Pressure Enthalpy Without Tears

Over the years, much has been written on the subject of pressure enthalpy. Although much of this material has been geared toward engineering and system design, this book presents the important concepts of pressure enthalpy in a manner that will appeal to the service technician. Each refrigerant has its own properties and these properties are compiled on the pressure enthalpy chart for that particular refrigerant. Pressure enthalpy charts should not be confused with pressure/temperature charts, which only provide information regarding saturated refrigerants. The pressure enthalpy chart enables us to create a complete picture, or "snapshot" of the entire system. With a completed pressure enthalpy plot, we can look at sensible and latent heat transfers, while looking at the major system components…all at the same time. The book starts by reviewing the basic vapor-compression refrigeration cycle, as well as the concepts of superheat, subcooling and the pressure/temperature relationship. The book then turns to pressure enthalpy and the p-h chart, giving an overview of the meaning and purpose for every line on the chart. Simplified charts are used to clarify the explanations. The plotting of actual systems follows next. With the completed plot in hand, we next turn to the evaluation of the system parameters that allow for the calculation of many system characteristics, including system capacity and system efficiency. Once we have learned to plot systems on the chart, we then start looking at systems that are operating with malfunctions such as dirty air filters, refrigerant overcharge, refrigerant undercharge, etc. It is here that the reader can appreciate the power of the pressure enthalpy chart and its usefulness to effectively and accurately start up, troubleshoot and evaluate air conditioning and refrigeration systems.