26 District Energy / Winter 2019 © 2019 International District Energy Association. ALL RIGHTS RESERVED.
was a prime location for the new East
Energy Station. The Science Complex has
the highest energy-use intensity on campus. It is also centrally located and remote
from the existing facilities building. Integrating the East Energy Station into this
project drove a sequencing scenario that
began implementing the 120 F heating
hot water system on the east side of campus. The new heating hot water system
would then connect to west campus buildings, working toward the existing facilities
building where decommissioning the
steam boilers would be the final step. It
was therefore imperative that the design
and funding for the East Energy Station be
accelerated to align with the Science Complex project.
This not only drove the timing of the
utility project but also allowed Carleton
to bundle financing with the science project. As soon as the steam system is fully
decommissioned and replaced with hot
water, the resulting operating savings of
approximately $1 million per year will
fund the annual debt payments on the
utility project portion of the loan.
Step 7: Obtain campus support and buy-in
Once Carleton’s operations team
concluded the replacement strategy was
the best way to achieve its utility planning goals, its next challenge was to gain
administration, board and campus community support. Besides presenting the
technical aspects of the project, operations staff established a long-term vision
built on concepts already approved and
accepted in prior campus plans. Tying the
Utility Master Plan to Carleton’s Climate
Action Plan was straightforward, given the
anticipated carbon emissions reductions;
but the team also highlighted key opportunities to intersect with specific objectives outlined in the 2014 Campus Master
Plan. Facilities staff employed professionally designed graphics, a project web page
and other communication tools to generate widespread project understanding
and excitement. With broad campus support, the board approved the Utility Master
Plan in spring 2017, and the team moved
directly into project implementation.
Carleton is now entering year three
of a five-year construction process (fig. 4).
The three geothermal bore fields are
complete, and the East Energy Station
will be on line in spring 2019 and com-
missioned by fall. Building conversions
on the east side of campus will be com-
pleted in summer 2019, which will be
running on the geothermal system by fall
2019. Conversion of the west-side campus systems from steam to hot water is
scheduled for summers 2020 and 2021.
The new geothermal system construction is still underway, but projections
show a positive return on investment.
The collaboration with MEP Associates
allowed Carleton’s team to adopt and
embrace the following key concepts: · Low-temperature hot water – Transi-
tioning from a steam to a low-tempera-
ture (120 F) hot water distribution sys-
tem is key to future system diversity,
flexibility, modernization and carbon
reductions. The lower temperature
threshold allows Carleton to engage at
a district energy scale such technolo-
gies as ground source heating and cool-
ing, condensing boilers, solar thermal
systems and future heating system
innovations. · Repurposing heat – A heat pump allows
Carleton to move heat out of the chilled-
water system and into the heating
water system, repurposing heat that
was previously exhausted via the cool-
ing tower. In simultaneous heating and
cooling mode, the heat pump is at its
most efficient operational condition
with a coefficient of performance of 7.0. · Electrification to boost carbon reduc-
tion – The heat pump lowers central
plant natural gas consumption by
75 percent, thereby reducing the car-
bon burden of fossil fuels burned on-
site. It shifts more of that load to elec-
tricity, which opens many more options
for carbon reduction through on-site
FIGURE 4. Carleton College Utility Master Plan timeline.
Source: Carleton College.
FIGURE 5. Central plant emissions and annual operating cost reductions. The proposed utility plan
reduces both annual operating costs and carbon emissions.
Source: Carleton College.
Metric tons of
CO2 equivalent Operating costs