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Vapor Compression-Cycle Systems
Published in Neil Petchers, Combined Heating, Cooling & Power Handbook: Technologies & Applications, 2020
As detailed in Chapter 35, since it is generally impractical to circulate large volumes of refrigerant throughout a facility, chillers that use refrigerant-to-liquid evaporators are almost always used for large central air conditioning systems with multiple terminal units and for small to large process loads. They are also sometimes used in smaller units. Vapor compression systems using refrigerant-to-air type evaporators are called direct expansion (DX) units. These systems provide direct cooling as the refrigerant absorbs heat directly from the medium (i.e., air) being cooled. DX systems typically range in capacity from fractional tonnage up to a few hundred tons (1,000 kWr) and use high-pressure refrigerants such as HCFC-22, R-410A, a mixture of difluoromethane (CH2F2, called R-32), or pentafluoroethane (CHF2CF3, called R-125).
Organic Air Pollutants
Published in Stanley Manahan, Environmental Chemistry, 2017
US Environmental Protection Agency regulations, imposed in accordance with the 1986 Montreal Protocol on Substances that Deplete the Ozone Layer, curtailed production of CFCs and halocarbons in the United States starting in 1989. The substitutes for these halocarbons are hydrogen-containing chlorofluorocarbons (HCFCs), hydrogen-containing fluorocarbons (HFCs), and some volatile hydrocarbon formulations. These have included CH2FCF3 (HFC-134a, 1,1,1,2-tetrafluoroethane, which became the standard substitute for CFC-12 in automobile air conditioners and refrigeration equipment), CHCl2CF3 (HCFC-123), CH3CCl2F (HCFC-141b), CHClF2 (HCFC-22), and CH2F2 (HFC-152a, a flammable material). Because of the more readily broken H–C bonds they contain, these compounds are more easily destroyed by atmospheric chemical reactions (particularly with hydroxyl radical) before they reach the stratosphere. The HFC compounds are favored as CFC substitutes because they contain only fluorine and hydrogen bound to carbon so that they cannot generate any ozone-destroying chlorine atoms. As of 2015, R-410A, a mixture of difluoromethane (CH2F2, called R-32) and pentafluoroethane (CHF2CF3 called R-125), had become popular as a refrigerant fluid.
Geophysics, Astronomy, and Acoustics
Published in W. M. Haynes, David R. Lide, Thomas J. Bruno, CRC Handbook of Chemistry and Physics, 2016
W. M. Haynes, David R. Lide, Thomas J. Bruno
Substances controlled by the Montreal Protocol Trichlorofluoromethane CFC-11 Dichlorodifluoromethane CFC-12 Chlorotrifluoromethane CFC-13 1,1,2-Trichloro-1,2,2-trifluoroethane CFC-113 1,2-Dichloro-1,1,2,2-tetrafluoroethane CFC-114 Chloropentafluoroethane CFC-115 Bromotrifluoromethane Halon-1301 Bromochlorodifluoromethane Halon-1211 1,2-Dibromotetrafluoroethane Halon-2402 Tetrachloromethane Carbontetrachloride Bromomethane Methyl bromide 1,1,1-Trichloroethane Methyl chloroform Chlorodifluoromethane HCFC-22 2,2-Dichloro-1,1,1-trifluoroethane HCFC-123 1-Chloro-1,2,2,2-tetrafluoroethane HCFC-124 1,1-Dichloro-1-fluoroethane HCFC-141b 1-Chloro-1,1-difluoroethane HCFC-142b 3,3-Dichloro-1,1,1,2,2HCFC-225ca pentafluoropropane 1,3-Dichloro-1,1,2,2,3HCFC-225cb pentafluoropropane Hydrofluorocarbons Trifluoromethane Difluoromethane Pentafluoroethane 1,1,1,2-Tetrafluoroethane HFC-23 HFC-32 HFC-125 HFC-134a
Effects of temperature and pressure on quenching distances of difluoromethane (R32) and ammonia (R717)
Published in Science and Technology for the Built Environment, 2018
Kenji Takizawa, Naoharu Igarashi, Kazuaki Tokuhashi, Shigeo Kondo
Difluoromethane (R32) is regarded as a promising alternative to R410A as a refrigerant for residential air conditioners due to its high performance (Kedzierski et al. 2015) and its GWP lower than R410A (Forster et al. 2007). Ammonia (R717) is known as a natural refrigerant used in refrigerating systems, as an important agricultural chemical, as a raw material for chemical manufacturing and as a new fuel. According to the ISO 817-2014 standard on safety classification of refrigerants (ISO 2014), both R32 and R717 are classified as “Class 2L” refrigerants. Class 2L is the flammable refrigerant gas class of lowest flammability, where low flammability is defined as maximum burning velocity (Su0,max) not faster than 10 cm s−1 (approximately one-fourth of that of typical hydrocarbons). Since R32 and R717 have mild flammability (they are not “nonflammable”), it is necessary to accumulate knowledge on whether combustion takes place in practical situations.