ASHRAE Journal - July 2023 - 34

SECOND PLACE 2023 ASHRAE TECHNOLOGY AWARDS
FIGURE 1 Modeled vs. Actual Electricity Consumption
25.0
20.0
15.0
10.0
5.0
Jan
Feb
Mar
Apr
May
Jun
Modeled
July
Aug
Actual
cooling for the entire building. The wellfield
design includes 308 wells at 220 ft (67 m) deep.
The integrated six-pipe heat recovery chiller is the
HVAC system's focal point. It comprises seven 50 ton
(176 kW) modules integrated into a single system. The
modular design improves the system's capability to
load match and provides redundancy. The unit can
create chilled and hot water directly without using
the geothermal wellfield system as the demand exists.
Excess energy from heat rejection in the cooling mode
or heat absorption in the heating mode is transferred
to the geothermal well field loop as demand requires.
Laboratory buildings typically have a high level
of reheat required in the summer to maintain
humidity levels and cooling requirements. During
this time, the six-pipe chiller provides heat as a waste
by-product, and the building requires no additional
energy input for reheating.
A heating-dominant, high-ventilation rate design
required for labs is a challenging application for
geothermal energy. Therefore, this challenge led
to a hybrid approach of designing the wellfield to
meet all annual cooling demands and a portion of
the heating demand. The offset heating demand is
provided by natural gas high-efficiency condensing
hot water boilers. The heating system is arranged so
that the geothermal system is the first source of heat,
and the boilers provide additional heat if required.
Functionally, the geothermal wellfield system is operated
until the ground loop temperature no longer
supports efficient operation, which is 35°F (1.7°C).
34
ASHRAE JOURNAL ashrae.o rg
J U LY 2023
Cost Effectiveness
The hybrid geothermal option installed cost
premium was approximately $857,000. In 2020 the
annual operating cost savings was approximately
$31,400 per year between hybrid geothermal and the
base boiler and chiller system. This resulted in 20%
savings in annual energy consumption, which is a
27-year payback.
Environmental Impact
The owner prioritized energy consumption and
utility cost, which reduced the carbon footprint.
The hybrid geothermal strategy over the more
traditional natural gas boiler and air-cooled chilled
option reduces site annual carbon emissions by
approximately 206 metric tons of CO2e/year, or about
18%. The geothermal well field is on agricultural
land. After installation, the land went back into
production.
PHOTO 1 The North Dakota State University Veterinary Diagnostic Laboratory.
Sept
Oct
Nov
Dec
CASE STUDY
Operation and Maintenance
All significant equipment is in two
adjacent grade-level mechanical
rooms. These two adjacent rooms
contain all major mechanical
equipment except two roof-mounted
exhaust fan systems serving the
general building and the BSL-3
lab space exhaust. Roof access is
provided from the mechanical
room, and all equipment, except
the roof exhaust fan systems, can be
serviced simply by walking up to the
equipment in a comfortable indoor
environment.
Electric Energy EUI (kBtu/ft2)
DAN FRANCIS PHOTOGRAPHY
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ASHRAE Journal - July 2023

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