The centralized concept at the Central Power Plant and Sterling Power Plant is not only efficient and low-emitting, it avoids the ground level impact were the University to serve these loads with many sources scattered around the campus. This design, one of the lowest emitting sources in the state of Connecticut, serves loads in the most efficient manner with the variety of equipment available at the plants.
Yale’s Central Power Plant
Constructed in the neo-Gothic style, the Central Power Plant has been meeting campus energy needs since 1918. The plant originally used coal to meet the University’s growing energy needs; however, today the plant is a co-generation facility that is primarily fueled by natural gas. The plant provides electricity, steam heating, and chilled water to buildings on Yale’s main campus, including the Science Hill area.
Consisting of three 6.1 megawatt gas turbines and three 1.5 megawatt peaking and emergency diesel generators, the Central Power Plant has a total capacity to produce 18 megawatts of electricity and 340,000 pounds per hour of steam for heating. The facility also has five steam driven chillers that can provide the campus with 14,600 tons of chilled water when at full capacity.
Steam and chilled water for heating and cooling are distributed through a series of linked pipes that make up 14 linear miles of steam tunnels, which pass under and interconnect nearly every central campus structure. Most of the steam and chilled water eventually returns to the plant, where they are cleaned of impurities.
Also part of the Central Power Plant is the Central Campus Chiller Plant. In 2016 two 7.9 MW combustion turbines were installed exhausting into their respective HRSG’s (that’s 95,000 pounds per hour, per turbine). The Chiller Plant also has three 100,000 pound per hour boilers, 6.5 MWs of on-site disel generation, 4.5 MWs of diesel generation which is electrically interconnected for emergencies. The seasonal steam flows range from 80,000 to 235,000 pounds per hour and there are 4,300 tons of steam turbine driven chiller capacity. The Central Campus Chiller Plant has 5,700 tons of electric drive chiller capacity which includes roughly 2,000 tons of “free cooling” during the winter months.
Sterling Power Plant
Converted to a 15 megawatt cogeneration facility in 2010, Sterling Power Plant supplies the Yale School of Medicine and Yale-New Haven Hospital with steam, chilled water and electricity.
Energy and Sustainability
The facility provides a significant step in the University’s goal to reduce greenhouse gas emissions, while helping to reduce energy costs at the Yale School of Medicine campus by approximately 25%. It generates up to 15 megawatts of electricity from two turbines, and recycles heat resulting from that process to help produce 180,000 pounds of steam per hour from two Heat Recovery Steam Generators. The electrical power generated by the facility serves the Medical School campus and the steam generated serves both the Medical School and Yale-New Haven Hospital.
Extensive dispersion modeling was conducted to establish the stack heights at 170 feet above ground in order to meet the latest EPA air quality standards. Exhaust gases from the two power trains are scrubbed in order to clean the exhaust before it enters the stacks. The dual wall steel stacks are also insulated in order to assure that the discharge temperature of the exhaust stays high enough to meet EPA standards for cleanliness.
Integral to the design are the improvements to the public open space pedestrian path network through the site starting with an new public plaza on College Street that is a regular stop on Yale’s bus line. Bicycle racks are also provided in multiple locations on the site.
The cogeneration plant site design results in a net reduction of impervious surface and includes a storm water retention galley that moderates the discharge of water into the municipal storm water system. An oil separation system is also employed to keep pollutants from the waste stream. Inside the plant, condensate from inlet air cooling coils is collected and recycled as make-up water for the facility’s cooling towers.
The steel structure is clad in stone, cast stone, and brick, all selected for their long-term durability and consistency with the general architectural context that defines the Yale Medical School Campus. The stainless steel cladding on the stacks was also chosen for its low maintenance longevity.
A significant sustainable aspect of the project is the re-use of the concrete walls and footings of a decommissioned 3 million gallon cold water storage tank as the foundation and underground walls of the facility. This left over 3800 cubic yards of heavily reinforced concrete in place.
Part of the reduction of impervious surface was achieved with the design of a new green roof which is an extension of the newly defined public open space over the middle of the building. In addition, mostly native plants were selected for their horticultural hardiness and suitability to the local climate and lower maintenance requirements. Through careful planning and construction logistics two mature Siberian elm trees were saved and other mature trees were transplanted elsewhere on campus.
Locating the primary equipment below grade, within the modified confines of the old Cool Pool, isolates most of the equipment noise from ground level and adjacent buildings. Noise generated by ground level equipment is blocked by 14-foot high masonry walls, with a net result that the sound generated by the new plant is at, or below the ambient noise level at the site prior to construction.
The new facility sits in an existing underground concrete structure formerly used to hold cold water. Converting Sterling to a cogeneration facility will enable the plant to simultaneously produce electrical and thermal energy similar to the Central Power Plant. The units will improve efficiency, saving up to 20,000 metric tons of carbon equivalent per year.
Photos by Phil Handler and Jim Fiora
For more information on Yale’s power plants please visit facilities.yale.edu.