ASHRAE Journal - August 2010 - 42
DOAS & Building Pressurization
By Stanley A. Mumma, Ph.D., P Fellow/Life Member ASHRAE .E.,
D
edicated outdoor air systems (DOASs) have become common and, for the most part, are delivering superb performance compared to conventional
all-air systems.1 However, the issue of building pressurization with DOAS warrants careful attention. The two main problems that occur with building pressurization using DOAS are: unbalanced flow through the total energy recovery (TER) equipment causing its performance to be compromised on the OA delivery side under design conditions; and, second, the return airflow has frequently been observed in the field to be only 20% to 40% that of the design supply airflow leading to such severe TER performance degradation that the cooling plant is unable to meet the load. In addition, there is always uncertainty during the design and operational phases of a project concerning the latent load that must be removed from the occupied spaces in the field. This uncertainty is
42 ASHRAE Journal
the result of nebulous initial occupancy information and changing future space use and density; and envelope integrity as a function of use and time. To avoid damaging condensation from chilled ceilings
ashrae.org
or beams, it is imperative that there be reserve capacity2 in the DOAS to accommodate such latent load uncertainties. In fact, even with packaged terminal equipment such as fan coil units, water source heat pumps, and variable refrigerant flow split systems, reserve capacity in the DOAS is necessary to prevent their condensate pans from becoming distributed septic3 amplifiers. This reserve capacity can be economically made a part of the pressurization unit when compared to putting the reserve capacity into an enlarged unbalanced flow DOAS. Or perhaps better, the reserve capacity could be simply added to the pressurization unit at a later time in stages, avoiding unnecessary first cost investments. (Achieving reserve capacity by introducing recirculated space air to save energy and capacity is About the Author
Stanley A. Mumma, Ph.D., P .E., is professor emeritus, Penn State University, University Park, Pa.
August 2010
ASHRAE Journal - August 2010
Table of Contents for the Digital Edition of ASHRAE Journal - August 2010
Contents
Commentary
Industry News
Letters
Meetings and Shows
2010-11 Presidential Address: Modeling a Sustainable World
Refrigeration Air Cooler Rating Methods
Implications of Current Thermal Guidelines for Data Center Energy Use
DOAS & Building Pressurization
Building Sciences
InfoCenter
Emerging Technologies
Special Products
Washington Report
Technical Topics
People
Classified Advertising
Advertisers Index
ASHRAE Journal - August 2010 - Intro
ASHRAE Journal - August 2010 - Cover1
ASHRAE Journal - August 2010 - Cover2
ASHRAE Journal - August 2010 - 1
ASHRAE Journal - August 2010 - 2
ASHRAE Journal - August 2010 - Contents
ASHRAE Journal - August 2010 - Commentary
ASHRAE Journal - August 2010 - 5
ASHRAE Journal - August 2010 - Industry News
ASHRAE Journal - August 2010 - 7
ASHRAE Journal - August 2010 - 8
ASHRAE Journal - August 2010 - 9
ASHRAE Journal - August 2010 - 10
ASHRAE Journal - August 2010 - 11
ASHRAE Journal - August 2010 - 12
ASHRAE Journal - August 2010 - 13
ASHRAE Journal - August 2010 - Letters
ASHRAE Journal - August 2010 - 15
ASHRAE Journal - August 2010 - Meetings and Shows
ASHRAE Journal - August 2010 - 17
ASHRAE Journal - August 2010 - 2010-11 Presidential Address: Modeling a Sustainable World
ASHRAE Journal - August 2010 - 19
ASHRAE Journal - August 2010 - 20
ASHRAE Journal - August 2010 - 21
ASHRAE Journal - August 2010 - 22
ASHRAE Journal - August 2010 - 23
ASHRAE Journal - August 2010 - Refrigeration Air Cooler Rating Methods
ASHRAE Journal - August 2010 - 25
ASHRAE Journal - August 2010 - 26
ASHRAE Journal - August 2010 - 27
ASHRAE Journal - August 2010 - 28
ASHRAE Journal - August 2010 - 29
ASHRAE Journal - August 2010 - Implications of Current Thermal Guidelines for Data Center Energy Use
ASHRAE Journal - August 2010 - 31
ASHRAE Journal - August 2010 - 32
ASHRAE Journal - August 2010 - 33
ASHRAE Journal - August 2010 - 34
ASHRAE Journal - August 2010 - 35
ASHRAE Journal - August 2010 - 36
ASHRAE Journal - August 2010 - 37
ASHRAE Journal - August 2010 - 38
ASHRAE Journal - August 2010 - 39
ASHRAE Journal - August 2010 - 40
ASHRAE Journal - August 2010 - 41
ASHRAE Journal - August 2010 - DOAS & Building Pressurization
ASHRAE Journal - August 2010 - 43
ASHRAE Journal - August 2010 - 44
ASHRAE Journal - August 2010 - 45
ASHRAE Journal - August 2010 - 46
ASHRAE Journal - August 2010 - 47
ASHRAE Journal - August 2010 - 48
ASHRAE Journal - August 2010 - 49
ASHRAE Journal - August 2010 - 50
ASHRAE Journal - August 2010 - 51
ASHRAE Journal - August 2010 - 52
ASHRAE Journal - August 2010 - 53
ASHRAE Journal - August 2010 - Building Sciences
ASHRAE Journal - August 2010 - 55
ASHRAE Journal - August 2010 - 56
ASHRAE Journal - August 2010 - 57
ASHRAE Journal - August 2010 - InfoCenter
ASHRAE Journal - August 2010 - 59
ASHRAE Journal - August 2010 - 60
ASHRAE Journal - August 2010 - 61
ASHRAE Journal - August 2010 - 62
ASHRAE Journal - August 2010 - 63
ASHRAE Journal - August 2010 - 64
ASHRAE Journal - August 2010 - 65
ASHRAE Journal - August 2010 - Emerging Technologies
ASHRAE Journal - August 2010 - 67
ASHRAE Journal - August 2010 - 68
ASHRAE Journal - August 2010 - 69
ASHRAE Journal - August 2010 - Special Products
ASHRAE Journal - August 2010 - Washington Report
ASHRAE Journal - August 2010 - Technical Topics
ASHRAE Journal - August 2010 - 73
ASHRAE Journal - August 2010 - 74
ASHRAE Journal - August 2010 - 75
ASHRAE Journal - August 2010 - People
ASHRAE Journal - August 2010 - 77
ASHRAE Journal - August 2010 - Classified Advertising
ASHRAE Journal - August 2010 - 79
ASHRAE Journal - August 2010 - Advertisers Index
ASHRAE Journal - August 2010 - Cover3
ASHRAE Journal - August 2010 - Cover4
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