【正文】 n 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. Refrigerant 22 is an HCFC, is used in many of the same applications, and is still the refrigerant 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 2020. In 2020, 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 5 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 approximately 50% higher pressure than R22 (Table )。F). An azeotropic mixture behaves like a single ponent refrigerant in that the saturation temperature does not change appreciably as it evaporates or condenses at constant pressure. R410A has a small enough temperature glide (less than 176。F), which gives it a temperature glide of 7176。F) and a condensation (dew) point of –37176。 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 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 4 affecting their use. The American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) has a standard numbering system,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。C (150176。英文 文獻(xiàn) Air Conditioning Systems Air conditioning has rapidly grown over the past 50 years, from a luxury to a standard system included in most residential and mercial buildings. In 1970, 36% of residences in the . were either fully air conditioned or utilized a room air conditioner for cooling (Blue, et al., 1979). By 1997, this number had more than doubled to 77%, and that year also marked the first time that over half (%) of residences in the . had central air conditioners (Census Bureau, 1999). An estimated 83% of all new homes constructed in 1998 had central air conditioners (Census Bureau, 1999). Air conditioning has also grown rapidly in mercial buildings. From 1970 to 1995, the percentage of mercial buildings with air conditioning increased from 54 to 73% (Jackson and Johnson, 1978, and DOE, 1998). Air conditioning in buildings is usually acplished with the use of mechanical or heatactivated equipment. In most applications, the air conditioner must provide both cooling and dehumidification to maintain fort in the building. Air conditioning systems are also used in other applications, such as automobiles, trucks, aircraft, ships, and industrial facilities. However, the description of equipment in this chapter is limited to those monly used in mercial and residential buildings. Commercial buildings range from large highrise office buildings to the corner convenience store. Because of the range in size and types of buildings in the mercial sector, there is a wide variety of equipment applied in these buildings. For larger buildings, the air conditioning equipment is part of a total system design that includes items such as a piping system, air distribution system, and cooling tower. Proper design of these systems requires a qualified engineer. The residential building sector is dominated by single family homes and lowrise apartments/condominiums. The cooling equipment applied in these buildings es in standard ―packages‖ that are often both sized and installed by the air conditioning contractor. The chapter starts with a general discussion of the vapor pression refrigeration cycle then moves to refrigerants and their selection, followed by packaged Chilled Water Systems。 2 Vapor Compression Cycle Even though there is a large range in sizes and variety of air conditioning systems used in buildings, most systems utilize the vapor pression cycle to produce the desired cooling and dehumidification. This cycle is also used for refrigerating and freezing foods and for automotive air conditioning. The first patent on a mechanically driven refrigeration system was issued to Jacob Perkins in 1834 in London, and the first viable mercial system was produced in 1857 by James Harrison and . vapor pression, there are two less mon methods used to produce cooling in buildings: the absorption cycle and evaporative cooling. These are described later in the chapter. With the vapo