2009 ASHRAE Handbook - Fundamentals (I-P Edition)

997 Pages·2009·22.84 MB·English

2009 ASHRAE® HANDBOOK

FUNDAMENTALS
Inch-Pound Edition
American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.
1791 Tullie Circle, N.E., Atlanta, GA 30329
[phone] http://www.ashrae.org
©2009 by the American Society of Heating, Refrigerating and Air-Conditioning Engineers,
Inc. All rights reserved.
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Volunteer members of ASHRAE Technical Committees and others compiled the infor-
mation in this handbook, and it is generally reviewed and updated every four years. Com-
ments, criticisms, and suggestions regarding the subject matter are invited. Any errors or
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tions to Handbook volumes in print will be published in the Handbook published the year
following their verification and, as soon as verified, on the ASHRAE Internet Web site.
DISCLAIMER
ASHRAE has compiled this publication with care, but ASHRAE has not investigated,
and ASHRAE expressly disclaims any duty to investigate, any product, service, process,
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ISBN 978-1-933742-54-0
ISSN 1523-7222
The paper for this book is both acid- and elemental-chlorine-free and was
manufactured with pulp obtained from sources using sustainable forestry
practices. The printing used soy-based inks.
ASHRAE Research: Improving the Quality of Life
The American Society of Heating, Refrigerating and Air- annually, enabling ASHRAE to report new data about material
Conditioning Engineers is the world’s foremost technical society in properties and building physics and to promote the application of
the fields of heating, ventilation, air conditioning, and refrigeration. innovative technologies.
Its members worldwide are individuals who share ideas, identify Chapters in the ASHRAE Handbook are updated through the
needs, support research, and write the industry’s standards for test- experience of members of ASHRAE Technical Committees and
ing and practice. The result is that engineers are better able to keep through results of ASHRAE Research reported at ASHRAE meet-
indoor environments safe and productive while protecting and pre- ings and published in ASHRAE special publications and in
serving the outdoors for generations to come. ASHRAE Transactions.
One of the ways that ASHRAE supports its members’ and indus- For information about ASHRAE Research or to become a mem-
try’s need for information is through ASHRAE Research. Thou- ber, contact ASHRAE, 1791 Tullie Circle, Atlanta, GA 30329; tele-
sands of individuals and companies support ASHRAE Research phone: [phone]; www.ashrae.org.
Preface
The 2009 ASHRAE Handbook—Fundamentals covers basic prin- (cid:127) Chapter 20, Space Air Diffusion, has been completely rewritten to
ciples and data used in the HVAC&R industry. The ASHRAE Tech- harmonize with related chapters in other volumes, with major sec-
nical Committees that prepare these chapters strive not only to tions on fully mixed, partially mixed, stratified, and task/ambient
provide new information, but also to clarify existing information, systems and the principles behind their design and operation.
delete obsolete materials, and reorganize chapters to make the Hand- (cid:127) Chapter 21, Duct Design, has new data for round and rectangular
book more understandable and easier to use. An accompanying CD- fittings in agreement with the ASHRAE Duct Fitting Database, as
ROM contains all the volume’s chapters in both I-P and SI units. well as new content on duct leakage requirements, spiral duct
This edition includes a new chapter (35), Sustainability, which roughness, and flexible duct pressure loss correction.
defines this concept for HVAC&R and describes the principles, (cid:127) Chapter 23, Insulation for Mechanical Systems, has added tables
design considerations, and detailed evaluations needed in designing from ASHRAE Standard 90.1-2007, and a new section on writing
sustainable HVAC&R systems. specifications.
Also new for this volume, chapter order and groupings have been (cid:127) Chapter 24, Airflow Around Buildings, has added a detailed dis-
revised for more logical flow and use. Some of the other revisions cussion on computational evaluation of airflow, plus new refer-
and additions to the volume are as follows: ences including updated versions of design standards and
manuals of practice.
(cid:127) Chapter 1, Psychrometrics, has new information on the composi-
(cid:127) Chapters 25, 26, and 27 carry new titles, reorganized as chapters
tion of dry air, and revised table data for thermodynamic proper-
on Heat, Air, and Moisture Control Fundamentals, Material Prop-
ties of water and moist air.
erties, and Examples, respectively, with updated content through-
(cid:127) Chapter 6, Mass Transfer, has added examples on evaluating diffu-
out.
sion coefficients, and on heat transfer and moisture removal rates.
(cid:127) Chapter 29, Refrigerants, has new content on stratospheric ozone
(cid:127) Chapter 7, Fundamentals of Control, includes new content on
depletion, global climate change, and global environmental char-
dampers, adaptive control, direct digital control (DDC) system
acteristics of refrigerants.
architecture and specifications, and wireless control.
(cid:127) Chapter 30, Thermophysical Properties of Refrigerants, has up-
(cid:127) Chapter 9, Thermal Comfort, has a new section on thermal com-
dated data for R-125, R-245fa, R-170, R-290, R-600, and R-600a.
fort and task performance, based on multiple new studies done in
(cid:127) Chapter 36, Measurement and Instruments, has revised content on
laboratory and office environments.
measurement of air velocity, infiltration, airtightness, and outdoor
(cid:127) Chapter 10, Indoor Environmental Health, was reorganized to
air ventilation, plus new information on particle image velocime-
describe hazard sources, health effects, exposure standards, and
try (PIV) and data acquisition and recording.
exposure controls. New and updated topics include mold, Legio-
nella, indoor air chemistry, thermal impacts, and water quality This volume is published, both as a bound print volume and in
standards. electronic format on a CD-ROM, in two editions: one using inch-
(cid:127) Chapter 14, Climatic Design Information, has new climate data pound (I-P) units of measurement, the other using the International
for 5564 stations (an increase of 1142 new stations compared to System of Units (SI).
2005 Fundamentals) on the CD-ROM accompanying this book. Corrections to the 2006, 2007, and 2008 Handbook volumes can
A subset of data for selected stations is also included in the be found on the ASHRAE Web site at http://www.ashrae.org and in
printed chapter for convenient access. the Additions and Corrections section of this volume. Corrections
(cid:127) Chapter 15, Fenestration, has been revised to include new exam- for this volume will be listed in subsequent volumes and on the
ples of solar heat gain coefficient (SHGC) calculations, and new ASHRAE Web site.
research results on shading calculations and U-factors for various Reader comments are enthusiastically invited. To suggest im-
specialized door types. provements for a chapter, please comment using the form on the
(cid:127) Chapter 16, Ventilation and Infiltration, has new, detailed exam- ASHRAE Web site or, using the cutout page(s) at the end of this vol-
ples, updates from ASHRAE Standards 62.1 and 62.2, discussion ume’s index, write to Handbook Editor, ASHRAE, 1791 Tullie Cir-
of relevant LEED® aspects, and new information on airtightness cle, Atlanta, GA 30329, or fax [phone], or e-mail mowen@
and ventilation rates for commercial buildings. ashrae.org.
(cid:127) Chapter 18, Nonresidential Cooling and Heating Load Calcu-
lations, has been updated to reflect new ASHRAE research results
on climate data and on heat gains from office equipment, lighting, Mark S. Owen
and commercial cooking appliances. Editor
The four-volume ASHRAE Handbook is a reference for engineers working in HVAC&R and for professionals in allied fields. The print edition is
revised on a four-year cycle, with one volume published each year. Tables of contents for the four most recent volumes appear on these pages, and a
composite index is at the end of this volume. In addition to the CD-ROM accompanying this book, ASHRAE publishes a HandbookCD+ containing
all four volumes plus supplemental material and features. The Society also produces educational materials, standards, design guides, databases, and
many other useful publications. See the online bookstore of the ASHRAE Web site (www.ashrae.org) for information on these publications.
2009 FUNDAMENTALS
PRINCIPLES 21. Duct Design
Chapter 1. Psychrometrics 22. Pipe Sizing
2. Thermodynamics and Refrigeration Cycles 23. Insulation for Mechanical Systems
3. Fluid Flow 24. Airflow Around Buildings
4. Heat Transfer
BUILDING ENVELOPE
5. Two-Phase Flow
6. Mass Transfer Chapter 25. Heat, Air, and Moisture Control in Building
7. Fundamentals of Control Assemblies—Fundamentals
8. Sound and Vibration 26. Heat, Air, and Moisture Control in Building
Assemblies—Material Properties
INDOOR ENVIRONMENTAL QUALITY 27. Heat, Air, and Moisture Control in Building
Chapter 9. Thermal Comfort Assemblies—Examples
10. Indoor Environmental Health
MATERIALS
11. Air Contaminants
12. Odors Chapter 28. Combustion and Fuels
13. Indoor Environmental Modeling 29. Refrigerants
30. Thermophysical Properties of Refrigerants
LOAD AND ENERGY CALCULATIONS 31. Physical Properties of Secondary Coolants (Brines)
Chapter 14. Climatic Design Information 32. Sorbents and Desiccants
15. Fenestration 33. Physical Properties of Materials
16. Ventilation and Infiltration
17. Residential Cooling and Heating Load Calculations GENERAL
18. Nonresidential Cooling and Heating Load Chapter 34. Energy Resources
Calculations 35. Sustainability
19. Energy Estimating and Modeling Methods 36. Measurement and Instruments
37. Abbreviations and Symbols
HVAC DESIGN 38. Units and Conversions
Chapter 20. Space Air Diffusion 39. Codes and Standards
2008 HVAC SYSTEMS AND EQUIPMENT
AIR-CONDITIONING AND HEATING SYSTEMS HEATING EQUIPMENT AND COMPONENTS
Chapter 1. HVAC System Analysis and Selection Chapter 30. Automatic Fuel-Burning Systems
2. Decentralized Cooling and Heating 31. Boilers
3. Central Heating and Cooling 32. Furnaces
4. Air Handling and Distribution 33. Residential In-Space Heating Equipment
5. In-Room Terminal Systems
34. Chimney, Vent, and Fireplace Systems
6. Panel Heating and Cooling
35. Hydronic Heat-Distributing Units and Radiators
7. Combined Heat and Power Systems
36. Solar Energy Equipment
8. Applied Heat Pump and Heat Recovery Systems
9. Small Forced-Air Heating and Cooling Systems COOLING EQUIPMENT AND COMPONENTS
10. Steam Systems
11. District Heating and Cooling Chapter 37. Compressors
12. Hydronic Heating and Cooling 38. Condensers
13. Condenser Water Systems 39. Cooling Towers
14. Medium- and High-Temperature Water Heating 40. Evaporative Air-Cooling Equipment
15. Infrared Radiant Heating 41. Liquid Coolers
16. Ultraviolet Lamp Systems 42. Liquid-Chilling Systems
17. Combustion Turbine Inlet Cooling
GENERAL COMPONENTS
AIR-HANDLING EQUIPMENT AND COMPONENTS
Chapter 43. Centrifugal Pumps
Chapter 18. Duct Construction 44. Motors, Motor Controls, and Variable-Speed Drives
19. Room Air Distribution Equipment 45. Pipes, Tubes, and Fittings
20. Fans
46. Valves
21. Humidifiers
47. Heat Exchangers
22. Air-Cooling and Dehumidifying Coils
23. Desiccant Dehumidification and Pressure-Drying PACKAGED, UNITARY, AND SPLIT-SYSTEM
Equipment EQUIPMENT
24. Mechanical Dehumidifiers and Related Components
25. Air-to-Air Energy Recovery Equipment Chapter 48. Unitary Air Conditioners and Heat Pumps
26. Air-Heating Coils 49. Room Air Conditioners and Packaged Terminal Air
27. Unit Ventilators, Unit Heaters, and Makeup Air Conditioners
Units
GENERAL
28. Air Cleaners for Particulate Contaminants
29. Industrial Gas Cleaning and Air Pollution Control Chapter 50. Thermal Storage
Equipment 51. Codes and Standards
CD-ROM with all content from 2009 Fundamentals inside back cover
2007 HVAC APPLICATIONS
COMFORT APPLICATIONS ENERGY-RELATED APPLICATIONS
Chapter 1. Residences Chapter 32. Geothermal Energy
2. Retail Facilities 33. Solar Energy Use
3. Commercial and Public Buildings 34. Thermal Storage
4. Places of Assembly
5. Hotels, Motels, and Dormitories BUILDING OPERATIONS AND MANAGEMENT
6. Educational Facilities Chapter 35. Energy Use and Management
7. Health Care Facilities 36. Owning and Operating Costs
8. Justice Facilities 37. Testing, Adjusting, and Balancing
9. Automobiles and Mass Transit 38. Operation and Maintenance Management
10. Aircraft
39. Computer Applications
11. Ships
40. Building Energy Monitoring
INDUSTRIAL APPLICATIONS 41. Supervisory Control Strategies and Optimization
42. HVAC Commissioning
Chapter 12. Industrial Air Conditioning
13. Enclosed Vehicular Facilities GENERAL APPLICATIONS
14. Laboratories
Chapter 43. Building Envelopes
15. Engine Test Facilities
44. Building Air Intake and Exhaust Design
16. Clean Spaces
45. Control of Gaseous Indoor Air Contaminants
17. Data Processing and Electronic Office Areas
46. Design and Application of Controls
18. Printing Plants
19. Textile Processing Plants 47. Sound and Vibration Control
20. Photographic Material Facilities 48. Water Treatment
21. Museums, Galleries, Archives, and Libraries 49. Service Water Heating
22. Environmental Control for Animals and Plants 50. Snow Melting and Freeze Protection
23. Drying and Storing Selected Farm Crops 51. Evaporative Cooling
24. Air Conditioning of Wood and Paper Product 52. Fire and Smoke Management
Facilities 53. Radiant Heating and Cooling
25. Power Plants 54. Seismic and Wind Restraint Design
26. Nuclear Facilities 55. Electrical Considerations
27. Mine Air Conditioning and Ventilation 56. Room Air Distribution
28. Industrial Drying Systems 57. Integrated Building Design
29. Ventilation of the Industrial Environment 58. Chemical, Biological, Radiological, and Explosive
30. Industrial Local Exhaust Systems Incidents
31. Kitchen Ventilation 59. Codes and Standards
2006 REFRIGERATION
REFRIGERATION SYSTEM PRACTICES 29. Chocolates, Candies, Nuts, Dried Fruits, and Dried
Vegetables
Chapter 1. Liquid Overfeed Systems
2 System Practices for Halocarbon Refrigerants
DISTRIBUTION OF CHILLED AND FROZEN FOOD
3. System Practices for Ammonia and Carbon Dioxide
Refrigerants Chapter 30. Cargo Containers, Rail Cars, Trailers, and Trucks
4. Secondary Coolants in Refrigeration Systems 31. Marine Refrigeration
5. Refrigerant System Chemistry 32. Air Transport
6. Control of Moisture and Other Contaminants in
Refrigerant Systems INDUSTRIAL APPLICATIONS
7. Lubricants in Refrigerant Systems Chapter 33. Insulation Systems for Refrigerant Piping
8. Refrigerant Containment, Recovery, Recycling, and 34. Ice Manufacture
Reclamation 35. Ice Rinks
36. Concrete Dams and Subsurface Soils
FOOD STORAGE AND EQUIPMENT
37. Refrigeration in the Chemical Industry
Chapter 9. Thermal Properties of Foods
10. Cooling and Freezing Times of Foods LOW-TEMPERATURE APPLICATIONS
11. Commodity Storage Requirements Chapter 38. Cryogenics
12. Food Microbiology and Refrigeration 39. Ultralow-Temperature Refrigeration
13. Refrigeration Load 40. Biomedical Applications of Cryogenic Refrigeration
14. Refrigerated-Facility Design
15. Methods of Precooling Fruits, Vegetables, and REFRIGERATION EQUIPMENT
Cut Flowers
Chapter 41. Absorption Cooling, Heating, and Refrigeration
FOOD REFRIGERATION Equipment
42. Forced-Circulation Air Coolers
Chapter 16. Industrial Food-Freezing Systems
43. Component Balancing in Refrigeration Systems
17. Meat Products
44. Refrigerant-Control Devices
18. Poultry Products
45. Factory Dehydrating, Charging, and Testing
19. Fishery Products
20. Dairy Products UNITARY REFRIGERATION EQUIPMENT
21. Eggs and Egg Products
22. Deciduous Tree and Vine Fruit Chapter 46. Retail Food Store Refrigeration and Equipment
23. Citrus Fruit, Bananas, and Subtropical Fruit 47. Food Service and General Commercial
24. Vegetables Refrigeration Equipment
25. Fruit Juice Concentrates and Chilled-Juice Products 48. Household Refrigerators and Freezers
26. Beverages
GENERAL
27. Processed, Precooked, and Prepared Foods
28. Bakery Products 49. Codes and Standards
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CONTENTS
Contributors vii
ASHRAE Technical Committees, Task Groups, and Technical Resource Groups ix
ASHRAE Research: Improving the Quality of Life x
Preface x
PRINCIPLES
Chapter 1. Psychrometrics (TC 1.1, Thermodynamics and Psychrometrics, TC 8.3, Absorption and Heat-
Operated Machines) 1.1
2. Thermodynamics and Refrigeration Cycles (TC 1.1) 2.1
3. Fluid Flow (TC 1.3, Heat Transfer and Fluid Flow) 3.1
4. Heat Transfer (TC 1.3) 4.1
5. Two-Phase Flow (TC 1.3) 5.1
6. Mass Transfer (TC 1.3) 6.1
7. Fundamentals of Control (TC 1.4, Control Theory and Application) 7.1
8. Sound and Vibration (TC 2.6, Sound and Vibration Control) 8.1
INDOOR ENVIRONMENTAL QUALITY
Chapter 9. Thermal Comfort (TC 2.1, Physiology and Human Environment) 9.1
10. Indoor Environmental Health (Environmental Health Committee) 10.1
11. Air Contaminants (TC 2.3, Gaseous Air Contaminants and Gas Contaminant Removal
Equipment) 11.1
12. Odors (TC 2 .3) 12.1
13. Indoor Environmental Modeling (TC 4.10, Indoor Environmental Modeling) 13.1
LOAD AND ENERGY CALCULATIONS
Chapter 14. Climatic Design Information (TC 4.2, Climatic Information) 14.1
15. Fenestration (TC 4.5, Fenestration) 15.1
16. Ventilation and Infiltration (TC 4.3, Ventilation Requirements and Infiltration ) 16.1
17. Residential Cooling and Heating Load Calculations (TC 4.1, Load Calculation Data and
Procedures) 17.1
18. Nonresidential Cooling and Heating Load Calculations (TC 4.1) 18.1
19. Energy Estimating and Modeling Methods (TC 4.7, Energy Calculations) 19.1
HVAC DESIGN
Chapter 20. Space Air Diffusion (TC 5.3, Room Air Distribution) 20.1
21. Duct Design (TC 5.2, Duct Design) 21.1
22. Pipe Sizing (TC 6.1, Hydronic and Steam Equipment and Systems) 22.1
23. Insulation for Mechanical Systems (TC 1.8, Mechanical Systems Insulation) 23.1
24. Airflow Around Buildings (TC 4.3) 24.1
BUILDING ENVELOPE
Chapter 25. Heat, Air, and Moisture Control in Building Assemblies—Fundamentals
(TC 4.4, Building Materials and Building Envelope Performance) 25.1
26. Heat, Air, and Moisture Control in Building Assemblies—Material Properties (TC 4.4) 26.1
27. Heat, Air, and Moisture Control in Insulated Assemblies—Examples (TC 4.4) 27.1
MATERIALS
Chapter 28. Combustion and Fuels (TC 6.10, Fuels and Combustion) 28.1
29. Refrigerants (TC 3.1, Refrigerants and Secondary Coolants) 29.1
30. Thermophysical Properties of Refrigerants (TC 3.1) 30.1
31. Physical Properties of Secondary Coolants (Brines) (TC 3.1) 31.1
32. Sorbents and Desiccants (TC 8.12, Dessicant Dehumidification Equipment and Components) 32.1
33. Physical Properties of Materials (TC 1.3) 33.1
GENERAL
Chapter 34. Energy Resources (TC 2.8, Building Environmental Impacts and Sustainability) 34.1
35. Sustainability (TC 2.8) 35.1
36. Measurement and Instruments (TC 1.2, Instruments and Measurements) 36.1
37. Abbreviations and Symbols (TC 1.6, Terminology) 37.1
38. Units and Conversions (TC 1.6) 38.A
39. Codes and Standards 39.1
ADDITIONS AND CORRECTIONS A.1
INDEX I.1
Composite index to the 2006 Refrigeration, 2007 HVAC Applications, 2008 HVAC Systems and
Equipment, and 2009 Fundamentals volumes
CLIMATIC DESIGN CONDITIONS TABLES T.1
CHAPTER 2
THERMODYNAMICS AND REFRIGERATION CYCLES
THERMODYNAMICS................................................................ 2.1 Theoretical Single-Stage Cycle Using Zeotropic
Stored Energy..............................................................................2.1 Refrigerant Mixture................................................................ 2.9
Energy in Transition....................................................................2.1 Multistage Vapor Compression Refrigeration Cycles.............. 2.10
First Law of Thermodynamics................................................... 2.2 Actual Refrigeration Systems................................................... 2.11
Second Law of Thermodynamics............................................... 2.2 ABSORPTION REFRIGERATION CYCLES........................... 2.13
Thermodynamic Analysis of Refrigeration Cycles..................... 2.3 Ideal Thermal Cycle................................................................. 2.13
Equations of State...................................................................... 2.3 Working Fluid Phase Change Constraints............................... 2.13
Calculating Thermodynamic Properties.................................... 2.4 Working Fluids......................................................................... 2.14
COMPRESSION REFRIGERATION CYCLES.......................... 2.6 Absorption Cycle Representations........................................... 2.15
Carnot Cycle.............................................................................. 2.6 Conceptualizing the Cycle....................................................... 2.15
Theoretical Single-Stage Cycle Using a Pure Refrigerant Absorption Cycle Modeling..................................................... 2.16
or Azeotropic Mixture............................................................. 2.7 Ammonia/Water Absorption Cycles......................................... 2.18
Lorenz Refrigeration Cycle........................................................ 2.8 Symbols.................................................................................... 2.19
THERMODYNAMICS is the study of energy, its transforma- Nuclear (atomic) energy derives from the cohesive forces hold-
tions, and its relation to states of matter. This chapter covers the ing protons and neutrons together as the atom’s nucleus.
application of thermodynamics to refrigeration cycles. The first part
reviews the first and second laws of thermodynamics and presents ENERGY IN TRANSITION
methods for calculating thermodynamic properties. The second and HeatQis the mechanism that transfers energy across the bound-
third parts address compression and absorption refrigeration cycles, aries of systems with differing temperatures, always toward the
two common methods of thermal energy transfer. lower temperature. Heat is positive when energy is added to the sys-
tem (see Figure 1).
THERMODYNAMICS Work is the mechanism that transfers energy across the bound-
aries of systems with differing pressures (or force of any kind),
Athermodynamic system is a region in space or a quantity of always toward the lower pressure. If the total effect produced in the
matter bounded by a closed surface. The surroundings include system can be reduced to the raising of a weight, then nothing but
everything external to the system, and the system is separated from
work has crossed the boundary. Work is positive when energy is
the surroundings by the system boundaries. These boundaries can
removed from the system (see Figure 1).
be movable or fixed, real or imaginary.
Mechanical or shaft work W is the energy delivered or ab-
Entropy and energy are important in any thermodynamic system.
sorbed by a mechanism, such as a turbine, air compressor, or inter-
Entropy measures the molecular disorder of a system. The more nal combustion engine.
mixed a system, the greater its entropy; an orderly or unmixed con-
Flow work is energy carried into or transmitted across the
figuration is one of low entropy. Energy has the capacity for pro- system boundary because a pumping process occurs somewhere
ducing an effect and can be categorized into either stored or
outside the system, causing fluid to enter the system. It can be
transient forms.
more easily understood as the work done by the fluid just outside
the system on the adjacent fluid entering the system to force or
STORED ENERGY push it into the system. Flow work also occurs as fluid leaves the
Thermal (internal) energy is caused by the motion of mole- system.
cules and/or intermolecular forces.
Flow work (per unit mass) = pv (3)
Potential energy (PE) is caused by attractive forces existing
between molecules, or the elevation of the system.
where p is the pressure and v is the specific volume, or the volume
PE = mgz (1) displaced per unit mass evaluated at the inlet or exit.
Aproperty of a system is any observable characteristic of the
where
system. The state of a system is defined by specifying the minimum
m = mass
g= local acceleration of gravity
z= elevation above horizontal reference plane
Fig. 1 Energy Flows in General Thermodynamic System
Kinetic energy (KE)is the energy caused by the velocity of mol-
ecules and is expressed as
KE = mV2/2 (2)
whereV is the velocity of a fluid stream crossing the system boundary.
Chemical energyis caused by the arrangement of atoms com-
posing the molecules.
The preparation of the first and second parts of this chapter is assigned to
TC 1.1, Thermodynamics and Psychrometrics. The third part is assigned to
TC 8.3, Absorption and Heat-Operated Machines. Fig. 1 Energy Flows in General Thermodynamic System
2.1
2.2 2009 ASHRAE Handbook—Fundamentals
set of independent properties. The most common thermodynamic
2
properties are temperature T, pressure p, and specific volume v or (cid:166)m (cid:167)u+pv+-V-----+gz(cid:183)
density (cid:85). Additional thermodynamic properties include entropy, in(cid:169) 2 (cid:185)in
stored forms of energy, and enthalpy. 2
Frequently, thermodynamic properties combine to form other –(cid:166)m (cid:167)u+pv+-V-----+gz(cid:183) +Q–W (5)
properties. Enthalpyh is an important property that includes inter- out(cid:169) 2 (cid:185)out
nal energy and flow work and is defined as = m (cid:167)u+-V-----2+gz(cid:183) –m(cid:167)u+V------2+gz(cid:183)
h(cid:123)u + pv (4) f(cid:169) 2 (cid:185)f i(cid:169) 2 (cid:185)i system
where subscripts i and f refer to the initial and final states, re-
whereuis the internal energy per unit mass.
spectively.
Each property in a given state has only one definite value, and
Nearly all important engineering processes are commonly mod-
any property always has the same value for a given state, regardless
eled as steady-flow processes. Steady flow signifies that all quanti-
of how the substance arrived at that state.
ties associated with the system do not vary with time. Consequently,
Aprocess is a change in state that can be defined as any change
ithne t hinei tpiraol paenrdti feisn aolf eaq suyilsitbermiu.m A s ptartoecse, stsh eis p daethsc (riifb iedde nbtyif isapbelcei)f,y ainngd (cid:166) m·(cid:167)h+-V-----2+gz(cid:183)
(cid:169) 2 (cid:185)
the interactions that take place across system boundaries during the all streams
process. entering
andA ficnyacl lset aitse sa opfr tohcee sssy sotre ma saerrei eids eonft ipcraol.c Teshseerse fwohree,r aeti nth teh ec oinncitliua-l – (cid:166) m·(cid:169)(cid:167)h+-V-2----2+gz(cid:185)(cid:183) +Q· –W· = 0 (6)
sion of a cycle, all the properties have the same value they had at the all streams
leaving
beginning. Refrigerant circulating in a closed system undergoes a
cycle. where h = u + pv as described in Equation (4).
Apure substance has a homogeneous and invariable chemical A second common application is the closed stationary system for
composition. It can exist in more than one phase, but the chemical which the first law equation reduces to
composition is the same in all phases.
Q – W = [m(u – u)] (7)
If a substance is liquid at the saturation temperature and pressure, f i system
it is called a saturated liquid. If the temperature of the liquid is
lower than the saturation temperature for the existing pressure, it is SECOND LAW OF THERMODYNAMICS
called either a subcooled liquid (the temperature is lower than the The second law of thermodynamics differentiates and quantifies
saturation temperature for the given pressure) or a compressed liq-
processes that only proceed in a certain direction (irreversible) from
uid (the pressure is greater than the saturation pressure for the given
those that are reversible. The second law may be described in sev-
temperature).
eral ways. One method uses the concept of entropy flow in an open
When a substance exists as part liquid and part vapor at the sat-
system and the irreversibility associated with the process. The con-
uration temperature, its quality is defined as the ratio of the mass of cept of irreversibility provides added insight into the operation of
vapor to the total mass. Quality has meaning only when the sub- cycles. For example, the larger the irreversibility in a refrigeration
stance is saturated (i.e., at saturation pressure and temperature).
cycle operating with a given refrigeration load between two fixed
Pressure and temperature of saturated substances are not indepen-
temperature levels, the larger the amount of work required to oper-
dent properties. ate the cycle. Irreversibilities include pressure drops in lines and
If a substance exists as a vapor at saturation temperature and heat exchangers, heat transfer between fluids of different tempera-
pressure, it is called a saturated vapor. (Sometimes the term dry ture, and mechanical friction. Reducing total irreversibility in a
saturated vapor is used to emphasize that the quality is 100%.) cycle improves cycle performance. In the limit of no irreversibili-
When the vapor is at a temperature greater than the saturation tem- ties, a cycle attains its maximum ideal efficiency.
perature, it is a superheated vapor. Pressure and temperature of a In an open system, the second law of thermodynamics can be
superheated vapor are independent properties, because the temper- described in terms of entropy as
ature can increase while pressure remains constant. Gases such as
air at room temperature and pressure are highly superheated vapors. (cid:71)Q
dS = -------+(cid:71)ms –(cid:71)m s +dI (8)
system T i i e e
FIRST LAW OF THERMODYNAMICS
where
The first law of thermodynamics is often called the law of con-
dS = total change within system in time dt during process
servation of energy. The following form of the first-law equation is system
(cid:71)ms = entropy increase caused by mass entering (incoming)
valid only in the absence of a nuclear or chemical reaction. i i
(cid:71)m s = entropy decrease caused by mass leaving (exiting)
Based on the first law or the law of conservation of energy, for (cid:71)Qe/Te = entropy change caused by reversible heat transfer between
any system, open or closed, there is an energy balance as system and surroundings at temperature T
dI = entropy caused by irreversibilities (always positive)
Net amount of energy = Net increase of stored Equation (8) accounts for all entropy changes in the system. Re-
added to system energy in system arranged, this equation becomes
or (cid:71)Q = T[((cid:71)mese – (cid:71)misi) + dSsys – dI] (9)
In integrated form, if inlet and outlet properties, mass flow, and
[Energy in] – [Energy out] = [Increase of stored energy in system]
interactions with the surroundings do not vary with time, the general
Figure 1 illustrates energy flows into and out of a thermodynamic equation for the second law is
system. For the general case of multiple mass flows with uniform
properties in and out of the system, the energy balance can be (cid:11)S –S(cid:12) = (cid:179) -(cid:71)---Q---+(cid:166)(cid:11)ms(cid:12) –(cid:166)(cid:11)ms(cid:12) +I (10)
written f i system rev T in out