2023 Fall Issue of Urban Land - 148

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TOMMY ZAKRZEWSKI
Practical Decarbonization
Helping a tight-budgeted charter school
save money and invest in solar
IncreasIng constructIon expenses
and pressure to decarbonize with
innovative climate solutions are challenging
traditional approaches in
design. For Austin Achieve, a tuitionfree,
open-enrollment public charter
school, HKS put innovative ideas into
action to balance sustainability and
the needs of a diverse community.
During the design process for the
Austin Achieve-Pflugerville Campus
in Pflugerville, Texas, which opens
this school year, our team challenged
restrictive energy code requirements
by taking a flexible approach. We
exchanged passive design elements
of the building enclosure-such as
insulation-with more cost-effective
active-solar-building technologies,
including photovoltaics. We sought
to reduce the embodied and operational
carbon footprint of the project,
in addition to providing energy and
cost savings.
At the time of building permitting,
requirements advanced from the
2018 International Energy Conservation
Code-2018 IECC-to 2021 IECC.
The new code addresses energy
efficiency on several fronts, including
cost, energy usage, use of natural
resources, and the impact of energy
usage on the environment.
Because of the code change and
required performance improvements,
the team needed to find more
efficiencies in the building design.
During design development, we
conducted building energy modeling
and generated response curves
to understand the interactive effects
of building-enclosure design and
mechanical and lighting demands.
We found that the building envelope
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URBAN LAND
FALL 2023
would have less of an influence on
the overall building performance
than expected, and that by removing
insulation, we'd be able to generate
cost savings that could be invested
in more active technologies.
In close collaboration with Austin
Achieve and the Pflugerville Building
Department, the team chose
to pursue code compliance based
on Total Building Performance, per
2021 IECC, a tradeoff method using
building-energy modeling where the
annual energy cost of the proposed
design must be less than or equal to
85 percent of the annual energy cost
of the standard reference design.
The modified envelope analysis
and design that reduced roof and
wall insulation from prescriptive
requirements resulted in projected
labor and material cost savings
of approximately $170,000 and
achieved cost savings of 31.8 percent
and energy savings of 34.5 percent
when compared with the standard
reference design. The savings generated
the idea to invest in a 100-kW
photovoltaic (PV) array that, once in
operation, could begin to decarbonize
the charter school.
Integrating a 100-kW PV array
presented a challenge, as the design
had already progressed into the
construction documents phase. Ideally,
the array would be mounted on
the roof, but the project's packaged
rooftop units made it impossible
to arrange it in a way that avoided
shading and provided a safe rooftop
environment for maintenance. The
team considered a second option
to position the array on the ground,
west of the project site and near the
property line, visible from the surface
parking lot.
Because of various logistical and
Tommy Zakrzewsk, principal and
director of building engineering
physics at HKS
financial constraints, especially current
inflation rates, the client and
team were unable to install the PV
array on the project. But the analysis
showed us that a PV array would
generate up to 144,000 kWh of
renewable energy per year, reduce
carbon emission by 14 percent annually,
and reduce operational costs
by 13 percent. Furthermore, the
reduction in insulation would reduce
the carbon intensity of the building
enclosure more than 47 percent.
The modified-envelope-approach
design analysis did not go to waste.
Austin Achieve asked the design
team to evaluate the area needed to
achieve net zero energy for potential
planning of a middle school and
high school. We found that PV arrays
supportive of net zero would require
seven times the area of the initial
budget diversion for the Pflugerville
Campus project-a helpful exercise
for Austin Achieve so it can plan
how to invest its resources for the
future sustainability of its growing
charter school network.
Solar technology is often an afterthought
to drive high performance
with little planning or maintenance.
This project speaks to the future of
solar and its dependence on energy
modeling early in design. UL
TOMMY ZAKRZEWSKI holds a PhD in civil
engineering and is a principal and director of building
engineering physics at HKS.
H KS

2023 Fall Issue of Urban Land

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