ASHRAE Journal - October 2024 - 56

2024 ASHRAE TECHNOLOGY AWARDS CASE STUDY
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a more traditional system would be. The
water-to-water heat pump is at the upper
end of its capability to make 130°F (54.4°C)
water, and this contributes to nuisance tripping,
requiring maintenance staff to reset the equipment.
This unit has three modules, with two stages each
so the unit can keep operating while providing
the desired energy results if a stage or two are
tripped. The system is also designed with multiple
temperature and fl ow meters that are integrated into
the BMS. This data is very helpful for maintenance
and repair to identify issues and monitor the results
of control sequences.
A commissioning agent ensured that all equipment
was installed and operating as specifi ed. A controls
checkout with the engineer once commissioning was
complete is also important to ensure the building is
operated per the design. Commissioning is essential
to achieve effi cient building operation and proper
controls programming.
COST EFFECTIVENESS
Construction cost for this building was $23.3
million. The mechanical and plumbing costs were
$3.66 million. It is estimated that in total the
mechanical system cost $341,500 more than a typical
mechanical system.
The owner uses Rocky Mountain Power rate
schedule 6a. This schedule charges more per kWh,
and less for kW demand than the standard rate
schedule. With on-site power generation, using the
photovoltaic (PV) array helps reduce the energy cost.
Unfortunately, the local utility company also charges
a penalty to the owner to help pay for infrastructure,
as the building does not use enough electricity to
cover that cost.
Sunburst Elementary is the fourth building of Davis
School District's " Zero Energy Building Prototype. " The
fi rst three prototype buildings had more PV generation
and met the Zero Energy Building criteria of the
Department of Energy's " Common Defi nition for Zero
Energy Buildings, " which came out in September 2015.
Davis School District has made a conscious decision
based on economics and penalties from local utility
companies to reduce how much PV offset is used so
that it offsets nearly all of the electricity, and offsets no
gas, rather than get penalized for overproduction with
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FIGURE 1 C02 emissions.
80.00
60.00
40.00
20.00
-20.00
Actual
Baseline
no return. Sunburst was the fi rst in the district with
this approach.
The actual energy cost for the year including the
penalty for not using enough electricity was $41,467.
Using the actual energy use data, we estimate that the
building energy costs not including PV generation and
not including the infrastructure penalties would be
$50,826. Compared to the code minimum building this
equates to a savings of $17,339 in energy costs per year,
and a payback of approximately 19.69 years.
When the cost of PV panels is added to the mechanical
system, the added total cost is estimated to be $811,548.
Estimating that the infrastructure penalties will only
be assessed for fi ve to 10 years, payback is estimated to
be approximately 25 - 26 years. The district recognizes
that the PV system does not have a good payback but
believes using clean energy is the right thing to do.
ENVIRONMENTAL IMPACT
The ground loop heat exchanger, heat pumps,
evaporative cooling and improved building envelope
all work together for the overall energy effi ciency
of the building. These measures, along with the
on-site PV electrical generation, result in a 89%
reduction in electricity consumption from the grid
when compared to the baseline. Using the EPA's
" Greenhouse Gas Equivalencies Calculator, " this is
equivalent to 262 tons in CO2 emissions.
The water-to-water heat pump is used to provide most
of the building's heat. This combined with the other
energy conservation measures reduces the natural gas
consumption by 81% compared to the baseline model,
reducing the CO2 emissions by 142 tons. These are a
combined reduction of 404 tons in CO2 emissions per
year. Additionally, the mechanical system does not use
any refrigerants that contain CFCs.
Tons
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ASHRAE Journal - October 2024

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