ASHRAE - American Society of Heating@ Refrigerating and Air-Conditioning Engineers@ Inc.
Latest
ASHRAE 90167-2013
Scope
"How to Use this Book vMIn general@ each chapter is written as a stand-alone section so that it is possible to pick and choose chapters and@ as such@ the text serves as a reference for those with prior knowledge of psychrometrics. The book also serves as a four- to six-hour introduction to the science of psychrometrics for those new to the subject@ and this influenced the sequencing of chapters. The clock in the margin of this paragraph and elsewhere in this book indicates the text that should be read in a four- to six-hour learning session. Since this bookwas written as both a learning module and a reference book@ many of the definitions@ physical phenomena@ and equations are explained in more detail than found in a basic book. The reader should have a general background knowledge equivalent to a high school physics or general science course. For those somewhat familiar with psychrometrics in inch-pound (I-P) units@ this text will not only provide an easy transition to psychrometrics in Syst??me International (SI) units but also a quick refresher on the underlying principles of psychrometrics. Learning psychrometrics today is easier because of the SI coherent system of units@ which eliminates duplicate units and conversions@ and because of the personal computer and software that has all but eliminated not only manual computations using approximate formulae but also graphical solutions using the psychrometric chart. Psychrometrics brings with it many new terms and concepts. Some texts introduce all of the terms and concepts in a single chapter. For many@ including the author@ this can produce brain overload and confusion and is an obstacle to the learning process@ which is@ after all@ the goal. In this book@ definitions and new concepts are introduced as needed and each psychrometric property is treated in a separate chapter. In general@ equations that interrelate the properties are introduced with the property. An exception to the as needed introduction of terms and concepts is Chapter 5@ ""Basics of the Psychrometric Chart@"" which precedes the individual chapters on psychrometric properties. The psychrometric chart is a convenient and useful tool for determining psychrometric properties and visualizing the changes to moist air properties in psychrometric processes. This early chapter is intended to give the reader an overview of the chart to help in overall understanding and to add clarity and meaning as each psychrometric property is developed and discussed in subsequent chapters. The choice of whether or not to read Chapter 8@ ""Psychrometric Pioneers and Charts from the First 100 Years@"" is left to the reader. It may pique the reader's interest. It may help to explain the evolution of this science and the plethora of sometimes overlapping and confusing terms introduced into psychrometrics from the fields of meteorology@ drying of materials@ air conditioning@ thermodynamics@ chemical engineering@ and agricultural engineering. Each of the chapters dealing with individual psychrometric properties defines and discusses the property at several levels of detail. Those new to psychrometrics and those interested in a quick refresher or overview may want to read only the definitions and the first level of detail and then move on to the next chapter. In most cases@ multiple definitions are provided. The first definition is suitable for general lay-person discussion. Subsequent definitions are more complete and technically more accurate. A definition serves no purpose unless it provides meaning and understanding for the reader. Multiple definitions allowthe reader to choose the definitions that have the most meaning. Readers are encouraged to customize definitions. A skeleton psychrometric chart highlighting only the isolines of the property under discussion is included in each property chapter. Chapter 25 on altitude effects for locations other than sea level is required reading for those readers who live in or design for deep underground applications or applications for projects at high elevations; but@ for most users concerned with psychrometrics within ??500 metres of sea level@ this chapter can be scanned for future reference or skipped altogether. This chapter also illustrates the change in altitude (or local barometric pressure) effect on the appearance of the psychrometric chart."