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better than CFCs. Although HFCs were shown to not deplete the ozone, they still possessed signifi cant global warming potential (GWP).
More recently, manufacturers of ULT freezers have started to turn their attention to natural hydrocarbon refrigerants. Hydrocarbons have excellent thermodynamic properties and have proven to be very effi cient refrigerants with low GWP and zero ozone depletion capacity.
Moving heat around
The heat transfer mechanism of ULT freezers is another important consideration when assessing the overall effi ciency of the unit. Many ULT freezers employ a direct mechanism, whereby the liquid refrigerant is actively pushed into the evaporator. Direct cooling mechanisms operate by removing heat from the cabinet through expansion of the refrigerant in a series of tubes attached to the outside of the inner tank of the unit. This tubing system is what makes up the evaporator, and it is the evaporation following expansion of the liquid refrigerant that produces the cooling effect. The direct cooling method allows the refrigeration system to more effi ciently react to door openings and entering sample loads.
Indirect mechanisms on the other hand, require the addition of an intermediate heat transfer fl uid – known as the secondary refrigerant – that is cooled by the evaporator and pumped to the heat exchangers (much like a building’s air conditioning system in which cold water is distributed to the air coolers).
Meeting standards
The inherent value of samples contained within a ULT freezer makes it important for end-users to be certain that their freezers meet quality manufacturing and safety standards. Most modern freezers will typically carry a visual confi rmation of this in the form of distinct marks. The most well-known of these are the CE and UL markings.
The letters CE appear on a variety of products that are traded in the European Economic Area. The CE marking is self-declared, meaning the manufacturer has checked that these products meet EU safety, health or environmental requirements and comply with EU legislation.
A UL marking means that a representative of Underwriters Laboratory (UL) has tested the product and determined that it successfully meets the UL’s requirements. This mark verifi es whether a product is suitable for factory and fi eld installation.
In addition to markings, the industry is also taking into account a product’s sustainability and environmental impact. Rating systems such as Leadership in Energy and Environmental Design (LEED) have been put in place to ensure designers make responsible and effi cient use of resources when constructing new laboratory workspaces or even entire buildings. In the US, federal agencies or
local governments reward or even require a LEED certifi cation for new buildings.
Good for the environment can be good for the wallet
The need to adopt sustainable technology is something more progressive manufacturers recognise. New ULT freezer models such as the Thermo Scientifi c TSX Series ULTs have substantially improved energy-consumption profi les. For example, the TSX600V ULT uses less than 0.015 kWh/day per box stored – up to 50% less than other conventional refrigerant-based freezers. Data from the UK demonstrates how switching to a more advanced freezer that employs a variable speed compressor, like a TSX600V ULT, can save as much as £4,413 whilst the TSX400V can save as much as £4,318 (approximately US$6,405 and $6,268 respectively) over a 10-year period.
Select manufacturers have even gone a step further by switching to more sustainable components, as well moving to reduced or even zero waste-to-landfi ll facilities that also support a greater amount of recycling. Implementation of zero waste programs have already helped a great number of companies by showing them how sustainable does not have to be expensive. Thermo Fisher Scientifi c’s site in Asheville, NC, for example, is zero-to-waste with 93% of materials being recycled and 7% waste to energy.
More than just sample storage
Modern ULT freezers need to go beyond simple reliability, and instead provide users with devices constructed in low environmental impact facilities, with modern, sustainable components and a fi nal product that has a low energy-consumption profi le. Technological advances to compressors and refrigerants help to afford peace of mind by ensuring samples remain safe and secure. While they may not seem like monumental changes, these critical adjustments are key to bringing sustainable practices to every aspect of the lab.
References
1. Calculated based on manufacturer published energy consumption data as of 2/26/2015 and energy cost assumption of 0.12 euros / kWh. Energy consumption is based on manufacturer published energy consumption data as of 2/26/2015. Data on fi le. Thermo Scientifi c TSU600V data with high-performance mode.
2. Calculated using data from the US Energy Information Administration Retail Sales of Electricity to Ultimate Customers published electricity and natural gas price statistics.
http://www.eia.gov/electricity. Accessed October, 2015.
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