ASHRAE Journal - May 2013 - 30

Flexibility for Future Tenant Improvements. Rigidly secured and piped chilled beams are much more expensive to
relocate than VAVR diffusers, which do not require seismic
bracing and are generally connected with flex duct. Not only
will HVAC cost be higher for tenant improvements but other
trades’ costs are also likely to be higher as a result of the “forest” of seismic bracing supporting the ACBs.
LEED EQ Credit 5 (Indoor Chemical and Pollutant Source
Control). This credit is generally achievable with a VAVR system

since it requires that all supply air be filtered, but not with an ACB
system because the secondary air induced through chilled beams
is unfiltered.
Thermal Comfort. When the zone minimum cooling output
exceeds the cooling load then the zone is overcooled and driven
to the reheating setpoint (e.g., 70°F [21°C]). When the minimum
zone output is less than the zone load, the space temperature drifts
up to the cooling setpoint (e.g., 74°F [23°C]). Most people are
more comfortable at the cooling setpoint than at the heating setpoint in the summertime when they are
wearing summer attire.7 Therefore, reducing the zone minimum cooling output improves comfort. As discussed earlier, the
ACB+DOAS design has a higher minimum zone cooling output than the VAVR
design and is likely to be less comfortable.

What-If Scenarios

www.info.hotims.com/44632-12

30

ASHRAE Journal

In this competition, VAVR is the clear
winner, but are there other applications
or designs for which ACB+DOAS or a
hybrid design using ACB would be lower first cost or lower energy cost?
Lower Primary Airflow. An
ACB+DOAS primary airflow rate of 0.3
cfm/ft2 (0.14 L/[s·m2]) instead of 0.5 or
0.6 cfm/ft2 (0.24 or 0.28 L/[s·m2]) would
reduce the cooling load in hot weather,
and the reheat load in cold weather but it
would increase the cooling load in mild
weather (less free cooling). The net result would likely be a lower annual energy use than 0.6 cfm/ft2 (0.28 L/[s·m2]),
but would lowering the primary airflow
rate allow the beams to achieve the necessary cooling capacity and provide sufficient latent capacity and meet the air
quality objectives?
Two-Pipe Chilled Beams. Using a
two-pipe beam that can switch between
heating and cooling, rather than a four
pipe beam, would reduce first costs but
not enough to make ACB less expensive
than VAVR, and it would have no real
impact on energy performance.
ACB+Recirculation. What if an
airside economizer was added to the
ACB+DOAS design so that the system
remained constant volume at 0.5 cfm/
ft2 (0.24 L/[s·m2]), but the outside airflow component could be modulated
between 0.15 cfm/ft2 and 0.5 cfm/ft2
(0.07 L/[s·m2]) and (0.24 L/[s·m2]) to
minimize the heating and cooling penalty
of the higher flow rates? This scenario
May 2013



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
ASHRAE Journal - May 2013 - 64
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
ASHRAE Journal - May 2013 - Cover3
ASHRAE Journal - May 2013 - Cover4
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