I was wondering what kind of redundancy strategies are people using for their mechanical -80C freezers? I am aware of the following. Please add if you are doing something different.
1) 1 Backup freezer for every 10 freezers – Empty and maintained at -80C at all times
2) Backup C02 sensor and tank
3) Backup LN2 sensor and tank*
4) Backup generator
*Does anyone have experience with this? Does backup LN2 successfully sustain the freezer and samples for a prolonged amount of time, i.e. days or 1 week? Or does it only buy you a couple hours, similar to backup CO2?
CSA Archive 
I cannot comment about the number of freezers to have, but I do know that when we have an extra freezer available for back-up, we run it at temperature (-80C) and have it at least half full of empty racks or styrofoam boxes.
We do this because we believe it’s easier on the equipment/more efficient than having the freezer operate while totally empty. After asking around for the basis of why we do this — all I can say is it’s anecdotal and not at all evidenced based!
Laurel,
In my opinion, a freezer in standby mode (no door open/close cycles) will be as efficient empty or partially full. You could argue it will take slightly more energy initially to cool down the load in a partially full freezer. Once the freezer is at operating temperature I don’t believe there is an efficiency gain in having a partially full cabinet.
In regular use (reasonably short door open/close cycles), there is an advantage in having volume taken up in the cabinet. With quick door open times in an upright freezer, the biggest energy loss is in the rapid outflow of the cold dense air from the cabinet into the room. Your empty containers, if they act to trap the cold air, will mean that less volume of cold air is lost.
In the case of long door open cycles, where the freezer load begins to warm, there is evidence that efficiency suffers with increased load. See “Investigation of Energy Consumption and Energy Savings of Refrigerator-Freezer During Open and Closed Door Conditions” by Hasanuzzaman, Saidur, and Masjuki in the Journal of Applied Sciences 8 (10): 1822-1831, 2008.
We operate 14 Ultra-Low Temperature (ULT) freezers in six of our labs, but all in the same building. They are all hooked to a central temperature/alarm monitoring system (24/7) and also to a back-up generator source on campus.
Of those 14 ULT freezers, only six are hooked to a LN2 back-up source. These six ULTs, part of the NWSB archive program, are also connected to LN2 back-up systems hooked to a LN2 bulk tank situated outside the building. The bulk tank purpose is mainly for maintaining three LN2 freezers.
As extra ULT freezer space, in case of mechanical failure or simply for annual defrost, we have one spare ULT chest freezer. That one is kept full with Styrofoam coolers/fiber board boxes containing ice packs, used in our lab process and for shipping samples. Those containers could easily be removed when the chest freezer space is needed in an emergency situation or for annual maintenance of other units.
Hope that helps!
These are some excellent suggestions so far, but some biorepositories may have practical limitations to implementing some of them. For those who have limited space or funds (and thus cannot have extra freezers, tanks, etc), there are a few more things you can do:
• If you are in a hospital, you can check to see if your area is (or can be) connected to emergency power – some are and some are not.
• If you do not have a spare freezer, make sure you know where you can rent one. Your maintenance company may swap in a rental if they have to take yours out for repairs.
• Keep a large dry shipper charged at ALL times and make sure you know exactly where your highest value samples are in each freezer – this can be used to store them safely for longer periods of time if needed.
• Have an arrangement with someone else in your facility or another biorepository to provide emergency storage if needed.
• Make sure you can get emergency dry ice delivery (and always keep some on hand) and that you have plenty of insulated containers available in case you need to empty a freezer or move samples. As previously suggested, make sure you have a dialer or other alert system and make sure you test it (and your team) to make sure everything is working, phone numbers are correct/unchanged, and everyone is well-versed in how to respond. Make sure there are clear SOPs detailing what to do in the event of a freezer crash. While some people may not have had problems with mechanical freezers, the wear and tear (and likelihood of problems) will be much greater if you run a biobank that is in and out of freezers frequently for rapid distribution (rather than long term storage). Similarly if your space is not optimal and you experience high ambient air temperatures, you will also have more problems. Good luck!
To my mind, a nearly fail-safe system for backup of -80 freezers is (multiple tanks) of liquid CO2 backup using a manifold such that refresher tanks can be added as others become empty, AND a WELL maintained backup generator. Ideally, the generator should be earthquake proofed and located in an area where there is no chance of flooding. A diesel generator is probably best because it is not affected by a gas line break (which could coincide with a power line cut). Diesel generators require quarterly maintenance and a weekly check/exercise.
Liquid nitrogen backup is also an option, however, I believe LCO2 is better than LN2 because it is almost exactly the same temp as -80 (-78 for liquid CO2 I believe).
LN2 is much colder; if the freezer stops working, LCO2 or LN2 can be maintained until the unit is fixed, even if it is weeks. I would stress once more that you need to have several CO2 tanks to buy extended backup time, and you need an auto dial-out and auto email send to alert freezer malfunction.
I believe the idea of empty backup freezers is not such a good idea. The samples are too precious. They could easily be exposed to warming and then their integrity would be in question, especially if a unit goes down in the middle of the night.
I will be looking into the possibility of switching our freezers from CO2 back-up to LN back-up when the service engineers come in today. We are having issues with the CO2 dispensing before it reaches the set-off temperature of -65C. On one occasion, the CO2 went off at -72C due to a door opening, and we went through 5 tanks of CO2 in 3 hours just to maintain the temperature at -68C. My understanding is that LN back-up works more efficiently and will keep the temperature closer to -80C.
Thought I would add to this as based on our experience and that of colleagues in the industry. Without knowing all of the details specific to your operation, I can only mention that the most cost efficient approach would be extra storage capacity in alternate -80C ULTs, as I’m sure you are already aware. And this is consistent with ISBER’s Best Practices…just be sure to have an SOP in place detailing the relocation of samples as required. Former colleagues have noted that although the CO2 or LN2 backup may be preferred, they have not had to utilize the backup in 20+ years of business. Mechanical freezers (new and old) will breakdown, but we have had good success with extra units.
As for generator, our preference was actually the natural gas over diesel. You can run into issues with either, but in our opinion, more positives than negatives