ASHRAE Journal - September 2024 - 63

2024 ASHRAE TECHNOLOGY AWARDS CASE STUDY
This allowed the facility to curve in multiple
directions, affording the maximum amount of
natural light and connecting it to the adjacent
maintenance garage.
ENERGY EFFICIENCY
The building obtained LEED Gold certification in
2020, using LEED v4 BD+C (Building Design and
Construction): New Construction. While the owner's
original goal was to achieve LEED Silver certification,
it was concluded during design that LEED Gold was
less than five points away. After conversations with
the owner, the design team worked toward including
additional sustainability measures to achieve Gold
certification. Today, MWEC is one of only 12 facilities
in North Dakota to achieve a LEED Gold certification.
The directive was for a 100% electric building with
a high-performance envelope and HVAC systems.
The ASHRAE/IES Standard 90.1-2010 baseline system
was modeled at an energy use intensity (EUI) of
69 kBtu/ft2/yr (784 MJ/m2/yr), while the project was
modeled at an EUI of 41.9 kBtu/ft2/yr (476 MJ/m2/yr).
After reviewing several different system types,
geothermal became the natural choice to achieve
maximum energy performance. Thermal energy is
moved throughout the building via hot and chilled
water piping systems with an integrated six-pipe
modular geothermal heat recovery-type chiller.
The geothermal loop services water source heat
pumps for the server room, computer room and
electrical room cooling and acts as a backup heat
pump for the control room. The hot water loop
directly serves perimeter radiant slab floor heating,
ceiling panels and heating coils on variable air
volume (VAV) boxes, cabinet unit heaters and
suspended unit heaters. The chilled water loop
services the air-handling unit (AHU) chilled water
coils.
The office spaces are served by VAV boxes for space
conditioning controls that allow ventilation air to
be turned off when occupancy sensors sense the
spaces are not in use. The entire building is fitted
with unoccupied setpoints to maximize energy
savings. Based on one year of energy data, the
Mountrail-Williams Electrical Co-op is operating
at 42 kBtu/ft2/yr (477 MJ/m2/yr)-a 0.1 kBtu/ft2/yr
(11 MJ/m2/yr) difference from the energy model.
INDOOR AIR QUALITY
ASHRAE Standard 62.1-2010 was used to calculate the
minimum ventilation rate and an airflow measuring
station (AFMS) was installed in the outside air duct
with controls to modulate the outside air damper.
These AFMSs ensure the minimum outside airflow
rate is being provided for spaces served by the AHU.
The outside air provided for each thermal zone was
analyzed across all VAV operating ranges to ensure the
appropriate outside air quantity was provided to each
thermal comfort zone. This also considers the 0.8 zone
air distribution effectiveness by having supply and
return air at the ceiling level. Densely occupied areas
such as the lunchroom, huddle rooms, open meeting
rooms, lineman's workstations and training rooms were
provided with local CO2 sensors. These sensors increase
airflow through the VAV, introducing more outside air to
densely occupied spaces.
A building flush-out was performed prior to
occupancy and provided 14,000 cfm/ft2 (71 120 L/s·m2)
of outside air for all spaces to reduce occupants'
exposure to pollutants like VOCs and particulate matter
inadvertently introduced by construction. The flush-out
occurred during September, which allowed all AHUs to
operate at 100% outside air mode during the flush-out.
The Center for the Built Environment's Thermal
Comfort Tool plotted each space on the psychrometric
chart to ensure that space temperatures and air
velocities were within the recommended ASHRAE
Standard 55-2010 guidelines. This tool allowed inputting
assumed activity levels and attire to ensure occupants
would be in the comfort range set by Standard 55-2010
throughout different seasons and weather conditions.
Many spaces had a metabolic rate of 1.0 met when
occupants sat or typed. The lunchroom and kitchen
areas used a metabolic rate of 1.7 met to 1.8 met for the
increased level of activities in those spaces. The final
design included 133 individual occupied spaces, 85 of
which had individual controls.
INNOVATION
The HVAC system uses geothermal heating and cooling
for the entire building. To accomplish this, the well field
design includes 150 wells drilled to 300 ft (91.4 m) deep.
The integrated six-pipe heat recovery chiller is the HVAC
system's focal point and includes multiple modules,
each featuring numerous compressors for redundancy.
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63
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ASHRAE Journal - September 2024

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