focus on Laboratory Products
Sustainably Cool: ULT freezers
Joe Arteaga, Director, Product Management, Cold Storage, Thermo Fisher Scientifi c
Laboratories have become heavily reliant upon the capability of freezers to reach exceedingly low temperatures (down to -80ºC) so that valuable biological samples can be preserved while remaining viable once thawed. For ultra-low temperature (ULT) freezers to be effective, they must be able to recover from fl uctuating temperatures that result from door-openings and sample heat loads. In doing so, they draw upon large amounts of energy, which can be costly.
Environmental impact is another critical parameter that more laboratory managers consider when making purchasing decisions. Thankfully, advances in technology and initiatives from labs and industry alike, have led not only to more effi cient, greener freezers, but to an investment in the future through implementation of sustainable practices.
Compressor ups and downs
Door-opening events place a heat load burden upon the freezer every time a user accesses the stored samples. It subsequently has to work hard to recover quickly from the resulting temperature change in order to maintain thermal stability and avoid any damage to the samples. This recovery period draws upon a relatively large amount of energy as the compressor is required to engage at full power to compensate for the rise in temperature. Technological advances such as the V-drive variable speed compressor of the Thermo Scientifi cTM
TSX ultra-low
temperature freezer increases compressor speed during activities such as door openings, while decreasing compressor speed during periods of stability (when the freezer door remains closed). As demonstrated in Figure 1 right, this decreases the freezer’s energy consumption when compared to traditional single speed compressor technology.
Energy usage in conventional refrigerant ULTs can be as high as 18 kWh/day, or 6570 kWh over a year. ULT freezers that have been designed to incorporate more advanced compressors, can reduce this fi gure to as low as 6.5 kWh/day at a -70°C setpoint, or 2884 kWh annually [1]. From a fi nancial point of view, this could equate to an annual savings of more than £293 (approximately US$426) [2]. It also leads to a reduction of more than two metric tons of CO2 produced every year [2]. As such, work is being devoted towards developing better, more energy effi cient compressor systems.
Greener, cooler chemicals
The choice of chemical refrigerant will also have a direct impact upon a freezer’s effi ciency, along with a range of potential
Figure 1. ULT freezers with traditional single speed compressors (shown in gray) cycle on and off, thus increasing energy usage. V-drive variable speed compressor technology (shown in blue) increases and decreases its speed responsively, enabling energy consumption costs to be decreased.
environmental effects. Prior to the mid-1990s, chlorofl uorocarbon (CFC) refrigerants were widely used in most commercial applications. CFCs, commonly known as Freon, were initially employed as very effective refrigerants that came with the added benefi ts of low toxicity, low reactivity and low fl ammability. However, they were soon found to have a signifi cantly destructive effect on the ozone layer. As a result, the Montreal Protocol called for the complete elimination of CFCs by the year 2000. This saw a shift towards the use of hydrofl uorocarbons (HFCs) as a seemingly viable refrigerant replacement that was originally deemed to be
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