The facilities engineering team at Princeton University is now well into the second decade of a capital investment program aimed at reducing CO2 emissions by 2020 to below 1990 levels. What began as an effort to reduce operating costs and secondarily, lower emission levels, has now become a preoccupation with lightening the university's carbon footprint in a cost-efficient manner.
Throughout the entire upgrade project, the team has been quick to acknowledge that it will take a combination of technologies to reach the 2020 target. To achieve this goal, the energy plant has recently installed direct-contact heat recovery equipment and is in the process of installing solar photovoltaic (PV) generation. Additionally, the energy plant features a highly efficient use of combined heat and power (CHP). All of these components contribute to the university being well-positioned for the successful reduction of CO2 emissions.
Surprisingly, the Princeton campus has had combined heat and power since 1876, long before CHP became recognized as a modern-day innovation. At that time, a steam driven generator was coupled with the campus' first boilers, enabling the exhaust steam to heat nearby buildings. But it was in 1996 that the energy plant really brought CHP to its current potential. It was then, after more than a decade of research and design studies, that a new facility, capable of meeting all the campus' heat and power requirements, plus environmental regulations, was built and equipped for long-term needs.
Obsolete boilers were replaced by new ones as part of a cogeneration system capable of generating 15 MW of power and 180,000 pounds of steam. These were followed by the acquisition of a highly efficient 2,500-ton electric chiller, bringing the plant cooling capacity to 15,500 tons. All chlorofluorocarbons in the chilled-water plant were replaced with hydrochlorofluorocarbons, and chiller speeds were increased to regain their original capacities. A few years after the plant went into operation, a 40,000 ton-hr chilled-water thermal storage system was added.
In 2006, the energy plant, ever on the lookout for new ways to move closer to the 2020 target, began researching direct-contact heat recovery technology. Once convinced that the technology offered value in terms of performance, emissions reductions and return on investment, the team invested in a Percotherm direct-contact heat recovery system. Custom-designed by Sofame Technologies Inc., the system recovers residual heat contained in the boiler's flue gas and transfers the heat to incoming make-up water and returning condensate. The complete system consists of a condensing economizer, an indirect-contact economizer, four plate-and-frame heat exchangers, four pumps, an induced-draft fan, three control dampers plus digital controls.
The heat recovery system has been up and running for three years, allowing plant engineers to monitor performance and assess results. The energy from approximately 300,000 lbs per hour of flue gases is being recovered and turned into usable energy. CO2 production has been reduced by approximately 5,000 metric tons/year while energy costs are proportionately lower.
Currently, the facilities engineering plant is also adding PV generation to its mix of CO2 lowering, cost saving solutions. The system provides a stable, long-term, low cost supply of power that takes Princeton closer to its 2020 target. In fact, based on a capacity of 5.3 MW producing 8.4 million KWh/year, PV generation helps avoid the production of 3,091 metric tons of CO2 per year. That amounts to 9.4 percent of Princeton's total CO2 reduction goal. It also provides Princeton with Solar Renewable Energy Certificates (SRECs). Until such time as the capital investment has been paid off, the university will sell the SRECs in the New Jersey market. Once the system has been paid for, the SRECs will be retired and the university will claim avoided carbon emissions itself.
Both technologies, direct-contact heat recovery and PV generation, constitute linchpins in a well-thought-out assault on CO2 emissions, and each offers a valid rationale for purchase. On one hand, PV generation is highly effective in eliminating CO2 emissions and the SRECs are impressive incentives, but the simple payback period can be from seven to 10 years, and will occupy 27 acres of land. The Percotherm system, on the other hand, reduces CO2 emissions by 5,000 metric tons per year, takes no additional real estate and has a payback timeframe of two to four years. These are just two of the many recent projects that the university is implementing to lower its carbon footprint and also save money now and over the long term.
With less than a decade remaining until the 2020 target date, Princeton University is making the kind of investments that illustrate a sustained commitment to its goal.