ASHRAE Journal - April 2020 - 38

2020

ASHRAE TECHNOLOGY AWARD CASE STUDIES

Previously, the building systems recirculated lab
general exhaust to AHUs serving other areas. Today's
environmental, health, and safety (EHS) standards
do not allow recirculation of exhaust air from labs
with fume hoods. The new design directs all wet-lab
lab exhaust to the lab exhaust system.
Displacement ventilation yields superior IAQ,
achieved with exhausting contaminated air from the
room, providing clean-to-dirty airﬂow.
Displacement ventilation with warmer dehumidiﬁed supply air (61°F at 48°F dew point [16.1°C at 8.9°C
dew point]), coupled with convective chilled beams,
minimizes air draft on scientists, which improves
occupant thermal comfort and productivity.
Dual-path air-handling units decouple the ventilation makeup air (OA deck) from space thermal control (RA deck), allowing precise control of the building humidity at 50°F (10°C) dew point (70°F [21.1°C]
and 50% RH), and outside air to meet makeup air
requirements, as well as those laid out in ASHRAE
Standards 62 and 55.
New high-plume dilution fans are strategically
located away from outside air intakes and are used
to extract and dilute lab, process, and fume-hood
efﬂuent air. Because of the nozzle design, the diluted
efﬂuent is displaced high into the atmosphere at a
constantly high discharge velocity. As a result, highplume fans have greater exhaust dilution, higher
discharge velocity, greater exhaust mass, and a
greater plume height than conventional blowers and
fans, improving building and campus IAQ. The stack
height plus momentum of airﬂow are designed to be
adequate to discharge air above the turbulent zone
around the building, preventing recirculation of contaminated air into intake air openings.
Pressure-independent chilled-water control valves
installed at cooling coils in the distribution system
stabilize system ﬂow and improve IAQ by more precisely controlling AHU discharge air temperature
and building humidity.
Previously, many labs in the building were pressurized incorrectly, displaying positive pressure with
respect to adjacent corridors. Air distribution systems that serve chemical laboratories should minimize transfer of odor and airborne contamination.
The new design maintains appropriate relative air

ASHRAE JOURNAL

ashrae.org

APRI L 2020

PHOTO COURTESY G/ BA

Indoor Air Quality (IAQ) and Thermal Comfort

New exhaust fans.

pressurization via volumetric airﬂow tracking, maintaining labs at a negative pressure for "dirty operations" (to keep what is in, in) and positive for "clean
operations" (to keep what is out, out).
Existing lab supply air diffusers were located too
close to fume hoods and delivered air at high velocities, creating turbulence. Supply air diffusers should
be located and oriented so supply air is introduced to
the lab without causing turbulence at or near the face
of any fume hoods or other sensitive equipment. The
new design provides displacement diffusers (sized at
40 fpm [0.2 m/s]) over work areas for dilution ventilation; diffusers were installed away from fume hoods.

Innovation

One of the primary challenges was replacing all
AHUs in a penthouse mechanical room packed full
of equipment while the building remained occupied.
Thus, new AHUs were installed outside the existing
penthouse. The lower roof, the location of the old
cooling tower, was structurally reinforced to support
the new DOAS, and the area was ultimately closed in
to create a new, indoor mechanical space. The upperroof of the penthouse was structurally reinforced
as required, and the new laboratory exhaust fans
were installed there. Once the units were secured in
place, the main exhaust and supply ductwork were
run across the roofs, down to the DOAS, and into the
building. The new main exhaust header was installed
with capped terminators, where each fan would
eventually be tied.

https://www.ashrae.org

ASHRAE Journal - April 2020

Table of Contents for the Digital Edition of ASHRAE Journal - April 2020