Principles of heating ventilating and air conditioning

Toward this end, the following major sections areincluded: Part I General Concepts, Chapters 1–10 Part II Air-Conditioning Systems, Chapters 11–16 Part III HVAC&R Equipment, Chapters 17–

Principles

of Heating Ventilating

and Air Conditioning

8th Edition

Based on the 2017 ASHRAE Handbook—Fundamentals

Ronald H Howell

200730781939

9

ISBN: 978-1-939200-73-0 (hardback) 978-1-939200-74-7 (PDF)

courses for professionals other than engineers, especially when combined with ASHRAE Handbook—

Fundamentals.

The material is divided into three major sections: general concepts, Chapters 1–10; air-conditioning systems, Chapters 11–16; and HVAC&R equipment, Chapters 17–20 There are several significant changes in this revised edition Chapter 4 has new values for climatic design information Chapter 7 has been extensively revised with new design data In addition, the chapters on system design and equipment have been significantly revised to reflect recent changes and concepts in modern heating and air-conditioning system practices

This book includes access to a website containing the Radiant Time Series (RTS) Method Load Calculation Spreadsheets, which are intended as an educational tool both for the student and for the experienced engineer wishing to explore the RTS method These spreadsheets allow the user to perform RTS cooling load calculations for lights, people, equipment, walls/roofs, and fenestration components using design day weather profiles for any month Cooling and heating loads can be calculated for individual rooms or block load zones Twelve-month cooling calculations can be done

to determine the month and time of peak cooling load for each room or block load zone In addition, room/zone worksheets can be copied and modified within the spreadsheet to analyze as many rooms

or zones as desired; the number of rooms/zones is limited only by the available computer memory.

ASHRAE

1791 Tullie Circle Atlanta, GA 30329-2305 404-636-8400 (worldwide) www.ashrae.org

Tai ngay!!! Ban co the xoa dong chu nay!!!

Ronald H Howell, PhD, PE, Fellow/Life Member ASHRAE, retired as professor and chair of mechanical engineering

at the University of South Florida and is also professor emeritus of the University of Missouri-Rolla For 45 years hetaught courses in refrigeration, heating and air conditioning, thermal analysis, and related areas He has been the prin-cipal or co-principal investigator of 12 ASHRAE-funded research projects His industrial and consulting engineeringexperience ranges from ventilation and condensation problems to the development and implementation of a completeair curtain test program

The following authors contributed significantly to the textbook Principles of Heating, Ventilating, and Air Conditioning.

They recently passed away and were not part of the 2017 revisions

William J Coad, PE, Fellow ASHRAE, was ASHRAE president in 2001-2002 He was employed with McClure

Engi-neering Associates, St Louis, Mo., for 45 years He was also president of Coad EngiEngi-neering Enterprises He served as

a consultant to the Missouri state government and was a lecturer in mechanical engineering for 12 years and an affiliate

professor in the graduate program for 17 years at Washington University, St Louis He was the author of Energy

Engi-neering and Management for Building Systems (Van Nostrand Reinhold) Mr Coad passed away in August 2014.

Harry J Sauer, Jr., PhD, PE, Fellow ASHRAE, was a professor of mechanical and aerospace engineering at the

Univer-sity of Missouri-Rolla He taught courses in air conditioning, refrigeration, environmental quality analysis and control,and related areas His research ranged from experimental boiling/condensing heat transfer and energy recovery equip-ment for HVAC systems to computer simulations of building energy use and actual monitoring of residential energy use

He served as an advisor to the Missouri state government and has conducted energy auditor training programs for the

US Department of Energy Dr Sauer passed away in June 2008

© 1990, 1994, 1998, 2001, 2005, 2009, 2013, 2017 ASHRAE

1791 Tullie Circle, N.E.

Atlanta, GA 30329 www.ashrae.org All rights reserved.

Printed in the United States of America ASHRAE is a registered trademark in the U.S Patent and Trademark Office, owned by the American Society of Heating, Refriger- ating and Air-Conditioning Engineers, Inc.

ASHRAE has compiled this publication with care, but ASHRAE has not investigated, and ASHRAE expressly disclaims any duty

to investigate, any product, service, process, procedure, design, or the like that may be described herein The appearance of any technical data or editorial material in this publication does not constitute endorsement, warranty, or guaranty by ASHRAE of any product, service, process, procedure, design, or the like ASHRAE does not warrant that the information in the publication is free

of errors, and ASHRAE does not necessarily agree with any statement or opinion in this publication The entire risk of the use of any information in this publication is assumed by the user.

No part of this publication may be reproduced without permission in writing from ASHRAE, except by a reviewer who may quote brief passages or reproduce illustrations in a review with appropriate credit, nor may any part of this publication be reproduced, stored in a retrieval system, or transmitted in any way or by any means—electronic, photocopying, recording, or other—without permission in writing from ASHRAE Requests for permission should be submitted at www.ashrae.org/permissions.

Names: Howell, Ronald H (Ronald Hunter), 1935- author.

Title: Principles of heating ventilating and air conditioning : a textbook

with design data based on the 2017 ashrae handbook of fundamentals /

Ronald H Howell.

Description: 8th edition | Atlanta : ASHRAE, [2017] | Includes

bibliographical references and index.

Identifiers: LCCN 2017033377| ISBN 9781939200730 (hardcover : alk paper) |

ISBN 9781939200747 (pdf)

Subjects: LCSH: Heating Textbooks | Ventilation Textbooks | Air

conditioning Textbooks.

Classification: LCC TH7012 H73 2017 | DDC 697 dc23 LC record available at https://lccn.loc.gov/2017033377

ASHRAE S TAFF S PECIAL P UBLICATIONS

Mark S Owen, Editor/Group Manager of Handbook and Special Publications Cindy Sheffield Michaels, Managing Editor

James Madison Walker, Managing Editor of Standards Lauren Ramsdell, Assistant Editor

Mary Bolton, Editorial Assistant

Michshell Phillips, Editorial Coordinator

Part I General Concepts

Introduction 1

Historical Notes 2

Building Energy Use 5

Conceptualizing an HVAC System 7

Sustainability and Green Buildings 7

Problems 8

Bibliography 9

Chapter 2 Thermodynamics and Psychrometrics Fundamental Concepts and Principles 11

Properties of a Substance 13

Forms of Energy 36

First Law of Thermodynamics 40

Second Law of Thermodynamics 42

Third Law of Thermodynamics 44

Basic Equations of Thermodynamics 44

Thermodynamics Applied to Refrigeration 44

Applying Thermodynamics to Heat Pumps 49

Absorption Refrigeration Cycle 49

Problems 50

Bibliography 55

SI Tables and Figures 55

Chapter 3 Basic HVAC System Calculations Applying Thermodynamics to HVAC Processes 67

Single-Path Systems 72

Air-Volume Equations for Single-Path Systems 72

Psychrometric Representation of Single-Path Systems 74

Sensible Heat Factor (Sensible Heat Ratio) 74

Problems 76

Bibliography 80

Chapter 4 Design Conditions Indoor Design Conditions 81

Outdoor Design Conditions: Weather Data 88

Other Factors Affecting Design 140

Temperatures in Adjacent Unconditioned Spaces 140

Problems 141

Bibliography 142

SI Tables and Figures 143

Chapter 5 Load Estimating Fundamentals General Considerations 145

Outdoor Air Load Components 145

Heat-Transfer Coefficients 156

Calculating Surface Temperatures 170

Problems 171

Bibliography 177

SI Figures and Tables 179

Chapter 6 Residential Cooling and Heating Load Calculations Background 191

General Guidelines 192

Cooling Load Methodology 197

Heating Load Methodology 200

Nomenclature 205

Load Calculation Example 207

Problems 209

Bibliography 212

SI Figures and Tables 214

Chapter 7 Nonresidential Cooling and Heating Load Calculations Principles 221

Initial Design Considerations 225

Heat Gain Calculation Concepts 225

Description of Radiant Time Series (RTS) 252

Cooling Load Calculation Using RTS 255

Heating Load Calculations 258

Design Loads Calculation Example 262

Problems 274

Bibliography 276

SI Figures and Tables 281

Chapter 8 Energy Estimating Methods General Considerations 297

Component Modeling and Loads 298

Overall Modeling Strategies 299

Integration of System Models 300

Degree-Day Methods 301

Bin Method (Heating and Cooling) 310

Problems 312

Bibliography 316

Chapter 9 Duct and Pipe Sizing Duct Systems 317

Fans 354

Air-Diffusing Equipment 362

Pipe, Tube, and Fittings 364

Pumps 369

Problems 371

References 375

SI Figures and Tables 377

Chapter 10 Economic Analyses and Life-Cycle Costs Introduction 381

Owning Costs 381

Service Life 381

Depreciation 384

Interest or Discount Rate 384

Periodic Costs 384

Operating Costs 385

Economic Analysis Techniques 389

Reference Equations 392

Problems 392

Symbols 393

References 394

Bibliography 394

Part II HVAC Systems Chapter 11 Air-Conditioning System Concepts System Objectives and Categories 397

System Selection and Design 398

Design Parameters 398

Performance Requirements 399

Focusing on System Options 399

Narrowing the Choice 400

Energy Considerations of Air Systems 401

Basic Central Air-Conditioning and Distribution System 402

Smoke Management 404

Components 404

Air Distribution 407

Space Heating 409

Primary Systems 409

Space Requirements 411

Problems 414

Bibliography 416

Chapter 12 System Configurations Introduction 417

Selecting the System 418

Multiple-Zone Control Systems 418

Ventilation and Dedicated Outdoor Air Systems (DOAS) 421

All-Air System with DOAS Unit 422

Air-and-Water Systems with DOAS Unit 422

In-Space Temperature Control Systems 423

Chilled-Beam Systems 425

Problems 429

Bibliography 432

Chapter 13 Hydronic Heating and Cooling System Design Introduction 433

Closed Water Systems 434

Design Considerations 442

Design Procedures 451

Problems 453

Bibliography 454

Chapter 14 Unitary and Room Air Conditioners Unitary Air Conditioners 455

Combined Unitary and Dedicated Outdoor Air Systems 457

Window Air Conditioners 457

Through-the-Wall Conditioner System 458

Typical Performance 459

Minisplits, Multisplits, and Variable-Refrigerant-Flow (VRF) Systems 459

Water-Source Heat Pumps 460

Problems 461

Bibliography 461

Chapter 15 Panel Heating and Cooling Systems General 463

Types 464

Design Steps 466

Problems 467

Bibliography 467

Chapter 16 Heat Pump, Cogeneration, and Heat Recovery Systems General 469

Types of Heat Pumps 469

Heat Sources and Sinks 471

Cogeneration 474

Heat Recovery Terminology and Concepts 475

Heat Recovery Systems 477

Problems 480

Bibliography 480

SI Figures 481

Part III HVAC Equipment Chapter 17 Air-Processing Equipment Air-Handling Equipment 483

Cooling Coils 483

Heating Coils 488

Evaporative Air-Cooling Equipment 489

Air Washers 490

Dehumidification 490

Humidification 492

Sprayed Coil Humidifiers/Dehumidifiers 494

Air Cleaners 494

Air-to-Air Energy Recovery Equipment 499

Economizers 506

Problems 507

Bibliography 508

SI Table 509

Chapter 18 Refrigeration Equipment Mechanical Vapor Compression 511

Absorption Air-Conditioning and Refrigeration Equipment 529

Cooling Towers 536

Problems 537

Bibliography 539

SI Tables 540

Chapter 19 Heating Equipment Fuels and Combustion 543

Burners 546

Residential Furnaces 547

Commercial Furnaces 549

Boilers 552

Terminal Units 554

Electric Heating 555

Problems 557

Bibliography 558

Chapter 20 Heat Exchange Equipment Modes of Heat Transfer 561

Heat Exchangers 567

Basic Heat Exchanger Design Equation 569

Estimation of Heat Load 569

Mean Temperature Difference 569

Estimation of the Overall Heat Transfer CoefficientU 570

Extended Surfaces, Fin Efficiency, and Fin-Tube Contact Resistance 571

Fouling Factors 572

Convective Heat Transfer Coefficientsh iandh o 573

Calculation of Heat Exchanger Surface Area and Overall Size 576

Fluids and Their Thermophysical Properties 576

Example Finned-Tube Heat Exchanger Design 576

Problems 576

Bibliography 578

Appendices Appendix A SI for HVAC&R General 579

Units 579

Symbols 580

Prefixes 581

Numbers 581

Words 582

Appendix B Systems Design Problems Combination Water Chillers 585

Absorption Chiller Selection 585

Owning and Operating Costs 586

Animal Rooms 586

Greenhouse 588

Drying Room 589

Air Washer 589

Two-Story Building 589

Motel 590

Building Renovation 590

Building with Neutral Deck Multizone 591

This book includes access to a website containing the Radiant Time Series (RTS) Method Load

Calculation Spreadsheets See www.ashrae.org/PHVAC8.

Principles of Heating, Ventilating, and Air Conditioning , a textbook based on the 2017 ASHRAE Handbook—Fundamentals, should provide an attractive text for air-conditioning courses at engi-neering colleges and technical institutes The text has been developed to give broad and current cov-

erage of the heating, ventilation, and air-conditioning field when combined with the 2017 ASHRAE Handbook—Fundamentals

The book should prove most suitable as a textbook and subsequent reference book for (a) graduate engineering courses in the general field of HVAC, (b) similar courses at technical institutes,(c) continuing education and refresher short courses for engineers, and (d) adult education coursesfor nonengineers It contains more material than can normally be covered in a one-semester course.However, several different single-semester or shorter courses can be easily planned by merely elim-inating the chapters and/or parts that are least applicable to the objectives of the particular course

under-This text will also readily aid in self-instruction of the 2017 ASHRAE Handbook—Fundamentals by

engineers wishing to develop their competence in the HVAC&R field

Although numerous references are made to the other ASHRAE Handbook volumes, sufficientmaterial has been included from these to make this text complete enough for various courses in theHVAC&R field The material covered for various audiences in regular university courses, technicalinstitute courses, and short courses can and will vary greatly This textbook needed to be complete

to satisfy all of these anticipated uses and needs Toward this end, the following major sections areincluded:

Part I General Concepts, Chapters 1–10

Part II Air-Conditioning Systems, Chapters 11–16

Part III HVAC&R Equipment, Chapters 17–20

Although the 2017 ASHRAE Handbook—Fundamentals is published in an SI edition, which uses international units, and an inch-pound (I-P) edition, this single version of Principles of Heating, Ven- tilating, and Air Conditioningis designed to serve the I-P edition with some SI interspersed through-out

There are several significant changes in this edition Chapter 4 has new values for climatic design

information Chapter 7 has been extensively revised with new design data These changes make ciples compatible with the 2017 ASHRAE Handbook—Fundamentals In addition, the chapters on

Prin-system design and equipment have been significantly revised to reflect recent changes and concepts

in contemporary heating and air-conditioning system practices The Solutions Manual has also been updated in line with the 2017 ASHRAE Handbook—Fundamentals.

A particular point of confusion must be pointed out Because this book was developed to be used

with the ASHRAE Handbook’s Fundamentals volume, a number of tables and figures have been reproduced in the original form, complete with references to material elsewhere in Fundamentals (not in this book) Thus, if the subheading in the table or figure indicates that it is a Fundamentals table or figure, then all references to other locations, equations, tables, etc., refer to those in Funda- mentals , not in Principles.

Dr Harry Sauer, Jr., one of the co-authors of this textbook, passed away in June 2008 Likewise,William J Coad was also a co-author of this textbook and passed away in August 2014 Both Dr.Sauer and Mr Coad made significant contributions to the book

On the National Academy of Engineering’s list of

engi-neering achievements “that had the greatest impact on the

quality of life in the 20th century,” air conditioning and

refrigerationcame in tenth, indicating the great significance

of this field in the world With many people in the United

States spending nearly 90% of their time indoors, it is hardly

surprising that providing a comfortable and healthy indoor

environment is a major factor in life today In fact, over $33

billion of air-conditioning equipment was sold in the US

during the year 2010 alone

Air-conditioning systems usually provide year-round

control of several air conditions, namely, temperature,

humidity, cleanliness, and air motion These systems may

also be referred to as environmental control systems,

although today they are usually called heating, ventilating,

and air-conditioning (HVAC) systems

The primary function of an HVAC system is either (1) the

generation and maintenance of comfort for occupants in a

conditioned space; or (2) the supplying of a set of

environ-mental conditions (high temperature and high humidity, low

temperature and high humidity, etc.) for a process or product

within a space Human comfort design conditions are quite

different from conditions required in textile mills or for

grain storage and vary with factors such as time of year and

the activity and clothing levels of the occupants

If improperly sized equipment or the wrong type of

equipment is used, the desired environmental conditions

usually will not be met Furthermore, improperly selected

and/or sized equipment normally requires excess power

and/or energy and may have a higher initial cost The design

of an HVAC system includes calculation of the maximum

heating and cooling loads for the spaces to be served,

selec-tion of the type of system to be used, calculaselec-tion of piping

and/or duct sizes, selection of the type and size of equipment

(heat exchangers, boilers, chillers, fans, etc.), and a layout of

the system, with cost, indoor air quality, and energy

conser-vation being considered along the way Some criteria to be

1 The location, elevation, and orientation of the structure

so that the effects of the weather (wind, sun, and itation) on the building heating and cooling loads can beanticipated

precip-2 The building size (wall area, roof area, glass area, floorarea, and so forth)

3 The building shape (L-shaped, A-shaped, rectangular,etc.), which influences equipment location, type ofheating and cooling system used, and duct or pipinglocations

4 The space use characteristics Will there be differentusers (office, bank, school, dance studios, etc.) of thespace from year to year? Will there be different concur-rent requirements from the tenants? Will there be nightsetback of the temperature controller or intermittent use

of the building’s facilities?

5 The type of material (wood, masonry, metal, and soforth) used in the construction of the building What isthe expected quality of the construction?

6 The type of fenestration (light transmitting partition)used, its location in the building, and how it might beshaded Is glass heat absorbing, reflective, colored, etc.?

7 The types of doors (sliding, swinging, revolving) andwindows (sealed, wood or metal frames, etc.) used.What is their expected use? This will affect the amount

11 Ventilation requirements for the structure Does it

require 100% outdoor air, a given number of CFM per

person, or a given number of CFM per square foot of

floor area?

12 Local and/or national codes relating to ventilation,

gas, and/or electric piping

13 Outside design temperatures and wind velocities for

the location

14 The environmental conditions that are maintained

Will fluctuations of these conditions with load be

detri-mental to the purpose served by the structure?

15 The heating and cooling loads (also consider the

mois-ture load, air contaminants, and noise)

16 The type of heating and cooling system to be used in

the structure Is it forced air, circulated water, or direct

expansion? Will it be a multizone, single zone, reheat,

variable air volume, or another type of system? What

method of control will be used? Will a dedicated

out-door air system be considered?

17 The heating and cooling equipment size that will

maintain the inside design conditions for the selected

outside design condition Electric heat or fossil fuel?

Mechanical vapor compression or absorption chiller?

18 The advantages and disadvantages of oversizing and

undersizing the equipment as applied to the structure

Survey any economic tradeoffs to be made Should a

different type of unit be installed in order to reduce

operating costs? Should a more sophisticated control

system be used to give more exact control of humidity

and temperature or should an on-off cycle be used? Fuel

economy as related to design will become an even more

important factor in system selection and operation

19 What is the estimated annual energy usage?

In general, no absolute rules dictate correct selections or

specifications for each of the above items, so only

engineer-ing estimates or educated guesses can be made However,

estimates must be based on sound fundamental principles

and concepts This book presents a basic philosophy of

envi-ronmental control as well as the basic concepts of design

These ideas relate directly to the ASHRAE Handbook series:

2014 Refrigeration, 2015 HVAC Applications, 2016 HVAC

Systems and Equipment , and most directly to 2017

Funda-mentals

1.2 Historical Notes

Knowing something of the past helps in understanding

current design criteria and trends As in other fields of

tech-nology, the accomplishments and failures of the past affect

current and future design concepts The following

para-graphs consist mainly of edited excerpts from ASHRAE

Journalarticles: “A History of Heating” by John W James,

“The History of Refrigeration” by Willis R Woolrich, and

“Milestones in Air Conditioning” by Walter A Grant, with

additional information obtained from ASHRAE’s Historical

Committee These excerpts provide a synopsis of the history

of environmental control

Obviously, the earliest form of heating was the open fire.The addition of a chimney to carry away combustionbyproducts was the first important step in the evolution ofheating systems By the time of the Romans, there was suf-ficient knowledge of ventilation to allow for the installation

of ventilating and panel heating in baths Leonardo da Vincihad invented a ventilating fan by the end of the 15th century.Robert Boyle’s law was established in 1659; John Dalton’s

in 1800 In 1775, Dr William Cullen made ice by pumping

a vacuum in a vessel of water A few years later, BenjaminFranklin wrote his treatise on Pennsylvania fireplaces,detailing their construction, installation, and operation.Although warming and ventilating techniques had greatlyimproved by the 19th century, manufacturers were unable toexploit these techniques because

• Data available on such subjects as transmission cients, air and water friction in pipes, and brine and ammo-nia properties were sparse and unreliable

coeffi-• Neither set design conditions nor reliable psychrometriccharts existed

• A definitive rational theory that would permit mance calculation and prediction of results had not yetbeen developed

perfor-• Little was known about physical, thermodynamic, andfluid dynamic properties of air, water, brines, and refrig-erants

• No authoritative information existed on heat transmissioninvolving combustion, conduction, convection, radiation,evaporation, and condensation

• No credible performance information for manufacturedequipment was available

Thanks to Thomas Edison, the first electric power plantopened in New York in 1882, making it possible for the firsttime to have an inexpensive source of energy for residentialand commercial buildings

1.1.1 Furnaces

By 1894, the year the American Society of Heating andVentilating Engineers (ASH&VE) was born, central heatingwas fairly well developed The basic heat sources werewarm air furnaces and boilers The combustion chambers ofthe first warm air furnaces were made of cast iron Circula-tion in a gravity warm air furnace system is caused by thedifference in air density in the many parts of the system Asthe force of combustion is small, the system was designed toallow air to circulate freely The addition of fans (circa 1899)

to furnace systems provided a mechanical means of air culation Other additions to the modern furnace includecooling systems, humidification apparatuses, air distribu-tors, and air filters Another important step for the modernheating industry was the conversion of furnaces from coal tooil and gas, and from manual to automatic firing

cir-1.1.2 Steam Systems

James Watt developed the first steam heating system in

1770 However, the first real breakthrough in design did not

occur until the early 1900s when circulation problems in

these systems were improved with the introduction of a

fluid-operated thermostatic trap

From 1900 to 1925, two-pipe steam systems with

thermo-static traps at the outlet of each radiator and at drip points in

the piping gained wide acceptance In smaller buildings,

gravity systems were commonly installed to remove

con-densate For larger systems, boiler return traps and

conden-sate pumps with receivers were used By 1926, the vacuum

return line system was perfected for installation in large and

moderate-sized buildings

Hot water heating systems were developed in parallel

with steam systems As mentioned before, the first hot water

heating system was the gravity system In 1927, the

circula-tor, which forced water through the system, was added to

two-pipe heating systems A few years later, a diverting tee

was added to the one-pipe system, allowing for forced

cir-culation

During the 1930s, radiators and convectors were

com-monly concealed by enclosures, shields, and cabinets In

1944, the baseboard radiator was developed Baseboard

heating improved comfort conditions as it reduced

floor-to-ceiling temperature stratification

Unit heaters and unit ventilators are two other forms of

convection heating developed in the 1920s Unit heaters

were available in suspended and floor types and were

clas-sified according to the heating medium used (e.g., steam, hot

water, electricity, gas, oil, or coal combustion) In addition to

the heating element and fan, unit ventilators were often

equipped with an air filter Many designs provided air

recir-culation and were equipped with a separate outdoor air

con-nection

Panel heating, another form of heat distribution, was

developed in the 1920s In panel heating, a fluid such as hot

water, steam, air, or electricity, circulates through

distribu-tion units embedded in the building components

1.1.3 Early Refrigeration

Early forms of refrigeration included the use of snow,

pond and lake ice, chemical mixture cooling to form

freez-ing baths, and the manufacture of ice by evaporative and

radiation cooling of water on clear nights

By the 18th century, certain mixtures were known to

lower temperatures One such mixture, calcium chloride and

snow, was introduced for commercial use This particular

mixture made possible a temperature down to –27°F (–

33°C) In Great Britain, machines using chemical mixtures

to produce low temperatures were introduced However, by

the time these machines were ready for commercial

exploitation, mechanical ice-making processes had been

perfected to such an extent that chemical mixture freezing

was rendered obsolete except for such batch processes as ice

cream making

1.1.4 Mechanical and Chemical Refrigeration

In 1748, in Scotland, Dr William Cullen and Joseph Blacklectured on the latent heat of fusion and evaporation and

“fixed air” (later identified as carbon dioxide) These eries served as the foundation on which modern refrigeration

discov-is based

In 1851, Dr John Gorrie, was granted US Patent No 8080for a refrigeration machine that produced ice and refrigeratedair with compressed air in an open cycle Also in 1851, Fer-dinand Carre designed the first ammonia absorption unit

In 1853, Professor Alexander Twining of New Haven,Connecticut, produced 1600 lb of ice a day with a doubleact-ing vacuum and compression pump that used sulfuric ether asthe refrigerant

Daniel L Holden improved the Carre machine by ing and building reciprocating compressors These compres-sors were applied to ice making, brewing, and meat packing

design-In 1872, David Boyle developed an ammonia compressionmachine that produced ice

Until 1880, mechanical refrigeration was primarily used tomake ice and preserve meat and fish Notable exceptions werethe use of these machines in the United States, Europe, andAustralia for beer making, oil dewaxing, and wine cooling Atthis time, comfort air cooling was obtained by ice or by chill-ing machines that used either lake or manufactured ice

1.1.5 History of ASHRAE

The American Society of Heating and Ventilating neers (ASHVE) was formed in New York City in 1894 to con-duct research, develop standards, hold technical meetings,and publish technical articles in journals and handbooks Itsscope was limited to the fields of heating and ventilating forcommercial and industrial applications, with secondaryemphasis on residential heating Years later the Society’sname was changed to the American Society of Heating andAir-Conditioning Engineers (ASHAE) to recognize theincreasing importance of air conditioning

Engi-In 1904, the American Society of Refrigerating Engineers(ASRE) was organized and headquartered at the AmericanSociety of Mechanical Engineers (ASME) The new Societyhad 70 charter members and was the only engineering group

in the world that confined its activities to refrigeration, which

at that time consisted mainly of ammonia systems

In 1905, ASME established 288,000 Btu in 24 hrs as thecommercial ton of refrigeration (within the United States) Inthe same year, the New York Stock Exchange was cooled byrefrigeration In 1906, Stuart W Cramer coined the term “airconditioning.”

The First International Congress on Refrigeration wasorganized in Paris in 1908 and a delegation of 26 was sentfrom the United States Most of the participants were mem-bers of ASRE

ASHAE and ASRE merged in 1959, creating the can Society of Heating, Refrigerating and Air-ConditioningEngineers

Ameri-Figure 1-1 depicts ASHRAE’s history ASHRAE

cele-brated its Centennial Year during society year 1994-1995 In

commemoration of the centennial, two books on the history of

ASHRAE and of the HVAC industry were published,

Pro-claiming the Truth and Heat and Cold: Mastering the Great

Indoors

1.1.6 Willis H Carrier

Willis H Carrier (1876-1950) has often been referred to as

the “Father of Air Conditioning.” His analytical and practical

accomplishments contributed greatly to the development of

the refrigeration industry

Carrier graduated from Cornell University in 1901 and was

employed by the Buffalo Forge Company He realized that

satisfactory refrigeration could not be installed due to the

inaccurate data that were available By 1902, he developed

formulas to optimize forced-draft boiler fans, conducted tests

and developed multirating performance tables on indirect

pipe coil heaters, and set up the first research laboratory in the

heating and ventilating industry

In 1902, Carrier was asked to solve the problem faced by

the lithographic industry of poor color register caused by

weather changes Carrier’s solution was to design, test, and

install at the Sackett-Wilhelms Lithographing Company of

Brooklyn a scientifically engineered, year-round

air-condi-tioning system that provided heating, cooling, humidifying,

and dehumidifying

By 1904, Carrier had adapted atomizing nozzles and

devel-oped eliminators for air washers to control dew-point

tem-perature by heating or cooling a system’s recirculated water

Soon after this development, over 200 industries were using

year-round air conditioning

At the 1911 ASME meeting, Carrier presented his paper,

“Rational Psychrometric Formulae,” which related dry-bulb,

wet-bulb, and dew-point temperatures of air, as well as its sible, latent, and total heat load, and set forth the theory of adi-abatic saturation The formulas and psychrometric chartpresented in this paper became the basis for all fundamentalcalculations used by the air-conditioning industry

sen-By 1922, Carrier’s centrifugal refrigeration machine,together with the development of nonhazardous, low-pressurerefrigerants, made water chilling for large and medium-sizecommercial and industrial applications both economical andpractical A conduit induction system for multiroom build-ings, was invented in 1937 by Carrier and his associate, Car-lyle Ashley

1.1.7 Comfort Cooling

Although comfort air-cooling systems had been built as ofthe 1890s, no real progress was made in mechanical air cool-ing until after the turn of the century At that time, several sci-entifically designed air-conditioning plants were installed inbuildings One such installation included a theater inCologne, Germany In 1902, Alfred Wolff designed a 400-tonsystem for the New York Stock Exchange Installed in 1902,this system was in operation for 20 years The Boston Float-ing Hospital, in 1908, was the first hospital to be equippedwith modern air conditioning Mechanical air cooling wasinstalled in a Texas church in 1914 In 1922, Grauman’s Met-ropolitan Theater, the first air-conditioned movie theater,opened in Los Angeles The first office building designedwith and built for comfort air-conditioning specifications wasthe Milam Building, in San Antonio, Texas, which was com-pleted in 1928 Also in 1928, the Chamber of the House ofRepresentatives became air conditioned The Senate becameair conditioned the following year and in 1930, the WhiteHouse and the Executive Office Building were air-condi-tioned

The system of air bypass control, invented in 1924 by L.Logan Lewis, solved the difficult problem of humidity controlunder varying load By the end of the 1920s, the first room airconditioner was introduced by Frigidaire Other importantinventions of the 1920s include lightweight extended surfacecoils and the first unit heater and cold diffuser

Thomas Midgley, Jr developed the halocarbon refrigerants

in 1930 These refrigerants were found to be safe and nomical for the small reciprocating compressors used in com-mercial and residential markets Manufacturers were soonproducing mass market room air conditioners that usedRefrigerant 12

eco-Fluorinated refrigerants were also applied to centrifugalcompression, which required only half the number of impel-lers for the same head as chlorinated hydrocarbons Space andmaterials were saved when pressure-formed extended-surfacetubes in shell-and-tube exchangers were introduced by WalterJones This invention was an important advance for centrifu-gal and reciprocating equipment

Other achievements of the 1930s included

• The first residential lithium bromide absorption machinewas introduced in 1931 by Servel

Fig 1-1 Background of ASHRAE

• In 1931, Carrier marketed steam ejector cooling units for

railroad passenger cars

• As of the mid-1930s, General Electric introduced the heat

pump; the electrostatic air cleaner was put out by

Westing-house; Charles Neeson of Airtemp invented the high-speed

radial compressor; and W.B Connor discovered that odors

could be removed by using activated carbon

With the end of World War II, air-conditioning technology

advanced rapidly Among the advances were air-source heat

pumps, large lithium-bromide water chillers, automobile air

conditioners, rooftop heating and cooling units, small,

out-door-installed ammonia absorption chillers, air purifiers, a

vapor cycle aircraft cabin cooling unit, and a large-capacity

Lysholm rotary compressor

Improvements on and expansions of products that already

existed include

• Dual-duct central systems for office buildings

• Change from open to hermetic compressors from the

small-est reciprocating units to large-capacity centrifugals

• Resurgence of electric heating in all kinds of applications

• Use of heat pumps to reclaim heat in large buildings

• Application of electrostatic cleaners to residences

• Self-contained variable volume air terminals for multiple

interior rooms

• Increasing use of total energy systems for large buildings

and clusters of buildings

• Larger sizes of centrifugals, now over 5000 tons in a single

unit

• Central heating and cooling plants for shopping centers,

colleges, and apartment and office building complexes

In the late 1940s and into the early 1950s, development

work continued on unitary heat pumps for residential and

small commercial installations These factory-engineered and

assembled units, like conventional domestic boilers, could be

easily and cheaply installed in the home or small commercial

businesses by engineers In 1952, heat pumps were placed on

the market for mass consumption Early heat pumps lacked

the durability needed to withstand winter temperatures Low

winter temperatures placed severe stress on the components

of these heat pumps (compressors, outdoor fans, reversing

valves, and control hardware) Improvements in the design of

heat pumps has continued, resulting in more-reliable

com-pressors and lubricating systems, improved reversing valves,

and refined control systems

In the 1950s came the rooftop unit for commercial

build-ings Multizone packaged rooftop units were popular during

the 1960s; however, most were very energy inefficient and

lost favor during the 1970s Beginning with the oil embargo of

1973, the air-conditioning field could no longer conduct

“business as usual,” with concern mainly for the initial cost of

the building and its conditioning equipment The use of crude

rules of thumb, which significantly oversized equipment and

wasted energy, was largely replaced with reliance upon more

scientifically sound, and often computer-assisted, design,

sizing, and selection procedures Variable air volume (VAV)

designs rapidly became the most popular type of HVACsystem for offices, hospitals, and some school buildings.Although energy-efficient, VAV systems proved to have theirown set of problems related to indoor air quality (IAQ), sickbuilding syndrome (SBS), and building related illness (BRI).Solutions to these problems are only now being realized

In 1987, the United Nations Montreal Protocol for ing the earth’s ozone layer was signed, establishing the phase-out schedule for the production of chlorofluorocarbon (CFC)and hydrochlorofluorocarbon (HCFC) refrigerants Contem-porary buildings and their air-conditioning equipment mustnow provide improved indoor air quality as well as comfort,while consuming less energy and using alternative refriger-ants

protect-1.3 Building Energy Use

Energy is generally used in buildings to perform functions

of heating, lighting, mechanical drives, cooling, and specialapplications A typical breakdown of the relative energy use

in a commercial building is given as Figure 1-2

Energy is available in limited forms, such as electricity,fossil fuels, and solar energy, and these energy forms must beconverted within a building to serve the end use of the variousfunctions A degradation of energy is associated with any con-version process In energy conservation efforts, two avenues

of approach were taken: (1) reducing the amount of use and/or(2) reducing conversion losses For example, the furnace thatheats a building produces unusable and toxic flue gas thatmust be vented to the outside and in this process some of theenergy is lost Table 1-1 presents typical values for buildingheat losses and gains at design conditions for a mid-Americaclimate Actual values will vary significantly with climate andbuilding construction

The projected total U.S energy consumption by end-usersector: transportation, industrial, commercial, and residential

is shown in Figure 1-3 The per capita energy consumption forthe U.S and the world is shown in Figure 1-4, showing that in

2007 the U.S consumption was the same as in 1965 This has

Fig 1-2 Energy Use in a Commercial Building

been achieved through application of energy conservation

principles as well as increased energy costs and changes in the

economy

The efficient use of energy in buildings can be achieved by

implementing (1) optimum energy designs, (2)

well-devel-oped energy use policies, and (3) dedicated management

backed up by a properly trained and motivated operating staff

Optimum energy conservation is attained when the least

amount of energy is used to achieve a desired result If this is

not fully realizable, the next best method is to move excess

energy from where it is not wanted to where it can be used or

stored for future use, which generally results in a minimum

expenditure of new energy A system should be designed so

that it cannot heat and cool the same locations simultaneously

ASHRAE Standard 90.1-2013, “Energy Standard for

Buildings Except Low-Rise Residential Buildings,” and the

100-2015 series standards, “Energy Conservation in Existing

Buildings,” provide minimum guidelines for energy

conser-vation design and operation They incorporate these types of

energy standards: (1) prescriptive, which specifies the

mate-rials and methods for design and construction of buildings; (2)

system performance, which sets requirements for each

com-ponent, system, or subsystem within a building; and (3) ing energy, which considers the performance of the building

build-as a whole In this lbuild-ast type, a design goal is set for the annualenergy requirements of the entire building on basis such asBtu/ft2per year (GJ/m2per year) Any combination of mate-rials, systems, and operating procedures can be applied, aslong as design energy usage does not exceed the building’sannual energy budget goal “Standard 90.1-2013 User’s Man-ual” is extremely helpful in understanding and applying therequirements of ASHRAE Standard 90.1

This approach allows greater flexibility while promotingthe goals of energy efficiency It also allows and encouragesthe use of innovative techniques and the development of newmethods for saving energy Means for its implementation arestill being developed They are different for new and for exist-ing buildings; in both cases, an accurate data base is required

as well as an accurate, verifiable means of measuring sumption

con-As energy prices have risen, more sophisticated schemesfor reducing energy consumption have been conceived.Included in such schemes are cogeneration, energy manage-ment systems (EMS), direct digital control (DDS), daylight-ing, closed water-loop heat pumps, variable air volume (VAV)systems, variable frequency drives, thermal storage, dessicantdehumidication, and heat recovery in commercial and institu-tional buildings and industrial plants

As detailed in a 1992 Department of Energy Report,

“Commercial Buildings Consumption and Expenditures,1989,” more than seventy percent of the commercial-indus-trial-institutional (C-I-I) buildings recently built in the UnitedStates made use of energy conservation measures for heatingand cooling

The type of building and its use strongly affects the energyuse as shown in Table 1-2

Heating and air-conditioning systems that are simple indesign and of the proper size for a given building generallyhave relatively low maintenance and operating costs For opti-mum results, as much inherent thermal control as is econom-ically possible should be built into the basic structure Such

Table 1-1 Typical Building Design Heat Losses or Gains

control might include materials with high thermal properties,

insulation, and multiple or special glazing and shading

devices The relationship between the shape, orientation, and

air-conditioning requirement of a building should also be

con-sidered Since the exterior load may vary from 30 to 60% of

the total air-conditioning load when the fenestration (light

transmitting) area ranges from 25 to 75% of the floor area, it

may be desirable to minimize the perimeter area For

exam-ple, a rectangular building with a 4-to-1 aspect ratio requires

substantially more refrigeration than a square building with

the same floor area

When a structure is characterized by several exposures and

multipurpose use, especially with wide load swings and

non-coincident energy use in certain areas, multiunit or unitary

systems may be considered for such areas, but not necessarily

for the entire building The benefits of transferring heat

absorbed by cooling from one area to other areas, processes,

or services that require heat may enhance the selection of such

systems

Buildings in the US consume significant quantities of

energy each year According to the US Department of Energy

(DOE), buildings account for 36% of all the energy used in the

US, and 66% of all the electricity used Beyond economics,

energy use in the buildings sector has significant implications

for our environment Emissions related to building energy use

account for 35% of carbon dioxide emissions, 47% of sulfur

dioxide emissions, and 22% of nitrogen oxide emissions

1.4 Conceptualizing an HVAC System

An important tool for the HVAC design engineer is the

ability to develop a quick overview or “concept” of the

mag-nitude of the project at hand Toward this goal, the industry

has developed a number of “rules of thumb,” some more

accu-rate than others As handy as they might be, these

approxima-tions must be treated as just that—approximaapproxima-tions Don’t use

them as “rules of dumb.”

Tables 1-1 and 1-2 are examples of such rules-of-thumb,

providing data for a quick estimate of heating and cooling

equipment sizes and of building energy use, requiring

knowl-edge only of the size and intended use of the building Other

rules-of-thumb include using a face velocity of 500 fpm in

determining the face area for a cooling coil, the use of

400 cfm/ton for estimating the required cooling airflow rate,

the use of 2.5 gpm/ton for determining the water flow ratethrough the cooling coil and chiller unit, using 1.2 cfm/sq ft ofgross floor area for estimating the required conditioned air-flow rate for comfort cooling, and the estimation of 0.6kW/ton as the power requirement for air conditioning Table1-3 provides very approximate data related to the cost ofHVAC equipment and systems

Table 1.4 provides approximate energy costs for cial consumers in the United States for 2015 Keep in mindthat these energy costs are very volatile at this time

commer-Table 1.5 gives approximate total building costs for officesand medical offices averaged for twenty U.S locations in 2007.The material presented in this book will enable the reader

to validate appropriate rules as well as to improve upon theseapproximations for the final design

1.5 Sustainability and Green Buildings

The following discussion concerning sustainable designand green buildings has been extracted from Chapters 34 and

35 of the 2017 ASHRAE Handbook—Fundamentals.

Pollution, toxic waste creation, waste disposal, global mate change, ozone depletion, deforestation, and resourcedepletion are recognized as results of uncontrolled technolog-ical and population growth Without mitigation, currenttrends will adversely affect the ability of the earth’s ecosystem

cli-to regenerate and remain viable for future generations.The built environment contributes significantly to theseeffects, accounting for one-sixth of the world’s fresh wateruse, one-quarter of its wood harvest, and two-fifths of itsmaterial and energy flows Air quality, transportation pat-terns, and watersheds are also affected The resourcesrequired to serve this sector are considerable and many ofthem are diminishing

Table 1-2 Annual Energy Use Per Unit Floor Area

Building Type Annual Energy Use kWh/ft 2

Table 1-5 Approximate Total Building Costs ($/sq ft.)

(Adapted from RSMeans Costs Comparisons 2007)

2–4-Story Office Building

5–10-Story Office Building

11–20-Story Office Building

Medical Office Building High 194 181 167 219

Average 149 130 121 169

Recognition of how the building industry affects the

envi-ronment is changing the approach to design, construction,

operation, maintenance, reuse, and demolition of buildings

and focusing on environmental and long-term economic

con-sequences Although this sustainable design

ethic—sustain-ability—covers things beyond the HVAC industry alone,

efficient use of energy resources is certainly a key element of

any sustainable design and is very much under the control of

the HVAC designer

Research over the years has shown that new commercial

construction can reduce annual energy consumption by about

50% using integrated design procedures and energy

conserva-tion techniques In the past few years several programs

pro-moting energy efficiency in building design and operation

have been developed One of these is Energy Star Label

(www.energystar.gov) and another one, which is becoming

well known, is Leadership in Energy and Environmental

Design (LEED) (www.usgbc.org/leed)

In 1999 the Environmental Protection Agency of the US

government introduced the Energy Star Label for buildings

This is a set of performance standards that compare a

build-ing’s adjusted energy use to that of similar buildings

nation-wide The buildings that perform in the top 25%, while

conforming to standards for temperature, humidity,

illumina-tion, outdoor air requirements, and air cleanliness, earn the

Energy Star Label

LEED is a voluntary points-based national standard for

developing a high-performance building using an integrated

design process LEED evaluates “greenness” in five

catego-ries: sustainable sites, water efficiency, energy and

atmo-sphere, materials and resources, and the indoor air

environmental quality

In the energy and atmosphere category, building systems

commissioning and minimum energy usages are necessary

requirements The latter requires meeting the requirements

ANSI/ASHRAE/IESNA Standard 90.1-2013, Energy Standard

for Buildings Except Low-Rise Residential Buildings, or the

local energy code, whichever is more stringent

Basically LEED defines what makes a building “green”

while the Energy Star Label is concerned only with energy

performance Both of these programs require adherence to

ASHRAE standards Chapter 35 of the 2017 ASHRAE

Hand-book—Fundamentalsprovides guidance in achieving

sustain-able designs

The basic approach to energy-efficient design is reducing

loads (power), improving transport systems, and providing

efficient components and “intelligent” controls Important

design concepts include understanding the relationship

between energy and power, maintaining simplicity, using

self-imposed budgets, and applying energy-smart design

prac-tices

Just as an engineer must work to a cost budget with most

designs, self-imposed power budgets can be similarly helpful

in achieving energy-efficient design For example, the

follow-ing are possible goals for mid-rise to high-rise office buildfollow-ings

in a typical midwestern or northeastern temperature climate:

• Installed lighting (overall) 0.8 W/ft2

• Space sensible cooling 15 Btu/h·ft2

• Space heating load 10 Btu/h·ft2

• Electric power (overall) 3 W/ft2

• Thermal power (overall) 20 Btu/h·ft2

• Hydronic system head 70 ft of water

• Water chiller (water-cooled) 0.5 kW/ton

• Chilled-water system auxiliaries 0.15 kW/ton

• Unitary air-conditioning systems 1.0 kW/ton

• Annual electric energy 15 kWh/ft2·yr

• Annual thermal energy 5 Btu/ft2·yr·°F·dayThese goals, however, may not be realistic for all projects

As the building and systems are designed, all decisionsbecome interactive as the result of each subsystem’s power orenergy performance being continually compared to the “bud-get.”

Energy efficiency should be considered at the beginning

of building design because energy-efficient features are mosteasily and effectively incorporated at that time Active par-ticipation of all members of the design team (includingowner, architect, engineer, and often the contractor) should

be sought early Consider building attributes such as buildingfunction, form, orientation, window/wall ratio, and HVACsystem types early because each has major energy implica-tions

1.3 Plot the history of the annual energy use per square foot

of floor space for nonresidential buildings and predict thevalues for the years 2014 and 2015

1.4 Estimate the size of cooling and heating equipment that

is needed for a new bank building in middle America that is

140 ft by 220 ft by 12 ft high (42.7 m by 67 m by 3.7 m high).[Answer: 123 tons cooling, 11,109,000 Btu/h heating]

1.5 Estimate the size of heating and cooling equipment thatwill be needed for a residence in middle America that is 28 ft

infor-1.7 Bibliography

ASHRAE 2014 2014 ASHRAE Handbook—Refrigeration.

ASHRAE 2015 2015 ASHRAE Handbook—HVAC

Applica-tions

ASHRAE 2016 2016 ASHRAE Handbook—HVAC Systems

and Equipment

ASHRAE 2017 2017 ASHRAE Handbook—Fundamentals.

ASHRAE 1995 Proclaiming the Truth.

BP 2012 Statistical review of world energy 2012.

http://www.bp.com/sectionbodycopy.do?categoryId=7500

&contentId=7068481

EIA 2001 Annual energy review 2000

DOE/EIA-0384(2000) Energy Information Administration, U.S

Department of Energy, Washington, D.C

EIA 2011 International energy statistics U.S Energy

Infor-mation Administration, Washington, D.C

Coad, W.J 1997 Designing for Tomorrow,

Heating/Pip-ing/Air Conditioning, February

Donaldson, B and B Nagengast 1995 Heat and Cold:

Mas-tering the Great Indoors ASHRAE

Downing, R 1984 Development of Chlorofluorocarbon

Refrigerants ASHRAE Transactions 90(2).

Faust, F.H 1992 The Merger of ASHAE and ASRE: TheAuthor Presents An Overview on Events Leading up to

ASHRAE’s Founding ASHRAE Insights 7(5).

Ivanovich, M.G 1997 HVAC&R and the Internet: Where to

Go, Heating/Piping/Air Conditioning, May.

Nagengast, B.A 1988 A historical look at CFC refrigerants

ASHRAE Journal30(11)

Nagengast, B.A 1993 The 1920s: The first realization of

public air conditioning ASHRAE Journal 35(1).

Nelson, L.W 1989 Residential comfort: A historical look at

early residential HVAC systems ASHRAE Journal 31(1).

Woolrich, W.R 1969 The History of Refrigeration; 220Years of Mechanical and Chemical Cold: 1748-1968

ASHRAE Journal33(7)

THERMODYNAMICS AND PSYCHROMETRICS

This chapter reviews the principles of thermodynamics, evaluates thermodynamic properties, and applies namics and psychrometrics to air-conditioning and refrigeration processes and systems Greater detail on thermodynamics,

thermody-particularly relating to the Second Law and irreversibility, is found in Chapter 2, 2017 ASHRAE

Handbook—Fundamen-tals Details on psychrometric properties can be found in Chapter 1 of the 2017 ASHRAE Handbook—Fundamentals.

2.1 Fundamental Concepts and

Principles

2.1.1 Thermodynamics

Thermodynamics is the science devoted to the study of

energy, its transformations, and its relation to status of matter

Since every engineering operation involves an interaction

between energy and materials, the principles of

thermody-namics can be found in all engineering activities

Thermodynamics may be considered the description of the

behavior of matter in equilibrium and its changes from one

equilibrium state to another The important concepts of

ther-modynamics are energy and entropy; the two major principles

of thermodynamics are called the first and second laws of

thermodynamics The first law of thermodynamics deals with

energy The idea of energy represents the attempt to find an

invariant in the physical universe, something that remains

constant in the midst of change The second law of

thermody-namics explains the concept of entropy; e.g., every naturally

occurring transformation of energy is accompanied

some-where by a loss in the availability of energy for future

perfor-mance of work

The German physicist, Rudolf Clausius (1822–1888),

devised the concept of entropy to quantitatively describe the

loss of available energy in all naturally occurring

transforma-tions Although the natural tendency is for heat to flow from

a hot to a colder body with which it is in contact,

correspond-ing to an increase in entropy, it is possible to make heat flow

from a colder body to a hot body, as is done every day in a

refrigerator However, this does not take place naturally or

without effort exerted somewhere

According to the fundamental principles of

thermodynam-ics, the energy of the world stays constant and the entropy of

the world increases without limit If the essence of the first

principle in everyday life is that one cannot get something for

nothing, the second principle emphasizes that every time one

does get something, the opportunity to get that something in

the future is reduced by a measurable amount, until

ulti-mately, there will be no more “getting.” This “heat death,”

envisioned by Clausius, will be a time when the universe

reaches a level temperature; and though the total amount of

energy will be the same as ever, there will be no means of

making it available, as entropy will have reached its mum value

maxi-Like all sciences, the basis of thermodynamics is mental observation Findings from these experimental obser-vations have been formalized into basic laws In the sectionsthat follow, these laws and their related thermodynamic prop-erties will be presented and applied to various examples.These examples should give the student an understanding ofthe basic concepts and an ability to apply these fundamentals

experi-to thermodynamic problems It is not necessary experi-to memorizenumerous equations, for problems are best solved by applyingthe definitions and laws of thermodynamics

Thermodynamic reasoning is always from the general law

to the specific case; that is, the reasoning is deductive ratherthan inductive To illustrate the elements of thermodynamicreasoning, the analytical processes may be divided into twosteps:

1 The idealization or substitution of an analytical model for

a real system This step is taken in all engineering sciences.Therefore, skill in making idealizations is an essential part

of the engineering art

2 The second step, unique to thermodynamics, is thedeductive reasoning from the first and second laws ofthermodynamics

These steps involve (a) an energy balance, (b) a suitableproperties relation, and (c) accounting for entropy changes

2.1.2 System and Surroundings

Most applications of thermodynamics require the tion of a system and its surroundings A system can be anobject, any quantity of matter, or any region of space selectedfor study and set apart (mentally) from everything else, whichthen becomes the surroundings The systems of interest inthermodynamics are finite, and the point of view taken is mac-roscopic rather than microscopic No account is taken of thedetailed structure of matter, and only the coarse characteris-tics of the system, such as its temperature and pressure, areregarded as thermodynamic coordinates

defini-Everything external to the system is the surroundings, andthe system is separated from the surroundings by the systemboundaries These boundaries may be either movable or fixed;either real or imaginary

2.1.3 Properties and State

A property of a system is any observable characteristic of

the system The more common thermodynamic properties are

temperature, pressure, specific volume or density, internal

energy, enthalpy, and entropy

The state of a system is its condition or configuration

described in sufficient detail so that one state may be

distin-guished from all other states A listing of a sufficient number

of independent properties constitutes a complete definition of

the state of a system

The state may be identified or described by observable,

macroscopic properties such as temperature, pressure, and

density Each property of a substance in a given state has only

one value; this property always has the same value for a given

state, regardless of how the substance arrived at that state In

fact, a property can be defined as any quantity that depends on

the state of the system and is independent of the path (i.e., the

prior history) by which the system arrived at that given state

Conversely, the state is specified or described by its properties

The state of a macroscopic system is the condition of the

system as characterized by the values of its properties This

chapter directs attention to equilibrium states, with

equilib-rium used in its generally accepted context—the equality of

forces, or the state of balance In future discussion, the term

state refers to an equilibrium state unless otherwise noted

The concept of equilibrium is important, as it is only in an

equilibrium state that thermodynamic properties have

mean-ing A system is in thermodynamic equilibrium if it is

incapa-ble of finite, spontaneous change to another state without a

finite change in the state of the surroundings

Included in the many types of equilibria are thermal,

mechanical, and chemical A system in thermal equilibrium is

at the same temperature as the surroundings and the

tempera-ture is the same throughout A system in mechanical

equilib-rium has no part accelerating ( F = 0) and the pressure within

the system is the same as in the surroundings A system in

chemical equilibrium does not tend to undergo a chemical

reaction; the matter in the system is said to be inert

Any property of a thermodynamic system has a fixed value

in a given equilibrium state, regardless of how the system

arrives at that state Therefore, the change that occurs in the

value of a property when a system is altered from one

equilib-rium state to another is always the same This is true

regard-less of the method used to bring about a change between the

two end states The converse of this statement is equally true

If a measured quantity always has the same value between two

given states, that quantity is a measure of the change in a

prop-erty This latter assertion is useful in connection with the

con-servation of energy principle introduced in the next section

The uniqueness of a property value for a given state can be

described mathematically in the following manner The

inte-gral of an exact differential dY is given by

Thus the value of the integral depends solely on the initialand final states Likewise, the change in the value of a prop-erty depends only on the end states Hence the differential

change dY in a property Y is an exact differential Throughout

this text, the infinitesimal variation of a property will be

iden-tified by the differential symbol d preceding the property bol For example, the infinitesimal change in the pressure p of

sym-a system is given by dp The finite chsym-ange in sym-a property is

denoted by the symbol(capital delta), for example, p The

change in a property value Y always represents the final

value minus the initial value This convention must be kept inmind

The symbol is used instead of the usual differential

oper-ator d as a reminder that some quantities depend on the

pro-cess and are not a property of the system.Q represents only

a small quantity of heat, not a differential.m represents only

a small quantity of matter

The same qualifications for hold in the case of

thermo-dynamic work As there is no exact differential dW, small quantities of W similar in magnitude to differentials are

expressed asW.

2.1.4 Processes and Cycles

A process is a change in state which can be defined as any

change in the properties of a system A process is described inpart by the series of states passed through by the system.Often, but not always, some interaction between the systemand surroundings occurs during a process; the specification ofthis interaction completes the description of the process.Describing a process typically involves specifying the ini-tial and final equilibrium states, the path (if identifiable), andthe interactions which take place across the boundaries of thesystem during the process The following terms define specialprocesses:

isobaric or constant pressure—process wherein the pressure

does not change;

isothermal—process that occurs at constant temperature;

isometric—process with constant volume;

adiabatic—process in which no heat is transferred to or fromthe system;

isentropic—process with no change in entropy

A cycle is a process, or more frequently, a series of

pro-cesses wherein the initial and final states of the system areidentical Therefore, at the conclusion of a cycle, all the prop-erties have the same value they had at the beginning

2.1.5 Reversibility

All naturally occurring changes or processes are ible Like a clock, they tend to run down and cannot rewindthemselves without other changes in the surroundings occur-ring Familiar examples are the transfer of heat with a finitetemperature difference, the mixing of two gases, a waterfall,

irrevers-and a chemical reaction All of the above changes can be

reversed, however.Heat can be transferred from a region of

Y

1 2

low temperature to one of higher temperature; gas can be

sep-arated into its components; water can be forced to flow uphill

The important point is that these things can be done only at the

expense of some other system, which itself becomes run down

A process is reversible if its direction can be reversed at

any stage by an infinitesimal change in external conditions If

a connected series of equilibrium states is considered, each

representing only an infinitesimal displacement from the

adjacent one, but with the overall result a finite change, then

a reversible process exists

All actual processes can be made to approach a reversible

process by a suitable choice of conditions; but like the absolute

zero of temperature, the strictly reversible process is only a

concept that aids in the analysis of problems The approach of

actual processes to this ideal limit can be made almost as close

as is desired However, the closeness of approach is generally

limited by economic factors rather than physical ones The

truly reversible process would require an infinite time for

com-pletion The sole reason for the concept of the reversible

pro-cess is to establish a standard for the comparison of actual

processes The reversible process is one that gives the

maxi-mum accomplishment, i.e., yields the greatest amount of work

or requires the least amount of work to bring about a given

change It gives the maximum efficiency toward which to

strive, but which will never be equalled The reversible process

is the standard for judging the efficiency of an actual process

Since the reversible process represents a succession of

equilibrium states, each only a differential step from its

neigh-bor, the reversible process can be represented as a continuous

line on a state diagram (p-v, T-s, etc.) The irreversible process

cannot be so represented The terminal states and general

direction of change can be noted, but the complete path of

change is an indeterminate, irreversible process and cannot be

drawn as a line on a thermodynamic diagram

Irreversibilities always lower the efficiencies of processes

Their effect is identical to that of friction, which is one cause

of irreversibility Conversely, no process more efficient than a

reversible process can be imagined The reversible process

represents a standard of perfection that cannot be exceeded

because

1 It places an upper limit on the work that may be obtained

for a given work-producing process;

2 It places a lower limit on the work input for a given

work-requiring process

2.1.6 Conservation of Mass

From relativistic considerations, mass m and energy E are

related by the well-known equation:

where c = velocity of light.

This equation shows that the mass of a system does change

when its energy changes However, for other than nuclear

reactions, the change is quite small and even the most accurate

chemical balance cannot detect the change in mass Thus,

conservation of mass and conservation of energy are treated

as separate laws in basic thermodynamics

The mass rate of flow of a fluid passing through a

be extended to any number of system inlets and outlets and isused in nearly all energy analyses

2.2 Properties of a Substance

2.2.1 Specific Volume and Density

The specific volume of a substance v is the volume per unit

mass The density of a substance  is the mass per unit ume, and is therefore the reciprocal of the specific volume.Specific volume and density are intensive properties in thatthey are independent of the size of the system

vol-2.2.2 Pressure

When dealing with liquids and gases, we ordinarily speak

of pressure; in solids we speak of stresses The pressure in a

fluid at rest at a given point is the same in all directions sure is defined as the normal component of force per unit area.Absolute pressure is the quantity of interest in most ther-modynamic investigations Most pressure and vacuum gages,however, read the difference between absolute pressure andthe atmospheric pressure existing at the gage (Figure 2-1)

Pres-2.2.3 Temperature

Because temperature is difficult to define, equality of

perature is defined instead Two bodies have equality of

tem-perature if no change in any observable property occurswhen they are in thermal communication

The zeroth law of thermodynamics states that when two

bodies have equality of temperature with a third body, they inturn have equality of temperature with each other Since thisfact is not derivable from other laws, and since in the logicalpresentation of thermodynamics it precedes the first and sec-ond laws of thermodynamics, it has been called the zerothlaw of thermodynamics This law is the basis of temperaturemeasurement Every time a body has equality of temperaturewith a thermometer, it is said that the body has the tempera-ture read on the thermometer The problem remains, how-ever, of relating temperatures that might be read on differentthermometers, or that are obtained when differenttemperature-measuring devices are used, such as thermocou-ples and resistance thermometers The need for a standardscale for temperature measurements is apparent

E = mc2

m1 = m2 = A1V1v1 = A2V2v2

Fahrenheit and Celsius are two commonly used

tempera-ture measuring scales The Celsius scale was formerly called

the Centigrade scale

In this text, the abbreviations °F and °C denote the

Fahren-heit and Celsius scales, respectively The symbols t and T are

both used in the literature for temperature on all temperature

scales Unfortunately, little uniformity exists with

nomencla-ture in engineering

The absolute scale related to the Celsius scale is referred to

as the Kelvin scale and is designated K For SI units, the

degree sign is not used with the Kelvin scale The relation

between the SI temperature scales is

K = °C + 273.15The absolute scale related to the Fahrenheit scale is

referred to as the Rankine scale and is designated °R The

relation between these scales is

°R = °F + 459.67

2.2.4 Internal Energy

Internal energy refers to the energy possessed by a

mate-rial due to the motion and/or position of the molecules This

form of energy may be divided into two parts: (1) kinetic

internal energy, which is due to the velocity of the molecules;

and (2) potential internal energy, which is due to the attractive

forces existing between molecules Changes in the average

velocity of molecules are indicated by temperature changes of

the system; variations in relative distance between molecules

are denoted by changes in phase of the system

The symbol U designates the internal energy of a given

mass of a substance Following the convention used with

other extensive properties, the symbol u designates the

internal energy per unit mass As in the case of specific

vol-ume, u can represent specific internal energy.

2.2.5 Enthalpy

In analyzing specific types of processes, certain tions of thermodynamic properties, which are therefore alsoproperties of the substance undergoing the change of state, are

combina-frequently encountered One such combination is U + pV It is convenient to define a new extensive property, called enthalpy:

H = U + pV

or, per unit mass

h = u + pv (2-2)

As in the case of internal energy, specific enthalpy can be

referred to as h, and total enthalpy H However, both may be

called enthalpy, since the context makes it clear which ismeant

2.2.6 Entropy

Entropy Sis a measure of the molecular disorder or of theprobability of a given state The more disordered a system, thegreater is its entropy; conversely, an orderly or unmixed con-figuration is one of low entropy

By applying the theory of probability to molecular tems, Boltzmann showed a simple relationship between theentropy of a given system of molecules and the probability ofits occurrence This relationship is given as

sys-S = k lnW where k is the Boltzmann constant and W is the thermody-

namic probability

Since entropy is the property used in quantifying the ond Law of Thermodynamics, additional discussion from aclassical thermodynamic viewpoint will be presented whenthe Second Law is discussed

Sec-2.2.7 Specific Heats

The constant-volume specific heat and the sure specific heat are useful functions for thermodynamic cal-culations—particularly for gases

constant-pres-The constant-volume specific heat c v is defined by therelation

(2-3)

The constant-pressure specific heat c pis defined by therelation

(2-4)Note that each of these quantities is defined in terms ofproperties Thus, the constant-volume and constant-pressurespecific heats are thermodynamic properties of a substance

2.2.8 Dimensions and Units

The fundamental and primitive concepts which underlieall physical measurements and all properties are time,length, mass, absolute temperature, electric current, andamount of substance Arbitrary scales of measurement must

Fig 2-1 Terms Used in Pressure Measurement

c v = u T v

c p = h T p

be established for these primary dimensions, with each scale

divided into specific units of size The internationally

accepted base units for the six quantities are as follows:

length metre (m)

mass kilogram (kg)

time second (s)

electric current ampere (A)

thermodynamic temperature kelvin (K)

amount of substance mole (mol)

Each of these has a precise definition according to

interna-tional agreement They form the basis for the SI from the

French document, Le Système International d’Unités (SI ), or

International System of Units

The mass of a system is often given by stating the number

of moles it contains A mole is the mass of a chemical species

equal numerically to its molecular mass Thus, a kilogram

mole of oxygen (O2) contains 32 kilograms In addition, the

number of molecules in a kilogram mole is the same for all

substances This is also true for a gram mole, and in this case

the number of molecules is Avogadro’s number, equal to

6.0225 1023molecules

Many derived units are important in thermodynamics

Examples are force, pressure, and density Force is

deter-mined through Newton’s second law of motion, F = ma, and

has the basic unit (kg·m)/s2 The SI unit for this composite set

is the newton (N) Pressure is defined as force per unit area

(N/m2), called the pascal (Pa); and density is mass per unit

volume (kg/m3)

The US customary engineering system of units also

recog-nizes the second as the basic unit of time, and the ampere as

the unit of current However, absolute temperature is

mea-sured in degrees Rankine (°R) The foot (ft) is the usual unit

of length and the pound mass (lbm) is the unit of mass The

molar unit is the pound mole ASHRAE calls this system the

inch-pound (I-P) unit system

The unit of force, the pound force (lbf), is defined without

reference to Newton’s second law, so this law must be written

to include a dimensional proportionality constant:

F = ma/g c

where g cis the proportionality constant In the I-P system, the

proportionality constant is

g c= 32.174 (lbm/lbf)(ft/s2)The unit of density is lbm/ft3, and the unit of pressure is lbf/ft2

or lbf/in2, often written psi Pressure gages usually measure

pressure relative to atmospheric pressure The term absolute

pressureis often used to distinguish thermodynamic (actual)

pressure (psia) from gage (relative) pressure (psig)

In SI units, the proportionality constant g cin Newton’s law

is unity or

g c= 1 (kg/N)(m/s2)

In this book, all equations that derive from Newton’s law

carry the constant g c

2.2.9 Pure Substance

A pure substance is one that has a homogeneous andinvariable chemical composition It may exist in more thanone phase, but the chemical composition is the same in allphases Thus, liquid water, a mixture of liquid water and watervapor (steam), or a mixture of ice and liquid water are all puresubstances, for every phase has the same chemical composi-tion On the other hand, a mixture of liquid air and gaseous air

is not a pure substance, since the composition of the liquidphase is different from that of the vapor phase

Sometimes a mixture of gases is considered a pure stance as long as there is no change of phase Strictly speak-ing, this is not true A mixture of gases, such as air, exhibitssome of the characteristics of a pure substance as long as there

sub-is no change of phase

Consider as a system that water is contained in the cylinder arrangement of Figure 2-2 Suppose that the pistonmaintains a pressure of 14.7 lbf/in (101.3 kPa) in the cylindercontaining H2O, and that the initial temperature is 59°F(15°C) As heat is transferred to the water, the temperatureincreases appreciably, the specific volume increases slightly,and the pressure remains constant When the temperaturereaches 212°F (100°C), additional heat transfer results in achange of phase That is, some of the liquid becomes vapor,and during this process both the temperature and pressureremain constant, while the specific volume increases consid-erably When the last drop of liquid has vaporized, furtherheat transfer results in an increase in both temperature andspecific volume of the vapor

piston-Saturation temperature designates the temperature atwhich vaporization takes place at a given pressure; this pres-

sure is called the saturation pressure for the given

tempera-ture Thus for water at 212°F (100°C), the saturation pressure

is 14.7 lbf/in.2 (101.3 kPa), and for water at 14.7 lbf/in.2

(101.3 kPa), the saturation temperature is 212°F (100°C)

If a substance exists as liquid at the saturation temperatureand pressure, it is called saturated liquid If the temperature ofthe liquid is lower than the saturation temperature for theexisting pressure, it is called a subcooled liquid (implying thatthe temperature is lower than the saturation temperature forthe given pressure) or a compressed liquid (implying that thepressure is greater than the saturation pressure for the giventemperature)

When a substance exists as part liquid and part vapor at thesaturation temperature, its quality is defined as the ratio of themass of vapor to the total mass The quality may be consid-

ered as an intensive property, and it has the symbol x Quality

has meaning only when the substance is in a saturated state,i.e., at saturation pressure and temperature

If a substance exists as vapor at the saturation temperature,

it is called saturated vapor (Sometimes the term dry saturated

vapor is used to emphasize that the quality is 100%.) When thevapor is at a temperature greater than the saturation tempera-

ture, it is said to exist as superheated vapor The pressure and

temperature of superheated vapor are independent properties

because the temperature may increase while the pressure

remains constant Actually, gases are highly superheated

vapors

The entire range of phases is summarized by Figure 2-3,

which shows how the solid, liquid, and vapor phases may exist

together in equilibrium Along the sublimation line, the solid

and vapor phases are in equilibrium, along the fusion line, the

solid and liquid phases are in equilibrium, and along the

vapor-ization line, the liquid and vapor phases are in equilibrium The

only point at which all three phases may exist in equilibrium is

the triple point The vaporization line ends at the critical point

because there is no distinct change from the liquid phase to the

vapor phase above the critical point

Consider a solid in state A, Figure 2-3 When the

tempera-ture is increased while the pressure (which is less than the triple

point pressure) is constant, the substance passes directly from

the solid to the vapor phase Along the constant pressure line

EF, the substance first passes from the solid to the liquid phase

at one temperature, and then from the liquid to the vapor phase

at a higher temperature Constant-pressure line CD passes

through the triple point, and it is only at the triple point that the

three phases may exist together in equilibrium At a pressure

above the critical pressure, such as GH, there is no sharp

dis-tinction between the liquid and vapor phases

One important reason for introducing the concept of a pure

substance is that the state of a simple compressible pure

sub-stance is defined by two independent properties This means,

for example, if the specific volume and temperature of

super-heated steam are specified, the state of the steam is determined

To understand the significance of the term independent

property, consider the saturated-liquid and saturated-vaporstates of a pure substance These two states have the same pres-sure and the same temperature, but are definitely not the samestate Therefore, in a saturation state, pressure and temperatureare not independent properties Two independent propertiessuch as pressure and specific volume, or pressure and quality,are required to specify a saturation state of a pure substance.Thus, a mixture of gases, such as air, has the same charac-teristics as a pure substance, as long as only one phase is pres-ent The state of air, which is a mixture of gases of definitecomposition, is determined by specifying two properties aslong as it remains in the gaseous phase, and in this regard, aircan be treated as a pure substance

2.2.10 Tables and Graphs of Thermodynamic

Properties

Tables of thermodynamic properties of many substancesare available, and they all generally have the same form Thissection refers to the tables for H2O and R-134a, as well as their

respective Mollier diagrams, the h-s chart for steam, and the

p-hdiagram for R-134a

Table 3 in Chapter 1 of the 2017 ASHRAE Handbook—

Fundamentalsgives thermodynamic properties of water at uration and is reproduced in part as Table 2-1 on the followingpages In Table 2-1, the first two columns after the temperaturegive the corresponding saturation pressure in pounds force persquare inch and in inches of mercury The next three columnsgive specific volume in cubic feet per pound mass The first of

sat-these gives the specific volume of the saturated solid (v i) orliquid (vf); the third column gives the specific volume of satu-

rated vapor v g The difference between these two values, v g–

v i or v g – v f, represents the increase in specific volume whenthe state changes from saturated solid or liquid to saturated

vapor, and is designated v or v

Fig 2-2 Thermodynamic Fluid States

Fig 2-3 The Pure Substance

Table 2-1 Thermodynamic Properties of Water

(Table 3, Chapter 1, 2017 ASHRAE Handbook—Fundamentals)

Table 2-1 Thermodynamic Properties of Water (Continued)

(Table 3, Chapter 1, 2017 ASHRAE Handbook—Fundamentals)

Table 2-1 Thermodynamic Properties of Water (Continued)

(Table 3, Chapter 1, 2017 ASHRAE Handbook—Fundamentals)

Table 2-1 Thermodynamic Properties of Water (Continued)

(Table 3, Chapter 1, 2017 ASHRAE Handbook—Fundamentals)

Table 2-1 Thermodynamic Properties of Water (Continued)

(Table 3, Chapter 1, 2017 ASHRAE Handbook—Fundamentals)

The specific volume of a substance having a given quality

can be found by using the definition of quality Quality is

defined as the ratio of the mass of vapor to total mass of liquid

plus vapor when a substance is in a saturation state Consider

a mass of 1 kg having a quality x The specific volume is the

sum of the volume of the liquid and the volume of the vapor

The volume of the liquid is (1 – x)v f, and the volume of the

vapor is xv g Therefore, the specific volume v is

v = xv g+ (1 – x)v f (2-5)

Since v f + v fg = v g, Equation 2-5 can also be written in the

following form:

v = v f + xv fg (2-6)The same procedure is followed for determining the

enthalpy and the entropy for quality conditions:

h = xh g+ (1 – x)h f (2-7)

s = xs g+ (1 – x)s f (2-8)Internal energy can then be obtained from the definition of

enthalpy as u = h – pv.

If the substance is a compressed or subcooled liquid, the

thermodynamic properties of specific volume, enthalpy,

inter-nal energy, and entropy are strongly temperature dependent

(rather than pressure dependent) If compressed liquid tables

are unavailable, they may be approximated by the

correspond-ing values for saturated liquid (v f , h f , u f , and s f) at the existing

temperature

In the superheat region, thermodynamic properties must be

obtained from superheat tables or a plot of the thermodynamic

properties, called a Mollier diagram (Figure 2-4)

The thermodynamic and transport properties of the

refrig-erants used in vapor compression systems are found in

simi-lar tables typified by Table 2-2, which is a section of the

R-134a property tables from Chapter 30 of the 2017 ASHRAE

Handbook—Fundamentals However, for these refrigerants

the common Mollier plot is the p-h diagram as illustrated in

Figure 2-5

For fluids used in absorption refrigeration systems, the

thermodynamic properties are commonly found on a different

type of plot—the enthalpy-concentration diagram, as

illus-trated in Figure 2-6 for aqua-ammonia and in Figure 2-7 for

lithium-bromide/water

2.2.11 Property Equations for Ideal Gases

An ideal gas is defined as a gas at sufficiently low density

so that intermolecular forces are negligible As a result, an

ideal gas has the equation of state

pv = RT (2-9)For an ideal gas, the internal energy is a function of tem-

perature only, which means that regardless of the pressure, an

ideal gas at a given temperature has a certain definite specific

internal energy u.

The relation between the internal energy u and the

tem-perature can be established by using the definition of stant-volume specific heat given by

con-Since the internal energy of an ideal gas is not a function ofvolume, an ideal gas can be written as

c v = du/dT

du = c v dt (2-10)This equation is always valid for an ideal gas regardless of thekind of process considered

From the definition of enthalpy and the equation of state of

an ideal gas, it follows that

h = u + pv = u + RT Since R is a constant and u is a function of temperature only, the enthalpy h of an ideal gas is also a function of temperature

Entropy, however, remains a function of both temperatureand pressure, and is given by the equation

ds = c p (dT/T ) − R(dp/p) (2-12)

where c pis frequently treated as being constant

The ratio of heat capacities is often denoted by

k = c p /c v (2-13)and is a useful quantity in calculations for ideal gases Idealgas values for some common gases are listed in Table 2-3

No real gas exactly satisfies these equations over any finiterange of temperature and pressure However, all real gasesapproach ideal behavior at low pressures, and in the limit as

p0 do in fact meet the above requirements

Thus, in solving problems, ideal behavior is assumed intwo cases First, at very low pressures, ideal gas behavior can

be assumed with good accuracy, regardless of the ture Second, at temperatures that are double the critical tem-perature or above (the critical temperature of nitrogen is

tempera-126 K), ideal gas behavior can be assumed with good racy to pressures of at least 1000 lbf/in2(7000 kPa) In thesuperheated vapor region, when the temperature is less thantwice the critical temperature and the pressure is above a very

accu-c v = u T v

c p = h T p

Table 2-2 Refrigerant 134a Properties of Saturated Liquid and Saturated Vapor

(Table Refrigerant 134a, Chapter 30, 2017 ASHRAE Handbook—Fundamentals)

Enthalpy, Btu/lb

Entropy, Btu/lb·°F

Specific Heat c p, Btu/lb·°F c p /c v

Vel of Sound, ft/s

Viscosity,

lbm/ft·h

Thermal Cond., Btu/h·ft·°F Surface

Tension, dyne/cm Temp.,*

°F Liquid Vapor Liquid Vapor Liquid Vapor Vapor Liquid Vapor Liquid Vapor Liquid Vapor