door gasket can prevent the door from shutting fully; without a proper seal, heat enters the freezer and more energy is required to maintain cold temperature. Gaskets can become damaged, leading to expensive repairs. Ensure that the gasket is sealed by cleaning off frost. A simple test to check the seal is to close the door on a sheet of paper; if the paper slips out then the door is not sealing properly.
It is recommended that you defrost your ULT freezer once a year. Find an additional freezer with room for temporary storage of your samples or arrange in advance for a spare freezer (or dry ice bath) to be made available. Place basins and adsorbent pads around the freezer to collect melt water. Defrosting allows you to get rid of frost buildup, which can prevent effective cooling and cause temperature disparities to form.
The condenser coils allow refrigerant to cool and condense as it passes through. Dust can accumulate on these coils, preventing them from releasing heat efficiently and causing the compressor to work harder. If they can be accessed, cleaning them off is another good practice to do regularly. Clean by gently vacuuming or brushing in the direction of the coils; alternatively, wipe them down with a damp cloth or paper towel.
Clogged filters on the freezer can block airflow passing over the condenser coils. Remove the filter and rinse with water, allowing water to flow opposite normal airflow direction in order to effectively dislodge lint and dust. Make sure that there are no objects blocking airflow, either behind the unit or in front of the filters.
Space and Inventory
With such a high energy price tag on ULT freezers, it makes sense to maximize the use of the sample storage space within them. However, it is often surprising when taking a look inside a freezer to realize just how much space is underutilized due to old or unknown samples being stored, suboptimal sample storage containers, or general clutter.
Scheduling a freezer audit with those working in your lab is a powerful way to clear out old inventory, free up space, and get samples in order. Consolidate items from other freezers or engage in freezer sharing between labs to free up storage space and limit the need for purchase of additional freezers. Remove old, unused, or unlabeled samples, as well as those that do not require storage at such low temperatures. Ensuring that all researchers label and date their items helps everyone to keep track of what is being stored inside and promotes freezer organization. A map or inventory posted on the door with contents and locations of all items stored in the freezer helps facilitate quick access, which reduces cooling load by minimizing heat entering through the door.
Implementing high-density storage racks or boxes in your freezer can dramatically boost the overall volume of samples that can be stored, while promoting organization as well. Thoughtful selection of sample tube specifications, such as volume and durability, can also improve space utilization and sample longevity.5,6
Raise Temperature Set Point from -80 °C to -70 °C
Depending on the type of samples that are being stored in your lab, it may be possible to reduce the freezer’s cooling load by raising the temperature setting from -80 °C to -70 °C. This reduces the total plug load by approximately 20%. This can also extend the lifetime of the freezer since the compressor will not need to work as hard and risk of failure is reduced. Reduced power also results in significant energy savings. A database maintained by Colorado University-Boulder along with University of California-Riverside, UC San Diego, UC Davis, and University of Alabama-Birmingham is available for free that lists a wide variety of samples that researchers have successfully stored at higher temperatures.
- Freezer Challenge
- Good Freezer Management Practices
- List of Biological Samples Stored at -70 C or Warmer
- Ultra -Low Temperature Freezer Cleanout Practices
- University of California, Riverside – Office of Sustainability (2016). Ultra-Low Temperature Freezer Performance and Energy Use Tests
- Freezer Challenge: ULT Freezer Total Cost of Ownership
- Store Smart (2013): Everything You Wanted to Know about Running an Ultra Low Temperature (ULT) Freezer Efficiently but Were Afraid to Ask
- Freezer Challenge: Blast the Ice Jam
- Freezer Challenge: Create Freezer Space as if by Magic
- Freezer Challenge: Increasing ULT Freezer Storage Capacity with Limited Space and Budgets