ASHRAE Journal - April 2020 - 42

2020

ASHRAE TECHNOLOGY AWARD CASE STUDIES

Global CLA
Humidity

Global CLA
Temperature

Data
Connection

AO R.F. Speed Control

Data Connection
Return Air
Temp

DI R.F. VFD Fault

FMCS

DO R.F. Start/Stop

VFD

Return
CO2

DI R.F. VFD Status

AFMS

TS4

RA
Humidity
HS2

CO2

Safety
Interlock
hi

DPS3

low

Smoke Smoke
Detector Detector
Safety
Interlock

DI 26
DI
Safety
Interlock
SD3
SD4

D-2
NC

Building
Pressure
AI

Return Fan
Array

ACT

DPS5

Data
Connection

To Space To OA

AO S.A. Speed Control

Floor Mixed Air
Status Temp 40°F Freezestat

D-3
NC

ACT
DO
MAX OA Damper

Filter

D-1
NC

MAX

DPS2

low

DPT1

TS1

low

Safety
Interlock
low

Preﬁlter Final Filter
hi

AI
Mixed Air S.P.

Safety
Interlock
FZ2 Set @ 40°F

Filter

IAQ
Sensors

DPS2

Safety
Interlock
DP

DI
SD1

Safety
Interlock

Smoke
Detector
DI
SD2

AI
hi

DPT4

low

AFMS
AF

AI
Supply Static Pres SW

CHW

AFMS

Data Connection

Smoke
S.A. Dewpoint Detector

DI S.A. VFD Status

AO
CHW Valve

AFMS

DPS1

low

Safety
Interlock

Supply Fan
Array

N.O.

DO S.A. Start/Stop

CHWR
CHWS

ACT

DI S.A. VFD Fault
VFD

TS3
AI

Supply Fan
Temp

DPT3

low

AI
Supply Side Pres SW

D-4
NC

DPT4

low

AI
Supply Static Pressure
Interpass (Alternate 5)

ACT
AO

FIGURE 3 Dual-path air-handler diagram.

poor condition and well beyond their service life
expectancy. The prior fume exhaust air conﬁguration allowed discharge into workers' breathing
zones and at velocities below 1,000 fpm [5 m/s].
In the new design, fume hoods, chemical storage
cabinets, and so on are served by one manifolded
exhaust system with N + 1 redundancy, facilitating
safe and efﬁcient maintenance. Each exhaust fan
was sized, conﬁgured, and controlled so full system
design capacity can be maintained when any one
fan fails or is taken out of service. Isolation dampers were provided to allow each fan to be taken out
of service for maintenance, repair, or replacement,
while the exhaust system remains in operation at
full capacity.
Preheating/precooling of outside air via a refrigerant coil heat recovery system has low maintenance
requirements; it is a passive system with minimal
moving parts.

Cost-Effectiveness

The new, single-duct VAV design reuses existing
dual-duct air distribution (converted to all cold deck

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operation). The original supply air and associated
ductwork was sized at 4,000 to 5,000 fpm (20 to 25
m/s). When the supply air was reduced and the hot
and cold deck ductwork connected to be served by a
single-duct VAV system, air velocities were reduced
to 1,500 to 2,000 fpm (7.6 to 10.2 m/s). This created
signiﬁcant fan energy savings, while allowing costeffective reuse of most of the high-pressure supply
ductwork.
The original supply air total of 206,000 cfm
(97 221 L/s) was reduced to 150,000 cfm (70 792 L/s).
This reduction was supported by detailed load
analysis and made possible by consolidation of
AHUs, reduced lab air change rates, and use of passive chilled beams and low-velocity displacement
ventilation.
The consolidation of AHUs and lab exhaust fans
reduced initial, operational, and maintenance costs.
Baseline water and energy expenditure was
$1,577,493, annually. Through the project, ﬁve major
AHUs and eight smaller ones were replaced and
consolidated with two central, dual-path (outside
and return air), low-velocity AHUs. Sixty lab exhaust

IMAGE COURTESY G/ BA

From
Dedicated
Outdoor Air
System-1

https://www.ashrae.org

ASHRAE Journal - April 2020

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