X-Message-Number: 2122 Date: Fri, 16 Apr 93 18:02:00 CDT From: Brian Wowk <> Subject: CRYONICS Cost of LN2 I talked to a local LN2 supplier today (Canadian Liquid Air) and was quoted 34 cents per liquid liter for bulk purchased LN2. This is the retail price. The rep wouldn't give me an exact wholesale price (after all, these things are negotiated) but suggested he might give a 1000-liter-per-week user a 30% discount off retail. That would be 26 cents per liter. Winnipeg is a reasonable-sized city with several competing LN2 suppliers. It also has some of the cheapest electricity in the world (a major cost of producing LN2). I therefore doubt you could do much better than 26 cents per liter anywhere. What follows below is intended to convince Mike Darwin and any other remaining sceptics that cooling a -130'C Cold Room with liquid nitrogen (except as emergency backup) is a profligate waste of money. Our Cold Room as currently conceived (100+ patient capacity) will require the removal of 500 watts at -130'C. This would consume 185 liters of LN2 per day, with an annual expense of $17500 at 26 cents per liter (*not* including transfer losses). Alternatively, we can pump 500 watts from -130'C using two P-550 cryocoolers with an annual electric bill of $7000 at 8 cents per kilowatt hour. The cryocoolers save $10,000 per year. This is a 60% saving, not including amortization of the cryocooler cost ($12500 each). What time period should we amortize over? Well, it almost doesn't matter. Even if the reliability was so bad that we had to buy a brand new cryocooler every other year, we would *still* save money. None of this should be surprising. As Perry Metzger has pointed out, even liquid nitrogen ultimately comes from a refrigerator. And refrigerating down to -196'C (even using the relatively simple Joule Thomson process) is far more energy inefficient and mechanically complicated than refrigerating down to -130'C. LN2 suppliers have to pay electric bills and repair breakdowns too. All this is going to end up in the cost of LN2 that the end user pays. Let me recap: We have two P-550s operating together to keep the Cold Room at -130'C. The room has 30000 liters of water ice ballast. If one of the units fails, we have one month to repair it or replace it before the room temperature rises to -123'C and *stays* there, held by just one unit. If *both* units fail, the room temperature will rise at 1'C per day until we get some LN2 for backup. Backup is simple. Once a day, you just pour 200 liters of LN2 into the heat exchanger tank. The tank insulation is fine tuned during commissioning of the room (before thermal ballast is added) to keep the room at -130'C automatically. Finally, there is one very important reason to design this room with a mechanical refrigerator even if the mechanical system was less economical than LN2. (In such a case, the refrigerator would be the backup instead of LN2). During times of civil unrest, a few thousand liters of diesel fuel could run an emergency generator that would keep one of the cryocoolers going for months. At some point we might even consider a solar electric energy plant I hope this posting isn't overkill. But when respected critics use language like "I hate them" (mechanical systems), I feel the need to respond strongly and decisively. Are there still any dissenters? --- Brian Wowk Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=2122