ix This second edition represents a major update and revision of the ASHRAE Air-Conditioning System Design Manual. The request that drove this revision effort was simply to make a success- ful resource more current. The revision process involved a thorough editing of all text in the manual, the addition of SI units throughout, the updating of references, and the editing of many illustrations. New material dealing with design process, indoor air quality, desic- cant dehumidification, and “green” HVAC&R systems was added. The editor acknowledges the active assistance of a Project Monitoring Subcommittee (with Warren Hahn as Chairman) from ASHRAE Technical Committee 9.1, which supervised the revision of this manual. The editor and committees are grateful to several individuals who reviewed all or parts of the draft of this revision and made valuable suggestions for improvements and clarifications (see list of contributors). Andrew Scheidt, University of Oregon, provided graphic assistance for the editing of many illustrations. Walter Grondzik, PE, Editor PREFACE xi LIST OF CONTRIBUTORS Final Voting Committee Members Dennis J. Wessel, PE, LEED Karpinski Engineering, Inc. Stephen W. Duda, PE Ross & Baruzzini, Inc. Rodney H. Lewis, PE Rodney H. Lewis Associates, Inc. Howard J. McKew, PE, CPE RDK Engineers, Inc. Mark W. Fly, PE AAON, INc. Gene R. Strehlow, PE Johnson Controls, Inc. Lynn F. Werman, PE Self-Employed Harvey Brickman Warren G. Hahn, PE CEO, Hahn Engineering, Inc. William K. Klock, PE EEA Consulting Engineers, Inc. John L. Kuempel Jr. Debra-Kuempel Kelley Cramm, PE Integrated Design Engineering Associates John E. Wolfert, PE Retired Phillip M. Trafton, VC Donald F. Dickerson Associates Hollace S. Bailey, PE, CIAQP Bailey Engineering Corporation Charles E. Henck, PE, LEED Whitman, Requardt & Associates K. Quinn Hart, PE US Air Force Civil Engineer Support Agency John I. Vucci University of Maryland ACKNOWLEDGMENTS xii Other Major Contributors and Reviewers (Only major reviewers and contributors are listed. The committee is very thankful to numerous individuals who freely gave their time to review special parts of this manual.) Charles G. Arnold, PE HDR One Company Rodney H. Lewis, PE Rodney H. Lewis Associates Joseph C. Hoose Cool Systems, Inc. Paul A. Fiejdasz, PE Member ASHRAE Hank Jackson, PE Member ASHRAE William G. Acker Acker & Associates Arthur D. Hallstrom, PE Trane David Meredith, PE Penn State Fayette, The Eberly Campus James Wilhelm, PE Retired John G. Smith, PE Michaud Cooley Erickson Con- sulting Engineers Chuck Langbein, PE Retired A special thanks to John Smith, David Meredith, and Chuck Langbein, who reviewed and commented on each chapter through all revisions. Warren G. Hahn, PE, TC 9.1, Air-Conditioning System Design Manual Update and Revision Subcommittee Chairman 1 1.1 PURPOSE OF THIS MANUAL This manual was prepared to assist entry-level engineers in the design of air-conditioning systems. It is also usable—in conjunc- tion with fundamental HVAC&R resource materials—as a senior- or graduate-level text for a university course in HVAC system design. This manual was intended to fill the void between theory and practice, to bridge the gap between real-world design practices and the theoretical knowledge acquired in the typical college course or textbook. Courses and texts usually concentrate on theoretical calculations and analytical procedures or they focus upon the design of components. This manual focuses upon applications. The manual has two main parts: (1) a narrative description of design procedures and criteria organized into ten chapters and (2) six appendices with illustrative examples presented in greater detail. The user/reader should be familiar with the general concepts of HVAC&R equipment and possess or have access to the four-volume ASHRAE Handbook series and appropriate ASHRAE special publi- cations to obtain grounding in the fundamentals of HVAC&R sys- tem design. Information contained in the Handbooks and in special publications is referenced—but not generally repeated—herein. In addition to specific references cited throughout the manual, a list of general references (essentially a bibliography) is presented at the end of this chapter. The most difficult task in any design problem is how to begin. The entry-level professional does not have experience from similar projects to fall back on and is frequently at a loss as to where to start a design. To assist the reader in this task, a step-by-step sequence of design procedures is outlined for a number of systems. CHAPTER 1 INTRODUCTION 2⏐ INTRODUCTION Simple rules are given, where applicable, to assist the new designer in making decisions regarding equipment types and size. Chapter 2 addresses the difference between analysis and design. The chapter covers the basic issues that are addressed dur- ing the design phases of a building project and discusses a number of factors that influence building design, such as codes and eco- nomic considerations. Human comfort and indoor air quality, and their implications for HVAC&R systems design, are discussed in Chapter 3. Load calculations are reviewed in Chapter 4. The specif- ics of load calculation methodologies are not presented since they are thoroughly covered in numerous resources and are typically conducted via computer programs. HVAC&R system components and their influence on system design are discussed in Chapter 5. Chapters 6 through 8 cover the design of all-air, air-and-water, and all-water systems, respectively. Here, again, a conscious effort was made not to duplicate material from the ASHRAE Handbook— HVAC Systems and Equipment, except in the interest of continuity. Chapter 6 is the largest and most detailed chapter. Its treatment of the air side of air-conditioning systems is equally applicable to the air side of air-and-water systems; thus, such information is not repeated in Chapter 7. Chapter 9 covers a variety of special HVAC&R systems. Controls are treated in Chapter 10. The appendices contain detailed descriptions and design calcu- lations for a number of actual HVAC&R-related building projects. They serve to illustrate the procedures discussed in the main body of the manual. The projects in the appendices were chosen to cover a variety of building applications and HVAC system types. They help to give the entering professional a “feel” for the size of HVAC&R equipment, and they indicate how a designer tackles par- ticular design problems. Since these examples come from actual projects, they include values (such as thermal properties, utility costs, owner preferences) that are particular to the specific contexts from which they were drawn. The purpose of the examples is to show process, not to suggest recommended or preferred outcomes. A few words of advice: do not hesitate to make initial design assumptions. No matter how far off the specific values of a final solution they might prove to be, assumptions enable the designer to start on a project and to gradually iterate and improve a proposed design until a satisfactory solution has been obtained. Frequently, more experienced colleagues may be able to assist by giving coun- sel and the benefit of their experience, but do not hesitate to plunge ahead on your own. Good luck! AIR-CONDITIONING SYSTEM DESIGN MANUAL⏐3 1.2 HOW BEST TO USE THIS MANUAL The following suggestions are made to obtain maximum bene- fit from this manual: 1. Consider the general category of the building being designed and read the appropriate chapters in the ASHRAE Handbook— HVAC Applications and the ASHRAE Handbook—HVAC Sys- tems and Equipment to determine likely systems to consider for application to the project. 2. Familiarize yourself with the theory and basic functions of common HVAC&R equipment. The best sources for this information are HVAC&R textbooks and the ASHRAE Hand- book series. 3. Read the chapters in this manual that address the systems of interest. 4. Review the example problems in the appropriate appendices of this manual. 5. Become familiar with state and local building codes, ASHRAE standards and guidelines, and applicable National Fire Protec- tion Association (NFPA) resources. Remember that this manual, in general, does not repeat infor- mation contained in ASHRAE Handbooks and special publications. You cannot, therefore, rely on this manual as the only reference for design work. As you gain experience, make notes of important con- cepts and ideas (what worked and what did not work) and keep these notes in a readily accessible location. This manual is intended to point the way toward building such a design database. The best design reference available is the experience of your colleagues and peers. While an attempt has been made in this man- ual to incorporate the experience of design professionals, no static written material can replace dynamic face-to-face interaction with your colleagues. Use every opportunity to pick their brains, and let them tell you what did not work. Often, more is learned from fail- ures than from successes. 1.3 UNITS The first edition of this manual was written using I-P (inch- pound) units as the primary measurement system. In this edition SI (System International) units are shown in brackets following the I-P units. Conversions to SI units are “soft approximations” with, for example, 4 in. being converted as 100 mm (versus the more accu- 4⏐ INTRODUCTION rate conversion to 101.6 mm or use of a true SI commercial size increment for a given product). See the ASHRAE guide “SI for HVAC&R” (available at no cost from the ASHRAE Web site, www.ashrae.org) for detailed information on preferred measure- ment units and conversion factors for HVAC&R design work. 1.4 GENERAL BIBLIOGRAPHY In addition to specific references listed in each of the chapters of this manual, the following publications are generally useful to HVAC&R system designers. They should be available in every design office. ASHRAE publications are available from the Ameri- can Society of Heating, Refrigerating and Air-Conditioning Engi- neers, Inc., 1791 Tullie Circle, NE, Atlanta, GA 30329-2305. ASHRAE publications are updated on a regular basis (every four years for handbooks, often more frequently for standards and guidelines). The publication dates shown below are current as of the updating of this manual but will change over time. Consult the ASHRAE Web site (www.ashrae.org) for information on current publication dates. ASHRAE Handbooks (available on CD or as printed volumes, in I-P or SI units) ASHRAE. 2003. 2003 ASHRAE Handbook—HVAC Applications. Atlanta: American Society of Heating, Refrigerating and Air- Conditioning Engineers, Inc. ASHRAE. 2004. 2004 ASHRAE Handbook—HVAC Systems and Equipment. Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. ASHRAE. 2005. 2005 ASHRAE Handbook—Fundamentals. Atlanta: American Society of Heating, Refrigerating and Air- Conditioning Engineers, Inc. ASHRAE. 2006. 2006 ASHRAE Handbook—Refrigeration. Atlanta: American Society of Heating, Refrigerating and Air- Conditioning Engineers, Inc. ASHRAE Standards and Guidelines ASHRAE. 1995. ANSI/ASHRAE Standard 100-1995, Energy Conservation in Existing Buildings. Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. ASHRAE. 1996. ASHRAE Guideline 1-1996, The HVAC Commissioning Process. Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. AIR-CONDITIONING SYSTEM DESIGN MANUAL⏐5 ASHRAE. 2004a. ANSI/ASHRAE Standard 55-2004, Thermal Environmental Conditions for Human Occupancy. Atlanta: American Society of Heating, Refrigerating and Air- Conditioning Engineers, Inc. ASHRAE. 2004b. ANSI/ASHRAE Standard 62.1-2004, Ventilation for Acceptable Indoor Air Quality. Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. ASHRAE. 2004c. ANSI/ASHRAE Standard 62.2-2004, Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings. Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. ASHRAE. 2004d. ANSI/ASHRAE/IESNA Standard 90.1-2004, Energy Standard for Buildings Except Low-Rise Residential Buildings. Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. ASHRAE. 2004e. ANSI/ASHRAE Standard 90.2-2004, Energy Efficient Design of Low-Rise Residential Buildings. Atlanta: American Society of Heating, Refrigerating and Air- Conditioning Engineers, Inc. ASHRAE. 2005a. ASHRAE Guideline 0-2005, The Commissioning Process. Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. Other ASHRAE Publications ASHRAE. 1991. ASHRAE Terminology of HVAC&R. Atlanta: American Society of Heating, Refrigerating and Air- Conditioning Engineers, Inc. ASHRAE. 1997. SI for HVAC&R. Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. ASHRAE. 1998. Cooling and Heating Load Calculation Principles. Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. ASHRAE. 2002. Psychrometric Analysis (CD). Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. ASHRAE. 2004f. Advanced Energy Design Guide for Small Office Buildings. Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. ASHRAE. 2005b. ASHRAE Pocket Guide for Air Conditioning, Heating, Ventilation, Refrigeration. Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. 6⏐ INTRODUCTION ASHRAE. 2005c. Principles of Heating, Ventilating and Air- Conditioning. Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. ASHRAE. 2006a. Advanced Energy Design Guide for Small Retail Buildings. Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. ASHRAE. 2006b. ASHRAE GreenGuide: The Design, Construction, and Operation of Sustainable Buildings. Atlanta: ASHRAE and Elsevier/B-H. NFPA Publications (updated on a regular basis) NFPA. 2000. NFPA 92A-2000, Recommended Practice for Smoke- Control Systems. Quincy, MA: National Fire Protection Association. NFPA. 2002. NFPA 90A-2002, Installation of Air Conditioning and Ventilating Systems. Quincy, MA: National Fire Protection Association. NFPA. 2003. NFPA 101-2003, Life Safety Code. Quincy, MA: National Fire Protection Association. NFPA. 2005. NFPA 70-2005, National Electrical Code. Quincy, MA: National Fire Protection Association. Other Resources Climatic Data: Climatic Atlas of the United States. 1968. U.S. Government Printing Office, Washington, DC. Ecodyne Corporation. 1980. Weather Data Handbook. New York: McGraw-Hill. Kjelgaard, M. 2001. Engineering Weather Data. New York: McGraw-Hill. USAF. 1988. Engineering Weather Data, AFM 88-29. U.S. Government Printing Office, Washington, DC. Estimating Guides: Konkel, J. 1987. Rule-of-Thumb Cost Estimating for Building Mechanical Systems. New York: McGraw-Hill. R.S. Means Co. 2005. Means Mechanical Cost Data, 28th ed. Kingston, MA. AIR-CONDITIONING SYSTEM DESIGN MANUAL⏐7 R.S. Means Co. 2005. Means Facilities Construction Cost Data, 20th ed. Kingston, MA. Thomson, J. 2004. 2005 National Plumbing & HVAC Estimator. Carlsbad, CA: Craftsman Book Company. General Resources: BOMA. 2004. Experience Exchange Report. An annual publication of the Building Owners & Managers Association International, Washington, DC. McQuiston, F.C., and J.D. Spitler. 1992. Cooling and Heating Load Calculation Manual. Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. SMACNA. 1988. Duct System Calculator. Chantilly, VA: Sheet Metal and Air Conditioning Contractors’ National Association. SMACNA. 1990. HVAC Systems—Duct Design, 3d ed. Chantilly, VA: Sheet Metal and Air Conditioning Contractors’ National Association. USGBC. 2005. LEED-NC (Leadership in Energy and Environmental Design—New Construction). U.S. Green Building Council, Washington, DC. (Look also for information regarding other USGBC green building certification programs.) A number of equipment manufacturers have developed HVAC design manuals and/or equipment application notes. These are not specifically listed here, in accordance with ASHRAE’s commer- cialism policy, but are recommended as sources of practical design and application advice. A search of manufacturers’ Web sites (for manuals or education) will usually show what is currently available (for free or for a fee). An extensive list of applicable codes and standards, including contact addresses for promulgating organizations, is provided in a concluding chapter in each of the ASHRAE Handbooks. 9 2.1 DESIGN PROCESS CONTEXT There are numerous variations of the design process, perhaps as many as there are designers. To try and place the following infor- mation into a common context, the design process structure used in ASHRAE Guideline 0-2005, The Commissioning Process (ASHRAE 2005a) will be used. For purposes of building commis- sioning, the acquisition of a building is assumed to flow through several broad phases: predesign, design, construction, and occu- pancy and operation. The design phase is often broken into concep- tual design, schematic design, and design development subphases. Although the majority of design hours will be spent in the design development phase, each of these phases plays a critical role in a successful building project. Each phase should have input from the HVAC&R design team. The HVAC&R design team should strive to provide input during the earliest phases (when HVAC&R design input has historically been minimal) since these are the most critical to project success, as they set the stage for all subsequent work. Design should start with a clear statement of design intent. In commissioning terms, the collective project intents form the Owner’s Project Requirements (OPR) document. Intent is simply a declaration of the owner’s (and design team’s) needs and wants in terms of project outcomes. HVAC&R design intents might include exceptional energy efficiency, acceptable indoor air quality, low maintenance, high flexibility, and the like. Each design intent must be paired with a design criterion, which provides a benchmark for minimum acceptable performance relative to the intent. For exam- ple, an intent to provide thermal comfort might be benchmarked via a criterion that requires compliance with ANSI/ASHRAE Standard 55-2004, Thermal Environmental Conditions for Human Occu- pancy (ASHRAE 2004b), and an intent for energy efficiency might CHAPTER 2 THE DESIGN PROCESS 10⏐ THE DESIGN PROCESS be benchmarked with a criterion that requires compliance with ANSI/ASHRAE/IESNA Standard 90.1, Energy Standard for Build- ings Except Low-Rise Residential Buildings. Design validation involves the use of a wide range of esti- mates, calculations, simulations, and related techniques to confirm that a chosen design option will in fact meet the appropriate design criteria. Design validation is essential to successful design; other- wise there is no connection between design intent and design deci- sions. Pre- and post-occupancy validations are also important to ensure that the construction process and ensuing operational proce- dures have delivered design intent. Such validations are a key aspect of building commissioning. 2.2 DESIGN VERSUS ANALYSIS Anyone who has taken a course in mathematics or any of the physical sciences is familiar with the process of analysis. In a typi- cal analysis, a set of parameters is given that completely describes a problem, and the solution (even if difficult to obtain) is unique. There is only one correct solution to the problem; all other answers are wrong. Design problems are inherently different—much different. A design problem may or may not be completely defined (some of the parameters may be missing) and there are any number of potentially acceptable answers. Some solutions may be better than others, but there is no such thing as a single right answer to a design problem. There are degrees of quality to design problem solutions. Some solutions may be better (often in a qualitative or conceptual sense) than others from a particular viewpoint. For a different context or client, other solutions may be better. It is important to clearly understand the difference between analysis and design. If you are used to looking for the correct answer to a problem (via analysis), and are suddenly faced with problems that have several acceptable answers (via design), how do you decide which solution to select? Learn to use your judgment (or the advice of experienced col- leagues) to weigh the merits of a number of solutions that seem to work for a particular design problem in order to select the best among them. Figures 2-1 and 2-2 illustrate the analysis and design pro- cesses, respectively. Analysis proceeds in a generally unidirectional flow from given data to final answer with the aid of certain analyti- cal tools. Design, however, is an iterative process. Although there are certain “givens” to start with, they are often not immutable but AIR-CONDITIONING SYSTEM DESIGN MANUAL⏐11 subject to modification during the design process. For example, an owner or architect may be confronted with the energy implications of excessively large expanses of glass that had been originally spec- ified and may decide to reduce the area of glazing or change the glazing properties. The mechanical designer may try various sys- tem components and control strategies before finding one that best suits the particular context and conditions. Thus, design consists of a continuous back-and-forth process as the designer selects from a universe of available systems, components, and control options to synthesize an optimum solution within the given constraints. This iterative design procedure incorporates analysis. Analysis is an important part of any design. Since the first step in design is to map out the general bound- aries within which solutions are to be found, it may be hard to know where and how to start because there is no background from which to make initial assumptions. To overcome this obstacle, make informed initial assumptions and improve on them through subse- quent analysis. To assist you in making such initial assumptions, simple rules are given throughout the chapters in this manual, and illustrative examples are provided in the appendices. 2.3 DESIGN PHASES A new engineer must understand how buildings are designed. Construction documents (working drawings and specifications) Figure 2-1. Diagram illustrating analysis. 12⏐ THE DESIGN PROCESS for a building are developed as a team effort. The architect usually acts as the prime design professional and project coordinator, although experienced owners and developers may deal directly with pre-selected HVAC&R consultants. The architect interfaces with the owner, directs the architectural staff, and coordinates the work of outside or in-house mechanical, electrical, and structural engineers (among other consultants). The negotiated design fees for the consultants’ work establish an economically viable level of effort. This fiscal constraint usually seriously limits the amount of time that can be allocated to studies of alternative systems or innovative approaches. The project phases outlined below are those adopted by ASHRAE Guideline 0-2005 and are those generally recognized by the architecture profession. More explicit phases may be defined for certain projects or under certain contracts. Figure 2-2. Diagram illustrating design.