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Cool solutions: under close scrutiny for dependability and energy efficiency, laboratory freezers are a staple in many laboratory environments and offer new improvements.

In May 2011 at McLean Hospital, Belmont, Mass., a freezer failed that contained brains provided by Autism Speaks for research conducted by the Harvard Brain Tissue Resource Center. The typically -80 C temperatures climbed to about 7 C, which damaged over 54 samples. This raised awareness about the value of keeping samples frozen.

Very low temperatures are needed to store biological samples for research, such as cell lines. And ultra-low-temperature (ULT) freezers can keep samples at temperatures below -80 C.

In the ULT freezer market there's a continued focus on sample protection. As users store priceless samples, they need to have ULT freezers that provide them with quick recovery and uniformity after door openings.

However, for most users, the trend is pointing to energy efficiency and cost, as ULT freezers cost as much to operate in a year as an average American household, according to the Univ. of California, Davis. So, anything that can be done to mitigate the energy use in an ULT freezer--particularly in the pharma, biotech and private sector--goes directly to the bottom line.

ULT freezers are high energy consumers relative to their higher-temperature general freezer counterparts, which operate around -10 to -30 C. Although their methods of providing refrigeration are similar, according to Joe LaPorte, Director of the Product Management Group, Panasonic Healthcare Corp. of North America, Wood Dale, Ill., cascade freezers require larger single or dual compressors operating together to provide temperatures below -50 C, which translates into a higher energy requirement while still maintaining rapid temperature recovery times.

Users of ULT freezers also want products that will store their samples in the most efficient manner by maximizing storage and footprint, leading the industry to be dominated by upright cascade refrigerant systems. Many of these ULT freezers are built with larger capacities to hold more biological samples, usually featuring 700 L of storage space that can hold up to 60,000 1-mL vials.

The issue of dependability

Examples like the McLean Hospital sample loss are frightening in the world of life science research, and can cost work hours and money. And while ULT freezer dependability will always be an issue, many institutions have freezers on standby, empty, ready to be loaded with frozen products in case an existing freezer fails. However, many users still have concerns about freezer temperature warm up. And in ULT freezers an unexpected warm up can often lead to reduction of the viability or destruction of the samples or products stored in the freezer, which can cost up to millions of dollars.

On the frontline of the dependability issue are alarm and monitoring systems. These are developed as cloud solutions that users can check their freezer's performance through their smartphones or tablets. Some of these systems provide exception reports, so if the temperature rises above -70 C, there would be a notification sent and a service call implemented. Other ULT freezers units provide a USB port to provide data logging capabilities.

The second aspect is in the reliability of the freezer's components. The compressors, the air-handling system that moves the heat out from the freezer and the motors are constantly improved by vendors. This is exemplified by the latest Panasonic ULT freezer, the Twin Guard. The system, according to LaPorte, utilizes two independent refrigeration systems so that if one refrigeration system suffers a mechanical fail, the second system can maintain ultra-low temperatures. This freezer utilizes a modified version of cascade technology called autoscade, which Panasonic has successfully used in their ULT freezer design for decades. The technology allows Panasonic to use only two compressors to provide two completed refrigeration systems while providing energy savings comparable to most ULT freezer technologies available.

The further advantage of the system is it can use the power of both refrigeration systems to quickly recover in the event of multiple door openings or the addition of warm products. When used for storage without multiple door openings, both systems alternate back and forth to maintain ultra-low temperature and provide energy savings.

However, the irony is while there have been significant efforts from vendors to build safety nets around the dependability of ULT freezers, the task is inherently difficult. All of these bells and whistles are essentially built into a system that's inherently under a great deal of stress.

Cascade vs. Stirling: The battle of the refrigeration systems

While cascade refrigeration has proven the preferred method of providing reliable low-temperature storage, a new ULT freezer developed by Global Cooling, Athens, Ohio, the Stirling Ultracold, has made a splash both in dependability and energy efficiency.

Refrigeration is defined as the transfer of heat energy from a place where it isn't wanted to a place where it isn't objectionable. In the case of ULT freezers, that means removing heat energy from the chamber and rejecting it into the surrounding room or water chiller piping. "The basic principal in achieving this requires the refrigerant circulating in the walls of the freezer to change from a liquid to a gas," says LaPorte. "This change of state will absorb heat energy, as 'cold' is simply the absence of heat energy." The more refrigerant pumped through the system and available to change state, the more heat can be removed.

"In ULT freezers, since we are removing heat down to the levels of -80 C, we use a cascade refrigeration system design since the refrigerants capable of changing state at -80 C require high pressures to operate if we were trying to reject the heat from the system at room temperature," says LaPorte.

Cascade systems use two compressors and two "stages". The first stage's job is to remove heat from the second stage and keep the operating pressures low. The second stage performs the heat removal, or cooling of the chamber, allowing the freezers to achieve ultra-low temperatures. This system, according to Gordon Shields, commercial director of cold storage products at Thermo Fisher Scientific, Asheville, N.C., accomplishes a reliable way of protecting samples as typical users open their ULT freezer's doors multiple times a day and need a system that can quickly recover.

However, the Stirling Ultracold -80 C upright ULT freezer (Model SU780UE) doesn't have a high and low stage like cascade systems. It has a free-piston Stirling engine that uses helium, a natural refrigerant. "It uses a very old law of physics to make one end of that engine cold," says Neill Lane, CEO of Global Cooling. "The engine end is attached physically to a thermosiphon, a copper pipe that wraps itself around the inside of the freezer." There's no mixing of the refrigerant. The engine uses helium and the thermosiphon uses ethane, which is the most commonly used refrigerant used internationally and is now approved in the U.S. This is a much more energy-efficient way to remove heat from the chamber. There's no oil, lubrication or gas bearings in the Stirling model; and unlike cascade systems, the Stirling engine doesn't turn on and off to control the temperature, allowing for a fast door opening temperature recovery and a steady temperature in the chamber.

Since the Model SU780UE relies on one engine, it runs continuously. And the system only has two moving parts. Since there are only two moving parts in the Stirling system, which never touch as they float on the helium, they don't wear, providing a cost benefit. The Stirling Ultracold Model SU780UE has a large storage volume of 780 L and uses a universal power system, allowing an input voltage range of 100 to 240 V at either 50 or 60 Hz with minimal current surge.

"The Stirling is really the first innovation in years in this industry," says Lane. "The benefits of a Stirling system are energy efficiency--less than half the energy use of a cascade system--and it produces less than half the heat, so less air conditioning is needed in a given space." This all equals a lower cost in operation for laboratories, as they aren't paying for energy, and a lower carbon footprint, as many laboratories now turn their sights to the environment.

The energy-efficiency question

Newer compressor, heat exchanger and insulation technologies have allowed newer ULT freezers to be designed to operate with significant operation energy reductions.

Vacuum insulation panels have replaced polyurethane foam, as it isn't environmentally friendly. And vacuum insulated panels have permitted manufacturers to build more efficient insulated cabinets, which also make the walls thinner and improves the volume allowable in the same floor space.

"From Panasonic's perspective, energy consumption of our ULT freezers have been reduced dramatically over the past decade while increasing system performance," says LaPorte. "The majority of these reductions have been achieved through redesigning parts of the system customers don't see." By increasing the overall area of the heat exchange "touch points" in the cascade system through a patented process, Panasonic has the ability to reduce the amount of energy that the freezers consume; in some cases by over 50%.

The Thermo Scientific Revco UxF and Forma 88000 Series ULT freezers are designed with these latest refrigeration technologies to reduce energy usage by over 20% while still providing sample protection. This is accomplished, according to Thermo's Shields, with more efficient compressor designs, brazed plate heat exchangers and optimized cap tube designs. The units are also designed for maximum storage/footprint and use vacuum insulation panel technology, which allows more storage per footprint and fewer ULT freezers required in a given laboratory space. The modular design of the ULT freezers' refrigeration deck allows easy maintenance and reduction in variability, resulting in improved reliability.

And while there's a great pull towards energy efficiency, the industry currently lacks a unified standard in how freezer energy performance should be tested. Small differences in test methodology can translate to varying energy test results. However, this is changing as most manufacturers are working with the U.S. Dept. of Energy and the EPA Energy Star Program to develop a unified standard of testing for ULT freezers and other laboratory refrigeration equipment.

Thermo Fisher Scientific has developed a detailed methodology of measuring energy consumption including a 17-point temperature mapping procedure. "It's important to note that operating temperature, ambient temperature and actual average operating temperature are critical for accurate 'apples-to-apples' comparisons," says Shields. "Customers should be asking for testing parameters to ensure all things are equal."
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Comment:Cool solutions: under close scrutiny for dependability and energy efficiency, laboratory freezers are a staple in many laboratory environments and offer new improvements.(LAB DESIGN/EQUIPMENT)
Author:Hock, Lindsay
Publication:R & D
Geographic Code:4EUUK
Date:Aug 1, 2014
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