ASHRAE Journal - November 2022 - 52

TECHNICAL FEATURE
additional OA load, both sensible
and latent, and adding energy
recovery can mitigate the load
increase.
Blended Options
Each building has unique qualities
and design features that set it apart
from its peers. Unusual façades,
complicated HVAC systems or tenant
needs may require a blended or
hybrid solution to bring more OA
into the building.
Here, we present two case studies
of retrofit options for 1980s office
buildings with deficient ventilation
systems that are located in the
southeastern U.S. These case studies
may be useful to those who own,
operate or consult on buildings from
the 1980s, so that they can prepare
to make the changes necessary to
meet or exceed today's ventilation
standards.
Building A
Building Configuration
Building A is a 33-story 690,000 ft2
(64,000 m2) office tower designed
in 1985. A 1,400 ton (4,900 kW)
chilled water plant serves variable
air volume (VAV) AHUs on each
floor. Heating is provided by electric
resistance heat in perimeter fanpowered
VAV boxes. The ventilation
system has a design capacity
of 31,400 cfm (15,000 L/s), which
equates to less than 9 cfm/person
(4 L/s·person).
A single OA fan supplies a vertical
shaft with takeoffs into each floor's
mechanical room. The OA fan is
controlled with a variable frequency
drive (VFD) to maintain constant
static pressure in the shaft, and the
ventilation air is neither heated nor
cooled. Air is exhausted through
52
FIGURE 4 Schematics of Building A retrofit options.
Option 1: Upsized Equipment
Option 2: High- and Low-Rise Split
Existing Fan Remains Half Existing
Ductwork Remains
for OA Fan
New
Existing
New EA Fan
(Full Capacity)
and Ductwork
(All)
New Fan
New Ductwork
for Both OA and
EA Fans
TABLE 1 Building A retrofit options.
REQUIREMENT
OA Duct Enlargement
EA Duct Enlargement
New Ductwork Above Ceiling
Per Floor
New Mechanical Space
Required
Work Required in Tenant
Space
Change to Building Façade
Equipment Required
CHW Piping Required
AHU Coil Upgrade Required
Crane Required
Scheduling
ESTIMATED COST
New OA Fan
(Half Capacity)
New Partial OA
Ductwork
New
Option 3: Incremental
EA
OA
OA
OA
EA
EA
OA
EA
New Cabinet
Fans and
Ductwork
Per Floor
OPTION 1. UPSIZED
EQUIPMENT
Yes
Yes
No
No
No
No
OA Fan and EA Fan
With Electrical Service
No
No
Yes
One Large Project
$1.2 million
a single constant volume toilet
exhaust fan. Both fans are in the
mechanical penthouse.
To meet Standard 62.1-2019,
Building A needs 72,100 cfm
(34,000 L/s) of OA, an increase of
130%. Exhaust air will also need to
be increased. A floor-by-floor load
analysis showed the overall system
load, including that imposed by the
additional OA, could be met by the
existing chiller plant. The existing
AHU cooling coils and VAV electric
reheat coils were also verified as
capable of handling additional OA.
ASHRAE JOURNAL ashrae.o rg N O V E M B E R 2022
OPTION 2. HIGH- AND
LOW-RISE SPLIT
Yes
(Half as Much)
Yes
No
Yes
No
No
OA Fan (Half Size) and
EA Fan With Electrical
Service
No
No
Yes
One Large Project
$825,000
OPTION 3. INCREMENTAL
No
No
Yes
No
Yes
Yes
Small OA and EA Fan
Per Floor, With Electrical
Service
No
No
No
One Small Project Per Floor
$30,000 Per Floor
Retrofit Options
Option 1: Upsized Equipment
Replace the existing OA fan and EA
fan with larger fans and motors and
increase the cross-sectional area of
the OA duct and the EA duct for the
full height of the building. The new
fans would require a crane to get
to the roof. The existing OA and EA
ductwork runs through a chase from
the penthouse to the lowest floor.
To remove the existing duct and to
install the larger duct, the chase
must be accessed on every floor.
This alternative requires larger
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ASHRAE Journal - November 2022

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