Running hot and cold
As the largest geothermal hospital project under construction in the world today, Sherman Hospital offers a powerful example of the economic and environmental value of innovative design.
When Sherman Hospital, in Elgin, Illinois, opens the doors of its replacement campus in 2010, patients and staff will be greeted with a spectacular view across a 15-acre lake to a forest preserve beyond. The former 154-acre farmstead will be restored to a pristine prairie state, with no-mow grasses and plantings covering a large portion of the site. This is part of an ambitious agenda to integrate the project into its natural setting and create a tranquil environment conducive to the healing and health of patients, staff, and the wider community of Elgin.
But what the visitors might not realize is that the man-made lake (figure 1), situated adjacent to the hospital's public spaces and a majority of the patient rooms, is the most visible part of a geothermal heating and cooling system that will save 30% to 40% of Sherman's space conditioning costs—and upwards of a million dollars a year. It will make the new campus one of the most energy efficient healthcare facilities in the world. The geothermal system, which qualified Sherman for a $400,000 grant from the Illinois Clean Energy Community Foundation, was originally projected to have a payback period of eight years, but with rising energy prices, that period has shrunk to six years (figure 2).
The manmade lake is the most visible part of a geothermal heating and cooling system at Sherman Hospital in Elgin, Illinois
The geothermal system was originally projected to have a payback period of eight years, but with rising energy prices, that period has shrunk to six years
A replacement hospital offers a rare opportunity to think big, and Sherman President and CEO Rick Floyd set out with the goal “to become the best regional hospital in the nation.” Sherman had the foresight to purchase the large tract of land to control its own destiny and plan for expansion over time; a change for the 100-year-old institution and its land-starved campus in downtown Elgin. The scale of the project and the expansive greenfield site presented an ideal opportunity to make a substantive contribution to the environment that was economically viable at the same time. The design team, led by architects Shepley Bulfinch of Boston, recognized the potential for a geothermal lake system and lobbied for it from the outset. MEP and structural engineers KJWW Engineering had pioneered geothermal design for healthcare with the Great River Medical Center in Burlington, Iowa, in 2000. With energy prices rising, all the stars were aligned for a geothermal system at Sherman.
The geothermal system has many attractive selling points. It provides clean, reliable, renewable, environmentally friendly energy that replaces fossil fuel consumption. It is a relatively simple system to operate. It offers significant operational savings and eliminates the need for noisy, unsightly cooling towers. Mechanical plant size is reduced, and shaft sizes are 10% smaller compared to a conventional ducted heating and cooling system, because a portion of the energy is supplied hydronically. A geothermal system's constant, steady supply of energy is well-suited to a building type like a hospital that is occupied 24 hours a day.
In addition to its role as an efficient energy source, the lake has therapeutic value. For a leading healthcare institution, an investment in geothermal energy underscores the connection between a healthy campus and personal health. The lake provides recreational opportunities and also has the potential to irrigate the decorative planting areas close by the buildings and to save city water. Site development requirements mandated a four- to five-acre detention pond to control water runoff anyway; so the 15-acre geothermal lake could be thought of as a 10-acre premium above that requirement.
Operations and economics
But did it make sense operationally? Sherman administrators visited the installation at Great River to better understand the system, which had been operating for five years. They posed the question to their counterparts at Great River: Would you do it again? The answer was a resounding “Yes, in a heartbeat,” with a few minor design alterations.
Sherman does not possess an extraordinary endowment, and the project is confronted with the usual—even unusual— cost pressures. The design phase began during an inflationary period (construction costs in the Chicago area escalated 10% annually during 2005 and 2006) and the Illinois CON process locked in budget numbers and square footage early in the project's schematic design phase. The geothermal system provided a convenient target for construction managers looking to trim scope during several rounds of value engineering. But once the system's design and economic value were explained to Sherman's Board of Trustees, they stood firm—don't touch the geothermal system.
Compared to a conventional gas-fired mechanical plant with chillers, boilers, and cooling tower, the new system carried a first-cost price tag premium of $4.5 million, about 2% of the $230 million construction cost: $1 million to excavate the lake, and a $3.5 million premium for 177 miles of polyethylene pipe, 175 heat exchangers, an in-ground lakeside manifold room to house equipment, and 757 water-to-air heat pumps to circulate energy throughout the facility. The actual cost of this geothermal infrastructure was higher, but the investment was offset by fewer boilers and chillers, a smaller mechanical plant, and the elimination of cooling towers.
There is also the cost of land to consider—10 acres in this instance, purchased previously at $160,000 per acre. An argument can be made that the cost of the land should be excluded from the calculation, since it otherwise would be sitting idle pending future expansion, but its value was included for pricing analysis to assure the hospital's board that the investment was prudent. Calculations showed that the $4.5 million first cost, plus $1.6 million land cost, would be offset by an annual savings originally estimated at $750,000, for an eight-year payback; that projection has increased to $1.1 million savings per year as energy prices continue to rise and the payback period has been reduced to six years.
The design team retained a limnologist to size the lake and arrange the heat exchangers in a layout to derive maximum heat transfer. There is a delicate balance among acreage, water depth, and temperature gain to ensure that the lake functions geothermally while also serving as a wildlife habitat for fish and ducks, and not becoming choked with weeds or algae. The 18-foot deep lake will provide 2,450 tons of cooling, with room to expand to 3,400 tons as the campus grows. The heat exchangers, constructed of loops of piping structured in 30 × 8 pre-assembled grids, will be floated out onto the half-full lake later this summer, connected back to the manifold room, and then filled with water to sink into place on the lake bottom. The system is large but simple, with few moving parts, and the rafts can easily be retrieved should they spring a leak.
The design team also explored the idea of a supplemental geothermal wellfield sunk below the surface parking lots to augment the lake system during the coldest months of the year. This hybrid system would have further reduced the size of the conventional plant by one boiler, but the $1 million price tag to drill 200 wells carried a 15-20 year payback—too great to justify. “While geothermal systems have been used for years, their use has been primarily in residential, commercial, and K-12 facilities. Their usage in a hospital is new and much more difficult to design due to reliability, maintainability, and strict code compliance requirements,” says Warren Lloyd, PE, LEED AP, of KJWW Engineering.
The excavated lake fill remained on-site for environmental and cost reasons. Care was taken to pile and sort the soil, to reuse a seam of clay as a three-foot thick liner for the lake bottom. The remainder of the fill was placed and compacted under the building footprint to elevate the new hospital five feet above a very flat site (figure 3). The elevation increases the building's presence from surrounding roads and provides a better sectional relationship for overlooking the lake from the ground level cafeteria and patio.
The lake is now partially filled and the hospital (right) and its geothermal system (manifold room at left), are scheduled for completion in 2010
The location of the manifold room, tucked beneath the main entry circle, also provides an educational opportunity for visitors and staff to understand the inner workings of the geothermal system. A covered pedestrian concourse from the lower parking lot overlooks the lake on one side and provides a close-up view of the piping and pumps in the manifold room on the other. Eventually, the walkway will be enclosed with glass as a connector to a future medical office building that will flank the entry drive above. Another path circles the lake, providing recreational opportunities for bikers and walkers, and further emphasizing the connection between personal health and a healthy site (figure 4).
With the initial phase of the project (left) now underway, the site has been planned to accommodate both the geothermal lake and a 75-year expansion plan (right)
The integration of hospital and environment is also carried forward in the design of the hospital facility, with particular attention paid to its succession of public spaces. The Hospital's entry and lake levels meet in a dramatic multistory atrium framed by a unique steel structure dubbed the “Tree of Life” by the design team. Together with a pair of courtyard healing gardens, prairie restoration, and art and signage programs based on indigenous flora, these features all underscore the goal to bring the natural world into the new facility and integrate site and building into one continuous experience to create an ideal healing environment.
Sherman Hospital and its geothermal system offer a powerful example of how economic and environmental interests can work in concert, with measurable benefits to patients and staff and an impact that extends well beyond the hospital campus.
Jonathan Gyory, AIA, LEED AP, is a Principal at Shepley Bulfinch Richardson & Abbott and is a senior member of the firm's healthcare practice.
For more information, visit http://www.sbra.com.
How does a geothermal system work?
Although there are certain volcanic areas in the world that superheat rock and water into steam, most of the earth beneath us exists year round at a steady 55°F state. A geothermal system, either through wells, a lake bed, or even a horizontal grid buried under soil, employs a liquid coolant in a closed loop that is pumped from building to ground and back to building to absorb or discharge heat. Like a huge automobile radiator, the network of thin pipe grids in the lake provides maximum surface area to exchange heat with the building. Lake water temperature at Sherman will vary from 38° to 85°F over the course of the year, but even at the extremes, there will still be enough of a temperature differential between the water and air temperature to harvest potential energy for the building.
The network of thin lake piping is gathered at the manifold room (pictured left) and channeled into a pair of 24 supply and return pipes that run to and from the building and fan out to individual heat pumps. These small, residential-sized pump units allow each patient room to be controlled individually by thermostat. The pumps are housed in small closets along the patient corridor for easy access and routine maintenance. This is an improvement over the design at Great River, where the units were located above the patient room ceiling, and filter replacement every three months proved disruptive for patients.
For critical life safety areas such as the Emergency Department, Inpatient Surgery, and the ICU, the geothermal system provides heating and cooling, but relies on conventional air handlers to deliver the high rates of ventilation and filtration required. Water-to-air heat pumps are not well suited for this sort of application.
Surprisingly, the geothermal system will operate in cooling mode 10 months of the year, even in its northern location west of Chicago. A hospital generates so much heat from occupants, medical equipment, and lighting—more than twice as much energy per square foot as commercial or residential building—that a well-engineered facility can capture and redistribute this excess load during the heating season to avoid paying twice for heat. The building will effectively heat itself when ambient temperatures rise above 20°F.