Cold Storage Study Outline
15/05/14
SRS Department - University of Edinburgh,
S-Lab, VWR, Eppendorf
Summary
The University of Edinburgh and its Roslin Institute, in partnership with Eppendorf,
VWR, and S-Lab, propose to investigate the relationship between energy efficiency and
storage temperature, use practices and other variables in Ultra Low Temperature (ULT)
freezers. An initial stage will focus on short-term experiments such as impact of door
opening, and responses to power failures. The main stage will last for around five years,
and examine the impact of different storage temperatures (-80C, -70C and -60C) and
methods on sample viability or experimental application. It will also provide associated
energy consumption and internal freezer condition data. Data will be collected and
processed upon completion of the 5-10 year project, though continually shared
throughout.
1. Background
Ultra Low Temperature (ULT) freezers are ubiquitous in life science research facilities.
They are expensive to purchase, have a large space footprint, have significant running
costs (energy, maintenance, management etc.) and can account for 5% or more of total
electricity consumption. Research and anecdotal evidence from the US LabRATS
initiative and the associated Freezer Challenge, and from the UK S-Lab initiative, have
indicated that there are many opportunities to reduce these impacts through more
effective use. Measures include regular and thorough maintenance, efficient use of
internal space, inventory management, and optimal positioning for heat shedding.
One area of very limited evidence is that of the impact of variations in storage
temperatures on sample viability. The first ULT freezers ran at around -60C, and their
minimum temperatures have since fallen. 10-15 years ago most ULT freezers were
running at -70C3 and today the -80C setting has become the ubiquitous temperature for
most researchers’ storage purposes including RNA, bacterial, plasma, cell line storage1
and more. Today most ULT freezers are marketed as being optimized to run at -80-86C2
with the factory default setting often being -85C.
Although most designs permit choice within a range of temperatures, research practice
has generally been to choose the lowest one possible. This is often not a deeply thought
through decision but, when pressed, researchers often state that sample longevity
increases as temperatures fall, and that lower temperatures give more time until sample
reach a critical temperature in the event of freezer failure or power cuts. However, there
is little evidence of the former, and some evidence that the latter is true but of minor
importance. For example, DNA has been shown to be stored with little to no denaturing
at either -80C or -20C over 24 months4. Vendor measurements also suggest that, in well
insulated ULT designs, time taken to reach a critical temperature when power is lost
takes many hours, with only a few minutes difference between an initial state of -70C and
one of -80C. In addition the increasing opportunity to remotely monitor in-freezer
temperatures with immediate alarm notifications transmitted to security or technical staff
has reduced anxiety about freezer failure passing un-noticed.
Crucially, running of ULT freezers 10C warmer at 70C has been measured to incur
significant energy savings of 20-30%5, which when multiplied by the quantity of models
most institutions posses makes for noteworthy potential savings (not to mention further
savings in reduced external cooling expenditure as less heat is emitted). New researchers
today are constantly being inducted to run ULT storage at -80C and thus are likely refuse
raising temperature for fear of endangering their samples hence the issue will continue to
grow until an evidenced based approach can alleviate unease.
While some studies have been conducted investigating energy consumption of models at
various running temperatures under short time periods, no parallel energy/sample
viability study has been run simultaneously over large extended time periods. In
particular, no study has investigated freezer compressor efficiency at varying
temperatures over long time periods (5+ years), and few studies have been conducted
looking at power cut reaction times, energy losses associated with door openings, or how
racking affects energy consumption. Identifying how freezers decrease efficiency and
consume energy (through internal temperature and energy consumption metering) can
give insight to allow more robust and enduring ULT design, and help identify long-term
mechanical issues while dispelling unfounded wasteful practices. Such studies have the
potential to be extremely wide reaching; with hundreds of ULT freezers running at most
research institutions worldwide.
2. The Experiment
The University of Edinburgh and its Roslin Institute, in partnership with suppliers
Eppendorf and VWR, and S-Lab, proposes to investigate a number of aspects of sample
storage in ultracold freezers. The work will be conducted in three new freezers, with
racking and have three stages:
1. Stage 1 – work orientated to everyday freezer use in research labs, with a focus on
the effects of short term changes on freezer contents and energy efficiency (JulyAugust 2014, controlled by the University of Edinburgh).
2. Stage 2 – freezer energy efficiency measurements, over a five year period with
primary relevance to bio repositories and manufacturers. (September 2014September 2019, controlled by VWR). Simultaneous long-term sample viability
verification will be conducted by the University of Edinburgh.
3. Stage 3 – continuing work after VWR immediate needs met on longer term
changes to samples in response to changing storage conditions, with primary
relevance to bio repositories (September 2019 onwards, controlled by University
of Edinburgh).
2.1 Stage 1 - Short-term Freezer Property Study
Methods: Prior to long-term study, the University of Edinburgh will investigate several
freezer energy and mechanic topics. Such studies will be conducted uniquely by
University of Edinburgh staff in partnership with S-Lab. All studies would be conducted
at the Roslin institute under identical conditions, and X freezers and X
temperature/energy monitors will be utilized.
1. Freezer door opening properties at varying temperatures: The 3 freezers will be
set at (-80C, -70C, and -60C) and fit with energy and internal temperature
monitors, the doors will be opened at 90 degree angles for 6 different time periods
(15 sec, 30 sec, 1 min, 2 min, 3min and 5 min). Freezers will be run both on
empty and full, and when full will contain polystyrene boxes to imitate being full.
2. Power cut response times will be investigated at varying temperatures (-80C, 70C, and -60C) via internal temperature measurements. Freezers will be allowed
24hrs to acclimate to their set temperatures, and then have their power cut.
Several internal temperature meters will allow heat loss to be continually
monitored providing real-time data. Freezers will be filled with polystyrene boxes
prior to commencement to imitate full shelves.
3. Energy consumption of the freezer at varying temperatures. Particular interest at
energy consumption at -85C (often the factory default setting), and -60C and -65C.
2.2 Stage 2 - Long-term Freezer Efficiency / Long-term Sample Storage
Methods: This study would look at three running temperatures: -80C, -70C, and -60C
Each freezer would be of the same year as well as make (U570HEF, Eppendorf). They
would be stored alongside each other at the Roslin Institute. Each freezer would receive
equal quantities (sufficient to conduct 10-20 separate viability tests) of the following
aliquoted samples: XXXXXX (to be determined). Viability studies would be conducted
on sample every 6 months over the course of 5 years under supervision of Dr. Jayne
Hope of the Roslin institute. Each freezer would be equipped XXX system to measure
energy consumption (kWhr) to provide accurate real time energy data as well as contain
internal temperature sensors. To ensure accuracy of data, freezer doors will not be opened
apart from once per week for 2 minutes at a time, with internal and external doors all
open to a 90 degree angle. No samples apart from those required for the viability study
will be placed in the freezers, and those present will be stacked in identically. The
freezers will be alarmed and monitored by Roslins freezer management team, with 24hr
security available to respond in case of emergencies.
2.3 Stage 3 – Long-term Sample Storage Continuation
Methods: Upon successful completion of the 5 year energy study controlled by VWR,
the University of Edinburgh (in partnership with S-Lab) will take sole control of the
project. Having initially aliquoted 20 samples per freezer, viability studies will continue
to be conducted for as long as resources permit (ideally to permit 10 years of data to
reflect 10 year storage times for archived medical studies). Final data compilation and
publication will occur when complete.
References
1. Parker KA., Storage of Cell Lines. Methods Mol Bio 731:27-34. doi: 10.1007/978-161779-080-5_3 (2011)
2. Thermo Scientific Revco Ultra-Low Temperature Freezer Brochure.
BRCSREVCOULT 0811 (2011)
3. Miller L., et. Al., Twenty Years Stability Study of HIV, HBV, and HCV Antibodies,
Antigen and Nucleic Acids in Plasma. Poster Presentation 1179 aabb annual meeting,
Montreal (2008)
4. Wu J., et. Al., Stability of Genomic DNA at Various Storage Conditions. Poster
Presentation QAC03 ISBER Meeting (2009)
5. Farley M., et. Al., Freezer Energy Consumption Report, (2013)