[The following content is previously published in the winter 2019 issue of District Energy Magazine]
In 2008, Brown University in Providence, R.I., set an ambitious goal to reduce campus greenhouse gas emissions by 42 percent from 2007 levels by 2020.
Ruth Simmons, the university’s president at the time, stated, “Brown is committed to doing our part to create a more sustainable environment. It is important to lead by example, taking action to preserve and protect the planet.”
This mandate empowered the university’s Office of Sustainability, which is housed in and is a key part of the Facilities Management office, with clear institutional goals and support. The office embarked on a comprehensive program of energy efficiency measures to lower Brown’s carbon footprint. It proved to be a major success, eliminating nearly 20,000 metric tons of carbon dioxide equivalent emissions in the past 10 years. To meet the president’s promised 42 percent reduction goal on time, however, a plan to improve the energy efficiency of Brown’s 1960s-vintage campus heating system was also needed.
That plan, the Thermal Efficiency Project, was launched in 2018. It involves converting Brown’s existing high-temperature hot water system – based on centrally produced high-pressure steam – to modern, highly efficient, lower-temperature hot water.
After Brown University announced its 42 percent emissions reduction target, the Office of Sustainability established a program to fund the energy efficiency measures. Utility incentives received as rebates from National Grid are directed into the fund, enabling future initiatives. This supplemental source of funding for the university’s annual greenhouse gas reduction budget allows the Office of Sustainability to support facilities improvements to provide greater value, by combining asset renewal with additional energy efficiency.
IT WAS CLEAR THAT SMALL, INCREMENTAL STEPS WOULD NOT HAVE SUFFICIENT IMPACT. A TRANSFORMATIONAL PROJECT OF THE DISTRICT HEATING SYSTEM WAS NECESSARY.
Thus far, the energy fund has paid for lighting retrofits, controls optimization and retrocommissioning of HVAC systems across the campus, and fuel-switching from oil to natural gas at the campus heating plant. To date, 527 projects of various sizes and scope have been completed, are in progress or are under development. Since 2008, Brown’s $27 million investment in these projects has reduced CO2e emissions by a total of 19,723 metric tons (27 percent) and resulted in annual energy expense savings of more than $4 million.
While these are impressive results, achieved over a short period of time, the path to attaining the full 42 percent green- house gas emissions reduction goal by 2020 was less clear. By 2015, many of the “low-hanging-fruit” measures had already been implemented, and little more could be achieved on that front. The sustainability department’s attention turned to the elephant in the room: the campus district heating system. It was clear that small, incremental steps would not have sufficient impact. A transformational project of the district heating system – potentially involving re-engineering and overhauling the central heating plant, distribution net- work and some building HVAC systems – was necessary.
Brown University’s existing district steam heating system, commissioned in 1967 to replace an earlier steam system, provides 350 degree F high-temperature hot water to approximately 4.5 million sq. ft of the roughly 6.5 million sq. ft of floor space on campus. It serves a variety of heating needs, from hot water space heating to high-pressure steam genera- tors used for important processes such as sterilization of lab equipment. The range of demands on the district heating system requires operating conditions that lead to certain inefficiencies – such as more energy- and labor-intensive startup and greater thermal losses in the piping networks, due to the higher-temperature hot water generation and distribution.
Inefficiencies aside, however, Brown University was fortunate to have a hot water district heating system – an asset that could certainly be built upon (piping was recently overhauled) and not replaced. Similar institutions across the northeastern states typically have district steam systems. Comparing the total efficiency of these legacy steam systems, not just boiler efficiency, reveals an average yearly efficiency of around 50 percent – meaning that half of every dollar of natural gas they burn is wasted. Brown University’s high-temperature hot water system was a generation ahead of such systems: Analysis of campus data showed that the system averaged a yearly efficiency of around 66 percent, better than the cohort average but still representing significant inefficiencies.
In addition to the central heating plant, any plan to upgrade Brown’s campus energy system had to take the distribution network into account. The campus relies on more than 30 district energy hubs – dedicated mechanical rooms that take energy from the high-temperature loop and convert it for a medium-temperature hot water loop and/or process steam generators. In fact, some of these hubs con- vert the high-temperature hot water into low-pressure steam, only for that steam to then be converted to medium-temperature hot water closer to the heating load. Out of all the district energy hubs, only 11 generate any steam. Six of these hubs, which date from the 1950s and predominately supply steam for space heating, are on the priority list for renewal per the university’s utility master plan; the cost to replace five of these six steam hubs (including a small amount of work at the central plant) was estimated at $16.8 mil- lion. (The other five steam-generating hubs are more modern and produce steam for process loads.)
In 2014, Brown commissioned a study of opportunities to raise efficiency at its central steam plant. This study was completed in early 2016. As expected, it determined that Brown’s campus steam/ hot water heating system – designed in an era when energy costs and associated emissions were not as much a priority as they are today – had a significant efficiency penalty associated with the high temperatures and high operating pressures.
Engineers from Ecosystem Energy Services received this study and, working closely with members of Brown’s sustainability office and Facilities Management team, started developing possible paths forward to improve the efficiency of the whole district heating system. The analysis began with a key question: What and where is the energy’s destination? It quickly became apparent that although the system was designed within parameters to serve high-pressure steam loads, these loads accounted for only a small amount of the plant’s total energy consumption. In a nutshell: The system could only be as efficient as its weakest link – the steam loads.
The next step was establishing a preliminary understanding of all the steam and high-temperature hot water loads served by the district system. Was it feasible to eliminate the need for steam loads served from the high-temperature loop? Was it possible to lower the district hot water heating loop below 350 F? Could the satellite steam hubs be eliminated? Could the steam heating be converted to something else, or decoupled? Ambient spaces are maintained at around 72 F, and domestic hot water is heated up to 140 F; so, leaving aside process loads (sterilization, humidification, kitchen equipment), did the campus really need 350 F hot water and steam to heat its buildings?
The team realized there were significant advantages to medium- or lower-temperature hot water (over high-temperature hot water and steam) heating. They include
Hot water systems also introduce the potential to use newer heating technologies, such as heat pumps, solar heating and even thermal storage. However, these advantages are only applicable to district energy loops well below 200 F, and the benefits compound at lower heating temperatures.
The next strategic questions were framed around leveraging the university’s broader plan for asset renewal to develop a transformational project that would deliver great energy-saving value and align with the institutional greenhouse gas emissions goal. In late 2016, Ecosystem Energy Services was contracted by Brown to further study and perform the engineering necessary to design a district energy system upgrade. Typically, asset renewal needs and deferred maintenance present some of the greatest facilities challenges. Often asset renewal budgets are directed toward the gravest outstanding issues on campus, without necessarily tackling energy and greenhouse gas reduction.
The utility master plan that Brown University had commissioned earlier proved to be a significant advantage when it came to developing a project that addressed university asset renewal concerns in the context of a broader energy savings mandate, making it easier to generate value for the campus. This carefully conceived plan enabled Brown to avoid a piecemeal approach to the district heating system asset renewal and potential upgrades and instead pursue a holistic and transformational project.
This project thus became known as the Thermal Efficiency Project (fig. 1).
One of the big challenges Brown University and Ecosystem faced was logistical, i.e., planning to manage energy demands in sensitive environments. The areas with the most energy consumption, and thus most important for the project, are also the most critical spaces on cam- pus, including those that house important research facilities. Installing temporary HVAC equipment for these buildings while they undergo deep retrofits would eliminate some of the financial value that this project is set to achieve. Thanks to close collaboration and communication, strategies have been devised to ensure that this project achieves a win-win on asset renewal and energy reduction.
For each building, collaboration between engineering, facilities and faculty determined the acceptable level of impact to building operations. For instance, a time frame for equipment shutdown during certain seasons was agreed on by all parties involved. An implementation schedule was then carefully reviewed to ensure that the design could be installed during these time windows. Sometimes designs were altered to accommodate critical campus needs. In one instance, when heat recovery and preheating outside-air systems were to be installed, requiring two separate coils, a custom coil was developed instead that would need only one installation and shutdown.
In terms of engineering design, there were two main challenges with the Thermal Efficiency Project: converting steam loads to hot water and operating the existing district heating system at a lower temperature.
THERE WERE TWO MAIN DESIGN CHALLENGES: CONVERTING STEAM LOADS TO HOT WATER AND OPERATING THE EXISTING HEATING SYSTEM AT A LOWER TEMPERATURE.
The challenges of converting steam loads in any building can be significant, from effectively managing construction and mitigating occupant disruption to planning and implementing intrusive work to access steam equipment/piping. This challenge is magnified when trying to implement this work as part of an investable energy efficiency project on a bustling university campus that is largely occupied throughout the year.
However, the Thermal Efficiency Project team was confident it could be done.
The following strategies were selected for inclusion in project plans to minimize the impacts of the conversion on Brown’s students, faculty and staff:
During the design phase, it was essential to follow a case-by-case approach, as some buildings required institution-specific plans or represented greater value overall for conversion.
Across the campus, each individual steam load, whether a building or process, was analyzed. First, potential building-level energy savings were calculated to determine the standalone payback for a building’s conversion to hot water. This pay- back was then compared to any options for installing standalone steam equipment. Each building and its specific steam need were carefully analyzed to quantify the benefits and value of either converting the load and remaining with the district heating system or installing stand- alone steam. It was determined that all required steam loads, such as sterilization, would, of course, require standalone steam equipment.
The next design challenge involved utilizing the existing district system, which had been designed for a 100 F delta T, meaning a lot of energy could be passed through the pipes for little flow rate from the plant. Reducing the plant’s operating temperature would require lowering this temperature differential, so subsequently more flow would have to pass through the existing piping. In some cases, this change would increase flow rates beyond what was appropriate for the size of pipe.
To analyze piping demand, a simulation was developed, including all the piping of the district plant and location- specific energy loads. This problem was resolved by re-engineering sections of the district loop: specific high-energy-load buildings were identified and analyzed for the potential to convert to lower-temperature heating. With this understanding, high-energy-load buildings could be connected to the return piping of the district energy loop, meaning more energy could be extracted from the loop, increasing the temperature differential and reducing the flow rates below the limit of what the section of piping could accept. Existing hubs were re- engineered, again to reduce the temperature at which energy could be utilized, improving the delta T of the prospective new lower-temperature system.
Reducing energy demand at the hub/ building level was another key strategy. Local heat recovery systems could be installed across high-energy-consumption buildings and at locations with restricted pipe sizing. This measure can reduce the amount of energy that needs to be carried through the piping and further mitigate the potential flow issue.
A key example of this solution has already been implemented at the Sidney E. Frank Hall for Life Sciences and the Center for Biomedical Engineering. The two linked buildings are among the largest on campus, in terms of both square footage and energy consumption. Their location on the district heating system close to the central heating plant on the main line before piping splits and branches across campus – placed significant demand on the flow from the plant. They are also both research-intensive spaces, so they are HVAC- and energy-intensive. Both buildings also require a significant amount of 100 percent fresh- air ventilation.
Ecosystem designed a runaround loop across several HVAC systems that recovers heat from the building’s exhausted air, while also taking advantage of the opportunity to install a low- temperature building-level heating system. The new system incorporates a single heating coil that prioritizes exhaust heat recovery and gets supplemental heating from the return of the campus network. This design ensured a significant amount of flow from the central heating plant could be reduced, an essential step in enabling the district system to function at a lower, more efficient temperature.
Overall, the key lessons from the development of the Thermal Efficiency Project, and recipes for success, were already starting to be evident toward the end of the design phase. They include the following:
Brown University’s leadership was committed to turning the liability of district heating asset renewal into a trifecta of wins: reducing operating costs, lowering greenhouse gas emissions and renewing assets at the end of their service life while modernizing the system. The three-year Thermal Efficiency Project launched in 2018 will not only reduce operations costs but will also open the door to newer, greener technologies, compounding the environmental and economic benefits of the project. Brown University expects to reach its 2020 greenhouse gas emissions goal. With the Thermal Efficiency Project underway, the institution is in a much stronger position to address the next big challenge that the future holds for the campus, whatever it might be.
Jessica Berry is the director of the Office of Sustainability at Brown University. She provides leadership across the institution to identify, advise on, manage and implement sustainability best practices. Additionally, she is responsible for utility and waste management including identifying and implementing waste and green- house gas reduction strategies. Berry holds a Bachelor of Science degree in natural resources and environmental studies from the University of Vermont’s Rubenstein School of Environment and Natural Resources and a Master of Science degree in environmental studies from The Ever- green State College. She has over 15 years of experience in the environmental sector including nonprofit management, international environmental consulting and higher education.
J.P. Drouin, CEM, DBCP, is director of project development at Ecosystem Energy Services. He specializes in transformational energy measures and deep building retrofits such as steam-to-hot-water conversions, heat recovery chiller applications, district energy networks, and combined heat and power. He holds a bachelor’s degree in mechanical engineering from McGill University and is a recognized engineer by Ordre des ingénieurs du Québec (Quebec Order of Engineers). Drouin received the 2016 International Young Energy Professional of the Year Award from the Association of Energy Engineers.
Ben Milbank is a project development engineer in the New York City office of Ecosystem Energy Services. He was a member of the engineering team for the Brown University Thermal Efficiency Project. Originally from the U. K., Milbank came to the U.S. to study for his master’s degree in mechanical engineering at Columbia University, having graduated with first-class honors from the University of Sussex, where he studied mechanical engineering. At Columbia, he focused on energy systems design and thermofluids and was a Columbia Business School Social Enterprise Fellow, developing several energy efficiency projects for local churches and community centers.