RefrigerantsBackgroundOzone DepletionOzone Depletion, cont.Slide 5Montreal Protocol (1987)Slide 7Global WarmingSlide 9TEWIKyoto Protocol (1998)Numerical Designation of RefrigerantsSelection CriteriaSaturation Temperatures and PressuresSlide 15SafetyRefrigerant BlendsCurrent/Future RefrigerantsRefrigerantsBackground1850’s – 1870’s: ammonia, ammonia/water, CO2Early 1900’s: SO2, methyl chloride used for domestic refrigerators1930’s: halocarbon refrigerants discovered by Midgley (R-12, R-22, R-114, R-22)Halocarbon advantages – stable compounds, favorable thermodynamic properties, safer than existing refrigerantsAmmonia still used for large low-T industrial plantsOzone DepletionMolina & Rowland (1974) hypothesized that Cl in CFC’s contributed to depletion of ozone (O3) in upper atmosphere.CFC’s, HCFC’s, HFC’sOzone Depletion, cont.CFC’s Most stable – remain in atmosphere for many years, allowing them to diffuse to high altitudesCFC’s break down, and Cl combines with and consumes some ozoneHCFC’sHydrogenatedNot as stable – most of it breaks down before reaching high altitudesLess damaging to ozoneOzone Depletion, cont.HFC’sContains no ClCauses no depletion of ozoneMontreal Protocol (1987)Called for curtailment of production of CFC’sFollow-up conferences (London & Copenhagen)Complete cessation of CFC productionEventual discontinuance of HCFC productionGlobal WarmingShort wavelength radiation from sun passes easily through atmosphere.Earth emits long wavelength radiation.Greenhouse gases block transmission of long wavelength radiation, causing the earth to retain more heat.Greenhouse gases are removed from the atmosphere by natural processes at varying rates.NOTE THAT GLOBAL WARMING AND OZONE DEPLETION ARE DIFFERENT PROBLEMS WITH DIFFERENT CAUSES. (A lot of people mess up on this on exams.)TEWITotal Equivalent Warming ImpactConsider direct contributions to global warming (refrigerant emissions) and indirect (CO2 emitted due to electrical energy usage)Indirect contributions are up to 98% of the total contribution.System efficiency is important!After redesign, most HCFC and HFC systems now have lower a TEWI than CFC systems.Kyoto Protocol (1998)Requires reduction in six greenhouse gas emissions to a level seven percent below what existed in 1990.Signed by US in 1998 but not ratified by Senate.Numerical Designation of Refrigerants1st digit on right is number of F atoms in compound2nd digit from right is number of H atoms + 1 in compound3rd digit from right is number of C atoms –1 in compound. If zero, this digit is omitted.4th digit from right is number of unsaturated C-C bound in compound. If zero, it’s omitted.Azeotropes – 500 seriesInorganics – 700 seriesSelection CriteriaPhase-out due to ozone depletionGlobal warming (TEWI)EfficiencySafetyContainment/Vessel construction reliabilitySizeAvailability/PriceFuture ConversionSaturation Pressures and TemperaturesMaterial CompatibilityLow Freezing TemperatureSaturation Temperatures and PressuresOperating pressureLow enough to use pipe & vessels of standard wall thicknessesBelow atmospheric pressure undesirable because air may leak inShould have 5-10 degree temp difference between refrigerant and medium.SafetyAmerican Conference of Governmental Industrial Hygienists – Threshold Limit Values1st column for a 40-hr work week2nd column for short-term exposureRefrigerant BlendsAzeotropes – the blend acts as a single, different refrigerantZeotropes – the constituents remain at least partially separateCurrent/Future RefrigerantsR-134a has emerged as the primary substitution for many CFC’s.HCFC-22 and –123 are viable alternatives for now but will eventually be phased out.In Europe, natural refrigerants such as ammonia, CO2, propane, and water are being used more.Our legal system makes flammable refrigerants questionable in the