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Reproducibility of research from one laboratory to another, from one location to another and from one generation to the next, forms a tapestry of scientific knowledge. Frozen cells are often a starting point from which research is initiated or continued. Viability of these long-term preserved cells is dependent on many factors, including the protocol for pull-down to desired storage temperature, temperature stability, and uniformity in the frozen state.
While storage of critical research biospecimens in mechanically refrigerated freezers has offered significant advantages and convenience over liquid nitrogen vapor or liquid phase, severe temperature differences between laboratory conditions (as warm as 30°C) and deep storage conditions (-70°C, -80°C, or colder) have tested the boundaries of cabinet insulation, mechanical refrigerant circulation methods, refrigerant performance, and internal data monitoring necessary for efficient control.
The PHC Corporation has maintained a proactive ultra-low-temperature freezer development program focused on performance, reliability, and energy efficiency.
“Our engineers do not make concessions. They want to be absolutely sure they produce first-class products that our customers can use with ease and rely on long term and test every component from A to Z before a product is presented to the marketplace,” says Hans Brok, president of PHC Corporation of North America.
Brok cites an example. The LifeLines project is a prospective population-based cohort study investigating the biological, behavioral, and environmental determinants of healthy aging over a 30-year span among 167,729 participants from the Northeast region of the Netherlands. After rigorous testing, numerous PHCbi brand TwinGuard ultra-low-temperature freezers with Dual Cooling technology were selected due to their ability to achieve the required standards in price, quality, and temperature stability. These TwinGuard freezers now house over six million samples.
The world’s largest hereditary cancer biobank with data from over one million patients and their family members and DNA samples from 120,000 individuals, the Poland-based International Hereditary Cancer Center, (IHCC), also uses the same PHC product line to reliably protect their valuable samples.
And for decades, U.S.-based BioStorage Technologies and EPL Archives have relied on PHC Corporation freezers to consolidate, preserve, and manage biospecimens and other materials for their clients.
Performance, Reliability, and Energy Efficiency
Performance is the first and foremost consideration in ultra-low-temperature freezer design; the freezer cannot add uncertainty into the scientific terrain. Poor performance places critical cell lines and isolated biologicals at risk and, in situations where stored product is lost, creates a setback to the scientific community that can be irreplaceable.
Performance without reliability is unacceptable, especially with freezer applications under real-world conditions, which are difficult to manage. Without highly specific engineering, normal stress on components caused by frequent door openings, high ambient temperatures, voltage fluctuations, improper airflow, and poor installation decisions can result in total system failure, downtime, diminished credibility, or catastrophic destruction of priceless work.
Energy efficiency also has moved front and center due to exponential increases in biorepository volumes, environmental awareness, higher costs of power, and shifting economies of research institutions. New developments in ultra-low-temperature freezer platforms are now delivering energy efficiencies previously unmatched with conventional compressor platforms.
Engineering with Purpose
Focusing on optimizing cascade refrigeration platform technology, PHC Corporation says they have addressed the most valued deliverables—performance and reliability—while building their newest ENERGY STAR® certified refrigeration platform.
PHC’s variable differential cascade system uses variable speed inverter compressors, proprietary electronic controls, and naturally occurring refrigerants. The design achieves balance, without compromise, with improved technology in four primary areas, notes Brok.
“Independent test results confirm the new PHCbi VIP ECO upright ultra-low-temperature freezer has one of the lowest total daily energy usage ratings in its class in the industry. In addition, the failure rate of our compressors in the VIP ECO series is among the lowest in any industry. Our customers know their biospecimens are secure,” adds Brok.
Improved Technology in Four Primary Areas
The variable differential cascade platform uses the same energy twice by warming the outer door frame heater with warm bypass vapor, thereby controlling frost buildup on the replaceable door gasket without the need for added electrical power.
The inverter compressors modulate cooling capacity by varying compressor motor speed or output. Cooling needs are satisfied on demand by ramping up compressor speed to achieve desired refrigerant flow. Two compressors drive the cooling process in a time-tested high-stage/low-stage configuration.
The low stage cools the cabinet, while the high stage cools the interstage heat exchanger where energy (heat) is removed from the freezer. Since both compressors do not necessarily rotate simultaneously at the same speed, demand for cooling within the system is met with a more flexible response decreasing electrical demand while apportioning refrigeration flow throughout the system more efficiently. This flexible response results in reduced sound, reduced BTU output, and quicker response to cooling demand after door openings.
Natural refrigerants, which pose no threat to the environment and contribute to achieving facility sustainability goals, were adopted and tested thoroughly by PHC Corporation before implementation to ascertain that there were no impacts on other internal systems.
Perhaps most important, PHC Corporation engineers developed an exclusive proprietary microprocessor controller that manages system analytics in situ to orchestrate the variable differential cascade platform. Programmed with sophisticated algorithms, this controller directs high- or low-stage compressor speeds as required and compiles and reports internal data to a comprehensive control center where data can be displayed, logged, and offloaded in batch or real-time streaming.
ENERGY STAR® certification is based on the results of independent testing to a set of specific and controlled performance criteria established by the U.S. Environmental Protection Agency, as well as the U.S. Department of Energy (DOE), and agreed upon by leading ultra-low-temperature freezer manufacturers and user groups where PHC Corporation has played an influential role since the inception of the program.
The ENERGY STAR certification brings accountability through an expanding array of independently generated data to support manufacturers’ claims related to key performance metrics that define the function of an ultra-low-temperature freezer, including uniformity and power consumption.
Key Performance Metrics
Power consumption is central to the ENERGY STAR program. Any reduction in energy consumption quickly translates to the fiscal bottom line. For example, temperature recovery following door openings is a critical requirement. Under ENERGY STAR criteria, temperature recovery in an empty chamber must be measured under highly controlled conditions that account for ambient operating temperature, target setpoint, thermocouple location in air, and incoming voltage stability.
In addition to ENERGY STAR testing, PHC Corporation performed internal supplemental testing with simulated product loads in order to acquire a more comprehensive assessment of performance in real-world conditions.
Pull-down metrics are considered by some a meaningful indicator of reserve refrigeration power. The pull-down rate of an empty freezer depends on the desired operating set point, ambient temperature at start-up, and internal load. However, a “no load” pull-down rate can mislead with respect to reserve cooling power as many systems are designed to operate more efficiently at ultra-low-temperatures rather than ambient temperatures.
Uniformity is also measured over time and space to ensure that the location of stored product does not affect the viability of the materials.
Summing Up the Numbers
Today, total life cycle costs of acquiring, operating, and maintaining an ultra-low-temperature freezer may be more accurately predicted and factored into purchasing decisions. Common performance values provide consumers the data they need to make informed decisions to reliably preserve their valuable biospecimens, which is the fundamental purpose of an ultra-low-temperature freezer.
“Performance, reliability, and the design attributes that assure both take precedence at PHC Corporation,” says Brok.
Learn more at www.phchd.com/us/biomedical/vip-eco