Storage of samples at ultra-low temperatures can be a huge drain on both a lab’s energy bill and on the environment. Some older, less efficient ULT freezers use as much energy as an entire house.
A freezer’s energy expenditure is influenced by multiple factors, including
-Seals on freezer doors
-Type and thickness of insulation
-Type of coolant
-Efficiency of the compressor
New -80-degree freezers are designed to save energy and reduce their carbon footprint without compromising sample security. For example, Eppendorf’s CryoCube F740hi has been certified by ENERGY STAR® for its low energy consumption and received the ACT label from My Green Lab, certifying its low environmental impact factor. Freezers like this will help lower your energy costs as well as your lab’s environmental impact, while providing a safe, reliable storage space for your samples.
Cooling of a freezer requires two elements: passive support and active cooling. Passive support involves features around the chamber such as insulation and gaskets that seal cold air inside the chamber for a uniform, stable temperature. Quality insulation and gaskets act as a barricade between your samples and the outside environment, keeping your samples at a consistent set temperature. Features like insulated inner doors with gaskets and shelves with air vents minimize temperature fluctuations on door openings, providing greater efficiency and lower power consumption as well as faster recovery times.
Active cooling occurs via the compressor, where a gas coolant is compressed and becomes hot, then liquefies when it reaches the condenser.
In the past, many freezers used synthetic refrigerants like hydrofluorocarbons, which are known to be potent greenhouse gases. Many modern freezers now use natural refrigerants, such as ethane and propane instead. These refrigerants have little to no global warming potential and are more efficient coolants, requiring less power than older options.
Once the coolant has been liquefied, the built-up waste heat must be removed from the condenser.
When generating the freezing temperatures required for a minus-80-degree ULT freezer, the heat extracted from the chamber must be released. The two possible methods of removing this heat from the freezer are air cooling and water cooling.
Most ultra-low temperature freezers use the classic air cooling method, in which a fan blows air in toward the condenser and pushes warm air from the compressor out into the lab environment. This method can result in an increase in temperature in the room where the freezer is kept, so temperature in these rooms may be controlled either by passive air ventilation or by active air conditioning
An alternative method of heat removal is water cooling. Instead of using a fan to extract heat, a water-cooled ULT freezer connects to a facility’s recirculating water system. A constant stream of water removes the heat from the heat exchanger, lowering the amount of heat going into the air and reducing air conditioning power consumption. Additionally, the now-heated water can be reused for other heat-demanding systems in the facility, providing even greater energy efficiency.
Freezers are essential for sample storage, but they can be a strain on both the environment and your lab’s energy bill. Investing in a freezer that has features like thick walls with vacuum insulated panels, heavy duty flexible door seals, and insulated and gasketed inner doors improves not only efficiency but sample safety as well, by creating a uniform and stable environment inside your freezer chamber, even when accessing your samples. A freezer that uses natural refrigerants can also save money while reducing your environmental impact, and the ability to connect to your building’s recirculating water supply can realize these savings even more!
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