ASHRAE Journal - June 2024 - 61

2024 ASHRAE TECHNOLOGY AWARDS CASE STUDY
to achieve their individual potential, to contribute to
a changing society and to be receptive to learning as a
lifelong process. "
Sustainability is incorporated into the school's
curriculum, with lesson plans available at each grade
level that teach about renewable energy, and a new
initiative called " Renew our Schools " tasking students
with completing a hands-on learning experience
to expand knowledge and decisions on energy
consumption.
Two years into operation, the school has exceeded
expectations. Energy metering data to date has
shown annual energy production exceeding building
energy use, going beyond net zero to net positive and
also meeting International Living Future Institute's
requirements for Net Zero Energy Building Certification.
The innovative technological features of this project
include the following:
Ground-source vertical heat exchanger
system. Ninety vertical heat exchangers that were
400 ft (121.9 m) deep served as the heat sink for the
ground-source heat pump (GSHP) system.
Dedicated outdoor air system (DOAS) with air-toair
energy recovery wheel. A dedicated outdoor air
pretreatment system with total energy recovery wheel,
cooling coil and MERV 13 filtration was used to pretreat
all mechanically provided outdoor air and provide
heat recovery from the all-building general exhaust
air system. The system modulates based on a carbon
dioxide (CO2) control system and building pressure
control to maintain operational requirements.
Optimized pumping. A prefabricated pumping skid
was used for the geothermal loop in place of a traditional
lead/lag pump configuration. The skid used five smaller
pumps with electronically commutated motors (ECM)
and an integral controller to control the ground-source
hydronic loop down to minimal pump energy levels.
Ground-source water-to-air heat pumps.
Premium-efficient, ground-source, water-to-air
heat pumps with multispeed and ECM fans, MERV
14 filters and dehumidification control with variable
speed operation were placed in high density spaces for
primary space heating and cooling.
Water-cooled condensers. The condensing units
serving the kitchen equipment and freezers use the
geothermal loop to exchange heat instead of traditional
refrigeration systems.
Electrochromic glass. Self-shading glass along
southern walls is adjustable, providing additional shade
and control during the cooling and heating seasons.
Roof-mounted solar photovoltaics. A 646 kW dc
rooftop solar array made up of 1,704 photovoltaic (PV)
panels integrated into the slope of the butterfly roof was
designed to produce 805,000 kWh ac annually to offset
the annual building energy use.
Battery storage. A 125 kW battery storage system is
used for storing excess energy produced by the solar
array. That energy is used during high-demand times or
sold back to the utility.
No gas connection. Notably missing is a natural gas
connection, as being a fully electrified building was a
key goal of the project.
Energy Efficiency
The early energy use benchmarking defined a
target energy use intensity (EUI) of 20 kBtu/ft2·yr
(227.1 MJ/m2·yr) for the building based on other
elementary schools in the area and its net zero energy
goals. Once this value was confirmed with energy
modeling efforts, it was used to guide decisions for
energy efficiency. For the mechanical systems, a
geothermal/GSHP system was determined to be the most
effective at keeping the project on target.
Other mechanical considerations included adding
the kitchen and refrigeration systems to the geothermal
loop instead of traditional condensers. Energy
models indicated that the building envelope was also
a significant energy use driver. To keep the building
design within the energy use target, the energy models
were used to optimize the architectural elements of
the building. Different wall constructions, various
window-to-wall ratios and window placements were
all investigated. The use of electrochromic glass on
southern-facing walls was also introduced to assist
in the energy efficiency of the building envelope by
providing additional shading or daylight when needed.
Through the various model iterations mentioned
above, the design team was able to maintain the building
EUI near the target of 20 kBtu/ft2·yr (227.1 MJ/m2·yr),
with the final proposed design at an EUI of
21.7 kBtu/ft2·yr (246.4 MJ/m2·yr). Additional systems
components such as roof-mounted solar, aggressive
lighting controls, low flow plumbing fixtures, metering
and building automation systems also contributed to
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ASHRAE Journal - June 2024

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