| The Future of Refrigeration: R-718 (also known as water vapor) |
| Written by John Barrie | ||
| Friday, 18 May 2007 | ||
With temperatures on the rise we're on the lookout for new technologies that can help us keep cool and save energy too. One new tech is the refrigerant known as "R-718", or more commonly "Water Vapor". But you've got to ask: How does it work? Is it efficient, and if it is so cool why doesn’t everyone use it? It turns out water refrigeration been around for a long time. In Europe they have used it for years, primarily driven by their high energy prices. R718 can be more efficient than our current refrigerants (R134A for example), but it takes a special type of compressor to make it work. The compressors used in Europe use titanium turbines. Expensive titanium is used because R718 compressors have to spin very fast to get the right pressures. In Europe where the energy costs are relatively high, R718 makes good economic sense. Here in the United States, with historically cheap energy it takes too long to recover the initial expense through energy savings. That is ’till now. The Stratos Company LLC (of which I am president) is working with Prof. Norbert Muller of Michigan State University on the development of a novel R718 air conditioner that is very inexpensive. The key to success has been the development of a special turbine that is made in a very cleaver way such that you can substitute relatively cheap carbon fiber plastic for titanium! No expensive metal, no toxic refrigerants and more efficient designs. Who knew that it was all possible with water? Additional Info: MSU (PDF Link)
Comments
(2)
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written by Tim , May 19, 2007
I think that CO2 has more potential as a refrigerant than H2O.
Compare CO2 to Water Vapor
written by jsbarrie , May 21, 2007
From an environmental and safety point of view carbon dioxide (CO2) is an excellent
refrigerant. It is non-flammable, odorless and non-toxic (although it can cause suffocation at very high concentrations), has zero ODP and low GWP. The main barriers to the use of CO2 is that it generally results in low energy efficiency because it has a low critical temperature (about 31.3oC). In certain applications this problem can be alleviated through special heat exchanger design. CO2 also operates at much higher pressures (around 100 bar) and has a substantially higher volumetric capacity than most other refrigerants, which means that existing equipment designs, including compressors, are unsuitable. Considerable development is taking place on CO2 for small refrigeration systems, including car air conditioning and cascade refrigeration systems in low temperature food storage and freezing plant. From an environmental and thermodynamic point of view, water is probably the ideal refrigerant for applications above 0C. However, there is a major practical difficulty caused by its high specific vapor volume which is around two orders of magnitude greater than a typical HFC refrigerant. This means that an extremely large compressor is required. The best compressor type is probably an axial or centrifugal machine, but suitable versions for water vapour are currently special items, are very expensive, and have long delivery times. Their high cost, large size and not being off-the-shelf items therefore rules them out as replacements for general air conditioning applications at the present time. Future development of commercial products, and possibly alternative steam ejector systems, holds out promise of water being a viable alternative in the longer term future. | ||
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