ASHRAE Journal - October 2011 - 26

cerns with this approach: 1) minimizing 6 Million comfort issues related to cold air dumpPumps ing on the occupants, and 2) avoiding Fans condensation on components of the air Heating 4 Million Cooling distribution system. A great resource for anyone designing a cold-air system is the ASHRAE Cold Air Distribution System Design Guide, which discusses 2 Million in detail how to avoid these problems.4 Linear slot diffusers with a high inHouston Los Angeles Philadelphia St. Louis duction ratio are good for any VAV sys1 | 2 | 3 1 | 2 | 3 1 | 2 | 3 1 | 2 | 3 tem, but work very well for a cold-air 1 Baseline Chilled Water VAV | 2 Active Chilled Beams | 3 High Performance Chilled Water VAV VAV system. They induce large quantities of air from the space to mix with the cold supply air, so the mixture drops Figure 7: Example energy analysis for a large office building. slowly into the occupied zone at nearly room temperature. On the other hand, many conventional dif• Insulate all the cold surfaces, including supply ducts, VAV fusers allow cold air to drop directly into the occupied zone, terminals, and diffusers. In addition, a properly sealed vapor which can result in occupant comfort complaints, especially retarder should be included on the warm side of the insulation at reduced airflows. to prevent condensation within the insulation. Since the surfaces of the air distribution components in a • If possible, use an open ceiling plenum for return air. This low-temperature system are colder than in a conventional sys- results in a conditioned plenum, which means a lower dew tem, there is often concern about condensation. To minimize point and less risk of condensation. the risk of condensation: • During humid weather, maintain positive building pressurization to reduce or eliminate the infiltration of humid outdoor air. • During startup, slowly ramp the SAT setpoint downward to slowly lower surface temperatures while lowering the dew point inside the building.
Annual HVAC Energy Use (kBtu/yr)

Putting It All Together
Although this article focused on the airside of VAV systems, many opportunities exist to reduce energy on the equipment or plant side of the system. Some examples include: • High-efficiency rooftop equipment, water chillers, and airhandling unit fans; • Air-to-air energy recovery; • Evaporative condensing; • Low-flow, low-temperature chilled-water systems; • Waterside heat recovery; • Central geothermal; and • Solar heat recovery for reheat. The impact of any of these strategies on overall operating costs depends on climate, building use, and utility costs. Therefore, whole-building energy simulation should be used to determine if a specific strategy makes sense for a given application. As an example, Figure 7 contains the results from a whole-building energy simulation of a large office building, comparing a typical VAV system to a high-performance chilled-water VAV system. The baseline building uses a conventional chilled-water VAV system, designed for 55°F (13°C) supply air, and modeled according to Appendix G of Standard 90.1-2007. The high-performance VAV system is designed for 48°F (9°C) supply air (ductwork has not been downsized) and uses the opOctober 2011

www.info.hotims.com/37991-17

26

ASHRAE Journal



ASHRAE Journal - October 2011

Table of Contents for the Digital Edition of ASHRAE Journal - October 2011

ASHRAE Journal - October 2011
Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
High-Performance VAV Systems
HVAC Selection for Envelope- Dominated Buildings
Saving Energy by Insulating Pipe Components On Steam & Hot Water Distribution Systems
Technology Award Case Studies
Aquifer for Cooling
Dual-Fan System
Special Sections
ASHRAE Research Report
ASHRAE Honor Roll
Standing Columns
Building Sciences
Emerging Technologies
IAQ Applications
Washington Report
Special Products
People
Products
Classified Advertising
Advertisers Index
ASHRAE Journal - October 2011 - ASHRAE Journal - October 2011
ASHRAE Journal - October 2011 - Cover2
ASHRAE Journal - October 2011 - 1
ASHRAE Journal - October 2011 - 2
ASHRAE Journal - October 2011 - Contents
ASHRAE Journal - October 2011 - Commentary
ASHRAE Journal - October 2011 - 5
ASHRAE Journal - October 2011 - Industry News
ASHRAE Journal - October 2011 - 7
ASHRAE Journal - October 2011 - 8
ASHRAE Journal - October 2011 - 9
ASHRAE Journal - October 2011 - Letters
ASHRAE Journal - October 2011 - 11
ASHRAE Journal - October 2011 - 12
ASHRAE Journal - October 2011 - 13
ASHRAE Journal - October 2011 - 14
ASHRAE Journal - October 2011 - 15
ASHRAE Journal - October 2011 - Meetings and Shows
ASHRAE Journal - October 2011 - 17
ASHRAE Journal - October 2011 - High-Performance VAV Systems
ASHRAE Journal - October 2011 - 19
ASHRAE Journal - October 2011 - 20
ASHRAE Journal - October 2011 - 21
ASHRAE Journal - October 2011 - 22
ASHRAE Journal - October 2011 - 23
ASHRAE Journal - October 2011 - 24
ASHRAE Journal - October 2011 - 25
ASHRAE Journal - October 2011 - 26
ASHRAE Journal - October 2011 - 27
ASHRAE Journal - October 2011 - 28
ASHRAE Journal - October 2011 - 29
ASHRAE Journal - October 2011 - HVAC Selection for Envelope- Dominated Buildings
ASHRAE Journal - October 2011 - 31
ASHRAE Journal - October 2011 - 32
ASHRAE Journal - October 2011 - 33
ASHRAE Journal - October 2011 - 34
ASHRAE Journal - October 2011 - 35
ASHRAE Journal - October 2011 - 36
ASHRAE Journal - October 2011 - 37
ASHRAE Journal - October 2011 - 38
ASHRAE Journal - October 2011 - 39
ASHRAE Journal - October 2011 - 40
ASHRAE Journal - October 2011 - 41
ASHRAE Journal - October 2011 - Saving Energy by Insulating Pipe Components On Steam & Hot Water Distribution Systems
ASHRAE Journal - October 2011 - 43
ASHRAE Journal - October 2011 - 44
ASHRAE Journal - October 2011 - 45
ASHRAE Journal - October 2011 - 46
ASHRAE Journal - October 2011 - 47
ASHRAE Journal - October 2011 - 48
ASHRAE Journal - October 2011 - 49
ASHRAE Journal - October 2011 - Aquifer for Cooling
ASHRAE Journal - October 2011 - 51
ASHRAE Journal - October 2011 - 52
ASHRAE Journal - October 2011 - 53
ASHRAE Journal - October 2011 - Dual-Fan System
ASHRAE Journal - October 2011 - 55
ASHRAE Journal - October 2011 - 56
ASHRAE Journal - October 2011 - 57
ASHRAE Journal - October 2011 - 58
ASHRAE Journal - October 2011 - 59
ASHRAE Journal - October 2011 - ASHRAE Research Report
ASHRAE Journal - October 2011 - 61
ASHRAE Journal - October 2011 - 62
ASHRAE Journal - October 2011 - 63
ASHRAE Journal - October 2011 - 64
ASHRAE Journal - October 2011 - 65
ASHRAE Journal - October 2011 - 66
ASHRAE Journal - October 2011 - 67
ASHRAE Journal - October 2011 - 68
ASHRAE Journal - October 2011 - 69
ASHRAE Journal - October 2011 - 70
ASHRAE Journal - October 2011 - 71
ASHRAE Journal - October 2011 - 72
ASHRAE Journal - October 2011 - ASHRAE Honor Roll
ASHRAE Journal - October 2011 - HR2
ASHRAE Journal - October 2011 - HR3
ASHRAE Journal - October 2011 - HR4
ASHRAE Journal - October 2011 - HR5
ASHRAE Journal - October 2011 - HR6
ASHRAE Journal - October 2011 - HR7
ASHRAE Journal - October 2011 - HR8
ASHRAE Journal - October 2011 - HR9
ASHRAE Journal - October 2011 - HR10
ASHRAE Journal - October 2011 - HR11
ASHRAE Journal - October 2011 - HR12
ASHRAE Journal - October 2011 - HR13
ASHRAE Journal - October 2011 - HR14
ASHRAE Journal - October 2011 - HR15
ASHRAE Journal - October 2011 - HR16
ASHRAE Journal - October 2011 - HR17
ASHRAE Journal - October 2011 - HR18
ASHRAE Journal - October 2011 - HR19
ASHRAE Journal - October 2011 - HR20
ASHRAE Journal - October 2011 - HR21
ASHRAE Journal - October 2011 - HR22
ASHRAE Journal - October 2011 - HR23
ASHRAE Journal - October 2011 - HR24
ASHRAE Journal - October 2011 - HR25
ASHRAE Journal - October 2011 - HR26
ASHRAE Journal - October 2011 - HR27
ASHRAE Journal - October 2011 - HR28
ASHRAE Journal - October 2011 - HR29
ASHRAE Journal - October 2011 - HR30
ASHRAE Journal - October 2011 - HR31
ASHRAE Journal - October 2011 - HR32
ASHRAE Journal - October 2011 - 73
ASHRAE Journal - October 2011 - Building Sciences
ASHRAE Journal - October 2011 - 75
ASHRAE Journal - October 2011 - 76
ASHRAE Journal - October 2011 - 77
ASHRAE Journal - October 2011 - 78
ASHRAE Journal - October 2011 - 79
ASHRAE Journal - October 2011 - 80
ASHRAE Journal - October 2011 - 81
ASHRAE Journal - October 2011 - 82
ASHRAE Journal - October 2011 - 83
ASHRAE Journal - October 2011 - Emerging Technologies
ASHRAE Journal - October 2011 - 85
ASHRAE Journal - October 2011 - 86
ASHRAE Journal - October 2011 - 87
ASHRAE Journal - October 2011 - 88
ASHRAE Journal - October 2011 - 89
ASHRAE Journal - October 2011 - IAQ Applications
ASHRAE Journal - October 2011 - 91
ASHRAE Journal - October 2011 - 92
ASHRAE Journal - October 2011 - 93
ASHRAE Journal - October 2011 - Washington Report
ASHRAE Journal - October 2011 - Special Products
ASHRAE Journal - October 2011 - People
ASHRAE Journal - October 2011 - 97
ASHRAE Journal - October 2011 - Products
ASHRAE Journal - October 2011 - 99
ASHRAE Journal - October 2011 - 100
ASHRAE Journal - October 2011 - 101
ASHRAE Journal - October 2011 - Classified Advertising
ASHRAE Journal - October 2011 - 103
ASHRAE Journal - October 2011 - Advertisers Index
ASHRAE Journal - October 2011 - Cover3
ASHRAE Journal - October 2011 - Cover4
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