ASHRAE Journal - May 2013 - 27

Figure 11: ACB+DOAS second floor supply mains.

SEE M2.02C FOR CONTINUATION

a total supply main area of 13 ft2 (1 m2)
per floor (Figure 11). On the same floor,
the VAVR design has one 54 × 16 in.
(1.37 × 0.40 m), main and one 30 × 16
in. (0.76 × 0.40 m), main for a total supply main area of 9 ft2 (0.8 m2) (Figure
12). So in this case the ACB+DOAS
design has larger supply mains and thus
has no advantage in terms of floor-tofloor height.
The ACB+DOAS supply mains are
larger because they are sized for a lower
velocity. To mitigate the fan energy penalty of a constant volume system relative
to a VAV system, an ACB+DOAS system must use lower duct velocities compared to a VAVR system. In this case, the Figure 12: VAVR second floor supply mains.
VAVR supply mains are sized at about
2,000 fpm (10 m/s) while the ACB+DOAS mains are sized at nual fan energy of a VAVR system at 0.9 cfm/ft2 and 2,500
about 900 fpm (5 m/s). VAVR mains can be sized for a higher fpm (0.42 L/[s·m2] and 13 m/s) (see Figure 10).
velocity because they are variable volume, and the actual flow
rate is almost always well below the design flow. VAVR supply Indoor Air Quality
mains can be sized up to about 2,500 fpm (13 m/s) with miniProponents of ACB+DOAS argue it provides better indoor
mal impact on annual fan energy or noise risk.
air quality than VAVR because it uses higher design ventilaAn ACB+DOAS design might have a floor-to-floor advan- tion rates. What this argument fails to capture, however, is the
tage over VAVR with different design choices. For example, IAQ benefits of the airside economizer in a VAVR design. As
if the ACB+DOAS system had been designed for 0.3 cfm/ part of the competition, a detailed eQuest simulation of the
ft2 instead of 0.6 cfm/ft2 and the duct mains sized at 1,500 GSB was performed to determine how the ventilation rates of
fpm, then the duct mains would be about 30% smaller than the designs compared to each other and to ASHRAE Standard
a comparable VAVR system sized at 2,500 fpm. Of course, 62.1 in every space and every hour of the year.5
an ACB+DOAS system at 0.3 cfm/ft2 and 1,500 fpm (0.14
Figure 13 shows the actual outside airflow in the VAVR deL/[s·m2] and 8 m/s) would still have more than double the an- sign met or exceeded the outside airflow required by Standard
May 2013

ASHRAE Journal

27



ASHRAE Journal - May 2013

Table of Contents for the Digital Edition of ASHRAE Journal - May 2013

ASHRAE Journal - May 2013
Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
VAV Reheat Versus Active Chilled Beams & DOAS
A Stable Whole Building Performance Method for Standard 90.1
Technology Award Case Studies:
PSU Design Build Project
Passive Cooling for School
Standing Columns
Building Sciences
InfoCenter
Refrigeration Applications
IAQ Applications
Engineer's Notebook
Products
Data Centers
Emerging Technologies
Classified Advertising
Advertisers Index
ASHRAE Journal - May 2013 - ASHRAE Journal - May 2013
ASHRAE Journal - May 2013 - Cover2
ASHRAE Journal - May 2013 - 1
ASHRAE Journal - May 2013 - 2
ASHRAE Journal - May 2013 - Contents
ASHRAE Journal - May 2013 - Commentary
ASHRAE Journal - May 2013 - 5
ASHRAE Journal - May 2013 - Industry News
ASHRAE Journal - May 2013 - 7
ASHRAE Journal - May 2013 - 8
ASHRAE Journal - May 2013 - 9
ASHRAE Journal - May 2013 - 10
ASHRAE Journal - May 2013 - 11
ASHRAE Journal - May 2013 - 12
ASHRAE Journal - May 2013 - 13
ASHRAE Journal - May 2013 - Letters
ASHRAE Journal - May 2013 - 15
ASHRAE Journal - May 2013 - Meetings and Shows
ASHRAE Journal - May 2013 - 17
ASHRAE Journal - May 2013 - VAV Reheat Versus Active Chilled Beams & DOAS
ASHRAE Journal - May 2013 - 19
ASHRAE Journal - May 2013 - 20
ASHRAE Journal - May 2013 - 21
ASHRAE Journal - May 2013 - 22
ASHRAE Journal - May 2013 - 23
ASHRAE Journal - May 2013 - 24
ASHRAE Journal - May 2013 - 25
ASHRAE Journal - May 2013 - 26
ASHRAE Journal - May 2013 - 27
ASHRAE Journal - May 2013 - 28
ASHRAE Journal - May 2013 - 29
ASHRAE Journal - May 2013 - 30
ASHRAE Journal - May 2013 - 31
ASHRAE Journal - May 2013 - 32
ASHRAE Journal - May 2013 - A Stable Whole Building Performance Method for Standard 90.1
ASHRAE Journal - May 2013 - 34
ASHRAE Journal - May 2013 - 35
ASHRAE Journal - May 2013 - 36
ASHRAE Journal - May 2013 - 37
ASHRAE Journal - May 2013 - 38
ASHRAE Journal - May 2013 - 39
ASHRAE Journal - May 2013 - 40
ASHRAE Journal - May 2013 - 41
ASHRAE Journal - May 2013 - 42
ASHRAE Journal - May 2013 - 43
ASHRAE Journal - May 2013 - 44
ASHRAE Journal - May 2013 - 45
ASHRAE Journal - May 2013 - PSU Design Build Project
ASHRAE Journal - May 2013 - 47
ASHRAE Journal - May 2013 - 48
ASHRAE Journal - May 2013 - 49
ASHRAE Journal - May 2013 - 50
ASHRAE Journal - May 2013 - 51
ASHRAE Journal - May 2013 - 52
ASHRAE Journal - May 2013 - 53
ASHRAE Journal - May 2013 - Passive Cooling for School
ASHRAE Journal - May 2013 - 55
ASHRAE Journal - May 2013 - 56
ASHRAE Journal - May 2013 - 57
ASHRAE Journal - May 2013 - 58
ASHRAE Journal - May 2013 - 59
ASHRAE Journal - May 2013 - 60
ASHRAE Journal - May 2013 - 61
ASHRAE Journal - May 2013 - Building Sciences
ASHRAE Journal - May 2013 - 63
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ASHRAE Journal - May 2013 - 65
ASHRAE Journal - May 2013 - 66
ASHRAE Journal - May 2013 - 67
ASHRAE Journal - May 2013 - 68
ASHRAE Journal - May 2013 - 69
ASHRAE Journal - May 2013 - InfoCenter
ASHRAE Journal - May 2013 - 71
ASHRAE Journal - May 2013 - 72
ASHRAE Journal - May 2013 - 73
ASHRAE Journal - May 2013 - 74
ASHRAE Journal - May 2013 - Refrigeration Applications
ASHRAE Journal - May 2013 - 76
ASHRAE Journal - May 2013 - 77
ASHRAE Journal - May 2013 - IAQ Applications
ASHRAE Journal - May 2013 - 79
ASHRAE Journal - May 2013 - 80
ASHRAE Journal - May 2013 - 81
ASHRAE Journal - May 2013 - 82
ASHRAE Journal - May 2013 - 83
ASHRAE Journal - May 2013 - Engineer's Notebook
ASHRAE Journal - May 2013 - 85
ASHRAE Journal - May 2013 - Products
ASHRAE Journal - May 2013 - 87
ASHRAE Journal - May 2013 - Data Centers
ASHRAE Journal - May 2013 - 89
ASHRAE Journal - May 2013 - 90
ASHRAE Journal - May 2013 - 91
ASHRAE Journal - May 2013 - Emerging Technologies
ASHRAE Journal - May 2013 - 93
ASHRAE Journal - May 2013 - 94
ASHRAE Journal - May 2013 - Classified Advertising
ASHRAE Journal - May 2013 - Advertisers Index
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ASHRAE Journal - May 2013 - Cover4
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