Advanced Variable Air Volume System Design Guide

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CALIFORNIA ENERGY
COMMISSION
Advanced Variable Air Volume
System Design Guide
DESIGN GUIDELINES
October 2003
500-03-082-A-11
Gray Davis, Governor

CALIFORNIA
ENERGY
COMMISSION
Prepared By:
Taylor Engineering
Mark Hydeman
Steve Taylor
Jeff Stein
Eley Associates
Erik Kolderup
Tianzhen Hong
Managed By:
New Buildings Institute
Cathy Higgins,
Program Director
White Salmon, WA
CEC Contract No. 400-99-013
Prepared For:
Donald Aumann,
Contract Manager
Nancy Jenkins,
PIER Buildings Program Manager
Terry Surles,
PIER Program Director
Robert L. Therkelsen
Executive Director
DISCLAIMER
This report was prepared as the result of work sponsored by the
California Energy Commission. It does not necessarily represent
the views of the Energy Commission, its employees or the State
of California. The Energy Commission, the State of California, its
employees, contractors and subcontractors make no warrant,
express or implied, and assume no legal liability for the
information in this report; nor does any party represent that the
uses of this information will not infringe upon privately owned
rights. This report has not been approved or disapproved by the
California Energy Commission nor has the California Energy
Commission passed upon the accuracy or adequacy of the
information in this report.

Advanced VAV System Design Guide Acknowledgements
i
Acknowledgements
Project Director: Erik Kolderup, Eley Associates.
Principal Investigator: Mark Hydeman, Taylor Engineering.
Research Team: Steve Taylor and Jeff Stein, Taylor Engineering; Tianzhen
Hong and John Arent, Eley Associates.
Editing and Document Production: Kimberly Got, Zelaikha Akram, and
Debra Janis, Eley Associates.
Review and Advisory Committee: Karl Brown, CIEE; David Claridge,
Texas A&M; Paul Dupont, Dupont Engineering; Ken Gillespie, Pacific Gas &
Electric; Tom Hartman, the Hartman Company; Henry Lau, Southern
California Edison; and David Sellers, PECI, Inc.
Project Management: Cathy Higgins, Program Director for the New
Buildings Institute and Don Aumann, Contract Manager for the California
Energy Commission. Additional review was provided by Alan Cowan and Jeff
Johnson, New Buildings Institute.

Advanced VAV System Design Guide Preface
ii
Preface
The Advanced Variable Air Volume (VAV) System Design Guide (Design
Guide) provides a powerful new resource for Heating, Ventilation, and Air-
Conditioning (HVAC) designers. It presents brand new information on fan
selection and modeling and provides the most current recommendations on
VAV airside system design.
Total large office building energy savings of up to
12% are achievable by applying the
recommendations in the Design Guide resulting in
an estimated annual statewide savings of 2,220
MWh/yr for new large office construction.
The Design Guide is a product of a three-year
research project that included field monitoring of five sites with built-up VAV
systems. It contains measures and recommendations from a range of sources
including our research, associated research1, ASHRAE Guidelines and
Standards, Title 24, team experience gained in the design and commissioning
of mechanical systems and controls for commercial buildings and in
performing peer reviews of mechanical designs of commercial buildings.
Throughout this document we refer to standard practice. This is a subjective
benchmark that is determined based on our experience as mechanical
engineers, reviewing the work of other firms, and through our conversations
with manufacturers and contractors.
The Advanced VAV System Design Guide was developed as part of the
Integrated Energy Systems — Productivity and Building Science project, a
Public Interest Energy Research (PIER) program administered by the
California Energy Commission under contract No. 400-99-013, and managed
by the New Buildings Institute.
The Buildings Program Area within the PIER Program produced this Design
Guide. The program includes new and existing buildings in both the
residential and the non-residential sectors. It seeks to decrease building
energy use through research that will develop or improve energy efficient
technologies, strategies, tools, and building performance evaluation methods.
This document is part of report #P500-03-082 (Attachment A-11 Product
3.6.2).. For other reports produced within this contract or to obtain more
information on the PIER Program, please see Project Reports in Appendix 7,
visit www.energy.ca.gov/pier/buildings or contact the Commission’s
Publications Unit at 916-654-5200. The Design Guide is also available at
www.newbuildings.org
1 PIER, ASHRAE, CBE and others
…a powerful new resource
for heating,ventilation, and
air conditioning designers.

Advanced VAV System Design Guide Abstract
iii
Abstract
The Advanced Variable Air Volume (VAV) System Design Guide (Design
Guide) is written for Heating, Ventilation, and Air-Conditioning (HVAC)
designers and focuses on built-up VAV systems in multi-story commercial
office buildings in California.
The Design Guide recommendations include best practices for airside system
design, covering fans, air handlers, ducts, terminal units, diffusers, and
controls, with emphasis on getting the air distribution system components to
work together in an integrated fashion. Key topics critical to optimal VAV
design and performance are addressed in the following chapters: 1) early
design issues, 2) zone issues, 3) VAV box selection, 4) duct design, 5) supply
air temperature reset, 5) fan type, size and control, 6) coils and filters, and 7)
outdoor air, return air and exhaust air. The intent of the information is to
promote efficient, practical designs that advance standard practice, achieve
cost effective energy savings and can be implemented using current
technology.
Author: Mark Hydeman, Steve Taylor, Jeff Stein, Taylor Engineering. Erik
Kolderup, Eley Associates
Keywords: Variable Air Volume, VAV, HVAC, Fans, Ducts, Commercial
Building, Distribution System, Energy Savings

Advanced VAV System Design Guide Abstract
iv

Advanced VAV System Guideline Table of Contents
v
TABLE OF CONTENTS
ACKNOWLEDGEMENTS ..........................................................................................................................I
PREFACE .................................................................................................................................................... II
ABSTRACT ................................................................................................................................................III
OVERVIEW ................................................................................................................................................. 1
AUDIENCE & OBJECTIVES ........................................................................................................................... 1
KEY RECOMMENDATIONS ........................................................................................................................... 1
ENERGY IMPACTS........................................................................................................................................ 4
DESIGN GUIDE ORGANIZATION ................................................................................................................... 5
INTRODUCTION ........................................................................................................................................ 9
OBJECTIVE .................................................................................................................................................. 9
ROLE OF THE DESIGNER ............................................................................................................................ 10
MARKET SHARE ........................................................................................................................................ 10
EARLY DESIGN ISSUES......................................................................................................................... 13
INTEGRATED DESIGN ISSUES ..................................................................................................................... 13
THE ROLE OF SIMULATION IN DESIGN....................................................................................................... 15
HVAC SYSTEM SELECTION ...................................................................................................................... 21
LOCATION AND SIZE OF AIRSHAFTS .......................................................................................................... 27
RETURN AIR SYSTEM ................................................................................................................................29
AUXILIARY LOADS.................................................................................................................................... 31
DESIGN AIRSIDE SUPPLY TEMPERATURE .................................................................................................. 32
CODE VENTILATION REQUIREMENTS ........................................................................................................ 34
DETERMINING INTERNAL LOADS .............................................................................................................. 35
SIMULATION AND PERFORMANCE TARGETS.............................................................................................. 46
ZONE ISSUES............................................................................................................................................ 49
THERMAL COMFORT ................................................................................................................................. 49
ZONING AND THERMOSTATS ..................................................................................................................... 50
DEMAND CONTROL VENTILATION (DCV) ................................................................................................ 51
OCCUPANCY CONTROLS............................................................................................................................ 54
WINDOW SWITCHES .................................................................................................................................. 54
DESIGN OF CONFERENCE ROOMS.............................................................................................................. 55
VAV BOX SELECTION ........................................................................................................................... 57
VAV BOX SELECTION SUMMARY ............................................................................................................. 57
VAV REHEAT BOX CONTROL ................................................................................................................... 58
MINIMUM AIRFLOW SETPOINTS ................................................................................................................. 61
SIZING VAV REHEAT BOXES .................................................................................................................... 68
OTHER BOX TYPES.................................................................................................................................... 73
OTHER ISSUES ........................................................................................................................................... 79
DUCT DESIGN .......................................................................................................................................... 83
GENERAL GUIDELINES .............................................................................................................................. 83
SUPPLY DUCT SIZING ................................................................................................................................88
RETURN AIR SYSTEM SIZING .................................................................................................................... 92
FAN OUTLET CONDITIONS......................................................................................................................... 93

Advanced VAV System Guideline Table of Contents
vi
NOISE CONTROL........................................................................................................................................ 95
SUPPLY AIR TEMPERATURE CONTROL ......................................................................................... 99
OPTIMAL SUPPLY AIR TEMPERATURE ....................................................................................................... 99
RECOMMENDED SEQUENCE OF OPERATION ............................................................................................ 101
SYSTEM DESIGN ISSUES .......................................................................................................................... 102
CODE REQUIREMENTS ............................................................................................................................. 103
FAN TYPE, SIZE AND CONTROL ......................................................................................................105
FAN SELECTION CRITERIA....................................................................................................................... 105
VISUALIZING FAN PERFORMANCE........................................................................................................... 110
FAN SELECTION CASE STUDIES ............................................................................................................... 116
COMPARING MANUFACTURERS............................................................................................................... 136
FAN CONTROL......................................................................................................................................... 137
CONCLUSIONS ......................................................................................................................................... 145
COILS AND FILTERS............................................................................................................................ 147
CONSTRUCTION FILTERS ......................................................................................................................... 147
PRE-FILTERS ........................................................................................................................................... 147
FINAL FILTER SELECTION........................................................................................................................ 147
FILTER AREA........................................................................................................................................... 148
EXTENDED SURFACE AREA FILTERS ....................................................................................................... 148
MONITORING FILTERS ............................................................................................................................. 148
COIL SELECTION ..................................................................................................................................... 148
COIL BYPASS........................................................................................................................................... 150
OUTSIDE AIR/RETURN AIR/EXHAUST AIR CONTROL.............................................................. 151
CONTROL OF MINIMUM OUTDOOR AIR FOR VAV SYSTEMS. ................................................................... 151
DESIGN OF AIRSIDE ECONOMIZER SYSTEMS ........................................................................................... 159
ECONOMIZER TEMPERATURE CONTROL .................................................................................................. 163
ECONOMIZER HIGH-LIMIT SWITCHES ..................................................................................................... 164
APPENDIX 1 – MONITORING SITES................................................................................................. 166
SITE 1...................................................................................................................................................... 166
SITE 2...................................................................................................................................................... 169
SITE 3...................................................................................................................................................... 172
SITE 4...................................................................................................................................................... 174
SITE 5...................................................................................................................................................... 177
APPENDIX 2 – MEASURED FAN PERFORMANCE ........................................................................ 180
ENERGY BENCHMARK DATA................................................................................................................... 180
APPENDIX 3 – AIRFLOW IN THE REAL WORLD.......................................................................... 186
APPENDIX 4 – COOLING LOADS IN THE REAL WORLD ........................................................... 194
APPENDIX 5 – DOE-2 FAN CURVES.................................................................................................. 198
APPENDIX 6 – SIMULATION MODEL DESCRIPTION.................................................................. 200
ASSUMPTIONS ......................................................................................................................................... 200
RESULTS.................................................................................................................................................. 202
APPENDIX 7 – REFERENCES.............................................................................................................. 208
GENERAL ................................................................................................................................................ 208
CONTROLS............................................................................................................................................... 209

Advanced VAV System Guideline Table of Contents
vii
SUPPLY AIR TEMPERATURE .................................................................................................................... 209
NIGHT FLUSHING .................................................................................................................................... 209
LOAD CALCULATIONS............................................................................................................................. 209
VAV BOX SIZING.................................................................................................................................... 210
FANS AND FAN SYSTEMS ........................................................................................................................ 210
FILTERS ................................................................................................................................................... 211
OUTSIDE AIR DAMPERS .......................................................................................................................... 211
CO2 AND DCV ........................................................................................................................................ 212
PROJECT REPORTS................................................................................................................................... 212
LIST OF FIGURES
Figure 1. San Francisco ................................................................................................................. 5
Figure 2. Sacramento..................................................................................................................... 5
Figure 3. Overview of Guideline Contents ................................................................................... 6
Figure 4 – Commercial New Construction Breakdown Forecast by Floor Area, Total
157,000,000 ft2/yr. Source: California Energy Commission .............................................. 11
Figure 5. The Role of Simulation in Design ............................................................................... 18
Figure 6. Measured System Airflow, Site 3................................................................................ 20
Figure 7. Measured Cooling Delivered by Air Handler, Site 3 (Light bar includes Aug-Oct
2002, dark bar covers Nov 2002 – Jan 2003) ...................................................................... 20
Figure 8. Typical Duct Shaft with Unducted Return ................................................................ 28
Figure 9. Typical Duct Riser ....................................................................................................... 29
Figure 10. Measured Lighting Schedules (90th percentile for design load calculation and 50th
percentile for energy simulations) for Small, Medium and Large Office Buildings –
ASHRAE 1093-RP................................................................................................................. 38
Figure 11. Measured Weekday Lighting Profile – Site 1 Office Area Showing Average (line)
and Min/Max (dashes) .......................................................................................................... 40
Figure 12. Measured Weekend Lighting Profile – Site 1 Office Area Showing Average (line)
and Min/Max (dashes) .......................................................................................................... 40
Figure 13. Office Equipment Load Factor Comparison – Wilkins, C.K. and N. McGaffin.
ASHRAE Journal 1994 - Measuring computer equipment loads in office buildings ....... 41
Figure 14. Measured Equipment Schedules (90th percentile for design load calculations and
50th percentile for energy simulations) for Small, Medium and Large Office Buildings –
ASHRAE 1093-RP................................................................................................................. 44
Figure 15. Measured Weekday Profile of Plug Power Density – Site 1 Office Area Showing
Average (line) and Min/Max (dashes).................................................................................. 45
Figure 16. Measured Weekend Profile of Plug Power Density – Site 1 Office Area Showing
Average (line) and Min/Max (dashes).................................................................................. 45
Figure 17. Measured Weekday Plug Load Profile of Site 5 (November 1999 – September
2000) Source: Naoya Motegi and Mary Ann Piette, “From Design Through Operations:
Multi-Year Results from a New Construction Performance Contract”, 2002 ACEEE
Summer Study ...................................................................................................................... 46
Figure 18. CalArch Benchmarking Tool Results, Office Building Electricity Use Intensity,
PG&E and SCE Data (indicated by different colors) for Total of 236 Buildings .............. 48
Figure 19. CalArch Benchmarking Tool Results, Office Building Gas Use Intensity, PG&E
Data for Total of 43 Buildings.............................................................................................. 48
Figure 20. Measured CO2 Levels At Site #4 on February 7th, 2003.......................................... 54
Figure 21. VAV Hot Water Reheat Box Control - Single Maximum ........................................ 58
Figure 22. VAV Hot Water Reheat Box – Dual Maximum........................................................ 60
Figure 23. Sample VAV Box Inlet Sensor Performance Chart, CFM vs. Velocity Pressure
Signal..................................................................................................................................... 67

Advanced VAV System Guideline Table of Contents
viii
Figure 24. Site 3 VAV Box Demand, 7am Monday August 5, 2002.......................................... 71
Figure 25. Site 3 VAV Box Demand, 9am Monday August 5, 2002.......................................... 71
Figure 26. Site 3 VAV Box Demand, 5pm Monday August 5, 2002.......................................... 72
Figure 27. Dual Duct - From Cooling to Heating....................................................................... 73
Figure 28. Dual Duct - From Heating to Cooling....................................................................... 74
Figure 29. Dual Duct Mixing - From Cooling to Heating .......................................................... 75
Figure 30. Dual Duct Mixing - From Heating to Cooling .......................................................... 75
Figure 31. Examples of Poor and Better Duct Design ............................................................... 85
Figure 32. Pressure Drop Through Elbows ................................................................................ 86
Figure 33. Pressure Drop Through Rectangular Tees............................................................... 87
Figure 34. Pressure Drop Through Duct Taps ........................................................................... 88
Figure 35. Example of Duct Sizing Using the Friction Rate Reduction Method ..................... 90
Figure 36. Poor Discharge Configuration Resulting in Significant Fan System Effect .......... 94
Figure 37. Measured Pressure in a System with Significant Fan and Duct System Effect ... 95
Figure 38. Comparison of Hot Day Simulation Results for Three Supply Air Temperature
Setpoints: 50°F, 55°F, and 60°F. August 18. Sacramento Climate. ................................ 100
Figure 39 – Comparison of Mild Day Simulation Results for Three Supply Air Temperature
Setpoints: 50°F, 55°F, and 60°F. March 4. Sacramento Climate..................................... 101
Figure 40. Recommended Supply Air Temperature Reset Method ........................................ 102
Figure 41. A Typical Manufacturer’s Fan Curve (60" Plenum Fan)....................................... 110
Figure 42. Three-Dimensional Fan Curve for 66" Plenum Airfoil Fan .................................. 111
Figure 43. Three-Dimensional Fan Curve for 49" Housed Airfoil Fan................................... 111
Figure 44. Gamma Curve .......................................................................................................... 112
Figure 45. Gamma Curves for Four Fan Types ....................................................................... 113
Figure 46. Gamma Curves for Several Fan Types and Sizes.................................................. 113
Figure 47. Gamma Curves for All Cook Housed Airfoil Fans ................................................. 114
Figure 48. Gamma Curves for All Greenheck Housed Airfoil Fans (Non-Surge Region Only)
.............................................................................................................................................. 114
Figure 49. Gamma Curves for Some Cook Backward Inclined Fans ..................................... 115
Figure 50. Gamma Curves for All Cook Airfoil Mixed Flow Fans .......................................... 115
Figure 51. Case Study A - Selection Software - Housed Airfoil and BI Choices.................... 117
Figure 52. Case Study A - Selection Software - Plenum and Mixed Flow Choices................ 117
Figure 53. Case Study A - Selection Software - Plenum Choices at Lower Design Pressure118
Figure 54. Case Study A - 66" Plenum Fan Design Point ....................................................... 118
Figure 55. Case Study A - 60" Plenum Fan Design Point ....................................................... 119
Figure 56. Case Study A - System Curves................................................................................ 120
Figure 57. Case Study A - Design Point Efficiency.................................................................. 120
Figure 58. Case Study A - Part Load Fan Efficiency............................................................... 121
Figure 59. Case Study A - Part Load Efficiency (Non-surge Region Only) ............................ 121
Figure 60. Case Study A - kW versus CFM.............................................................................. 122
Figure 61. Case Study A - Gamma Curves............................................................................... 123
Figure 62. Case Study A - Load Profiles................................................................................... 124
Figure 63. Case Study A Results - Perfect Static Pressure Reset .......................................... 124
Figure 64. Case Study A Results – No Static Pressure Reset................................................. 125
Figure 65. Case Study A - Acoustic Data (No Casing)............................................................. 126
Figure 66. Case Study A – Carrier Acoustic Data (With Casing) ........................................... 126
Figure 67. Case Study A - Cook Budget Prices ........................................................................ 129
Figure 68. Case Study B - Selection Software Airfoil and Plenum Fans ............................... 130
Figure 69. Case Study B - 73" Plenum Fan Curve................................................................... 130
Figure 70. Case Study B – 66” Plenum Fan Curve.................................................................. 131
Figure 71. Case Study B - Monitored Data .............................................................................. 131
Figure 72. Case Study B - Histogram of CFM ......................................................................... 132
Figure 73. Case Study B – Part Load Fan Efficiency .............................................................. 132

Advanced VAV System Guideline Table of Contents
ix
Figure 74. Case Study B Simulation Results - No Static Pressure Reset .............................. 133
Figure 75. Case Study B Simulation Results - Perfect Static Pressure Reset....................... 134
Figure 76. Plan View of Site 1 Air Handler.............................................................................. 135
Figure 77. Velocity Profile Off of Housed Fan.......................................................................... 135
Figure 78. Temtrol Plenum Fan Data ...................................................................................... 136
Figure 79. Peak Efficiency of Cook vs Greenheck Housed Airfoil Fans ................................. 137
Figure 80. SP Setpoint vs Fan System Energy ........................................................................ 138
Figure 81. Monitored Data Illustrating Static Pressure Reset............................................... 140
Figure 82. Optimal Staging (No Static Pressure Reset).......................................................... 141
Figure 83. Optimal Staging (Perfect Static Pressure Reset)................................................... 142
Figure 84. Optimal Staging Point vs. Minimum Duct Static Pressure Setpoint................... 142
Figure 85. Optimal Staging Point for Two Fan Types............................................................. 143
Figure 86. Parallel Fans in Surge............................................................................................. 143
Figure 87. "Paralleling" - High Flow......................................................................................... 144
Figure 88. "Paralleling" - Low Flow.......................................................................................... 144
Figure 89. VAV Reheat System with a Fixed Minimum outdoor air Damper Setpoint........ 152
Figure 90. Energy Balance Method of Controlling Minimum outdoor air ............................. 154
Figure 91. Return Fan Tracking ............................................................................................... 155
Figure 92. Airflow Measurement of 100% outdoor air............................................................. 156
Figure 93. Injection Fan with Dedicated Minimum outdoor air Damper .............................. 157
Figure 94. Minimum outdoor air Damper With Pressure Control ........................................ 158
Figure 95. Airside Economizer Configuration with Barometric Relief from ASHRAE
Guideline 16-2003 ............................................................................................................... 160
Figure 96. Airside Economizer Configuration with Relief Fan from ASHRAE Guideline 16-
2003...................................................................................................................................... 161
Figure 97. Airside Economizer Configuration with Return Fan from ASHRAE Guideline 16-
2003...................................................................................................................................... 163
Figure 98. Airside Economizer Control Staging from ASHRAE Guideline 16-2003 ............ 163
Figure 99. Electronic Enthalpy High Limit Controller. ......................................................... 165
Figure 100. Site #1 – Office Building in San Jose.................................................................... 166
Figure 101. Site 1, Monitored HVAC Electricity End Uses .................................................... 168
Figure 102. Site 1, Monitored HVAC Electricity End Uses .................................................... 169
Figure 103. Site #2 – Speculative Office Building in San Jose, CA........................................ 169
Figure 104. Relief Fan (one of six per penthouse).................................................................... 171
Figure 105. Relief Fan Discharge ............................................................................................. 171
Figure 106. Site #3 – Southwest Corner View (Main Entrance)............................................. 172
Figure 107. Site #3 – Northwest View...................................................................................... 172
Figure 108 – Monitored Cooling Loads for a Sample of Three Interior Zones, Site 3 (Office)
.............................................................................................................................................. 174
Figure 109. Site #4 – Federal Courthouse at Sacramento ...................................................... 174
Figure 110. Site #5 – Office Building in Oakland.................................................................... 177
Figure 111. Buildings Summary (Source: Naoya Motegi, LBNL)........................................... 178
Figure 112. Peak Day Fan Electric Demand, Three Sites....................................................... 182
Figure 113. Peak Day Electric Demand, Site 1, 9/3/2002 (Cumulative Graph; Total Peak is
3.9 W/ft2).............................................................................................................................. 182
Figure 114. Peak Day Electric Demand, Site 2, 8/9/2002 (Cumulative Graph; Total Peak is
6.4 W/ft2).............................................................................................................................. 183
Figure 115. Comparison of Fan and Chiller Energy at Site 1 (Cumulative Graph, e.g.
Combined Total is 0.30 kWh/ft2-yr in July)....................................................................... 183
Figure 116. Comparison of Fan and Chiller Energy at Site 2 (Cumulative Graph, e.g.
Combined Total is 0.34 kWh/ft2-yr in July)....................................................................... 184
Figure 117. Site 3, Sample of Interior Zones, Warm Period (8/8/02 - 9/7/02)......................... 187
Figure 118. Site 3, Sample of Interior Zones, Cool Period (12/12/02-1/11/03)........................ 187

Advanced VAV System Guideline Table of Contents
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Figure 119. Site 4, Sample of Interior Zones (10/18/02-2/24/03)............................................. 188
Figure 120. Site 3, Sample of Perimeter Zones, Warm Period (8/8/02 - 9/7/02)..................... 189
Figure 121. Site 3, Sample of Perimeter Zones, Cool Period (12/12/02-1/11/03).................... 189
Figure 122. Site 4, Sample of Perimeter Zones (10/18/02-2/24/03) ......................................... 190
Figure 123. Total System Airflow, Site 1.................................................................................. 190
Figure 124. Total System Airflow, Site 2.................................................................................. 191
Figure 125. Total System Airflow, Site 3.................................................................................. 191
Figure 126. Total System Airflow, Site 4.................................................................................. 192
Figure 127. Site 1 (Dark bar includes Jan-May 2002 and Nov-Dec 2002, light bar covers Jun-
Oct 2002).............................................................................................................................. 195
Figure 128. Site 2 (Light bar includes Jun-Oct 2002, dark bar covers Nov 2002 – Jan 2003)
.............................................................................................................................................. 195
Figure 129. Site 3 (Light bar includes Aug-Oct 2002, dark bar covers Nov 2002 – Jan 2003)
.............................................................................................................................................. 195
Figure 130. Site 4 (Dark bar includes Nov. 25, 2002 - Feb. 24, 2003) ................................... 196
Figure 131. Monitored Sensible Cooling Load for an Air Handler Serving 19 Interior Zones,
Site 4 .................................................................................................................................... 196
Figure 132. Fan Performance Curves for Simulation.............................................................. 204
Figure 133. Average Results Across All Simulation Runs ...................................................... 205
Figure 134. San Francisco ......................................................................................................... 207
Figure 135. Sacramento............................................................................................................. 207
LIST OF TABLES
Table 1: Key Recommendations ....................................................................................................2
Table 3. Simulation Results and End Use Savings Fractions .................................................................. 4
Table 4. HVAC and Architectural Coordination Issues ............................................................ 15
Table 5. Example System Selection Table.................................................................................. 24
Table 6. Tradeoffs Between Lower and Higher Supply Air Design Temperature (SAT) ........ 34
Table 7. Minimum Ventilation Rates for a Few Occupancy Types........................................... 35
Table 8. Lighting Power Allowances for Office Buildings ......................................................... 37
Table 9. EPD – US DOE Buildings Energy Databook (All States) 2002.................................. 42
Table 10. EPD – ASHRAE Standard 90.1 – 1989 Average Receptacle Power Densities (for
compliance simulations) ....................................................................................................... 43
Table 11. ASHRAE Handbook 2001 Fundamentals, Recommended EPD (note that these
values assume CRT monitors; the use of LCD monitors would result in significantly
lower values) ......................................................................................................................... 43
Table 12. UC Merced Building Energy Budgets for Classrooms, Office, and Library Buildings
................................................................................................................................................ 47
Table 13. VAV Box Minimums from Five Measured Sites........................................................ 62
Table 14. Sample Calculation of Box Minimum Flow ............................................................... 68
Table 15. VAV Box Maximum Airflows ...................................................................................... 70
Table 16. Summary of Sample Box Max and Min ..................................................................... 73
Table 17. Comparison of Dual-Duct VAV Controls.................................................................... 76
Table 18. VAV Box Turndown with Electric Reheat ................................................................. 81
Table 19. Conditions Affecting the Impact of Supply Air Temperature Reset ...................... 102
Table 20. Fan Classification ...................................................................................................... 107
Table 21. Comparison of Common VAV Supply Fan Types .................................................... 108
Table 22. Manufacturers Air Handler Selection Software Fan Data ..................................... 128
Table 23. Alternate Coil Selections for All Five Monitored Sites ........................................... 149
Table 24. Summary of Minimum outdoor air Control Strategies ........................................... 153
Table 25. High Limit Switch Requirements from Title 24. ..................................................... 164

Advanced VAV System Guideline Table of Contents
xi
Table 26. Summary of Monitoring Site Characteristics .......................................................... 166
Table 27. Office Building Energy End Use Consumption from Several Sources................... 181
Table 28. Basecase Design Air Flows ....................................................................................... 201
Table 29. Airside Control Strategies for Simulation of Standard Practice and Best Practice
.............................................................................................................................................. 203
Table 30. Simulation Results for Comparison of Standard Practice and Best Practice........ 203
Table 31. Supply Air Temperature Control Simulation Results............................................ 206

Advanced VAV System Guideline Table of Contents
xii

Advanced VAV System Guideline Overview
1
Overview
Audience & Objectives
The Advanced VAV System Design Guide (Design Guide) is written for
HVAC designers and focuses on built-up variable air volume (VAV) systems
in multi-story commercial office buildings in California. The Guidelines are
written to help HVAC designers create systems that capture the energy
savings opportunities, and at the same time feel comfortable that system
performance will meet client expectations. This is a best practices manual
developed through experience with design and commissioning of mechanical
and control systems in commercial buildings and informed by research on five
case study projects.
The recommendations address airside system design, covering fans, air
handlers, ducts, terminal units, diffusers, and their controls, with emphasis
on getting the air distribution system components to work together in an
integrated fashion.
The Design Guide promotes and employs the concept of early design decisions
and integrated design, meaning that the job of designing and delivering a
successful mechanical system is a team effort that requires careful
coordination with the other design disciplines, the contractors, the owner and
the building operators.
A primary emphasis of this manual is the
importance of designing systems and controls
to be efficient across the full range of operation.
This requires care in the sizing of the system
components (like terminal units) to make sure
that they can provide comfort and code
required ventilation while limiting the fan and
reheat energy at part load. It also requires
careful consideration of the system controls integrating the controls at the
zone to the controls at the air-handling unit and cooling/heating plants to
make the system respond efficiently to changes in demand.
The Design Guide also presents monitored data that emphasize the
importance of designing for efficient “turndown” of system capacity.
Measured cooling loads and airflows for several buildings show that both
zones and air handlers typically operate far below design capacity most of the
time.
The intent of the information is to promote efficient, practical designs that
are cost effective and can be implemented with off the shelf technology.
Key Recommendations
The Design Guide presents recommendations that are summarized per
Chapter in Table 1 below.
A primary emphasis of this
manual is the importance
of designing systems and
controls to be efficient
across the full range of
operation.

Advanced VAV System Guideline Overview
2
Table 1: Key Recommendations
Integrated
Design
1. Engage the architect and structural engineer early to coordinate shafts for
low pressure air paths.
2. Work with the architect to evaluate glazing and shading alternatives to
mitigate load, glare and radiant discomfort while providing daylight, views
and architectural pizzazz.
3. Prior to starting the mechanical design for any space, first consider the
potential to reduce or minimize the loads on each space.
4. Use simulation tools to understand the part-load performance and operating
costs of system alternatives.
5. Employ a system selection matrix to compare alternative mechanical system
designs.
6. Consider multiple air shafts for large floor plates
7. Place the air shafts close to, but not directly under, the air-handling
equipment for built-up systems.
8. Use return air plenums when possible because they reduce both energy costs
and first costs.
9. Design the HVAC system to efficiently handle auxiliary loads that operate
during off hours.
10. Select a design supply air temperature in the range of 52°F to 57°F.
11. Size interior zones for 60°F or higher supply air temperature to allow for
supply air temperature reset in mild and cold weather..
Early Design
Issues
12. Avoid overly conservative estimates of lighting and plug loads.
13. Consider demand control ventilation in any space with expected occupancy
load at or below 40 ft2/person.
Zone Issues
14. For conference rooms, use either a VAV box with a CO2 sensor to reset the
zone minimum or a series fan power box with zero minimum airflow setpoint.
15. Use a “dual maximum” control logic, which allows for a very low minimum
airflow rate during no- and low-load periods.
16. Set the minimum airflow setpoint to the larger of the lowest controllable
airflow setpoint allowed by the box and the minimum ventilation
requirement (often as low as 0.15 cfm/ft2).
VAV Box
Selection
17. For all except very noise sensitive applications, select VAV boxes for a total
(static plus velocity) pressure drop of 0.5” H2O. For most applications, this
provides the optimum energy balance.

Advanced VAV System Guideline Overview
3
18. Run ducts as straight as possible to reduce pressure drop, noise, and first
costs.
19. Use standard length straight ducts and minimize both the number of
transitions and of joints.
20. Use round spiral duct wherever it can fit within space constraints.
21. Use radius elbows rather than square elbows with turning vanes whenever
space allows.
22. Use either conical or 45° taps at VAV box connections to medium pressure
duct mains.
23. Specify sheet metal inlets to VAV boxes; do not use flex duct.
24. Avoid consecutive fittings because they can dramatically increase pressure
drop.
25. For VAV system supply air duct mains, use a starting friction rate of 0.25” to
0.30” per 100 feet. Gradually reduce the friction rate at each major juncture
or transition down to a minimum friction rate of 0.10” to 0.15” per 100 feet at
the end of the duct system.
26. For return air shaft sizing maximum velocities should be in the 800 fpm to
1200 fpm range through the free area at the top of the shaft (highest airflow
rate).
27. To avoid system effect, fans should discharge into duct sections that remain
straight for as long as possible, up to 10 duct diameters from the fan
discharge to allow flow to fully develop.
Duct Design
28. Use duct liner only as much as required for adequate sound attenuation.
Avoid the use of sound traps.
29. Use supply air temperature reset controls to avoid turning on the chiller
whenever possible.
Supply air
temperature
30. Continue to use supply air reset during moderate conditions when outdoor
air temperature is lower than about 70°F.
31. Reduce the supply air temperature to the design set point, typically about
55°F, when the outdoor air temperature is higher than about 70°F
32. Use demand-based static pressure setpoint reset to reduce fan energy up to
50%, reduce fan operation in surge, reduce noise and to improve control
stability.
Fan Type, Size
and Control
33. Use housed airfoil fans whenever possible.
34. Avoid using pre-filters.
35. Specify final filters with 80 percent to 85 percent dust spot efficiency (MERV
12).
36. Utilize the maximum available area in the air handler for filters rather than
installing blank-off panels.
37. Use extended surface filters.
38. Consider lower face velocity coil selections ranging from 400 fpm to 550 fpm
and selecting the largest coil that can reasonably fit in the allocated space.
Coils and Filters
39. Consider placing a bypass damper between coil sections where the
intermediate coil headers are located.
40. For outdoor air control use a dedicated minimum ventilation damper with
pressure control.
41. Use barometric relief if possible, otherwise relief fans (rather than return
fans) in most cases.
42. For economizer control, sequence the outdoor and return air dampers in
series rather than in tandem.
Outside
Air/Return
Air/Exhaust Air
Control
43. Specify differential drybulb control for economizers in California climates.

Advanced VAV System Guideline Overview
4
Energy Impacts
For buildings designed with the practices recommended in the Design Guide
HVAC electricity savings are estimated to be reduced 25% below standard
practice, corresponding to 12% of total building electricity consumption.
Natural gas heating savings are estimated to be 41%. Careful design could
exceed these savings. Additionally, building owners and developers can
expect reduced maintenance and improved ventilation and occupant comfort.
Expected annual savings are about 1.5 kWh/ft2 for electricity and 8.5 kBtu/ft2
for gas, with corresponding annual utility cost savings are about $0.20/ft2 for
electricity and $0.07/ft2 for gas, based on 2003 PG&E rates.2
The savings fractions for fan energy (57%),
cooling energy (14%), and heating energy
(41%) that are listed in Table 3 are based
on simulations comparing standard
practice to best practice for a 50,000 ft2
office building, with most of the savings
from supply air pressure reset controls and
sizing of VAV boxes to allow for 10%
minimum flow.
Table 2. Simulation Results and End Use Savings Fractions
Standard
Practice
Best
Practice
Savings Savings
Fraction
San Francisco (Climate Zone 3)
Cooling (kWh/yr) 111,522 89,428 22,094 19.8%
Fan (kWh/yr) 33,231 12,613 20,618 62.0%
Heating (kBtu/yr) 456,000 237,368 218,632 47.9%
Sacramento (Climate Zone 12)
Cooling (kWh/yr) 131,788 120,889 10,899 8.3%
Fan (kWh/yr) 38,158 18,432 19,726 51.7%
Heating (kBtu/yr) 528,800 347,901 180,899 34.2%
Average of San Francisco and Sacramento
Cooling (kWh/yr) 14.1%
Fan (kWh/yr) 56.9%
Heating (kBtu/yr) 41.1%
Typical vs. Best Practice Performance
Significant fan and reheat energy savings are possible through the design
strategies promoted in this Design Guide. The potential savings are
illustrated in the graphs below which present simulation results; in this
example the “Standard” case is a reasonably efficient code-complying system
and the “Best” case includes a number of the improvements suggested in this
guideline. The result of this simulation show that fan energy drops by 50% to
60%, and reheat energy reduces between 30% and 50%.
2 See the Statewide Energy Impact Report (Deliverable 3.4.1), August 2003 at URL. (tighten spacing between #
and text, like footnote #1)
HVAC electricity savings are
estimated to be 25%,
corresponding to 12% of total
building electricity
consumption.

Advanced VAV System Guideline Overview
5
This example is by no means comprehensive. For example these savings do
not include the impact of reducing duct pressure drop through careful design,
the impact of properly designing 24/7 spaces and conference rooms, or the
potential savings from demand based ventilation controls in high density
occupancies. The assumptions in this example are presented in Appendix 6 –
Simulation Model Description
Most of the savings are due to the efficient “turndown” capability of the best
practices design and the fact that HVAC systems operate at partial load
nearly all the time. The most important measures are careful sizing of VAV
boxes, minimizing VAV box supply airflow setpoints, controlling VAV boxes
using a “dual maximum” logic that allows lower airflows in the deadband
mode, and supply air pressure reset control. Together these provide
substantial fan and reheat savings because typical systems operate many
hours at minimum (yet higher than necessary) airflow. Appendix 6 provides
more details about this comparison, and the importance of turndown
capability is emphasized by examples of monitored airflow profiles in
Appendix 3 and cooling load profiles in Appendix 4.
0
1
2
3
4
Standard Best
kWh/yr/ft2
Cooling
Fan
0
2
4
6
8
10
12
Standard Bes t
kBtu/yr/f t2
Heat
Figure 1. San Francisco
0
1
2
3
4
Standard Best
kWh/yr/ft2
Cooling
Fan
0
2
4
6
8
10
12
Standard Best
kBtu/ yr /f t2
Hea t
Figure 2. Sacramento
Design Guide Organization
The Design Guide Chapters are organized around key design considerations
and components that impact the performance of VAV systems.
Appendices to the Design Guide present monitored data that emphasize the
importance of designing for efficient “turndown” of system capacity.
Measured cooling loads and airflows for several buildings show that both
zones and air handlers typically operate far below design capacity most of the
time.

Advanced VAV System Guideline Overview
6
The diagram in Figure 3 shows the Design Guide content followed by brief
descriptions of each of the Chapters.
Figure 3. Overview of Guideline Contents
Chapter Descriptions
Introduction
The HVAC designer faces many challenges in the design of a high performing
HVAC system. This chapter describes the objective of the guidelines, the role
of the designer and the market share of VAV systems in California.
Early Design Issues
According to an old adage, “An ounce of prevention is worth a pound of cure.”
This holds true for building design. An extra hour carefully spent in early
design can save weeks of time later in the process, not to mention improve
client relations, reduce construction costs, and reduce operating costs.

Advanced VAV System Guideline Overview
7
Zone Issues
Comfort is a complex sensation that reflects the heat balance between the
occupant and their environment but is tempered by personal preferences and
many other factors. This chapter covers zone design issues such as thermal
comfort, zoning, thermostats, application of CO2 sensors for demand control
ventilation, integration of occupancy controls, and issues affecting the design
of conference rooms.
VAV Box Selection
Selecting and controlling VAV reheat boxes has a significant impact on
HVAC energy use and comfort control. This chapter examines the selection
and control of VAV boxes to minimize energy usage (both fan and reheat)
while maintaining a high degree of occupant comfort. Guidelines are
provided for a range of terminal units including single duct boxes, dual-duct
boxes and fan powered terminal units.
Duct Design
Duct design is as much an art as it is a science; however, some rules of thumb
and guidelines are presented to help designers develop a cost-effective and
energy-efficient duct design.
Supply Air Temperature Control
This chapter covers the selection of the design temperature set point for VAV
systems in the climates of California. It also addresses energy efficient
control sequences for reset of supply temperature to minimize central plant,
reheat and fan energy.
Fan Type, Size and Control
A number of factors need to be considered when selecting fans, including
redundancy, duty, first cost, space constraints, efficiency, noise and surge.
This chapter discusses how to select fans for typical large VAV applications.
Information includes the best way to control single and parallel fans, as well
as presentation of two detailed fan selection case studies. Supply air pressure
reset control sequences are discussed in detail.
Coils and Filters
Selection of coils and filters needs to balance energy savings against first
costs. This chapter examines those issues as well as coil bypass dampers.
Outside Air/Return Air/Exhaust Air Control
Ventilation control is a critical issue for indoor environmental quality.
Maximizing “free” cooling through economizers is a cornerstone of energy
management. This chapter describes the design of airside economizers,
building pressurization controls, and control for code-required ventilation in a
VAV system.

Advanced VAV System Guideline Overview
8

Advanced VAV System Design Guide Introduction
9
Introduction
Objective
The intent of the Design Guide is to promote efficient, practical designs that advance
standard practice and can be implemented successfully today. The goal is having
HVAC systems that minimize life-cycle cost and can be assembled with currently
available technology by reasonably skilled mechanical contractors. In some cases, as
noted in specific sections, increased savings might be captured through more
advanced controls or with additional construction cost investment.
This document focuses on built-up VAV systems in multi-story commercial office
buildings in California or similar climates.3 But much of the information is useful for
a wider range of systems types, building types, and locations. Topics such as selection
guidelines for VAV terminal units apply equally well to systems using packaged VAV
air handlers. And recommendations on zone cooling load calculations are relevant
regardless of system type.
This guide addresses airside system design, covering fans, air handlers, ducts,
terminal units, diffusers, and their controls with emphasis on getting the air
distribution system components to work in an integrated fashion. Other research has
covered related topics that are also critical to energy efficiency such as chilled water
plant design 4 and commissioning of airside systems.5 The design of smaller packaged
HVAC systems has also been addressed through another PIER project.6
Following the practices in this Design Guide can lead to major improvements in
system performance, energy efficiency and occupant comfort.
3 California has 16 climate zones.
4 SeeCoolTools, www.hvacexchange.com/cooltools/ and the chiller analysis project www.hvacexchange.com/cooltools/CAP
5 See The Control System Design Guide and Functional Testing Guide for Air Handling Systems, available for download at
http://buildings.lbl.gov/hpcbs/FTG.
6 Small HVAC Package System Design Guide available for download at www.energy.ca.gov/pier/buildings or at
www.newbuildings.org/pier

Advanced VAV System Design Guide Introduction
10
Role of the Designer
Built-up HVAC systems are complex custom assemblies whose performance depends
on a range of players including manufacturers, design professionals, installing
contractors, Testing and Balancing (TAB) agents, controls technicians and operators.
The designer stands in the midst of this process coordinating the activities of the
various entities in producing a product that works for the
owner within the design constraints of time and budget. Due
to the complexity of the process, the lack of easily accessible
analysis tools and the limitations in fee and time, many
choices are made based on rules-of-thumb and experience
rather than analysis. In most cases, these factors lead to less
than optimal performance of the resulting system.
Risk is another powerful force influencing HVAC design
decisions. The penalty for an uncomfortable zone is almost always greater than the
reward for an optimally efficient system. If a system is undersized, the designer may
be financially responsible for the remediation, even if it is due to a change in
occupancy requirements or problems in installation. Even if the designer avoids
these out-of-pocket expenses, he or she will likely lose future business from an
unsatisfied client. As a result, the designer is likely to be overly conservative in load
calculations and equipment selection.
The design of high performing built-up VAV systems is fraught with challenges
including mechanical budgets, complexity, fee structures, design coordination, design
schedules, construction execution, diligence in test and balance procedures, and
execution of the controls and performance of the building operators.7 With care
however, a design professional can navigate this landscape to provide systems that
are cost effective to construct and robust in their ability to serve the building as it
changes through time. The mechanical design professional can also align their
services and expertise with the growing interests of owners and architects in “green”
or “integrated design” programs.
These guidelines are written for HVAC designers to help them create systems that
capture the energy savings opportunities, and at the same time feel comfortable that
system performance will meet client expectations. This is a best practices manual
developed through experience with design and commissioning of mechanical and
control systems in commercial buildings and informed