TAB Journal Summer 2019 - 10

The Mysterious Case of

THE MISSING AIR
Jason Parker, TBE
Systems Analysis, Inc.

It was a cool spring morning and all was quiet
on-site, when all of a sudden the rumbling of three
55-ton, custom-made modular rooftop units fired up,
disrupting the morning peace.
PARTS AND PIECES
The project consisted of three custom-made modular energy
recovery air handling units, each with a supply and exhaust
section totaling approximately 70,000 cubic feet per minute
(CFM) supply outside air and 70,000 CFM exhaust air sitting
on the roof of a large laboratory building. These units were
provided with an energy recovery coil between the two
sections, filled with refrigerant, to recover heat from the large
quantity of conditioned air being exhausted from the space.
Each unit had in excess of 200 variable air volume (VAV)
supply and exhaust boxes with custom-built control software
handling their operation. There were countless other HVAC
components to be tested & balanced, but these three units are
the focus of this case study.

these eight terminal units. We had to start over with a new
plan. After two additional weeks, we all found a rhythm and
began to comfortably work through the VAV boxes with the
control contractor operating the software.

WHAT NOW?

"This project must be cursed" was used a lot during
construction by all trades. There were countless setbacks
and multiple contractors lost over a period of two years
before our company ever stepped onto the premises. Ours
was just another chapter in the haunting tale of issues from
this project.

After the eventual completion of the setup and calibration
of the terminal boxes, countless corrective action lists, and
the fi nalization of other system components, we moved on
to the fi nal performance testing of the three energy recovery
air handling units. A discrepancy was found between the
terminal airflow total readings and the measured airflow
from the coil bank traverses. Duct pitot tube traverses were
not possible with the unit arrangement and ductwork. The
total air coil traverse of each unit was nearly 4,000 CFM
less than the total of the supply VAV terminals. The exhaust
unit total airflow was within three percent of the air volume
totaled from the exhaust VAV terminals. Since the duct was
leak pressure tested at 8 in. water column (w.c.) there was
little suspicion that there was any duct leakage. We began to
question the stability of the supply VAV calibration since that
was an issue earlier.

We began to test the VAV terminals with the control
contractor's assistance, manipulating the system and
calibrating each device. It was a daunting task since this
was new software developed specifically for this laboratory
application. After a week of testing and retesting with
building automated systems, we had completed the
calibration of four supply boxes and four exhaust boxes. We
went back and could not repeat the fi nal readings on any of

We spent two days revisiting the calibration of boxes, tracing
down ductwork to verify that no holes were allowing air to
leak, and to make certain duct systems were tight throughout
the building. After the inspection of the building systems,
we returned to retest all three units, and similar results were
found. We were confident we still had a lost airflow issue, but
other construction team members were reluctant to trust our
coil traverse measurements.

A ROCKY START

10

TAB Journal Summer 2019



TAB Journal Summer 2019

Table of Contents for the Digital Edition of TAB Journal Summer 2019

TAB Journal Summer 2019 - Cover1
TAB Journal Summer 2019 - Cover2
TAB Journal Summer 2019 - 1
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TAB Journal Summer 2019 - Cover3
TAB Journal Summer 2019 - Cover4
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