ASHRAE Journal - May 2013 - 20

VAV Reheat Design
The VAVR design includes
a single VAV air handler with
a cooling coil and an airside
economizer. Unlike the ACB
design, which had two supply
risers, the VAVR design only
has one supply riser. The air
handler is sized for about 0.9
cfm/ft2 (4.5 L/[s·m2]), at design conditions. There is no
return ductwork, even in the
return shaft, and building relief is accomplished with two
propeller relief fans.
All zones are served by
VAV boxes, most of which
have reheat coils. Zones that
serve open plan interior spaces that are open to perimeter
zones do not have reheat coils
because minimum ventilation for both the interior and
perimeter can be provided by
the perimeter zone reheat box
(Figure 5). The cooling-only Figure 3: Typical HVAC floor plan for ACB design.
VAV boxes have zero minimum flow rates. The reheat boxes use a dual maxiVFD
mum zone control sequence5 with minimum flow
Supply
rates in the deadband between heating and cooling
CHW
Fan
2 (0.07 L/[s·m2]). High ocCoil
of about 0.15 cfm/ft
Array
cupant density spaces, such as conference rooms
and classrooms, have CO2 controls that also allow
VAV Box
these spaces to have minimum flow rates in deadRH Coil
2 (0.07 L/[s·m2]) dynamband of about 0.15 cfm/ft
ically reset upwards based on CO2 concentration.
The air handler supply air temperature is reset
from 55°F to 65°F (13°C to 18°C) using zone
feedback to provide supply air just cold enough
to satisfy the worst-case zone. Similarly, duct
static pressure setpoint is reset to maintain the
worst-case zone damper nearly wide open.6

Relief
Fans

VFD
Return

Hybrid System

Figure 4: VAV reheat design.
The Hybrid system includes a single VAV air
handler with a chilled water coil and airside economizer the total area is conventional VAV reheat and about 30% is
ducted to two supply risers. Interior zones are served by hybrid VAV + ACB. The air handler is designed for about
conventional VAV reheat boxes because adding chilled 0.7 cfm/ft2 (0.33 L/[s·m2]). and 55°F (13°C) supply air
beams to these low load zones would not significantly re- temperature. Like the VAV reheat design, the air handler
duce primary airflow rates. Similarly, conference rooms controls include supply air temperature reset and duct static
and classrooms, which have relatively high peak ventilation pressure reset.
rates, are served by conventional reheat boxes with CO2
The chilled beams are two pipe, cooling-only beams, rathcontrols. Chilled beams are only provided in low density er than four pipe beams. Heating is provided by VAV reheat
perimeter zones where the chilled beams allow significant boxes that serve the chilled beams (Figure 7). As with the
reduction in the primary airflow rates. Thus about 70% of ACB+DOAS Design, one set of 45°F (7°C) chilled water pipes
20

ASHRAE Journal

ashrae.org

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
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ASHRAE Journal - May 2013 - 44
ASHRAE Journal - May 2013 - 45
ASHRAE Journal - May 2013 - PSU Design Build Project
ASHRAE Journal - May 2013 - 47
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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
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ASHRAE Journal - May 2013 - 60
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ASHRAE Journal - May 2013 - Building Sciences
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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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