ASHRAE Journal - July 2023 - 33

SECOND PLACE
2023 ASHRAE TECHNOLOGY AWARDS CASE STUDY
Energy Efficiency
Laboratory buildings require significant ventilation.
Therefore, the supply airstream for offsetting the
required exhaust and conditioning of the building
is 100% outdoor air. This building's main energyefficiency
features include a geothermal wellfield, an
energy recovery runaround loop between the exhaust
and outdoor air, a laboratory ventilation control system,
and a low ambient chilled water heat recovery system.
The building's location in Climate Zone 7, along
with the large outdoor air component, results in a
heating-dominant load profile, which is a challenge
for a 100% geothermal project. Therefore, the final
system selection is a hybrid model geothermal system
coupled with a high-efficiency, natural gas, hot water
boiler plant. The geothermal wellfield is designed to
provide all cooling needs and a significant portion of
the heating needs.
Thermal energy is moved in the building through
hot and chilled water systems with an integrated sixpipe
style modular geothermal heat recovery-type
chiller, creating 125°F (52°C) hot water supply and
42°F (6°C) chilled water supply. Heat is transferred
from exhaust air to the outdoor air system through a
glycol-based runaround loop system with optimized
coil selections.
Chilled water is used to cool high internal heat load
spaces such as data and electrical rooms through
blower coil units. When ambient temperatures are
less than 50°F (10°C), the chilled water is created
using the 100% outdoor air-handling unit chilled
water coil as a dry cooler. As a result, low-grade waste
heat is recovered and injected into the building's
incoming outdoor airstream.
The energy use intensity (EUI) in 2020 was
377 kBtu/ft2·yr (4281 MJ/m2·yr). The comparative
standard efficiency for a hot water boiler and aircooled
chiller system calculated EUI using normalized
weather data was 477 kBtu/ft2·yr (5417 MJ/m2·yr).
This results in an energy savings of 100 kBtu/ft2·yr
(1136 MJ/m2·yr) or 21% energy savings. (The facility
remained in normal operation during the COVID-19
pandemic.)
The most dramatic electrical energy savings occur
during the summer because there's more efficient
geothermal cooling versus the air-cooled chiller
(Figure 1). However, the electrical consumption is
higher in the fall since the heat pump is working in the
heating mode, consuming electricity and displacing
natural gas consumption. As the temperatures
continue to drop during the fall, the geothermal-wellfield
system's stored heat is depleted until all available
heat is removed, and the high-efficiency condensing
boilers manage the heating demands.
Indoor Air Quality and Thermal Comfort
A combination of radiant ceiling panels, fin tube
radiation, and in-floor heat increases local comfort
in sequence with ventilation hot water reheat
coils to provide warm and comfortable spaces.
Ventilation in the building's labs is maintained at a
minimum of 6 ACH. Ventilation rates increase with
the operation of a fume hood or other local exhaust
sources. Unoccupied laboratory ventilation rates are
maintained at 3 ACH, which is less than the standard,
recommended 4 ACH. The change was recommended
to and validated by the owner to increase unoccupied
energy efficiency.
Laboratory exhaust ductwork is under negative
pressure within the building, with redundant
exhaust fans on the roof. The fan discharges and
exit velocities are designed to prevent possible
entrainment of exhaust air into the fresh air intake.
The entire building is set up with a room pressure
cascade that progresses from the office spaces (most
positive) to the labs to confine contaminants to the
space in which they are generated.
The BSL-3 lab space is designed with an
independent ventilation system, including an airhandling
unit and exhaust system. A pressure cascade
and HEPA filter system contain contaminants to the
space along with provision in the ventilation system
for sterilization. Office areas are ventilated with the
laboratory supply air ventilation system, essentially
operating as a dedicated outdoor air system.
Innovation
The HVAC system uses geothermal heating and
Ned Rector, P.E., is the director of operations - Midwest and a principal engineer at CMTA in Minneapolis, Minn.. Jeremiah Christenson, P.E., is a mechanical engineer at CMTA in Fargo, North Dakota.
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33

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