【正文】 e . for building operations that use either carbon dioxide or flammable refrigerants. 外文翻譯 空調(diào)系統(tǒng) 內(nèi)蒙古科 技大學(xué)畢業(yè)設(shè)計說明書 7 過去 50 年以來，空調(diào)得到了快速的發(fā)展，從曾經(jīng)的奢侈品發(fā)展到可應(yīng)用于大多數(shù)住宅和商業(yè)建筑的比較標準的系統(tǒng)。C (–47176。 EPA 1993b) and international agreements (UNEP, 1987) have placed restrictions on the production and use of CFCs and HCFCs. Hydrofluorocarbons (HFCs) are now being used in some applications where CFCs and HCFCs 內(nèi)蒙古科 技大學(xué)畢業(yè)設(shè)計說明書 4 were used. Having an understanding of refrigerants can help a building owner or engineer make a more informed decision about the best choice of refrigerants for specific applications. This section discusses the different refrigerants used in or proposed for building air conditioning applications and the regulations affecting their use. The American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) has a standard numbering system (Table ) for identifying refrigerants (ASHRAE, 1992). Many popular CFC, HCFC, and HFC refrigerants are in the methane and ethane series of refrigerants. They are called halocarbons, or halogenated hydrocarbons, because of the presence of halogen elements such as fluorine or chlorine (King, 1986). Zeotropes and azeotropes are mixtures of two or more different refrigerants. A zeotropic mixture changes saturation temperatures as it evaporates (or condenses) at constant pressure. The phenomena is called temperature glide. At atmospheric pressure, R407C has a boiling (bubble) point of –44176。F) that it is considered a nearazeotropic refrigerant mixture. ASHRAE groups refrigerants (Table ) by their toxicity and flammability (ASHRAE, 1994).Group A1 is nonflammable and least toxic, while Group B3 is flammable and most toxic. Toxicity is based on the upper safety limit for airborne exposure to the refrigerant. If the refrigerant is nontoxic in quantities less than 400 parts per million, it is a Class A refrigerant. If exposure to less than 400 parts per million is toxic, then the substance is given the B designation. The numerical designations refer to the flammability of the refrigerant. The last column of Table shows the toxicity and flammability rating of mon refrigerants. 內(nèi)蒙古科 技大學(xué)畢業(yè)設(shè)計說明書 5 Refrigerant 22 is an HCFC, is used in many of the same applications, and is still the refrigerant 內(nèi)蒙古科 技大學(xué)畢業(yè)設(shè)計說明書 6 of choice in many reciprocating and screw chillers as well as small mercial and residential packaged equipment. It operates at a much higher pressure than either R11 or R12. Restrictions on the production of HCFCs will start in 2021. In 2021, R22 cannot be used in new air conditioning equipment. R22 cannot be produced after 2020 (EPA, 1993b). R407C and R410A are both mixtures of HFCs. Both are considered replacements for R22. R407C is expected to be a dropin replacement refrigerant for R22. Its evaporating and condensing pressures for air conditioning applications are close to those of R22 (Table ). However, replacement of R22 with R407C should be done only after consulting with the equipment manufacturer. At a minimum, the lubricant and expansion device will need to be replaced. The first residentialsized air conditioning equipment using R410A was introduced in the . in 1998. Systems using R410A operate at approximat