Appliance Design - April 2009 - (Page 16) COOLING TECHNOLOGIES Flammability Properties Flammability Index R LFLa UFLa (vol%) (vol%) (cm/s) Propane R152a R32 Ammonia 2.2 3.9 14.4 15 10.0 16.9 29.3 28 12.3 7.8 13.0 14.9 13 0.25 0.38 30-100b 100-300b 46 23 6.7 7.2 1.5c ∆ (vol%) MIE (mJ) BVc HFO1234yf 32 152a Propane Cst R= LFL F = 1− RF = LFL UFL UFL Q −1 × LFL M F 0.27 0.33 0.5 0.55 RF 3.6 4.6 16.6 56.7 RF2 0.6 2.3 17.9 37.2 0.97 1.31 1.78 1.99 HFO-1234yf 6.2 aFlame 6.1 5000-10000 limits measured at 21 C, ASTM 681-01 run in 12 litre flask to minimize wall quenching effects cBurning Velocity ISO 817 (HFO-1234yf BV measured by AIST, Japan) bTests RF 2 = {( (UFL× LFL) − LFL)/ LFL}× Qst × Su Cst = Stoichiometric composition in air, vol.% Q = Heat of Combustion per one mole Qst = Heat of Combustion per one mole of the Stoichiometric mixture, kJ/mol Su = Burning speed in Meters/Second M = Molecular weight Unilever’s ice cream freezer cabinet that uses propane refrigerant. The cabinet is one of 50 that are in trials in the U.S. A comparison of the flammability of various refrigerants. Graphic: DuPont The cooler from Coca-Cola runs on carbon dioxide refrigerant. HVAC systems, vending machines, and other appliances, it is being considered as an alternative refrigerant for use in European MAC applications. In a joint effort between Honeywell and DuPont, the two companies are working to develop a low-GWP, synthetic refrigerant that can compete with CO2 in terms of efficiency (see Chart), and beat CO2 on ease of replacement. The refrigerant, HFO-1234yf, is based on hydro-fluoro-olefins. Its initial target application is automotive, but David Diggs, global business director for Honeywell, believes that the refrigerant will eventually migrate into stationary operations. He could not give a timeframe for this other than to say that the work has begun, and there is a long way to go. The companies believe that HFO-1234yf can be a replacement for R-134a, but does not consider it a replacement for other refrigerants such as R-410a because that refrigerant has a higher operating pressure. When developing the product, Diane Iuliano Picho, global business manager for DuPont, says that they were looking to create a refrigerant that balanced low GWP with performance and overall economic attributes. Its disadvantage revolves around flammability issues. Picho says that the auto OEM industry wanted to make sure HFO-1234yf’s mild flammability was not going to be an issue, and this was accomplished. The Society of Automotive Engineers validated that HFO-1234yf as safe for use in automotive applications. In terms of the environment, Diggs says that HFO-1234yf has a GWP of 4 and it has an atmospheric lifetime of just 11 days, as opposed to 13 years for R-134a. (While the gas contains some of the same chemical elements as an HFC, it has an unsaturated, or olefin, carbon backbone. The olefin backbone allows the HFO to quickly decompose if it is released into the atmosphere, unlike conventional HFC molecules.) As a result of all these changes, OEMs have a number of possible design decisions they may need to make going forward. They can stay with HFCs for as long as the regulations will allow and wait for synthetic alternatives such as HFOs to arrive, but this could lay them open to criticisms of not being environmentally friendly. Or they can begin a conversion to a natural refrigerant now. They can convert to hydrocarbons and deal with flammability and regulatory issues, or they can convert to CO2 and be faced with significant redesign of their systems. Calculations involved in the decision will include technical issues, cost, politics and government, and changing customer attitudes. The result of these calculations may come out differently for different companies or different types of equipment, but one observation is likely to made across the board. In the realm of refrigerants, there are more changes to come. < For more information, email: Danfoss: solutions@danfoss.com DuPont: dimc@usa.dupont.com Embraco: accs@embraco.com.br Honeywell: david.diggs@honeywell.com Re-Phrige: d.colbourne@re-phridge.co.uk www.applianceDESIGN.com 16 applianceDESIGN April 2009 http://www.appliancedesign.com
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