The process toward developing Carleton’s Utility Master Plan began with the 2011 Climate Action Plan, which laid out a plan for the College to achieve carbon neutrality by 2050. Work on the Utility Master Plan began in earnest in 2014, following the publication of the Facilities Master Plan, which detailed how Carleton will address the most pressing and the longer-range facilities and physical plant priorities identified in the College’s 2012 Strategic Plan.
After nearly two years of engineering analysis and cost modeling, the Utility Master Plan Team presented the following proposal to Carleton’s Board of Trustees in October 2016.
The process culminated in an October 2016 report to the Board of Trustees, which is presented below.
At the turn of the twentieth century, Carleton transitioned from coal furnaces and wood-burning fireplaces in each building to a centrally distributed steam heating system. This system was constructed at the beginning of President Cowling’s administration, an era that launched considerable expansion of Carleton’s campus and elevation of its stature as a renowned liberal arts institution. Throughout the past 100 years, including multiple periods of expansion, this system has served the campus well. Around 1950, the central heating plant was converted from coal to natural gas.
Beginning in the 1960’s, hot water began to displace steam as the standard heat transfer medium used in buildings. Hot water systems provide much better control, more even heating, greater energy efficiency, and are safer and easier to maintain. Over the past five decades, Carleton has transitioned nearly all of its buildings from steam to hot water heat, while still maintaining a central steam plant and steam distribution infrastructure to those buildings. Evans Hall, Skinner Chapel, and Scoville Hall are recent examples of Carleton’s transition from steam to hot water heating in buildings. Only a few buildings — Old Music, Goodsell Observatory, Laird Stadium, and Faculty Club — remain yet to be converted.
Under President Poskanzer’s administration, the campus undertook — and the Board approved — a Climate Action Plan, Strategic Plan, and Facilities Master Plan, which provided vision and insight on how the built environment at Carleton is expected to evolve over the next 20–30 years. The 2016 Utility Master Plan assessed the condition of Carleton’s existing central utility systems, quantifying the scope and cost to repair or replace aging piping and major components — some of which are 50–100 years old. It then examined the best way to support the goals of the campus Facilities Master Plan and the Climate Action Plan, and to provide flexibility for future generations.
The planning process closely examined current mechanical technology and engineering practices, which are evolving to operate heating systems more efficiently using a lower supply water temperature (typically 120 degrees vs. the traditional 180 degrees). This seemingly minor change opens up opportunities to utilize significantly more efficient technologies such as condensing boilers, heat pumps, geothermal systems and solar thermal systems.
Evaluation: Concept Phase
The Utility Master Plan concept phase began in fall 2014, following publication of the campus Facilities Master Plan. Facilities staff and engineering consultants assessed the scope of current and future campus plans and performed a cost/benefit analysis of maintaining the existing central steam plant vs. transitioning to a central hot water system. The concept phase focused on taking advantage of existing assets such as Carleton’s recently upgraded electrical system, existing chillers and cooling towers, and underground tunnel system. It also capitalized on synergies with planned construction activities, most importantly the renovation and expansion of the science facilities.
The concept phase also explored technologies that would help reduce Carleton’s carbon emissions. These include:
- heat pumps, which transfer heat between heating and cooling systems to make use of simultaneous heating and cooling loads
- geothermal bores, which supplement heating and cooling requirements by using the earth as a heat source or sink, and
- combined heat and power (CHP) engines, which simultaneously produce electricity and heat. (Note: this scope of work is now referred to as “Phase 3 – Electric Generation Systems” and could be CHP, wind, solar PV or other lower carbon technology)
These systems complement each other in such a way that it makes more sense to do them together than to implement any one system on its own.
Benefits of a Transition
The Utility Master Plan Concept Phase concluded that the transition to a hot water system, coupled with geothermal heat pump and combined heat and power (CHP) technology, could offer:
- a full renewal of Carleton’s aging heating plant and distribution infrastructure,
- a significant reduction in Carleton’s carbon emissions, and
- a significant reduction in Carleton’s annual plant operating costs (plant operation + utilities) that could repay the entire capital investment in less than twenty years.
The concept phase also concluded that a satellite plant — housing proposed new utility equipment — could be built as part of the new science addition.
Evaluation: Design and Pricing Phase
In February 2016, the Buildings and Grounds Committee authorized Facilities Staff to proceed with a more detailed phase of design and contractor pricing. This authorization also included approval to proceed with geothermal test bores to confirm the viability of possible bore field locations on Carleton’s campus. This six-month effort resulted in a design package, market-tested contractor pricing, and a preliminary phasing plan beginning in summer 2017.
The Utility Master Plan team evaluated the capital cost, operating cost, utility cost, and carbon emissions for the base case of maintaining the existing steam system vs. a transition to a hot water central heating system:
- Base Case: Maintain Existing Steam System — Continuing to replace and maintain existing central steam plant equipment and distribution piping has an estimated capital cost of $21 million spread out over the next 20 years. This option generates no operating or carbon savings relative to current conditions.
- Recommendation: Transition to a Hot Water System — Transitioning from central steam to a central hot water system tied to heat pump, geothermal bore field and combined heat and power (CHP) technologies has an estimated capital cost of $38 million over the next five years. This option would reduce plant utility and operating costs by an estimated 36 percent and Scope 1 and 2 carbon emissions by an estimated 38 percent relative to current conditions. The annual savings would pay back the Capital investment in approximately 17 years, for a positive 30-year net present value of $9.8M versus the Base Case.
Facilities Staff therefore recommend transitioning to a hot water system. This recommendation includes the following components:
- Complete the transition from steam to hot water heating by replacing the central steam plant equipment and distribution piping with hot water infrastructure.
- Design the central plant to operate at a 120 degree hot water supply temperature, working over time to transition all campus buildings to 120 degree systems.
- Retrofit some of Carleton’s existing buildings to utilize 120 degree heating supply water as part of this project; establish this as our standard for all new construction or major renovations.
- Install decentralized gas domestic hot water heaters to replace the existing steam heat exchangers.
- Add a heat pump coupled with a geothermal bore field to take advantage of simultaneous heating and cooling loads across campus; locate this equipment in a utility sub-basement constructed as part of the New Science Addition.
- Add a combined heat and power (CHP) reciprocating engine in the Facilities Building to benefit from the efficiencies of generating electricity and heat simultaneously and to supply the electricity demand of the heat pump system. [Note: Facilities staff later assessed that the Xcel Energy electricity grid is reducing its carbon emissions much faster than anticipated. Carleton thus opted to rely on increasingly “greener” public electricity and on-site renewable energy systems rather than investing in CHP.]