ASHRAE Journal - May 2013 - 31

was simulated with EnergyPlus during the competition. As expected, the ACB+Recirculation energy use went down but still
was considerably higher than the VAVR energy use, and the
ACB+Recirculation is even more expensive with the economizer. And, of course, the system is no longer DOAS and, therefore,
loses most of the supposed advantages of DOAS.
Heat Recovery. What if, instead of an air economizer, the
ACB design included a heat exchanger between the exhaust
air and the outside air? In many climates, like most of California, the added supply and exhaust fan energy from the added
pressure drop of the heat exchanger would outweigh most or
all of the energy savings from heat recovery. Even if heat recovery was a net energy saver it would not save as much as
the previous ACB+Recirculation option, which is still less efficient than VAVR. And, of course, adding heat recovery only
makes ACB+DOAS more expensive.
Waterside Economizer. A waterside economizer will not
help the ACB+DOAS design catch up to VAVR in terms of
fan energy or mechanical cooling load, but it will allow the
ACB+DOAS to meet the cooling load more efficiently. However, a waterside economizer is usually less efficient than an
airside economizer due to the cooling tower and pump energy
required and due to the fact that it has three temperature approaches (compared to no approaches for an air economizer)
that determine when the economizer is available and what

fraction of the load it can serve. There is the approach of the
tower to the ambient wet bulb (which gets worse as the wet
bulb goes down), the approach across the heat exchanger, and
the approach from the chilled beam to the supply air. Chilled
beams also generally have a low chilled water DT (e.g., 6°F
[3°C]), which limits waterside economizing.
Multiple Chillers. To have any chance of competing with
a VAVR system on energy use, the ACB+DOAS design must
have separate high and low temperature chillers—low temperature (e.g., 45°F [7°C]) chillers to serve the air handlers
and high temperature chillers (e.g., 57°F [14°C]) to serve the
chilled beams. This will improve the mechanical cooling efficiency of the ACB design, but will also significantly increase
the first cost and complexity of the system.
Other Hybrid Designs. The hybrid design in this competition
failed to compete with the VAVR design on energy or first cost,
but there are other hybrid designs that might fare better. Livchak
suggests adding parallel or series fan-powered boxes to the ACB
to reduce primary air.8 Although this will reduce the heating/
cooling penalties associated with high primary air, it will also
increase fan energy and maintenance (due to all the small fans)
and will likely not result in lower total energy than VAVR and will
reduce indoor air quality. It will also significantly increase the
first cost of the ACB design, which as noted earlier would already
take 80 years to pay for itself even if it used no energy at all.

www.info.hotims.com/44632-34

May 2013

ASHRAE Journal

31



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
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ASHRAE Journal - May 2013 - Cover4
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