2008 ASHRAE Handbook - Heating, Ventilating, and Air-Conditioning Systems and Equipment (I-P Edition)

853 Pages·2008·30.89 MB·English

2008 ASHRAE® HANDBOOK
Heating, Ventilating,
and
Air-Conditioning
SYSTEMS AND EQUIPMENT
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
©2008 by the American Society of Heating, Refrigerating and Air-Conditioning Engineers,
Inc. All rights reserved.
DEDICATED TO THE ADVANCEMENT OF
THE PROFESSION AND ITS ALLIED INDUSTRIES
No part of this book 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 book be reproduced, stored in a retrieval
system, or transmitted in any form or by any means—electronic, photocopying, recording,
or other—without permission in writing from ASHRAE.
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
omissions in the data should be brought to the attention of the Editor. Additions and correc-
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,
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 this publication is free of errors. The
entire risk of the use of any information in this publication is assumed by the user.
ISBN 978-1-933742-33-5
ISSN 1078-6066
The paper for this book is acid free and was manufactured with post-consumer
pulp from sources using sustainable forestry practices.
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 2008 ASHRAE Handbook—HVAC Systems and Equipment (cid:129) Chapter 27, Unit Ventilators, Unit Heaters, and Makeup Air
discusses various systems and the equipment (components or Units, has updated content on makeup air units.
assemblies) that comprise them, and describes features and differ- (cid:129) Chapter 30, Automatic Fuel-Burning Systems, extensively reor-
ences. This information helps system designers and operators in ganized and revised, contains updated information on new tech-
selecting and using equipment. An accompanying CD-ROM con- nology and code requirements.
tains all the volume’s chapters in both I-P and SI units. (cid:129) Chapter 31, Boilers, has new material on condensing boilers,
This edition includes two new chapters, described as follows: burner types, and operating and safety controls.
(cid:129) Chapter 32, Furnaces, has been thoroughly revised to reflect new
(cid:129) Chapter 16, Ultraviolet Lamp Systems, includes a review of the
technology and code requirements.
fundamentals of UVC germicidal energy’s impact on microor-
(cid:129) Chapter 34, Chimney, Vent, and Fireplace Systems, has been reor-
ganisms; how UVC lamps generate germicidal radiant energy;
ganized for clarity and has new content on designing fireplaces
common approaches to the application of UVGI systems for
and their chimneys.
upper-air room, in-duct, and surface cleansing; and a review of
(cid:129) Chapter 36, Solar Energy Equipment, has been reorganized and
human safety and maintenance issues.
has new content on photovoltaic systems and testing/rating.
(cid:129) Chapter 17, Combustion Turbine Inlet Cooling (CTIC), provides
(cid:129) Chapter 37, Compressors, has been reorganized and has updates
a detailed discussion of how CTIC is used to help improve com-
on bearings and variable-speed drive technology.
bustion turbine performance.
(cid:129) Chapter 38, Condensers, contains revised content on air-cooled
Some of the revisions and additions to the remainder of the vol- condensers, particularly on type descriptions, heat transfer, pres-
ume are as follows: sure drop, testing/rating, and installation and maintenance.
(cid:129) Chapter 40, Evaporative Air Cooling Equipment, has a rewritten
(cid:129) Chapters 1 to 5 have each been revised to include new system and section on indirect coolers.
process flow diagrams, plus new discussion content on com- (cid:129) Chapter 42, Liquid-Chilling Systems, has new discussion on both
missioning, building automation, maintenance management, sus- refrigerant selection and variable-flow chilled-water systems, as
tainability/green design, security, and various systems (e.g., well as new and improved figures.
underfloor air distribution, chilled beams). (cid:129) Chapter 44, Motors, Motor Controls, and Variable-Speed Drives,
(cid:129) Chapter 7, Combined Heat and Power Systems, formerly entitled has updates for new technology and codes.
Cogeneration Systems and Engine and Turbine Drives, was reor- (cid:129) Chapter 48, Unitary Air Conditioners and Heat Pumps, has new
ganized, as well as updated for new technology. content on multisplit units, variable-refrigerant-flow (VRF) equip-
(cid:129) Chapter 11, District Heating and Cooling, has new guidance on ment, certification, and sustainability.
construction cost considerations, central plants, and distribution
This volume is published, both as a bound print volume and in
systems.
electronic format on a CD-ROM, in two editions: one using inch-
(cid:129) Chapter 12, Hydronic Heating and Cooling, has revised text and
pound (I-P) units of measurement, the other using the International
figures on all aspects of system design, including design pro-
System of Units (SI).
cedure, water temperatures, heat transfer, distribution losses,
Corrections to the 2005, 2006, and 2007 Handbook volumes can
constant- and variable-speed pumping, sizing control valves, and
be found on the ASHRAE Web site at http://www.ashrae.org and in
terminal units.
the Additions and Corrections section of this volume. Corrections
(cid:129) Chapter 18, Duct Construction, has new guidance for installation
for this volume will be listed in subsequent volumes and on the
of flexible ducts.
ASHRAE Web site.
(cid:129) Chapter 19, Room Air Distribution Equipment, was reorganized Reader comments are enthusiastically invited. To suggest im-
to coordinate with its companion chapter in HVAC Applications, provements for a chapter, please comment using the form on the
with added content on equipment for stratified and partially strat- ASHRAE Web site or, using one of the cutout comment pages at
ified systems. the end of this volume’s index, write to Handbook Editor,
(cid:129) Chapter 24, Mechanical Dehumidifiers and Related Compo- ASHRAE, 1791 Tullie Circle, Atlanta, GA 30329, or fax 678-539-
nents, has new content on installation and service, indoor pool 2187, or e-mail mowen @ashrae.org.
dehumidifiers, and application considerations for various equip-
ment types.
(cid:129) Chapter 26, Air-Heating Coils, has new text on installation guide- Mark S. Owen
lines. 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.
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 Plants 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
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
47. Sound and Vibration Control
19. Textile Processing Plants
48. Water Treatment
20. Photographic Material Facilities
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
CD-ROM with all content from 2008 HVAC Systems and Equipment volume inside back cover
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
18. Poultry Products 44. Refrigerant-Control Devices
19. Fishery Products 45. Factory Dehydrating, Charging, and Testing
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
2005 FUNDAMENTALS
THEORY 23. Thermal and Moisture Control in Insulated
Assemblies—Fundamentals
Chapter 1. Thermodynamics and Refrigeration Cycles
2. Fluid Flow 24. Thermal and Moisture Control in Insulated
Assemblies—Applications
3. Heat Transfer
4. Two-Phase Flow 25. Thermal and Water Vapor Transmission Data
5. Mass Transfer 26. Insulation for Mechanical Systems
6. Psychrometrics
LOAD AND ENERGY CALCULATIONS
7. Sound and Vibration
Chapter 27. Ventilation and Infiltration
GENERAL ENGINEERING INFORMATION 28. Climatic Design Information
Chapter 8. Thermal Comfort 29. Residential Cooling and Heating Load Calculations
9. Indoor Environmental Health 30. Nonresidential Cooling and Heating Load
10. Environmental Control for Animals and Plants Calculations
11. Physiological Factors in Drying and Storing 31. Fenestration
Farm Crops 32. Energy Estimating and Modeling Methods
12. Air Contaminants
13. Odors DUCT AND PIPE DESIGN
14. Measurement and Instruments
Chapter 33. Space Air Diffusion
15. Fundamentals of Control
34. Indoor Environmental Modeling
16. Airflow Around Buildings
35. Duct Design
BASIC MATERIALS 36. Pipe Sizing
Chapter 17. Energy Resources
GENERAL
18. Combustion and Fuels
19. Refrigerants Chapter 37. Abbreviations and Symbols
20. Thermophysical Properties of Refrigerants 38. Units and Conversions
21. Physical Properties of Secondary Coolants (Brines) 39. Physical Properties of Materials
22. Sorbents and Desiccants 40. Codes and Standards
LICENSE AGREEMENT
2008 ASHRAE Handbook—HVAC Systems and Equipment CD-ROM
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which is available at www.ashrae.org.
CONTENTS
Contributors vii
ASHRAE Technical Committees, Task Groups, and Technical Resource Groups ix
ASHRAE Research: Improving the Quality of Life x
Preface x
AIR-CONDITIONING AND HEATING SYSTEMS
Chapter 1. HVAC System Analysis and Selection (TC 9.1, Large Building Air-Conditioning Systems) 1.1
2. Decentralized Cooling and Heating (TC 9.1) 2.1
3. Central Cooling and Heating (TC 9.1) 3.1
4. Air Handling and Distribution (TC 9.1) 4.1
5. In-Room Terminal Systems (TC 9.1) 5.1
6. Panel Heating and Cooling (TC 6.5, Radiant and In-Space Convective Heating and Cooling) 6.1
7. Combined Heat and Power Systems (TC 1.10, Cogeneration Systems) 7.1
8. Applied Heat Pump and Heat Recovery Systems
(TC 9.4, Applied Heat Pump/Heat Recovery Systems) 8.1
9. Design of Small Forced-Air Heating and Cooling Systems
(TC 6.3, Central Forced-Air Heating and Cooling Systems) 9.1
10. Steam Systems (TC 6.1, Hydronic and Steam Equipment and Systems) 10.1
11. District Heating and Cooling (TC 6.2, District Energy) 11.1
12. Hydronic Heating and Cooling System Design (TC 6.1) 12.1
13. Condenser Water Systems (TC 6.1) 13.1
14. Medium- and High-Temperature Water Heating Systems (TC 6.1) 14.1
15. Infrared Radiant Heating (TC 6.5) 15.1
16. Ultraviolet Lamp Systems (TC 2.9, Ultraviolet Air and Surface Treatment) 16.1
17. Combustion Turbine Inlet Cooling (TC 1.10) 17.1
AIR-HANDLING EQUIPMENT AND COMPONENTS
Chapter 18. Duct Construction (TC 5.2, Duct Design) 18.1
19. Room Air Distribution Equipment (TC 5.3, Room Air Distribution) 19.1
20. Fans (TC 5.1, Fans) 20.1
21. Humidifiers (TC 5.11, Humidifying Equipment) 21.1
22. Air-Cooling and Dehumidifying Coils (TC 8.4, Air-to-Refrigerant Heat Transfer Equipment) 22.1
23. Desiccant Dehumidification and Pressure-Drying Equipment
(TC 8.12, Desiccant Dehumidification Equipment and Components) 23.1
24. Mechanical Dehumidifiers and Related Components
(TC 8.10, Mechanical Dehumidification Equipment and Heat Pipes) 24.1
25. Air-to-Air Energy Recovery Equipment (TC 5.5, Air-to-Air Energy Recovery) 25.1
26. Air-Heating Coils (TC 8.4) 26.1
27. Unit Ventilators, Unit Heaters, and Makeup Air Units
(TC 6.1 and TC 5.8, Industrial Ventilation Systems) 27.1
28. Air Cleaners for Particulate Contaminants (TC 2.4, Particulate Air Contaminants and
Particulate Contaminant Removal Equipment) 28.1
29. Industrial Gas Cleaning and Air Pollution Control Equipment
[TC 5.4, Industrial Process Air Cleaning (Air Pollution Control)] 29.1
HEATING EQUIPMENT AND COMPONENTS
Chapter 30. Automatic Fuel-Burning Equipment (TC 6.10, Fuels and Combustion) 30.1
31. Boilers (TC 6.1) 31.1
32. Furnaces (TC 6.3) 32.1
33. Residential In-Space Heating Equipment (TC 6.5) 33.1
34. Chimney, Vent, and Fireplace Systems (TC 6.10) 34.1
35. Hydronic Heat-Distributing Units and Radiators (TC 6.1) 35.1
36. Solar Energy Equipment (TC 6.7, Solar Energy Utilization) 36.1
COOLING EQUIPMENT AND COMPONENTS
Chapter 37. Compressors (TC 8.1, Positive Displacement Compressors, and TC 8.2, Centrifugal Machines) 37.1
38. Condensers (TC 8.4, TC 8.5, Liquid-to-Refrigerant Heat Exchangers, and
TC 8.6, Cooling Towers and Evaporative Condensers) 38.1
39. Cooling Towers (TC 8.6) 39.1
40. Evaporative Air-Cooling Equipment (TC 5.7, Evaporative Cooling) 40.1
41. Liquid Coolers (TC 8.5) 41.1
42. Liquid-Chilling Systems (TC 8.1 and TC 8.2) 42.1
GENERAL COMPONENTS
43. Centrifugal Pumps (TC 6.1) 43.1
44. Motors, Motor Controls, and Variable-Speed Drives
(TC 1.11, Electric Motors and Motor Control) 44.1
45. Pipes, Tubes, and Fittings (TC 6.1) 45.1
46. Valves (TC 6.1) 46.1
47. Heat Exchangers (TC 6.1) 47.1
PACKAGED, UNITARY, AND SPLIT-SYSTEM EQUIPMENT
Chapter 48. Unitary Air Conditioners and Heat Pumps (TC 8.11, Unitary and Room Air Conditioners
and Heat Pumps) 48.1
49. Room Air Conditioners and Packaged Terminal Air Conditioners (TC 8.11) 49.1
GENERAL
50. Thermal Storage (TC 6.9, Thermal Storage) 50.1
51. Codes and Standards 51.1
Additions and Corrections A.1
Index
Composite index to the 2005 Fundamentals, 2006 Refrigeration, 2007 HVAC Applications, and
2008 HVAC Systems and Equipment volumes I.1
CHAPTER 2
DECENTRALIZED COOLING AND HEATING
System Characteristics............................................................... 2.1 Residential and Light Commercial Split Systems....................... 2.6
Design Considerations............................................................... 2.2 Commercial Self-Contained (Floor-by-Floor) Systems............. 2.6
Window-Mounted and Through-the-WallRoom Commercial Outdoor Packaged Systems.................................... 2.8
HVAC Units and Air-Cooled Heat Pumps............................. 2.3 Automatic Controls and Building Management Systems........... 2.9
Water-Source Heat Pump Systems............................................. 2.4 Maintenance Management......................................................... 2.9
Multiple-Unit Systems................................................................ 2.4 Building System Commissioning................................................ 2.9
FOR MOST small to mid-size installations, decentralized cool- These limitations make manufacture of low-cost, quality-controlled,
ing and heating is usually preferable to a centralized system factory-tested products practical. For a particular kind and capacity
(see Chapter 3). Frequently classified as packaged unit systems (al- of unit, performance characteristics vary among manufacturers. All
though many are far from being a single packaged unit), decentral- characteristics should be carefully assessed to ensure that the equip-
ized systems can be found in almost all classes of buildings. They ment performs as needed for the application. Several trade associa-
are especially suitable for smaller projects with no central plant, tions have developed standards by which manufacturers may test and
where low initial cost and simplified installation are important. rate their equipment. See Chapters 48 and 49 for more specific infor-
These systems are installed in office buildings, shopping centers, mation on pertinent industry standards and on decentralized cooling
manufacturing plants, schools, health care facilities, hotels, motels, and heating equipment used in multiple-packaged unitary systems.
apartments, nursing homes, and other multiple-occupancy dwell- Large commercial/industrial-grade equipment can be custom-
ings. They are also suited to air conditioning existing buildings with designed by the factory to meet specific design conditions and job
limited life or income potential. Applications also include facilities requirements. This equipment carries a higher first cost and is not
requiring specialized high performance levels, such as computer readily available in smaller sizes.
rooms and research laboratories. Self-contained units can use multiple compressors to control
Although some of the equipment addressed here can be refrigeration capacity. For variable-air-volume (VAV) systems,
applied as a single unit, this chapter covers applying multiple compressors are turned on or off or unloaded to maintain discharge
units to form a complete air-conditioning system for a building air temperature. As zone demand decreases, the temperature of air
and the distribution associated with some of these systems. For leaving the unit can often be reset upward so that a minimum ven-
guidance on HVAC system selection, see Chapter 1. tilation rate is maintained.
Multiple packaged-unit systems for perimeter spaces are fre-
SYSTEM CHARACTERISTICS quently combined with a central all-air or floor-by-floor system.
These combinations can provide better humidity control, air purity,
Decentralized systems can be one or more individual HVAC
and ventilation than packaged units alone. Air-handling systems
units, each with an integral refrigeration cycle, heating source, and
may also serve interior building spaces that cannot be conditioned
direct or indirect outside air ventilation. Components are factory-
by wall or window-mounted units.
designed and assembled into a package that includes fans, filters,
For supplementary data on air-side design of decentralized sys-
heating source, cooling coil, refrigerant compressor(s), controls,
tems, see Chapter 4.
and condenser. Equipment is manufactured in various configura-
tions to meet a wide range of applications. Examples of decentral- Advantages
ized HVAC equipment include the following:
(cid:129) Heating and cooling can be provided at all times, independent of
• Window air conditioners the mode of operation of other building spaces.
(cid:129) Through-the-wall room HVAC units (cid:129) Manufacturer-matched components have certified ratings and
(cid:129) Air-cooled heat pump systems performance data.
(cid:129) Water-cooled heat pump systems (cid:129) Assembly by a manufacturer helps ensure better quality control
(cid:129) Multiple-unit systems and reliability.
(cid:129) Residential and light commercial split systems (cid:129) Manufacturer instructions and multiple-unit arrangements sim-
(cid:129) Self-contained (floor-by-floor) systems plify installation through repetition of tasks.
(cid:129) Outside package systems (cid:129) Only one zone of temperature control is affected if equipment
(cid:129) Packaged, special-procedure units (e.g., for computer rooms) malfunctions.
(cid:129) The system is readily available.
For details on window air conditioners and through-the-wall
(cid:129) One manufacturer is responsible for the final equipment package.
units, see Chapter 49; the other examples listed here are discussed
(cid:129) For improved energy control, equipment serving vacant spaces
further in Chapter 48. (Multiple-unit systems are also covered in
can be turned off locally or from a central point, without affecting
Chapter 4.)
occupied spaces.
Commercial-grade unitary equipment packages are available
(cid:129) System operation is simple. Trained operators are not usually
only in preestablished increments of capacity with set performance
required.
parameters, such as the sensible heat ratio at a given room condition
(cid:129) Less mechanical and electrical room space is required than with
or the airflow per ton of refrigeration capacity. Components are
matched and assembled to achieve specific performance objectives. central systems.
(cid:129) Initial cost is usually low.
(cid:129) Equipment can be installed to condition one space at a time as a
The preparation of this chapter is assigned to TC 9.1, Large Building Air- building is completed, remodeled, or as individual areas are occu-
Conditioning Systems. pied, with favorable initial investment.
2.1
2.2 2008 ASHRAE Handbook—HVAC Systems and Equipment
(cid:129) Energy can be metered directly to each tenant. Advantages
(cid:129) Air- or water-side economizers may be applicable, depending on
(cid:129) Substantially reduces compressor, cooling tower, and condenser
type of decentralized system used.
water pump energy requirements, generally saving more energy
Disadvantages than a water-side economizer.
(cid:129) Has a lower air-side pressure drop than a water-side economizer.
(cid:129) Performance options may be limited because airflow, cooling coil
(cid:129) Reduces tower makeup water and related water treatment.
size, and condenser size are fixed.
(cid:129) May improve indoor air quality by providing large amounts of
(cid:129) Larger total building installed cooling capacity is usually required
outside air during mild weather.
because diversity factors used for moving cooling needs do not
apply to dedicated packages. Disadvantages
(cid:129) Temperature and humidity control may be less stable, especially
(cid:129) In systems with larger return air static pressure requirements,
with mechanical cooling at very low loads.
return or exhaust fans are needed to properly exhaust building air
(cid:129) Standard commercial units are not generally suited for large per-
and take in outside air.
centages of outside air or for close humidity control. Custom or
(cid:129) If the unit’s leaving air temperature is also reset up during the air-
special-purpose equipment, such as packaged units for computer
side economizer cycle, humidity control problems may occur and
rooms, or large custom units, may be required.
the fan may use more energy.
(cid:129) Energy use is usually greater than for central systems if efficiency
(cid:129) Humidification may be required during winter.
of the unitary equipment is less than that of the combined central
(cid:129) More and/or larger air intake louvers, ducts, or shafts may be
system components.
required.
(cid:129) Low-cost cooling by outside air economizers is not always avail-
able or practical.
Water-Side Economizer
(cid:129) Air distribution control may be limited.
The water-side economizer is another option for reducing energy
(cid:129) Operating sound levels can be high, and noise-producing
use. ASHRAE Standard 90.1 addresses its application, as do some
machinery is often closer to building occupants than with cen-
state energy codes. The water-side economizer consists of a water
tral systems.
coil in a self-contained unit upstream of the direct-expansion cool-
(cid:129) Ventilation capabilities are fixed by equipment design.
ing coil. All economizer control valves, piping between economizer
(cid:129) Equipment’s effect on building appearance can be unappealing.
coil and condenser, and economizer control wiring can be factory
(cid:129) Air filtration options may be limited.
installed.
(cid:129) Discharge temperature varies because of on/off or step control.
The water-side economizer uses the low cooling tower or evapo-
(cid:129) Condensate drain is required with each air-conditioning unit.
rative condenser water temperature to either (1) precool entering air,
(cid:129) Maintenance may be difficult or costly because of multiple pieces
(2) assist mechanical cooling, or (3) provide total system cooling if
of equipment and their location.
the cooling water is cold enough. If the economizer is unable to main-
tain the air-handling unit’s supply air or zone set point, factory-
DESIGN CONSIDERATIONS
mounted controls integrate economizer and compressor operation to
Rating classifications and typical sizes for equipment addressed meet cooling requirements. For constant condenser water flow con-
in this chapter can be found in Chapters 48 and 49, which also trol using a economizer energy recovery coil and the unit condenser,
address available components, equipment selection, distribution two control valves are factory-wired for complementary control, with
piping, and ductwork. one valve driven open while the other is driven closed. This keeps
Selection of a decentralized system should follow guidance pro- water flow through the condenser relatively constant. In variable-
vided in Chapter 1. The design engineer can use the HVAC system flow control, condenser water flow varies during unit operation. The
analysis selection matrix to analytically assess and select the opti- valve in bypass/energy recovery loop is an on/off valve and is closed
mum decentralized system for the project. Combined with the when the economizer is enabled. Water flow through the economizer
design criteria in Chapters 48 and 49, the basis of design can be coil is modulated by its automatic control valve, allowing variable
documented. cooling water flow as cooling load increases (valve opens) and
Unlike centralized cooling and heating equipment, capacity reduced flow on a decrease in cooling demand. If the economizer is
diversity is limited with decentralized equipment, because each unable to satisfy the cooling requirements, factory-mounted controls
piece of equipment must be sized for peak capacity. integrate economizer and compressor operation. In this operating
Noise from this type of equipment may be objectionable and mode, the economizer valve is fully open. When the self-contained
should be checked to ensure it meets sound level requirements. Chap- unit is not in cooling mode, both valves are closed. Reducing or elim-
ter 47 of the 2007 ASHRAE Handbook—HVAC Applications has inating cooling water flow reduces pumping energy.
more information on HVAC-related sound and vibration concerns.
Advantages
Air-Side Economizer (cid:129) Compressor energy is reduced by precooling entering air. Often,
With some decentralized systems, an air-side economizer is an op- building load can be completely satisfied with an entering con-
tion, if not an energy code requirement (check state code for criteria). denser water temperature of less than 55°F. Because the wet-bulb
The air-side economizer uses cool outside air to either assist mechan- temperature is always less than or equal to the dry-bulb tempera-
ical cooling or, if the outside air is cool enough, provide total cooling. ture, a lower discharge air temperature is often available.
It requires a mixing box designed to allow 100% of the supply air to (cid:129) Building humidification does not affect indoor humidity by intro-
be drawn from outside. It can be a field-installed accessory that in- ducing outside air.
cludes an outside air damper, relief damper, return air damper, filter, (cid:129) No external wall penetration is required for exhaust or outside air
actuator, and linkage. Controls are usually a factory-installed option. ducts.
Self-contained units usually do not include return air fans. A (cid:129) Controls are less complex than for air-side economizers, because
barometric relief, fan-powered relief fan, or return/exhaust fan may they are often inside the packaged unit.
be provided as an air-side economizer. The relief fan is off and dis- (cid:129) The coil can be mechanically cleaned.
charge/exhaust dampers are closed when the air-side economizer is (cid:129) More net usable floor area is available because large outside and
inactive. relief air ducts are unnecessary.