He is describing the background behind the installation of one of the world’s largest, single closed-loop geothermal hvac systems, totaling 1,741 tons of installed geothermal heating-cooling capacity. The college here in Pomona now uses a large number of heat exchange wells and water-source heat pump (WSHP) units to serve the heating and cooling needs of a large and growing campus.
The decision to consider geothermal technology to serve the campus arose from a number of circumstances.
In 1990, a new vice president, Charles Tantillo, Ph.D., expressed interest in reducing overhead expenses such as building heating and cooling. At the same time, the school was planning to replace its aging fleet of multizone rooftop hvac units, most of which dated to the school’s original construction in the 1970s.
The director of facilities planning, Marvin Witmer, put the funding together.
GROWING CAMPUS
Not only was the existing plant due for replacement, but in the early 1990s, the college was building new classroom buildings and living units for students, to keep up with growing enrollment.Stiles had previously researched the merits of modern geothermal WSHP technology and urged the college to seriously consider this option. This seemed the ideal time. The college engaged Vinokur-Pace Engineering Service, Jenkintown, PA, to perform a feasibility study of a geothermal system and prepare designs.
At the same time, the school searched for funding sources for this extensive hvac plant improvement. Ultimately, grants totaling $5.1 million were provided by the New Jersey State Department of Environmental Protection and Energy, New Jersey Department of Higher Education, and in the form of installation rebates from Atlantic City Electric Co. (today called Conectiv). Research grants totaling almost $1 million dollars were obtained in order to study the environmental and energy use impacts of the project.
The work done by the engineer demonstrated the feasibility of the concept and resulted in a decision to proceed.
PROJECT DETAILS
The project design featured 400 heat exchange wells located in boreholes to a depth of 425 ft. These were to be installed in a 3.5-acre area that included all of the college’s Parking Lot 1 plus some adjacent open space.Because of the protected environmental status of New Jersey’s Pine Barrens area, the college had to get special permits from the State’s Pinelands Commission. Use of the parking lot reduced the disturbance of undeveloped land on the campus. The commission was also concerned about protecting three underground aquifers that would be crossed by the wells.
According to Stiles, “Construction plans needed to demonstrate that there would be no compromise of ground water and that the aquifers would continue to be sealed from interchange with each other and with surface water.” The college’s decision to use only pure water (without glycol) as the heat exchange medium also helped assuage the commission’s concerns. The commission helped speed up the permitting process.
Heatec, Inc., of western Pennsylvania, developed the final design and with Anderson Engineering as a subcontractor, installed the ground-loop system and external horizontal piping. Approximately 4 ft of surface soil were removed from the loop area and stockpiled before starting the drilling and trenching operations.
After completion, the area was returned to its use as a large parking lot. The wells were located on a grid and spaced roughly 15 ft apart. This work was done by a group of local well drillers. The boreholes were 4 in. dia.
INSTALLATION DETAILS
Within the 4-in. borehole, the installers placed two 1.25-in., high-density polyethylene pipes with a U-shaped close-return coupling at the bottom.Pipe installation was complicated by the fact that the boreholes filled with groundwater and the pipes were buoyed upward. Installers overcame this problem by attaching weights to each loop and filling the heat exchange pipes with water.
After the pipes were installed in the boreholes, the holes were backfilled with a bentonite clay slurry to seal them and to enhance heat exchange.
The loop system comprises 64 miles of heat exchange pipe. In addition, 18 observation wells were located throughout and around the well field for long-term observation of ground water conditions.
The individual wells were connected to 20 4-in.-dia lateral supply and reverse-return pipes using a thermal butt fusion technique. These laterals, in turn, run to a building at the edge of the field, where they are manifolded into 16-in. primary supply and return lines. The primary lines go to a pump house containing two 125-hp, variable-speed pumps that pressurize the supply and return systems in the manifold house.
In the heating mode, the loop serves as a heat source, and in the cooling mode as a heat sink. The borehole field has a volume of 1.2 million cubic meters or, en masse, is equivalent to the heat capacity of about the same volume of water.
OLD MEETS NEW
From the pump house, water is distributed through six secondary loops to 62 rooftop water-source heat pump units (Model WPUD from The Trane Company), located throughout the campus. The units range in size from 10 to 35 tons and total 1,480 tons in capacity.Because the previous system had used multizone units, it was necessary for the mechanical plant contractor, Iannacone Construction Co., Berlin, NJ, to add 500 VariTrane™ variable air volume (vav) boxes at the conditioned air distribution points to meet zone-level requirements with the new system. All of the rooftop units are equipped for air economizer operation.
The pumps, rooftop units, economizers, and vav boxes are controlled by a Tracer Summit™ building automation system using 3,500 data points. The ddc system allows the college to take advantage of comfort and energy-saving options such as duty cycling, night setback, time-of-day scheduling, and vav box control. The control system also assists in identifying maintenance needs in the mechanical system, from the loop to the points of conditioned air distribution.
The system changeover took place during the inter-session period in the winter of 1993-94. The startup was relatively uneventful, and the system immediately demonstrated that it could carry the entire planned heating load.
In the first few years of operation, the average temperature of the well field drifted upward by several degrees, the schools facility operators report. That temperature now appears to have stabilized. This occurred because the cooling load annually releases more thermal energy to the ground than the heating load requires. Even in the cooler winter months, the system often operates with some units’ heating while others are in the cooling mode.
SAVINGS MEET ESTIMATES
According to Stiles, the original estimate was that the geothermal heat pump system would reduce the school’s electric consumption by 25% and natural gas consumption by 70%.“Because of the constant changes and additions to the system,” he says, “and other energy-conservation steps, it is difficult to verify energy savings exactly. Based on an extensive monitoring study, they turned out to be quite accurate.”
Stiles says the project has now passed the economic payback point and that the decision was more than justified. He points out that, in addition to the dollar savings achieved with the geothermal system, significant environmental and energy conservation benefits have accrued.
Alice Gitchell, from the college’s natural sciences and mathematics staff, is actively involved in studying and sharing information on the geothermal project and this type of technology in general. She notes that the project has substantially contributed to a calculated 13% overall reduction in the college’s CO2 emissions during a significant growth period on the campus.
“Additionally, there are the savings in fuel resources for heating and, on the cooling side, the more efficient use of electricity,” Gitchell points out.
Because of its size and design, the geothermal system has made the campus a destination for many visitors, engineers, and prospective owners from around the world. In addition, college staff members and engineers have given numerous presentations to professional groups and geothermal conferences.
The system was built with some additional loop capacity to allow for campus additions. For example, the Arts and Sciences Building completed in 1995 also uses the system to obtain another 261 tons of cooling capacity. Instead of using rooftop heat pumps, like the other campus buildings, this building uses packaged horizontal ceiling units.
On another part of the campus, nine new housing units completed in 1999 are equipped with four wells per building. The wells supply three console WSHP units per building for both heating and cooling.
ADVICE FOR OTHERS
Because of the extended history of the project, Stiles is frequently asked for advice by others contemplating geothermal solutions.“Sizing the system right is very important,” he says. “For that reason, you need buildings with well-executed shells and the heat loss and gain estimates need to be accurate.”
He also points to the importance of having access to the loop water and heat pump systems. “Heat pump units and the water pumps need to be accessible for inspection, cleaning, and repair.”
Stiles suggests that owners consider incorporating either a wet or dry model cooling tower to precondition the well field in winter months for cooling later in the summer. “For situations like ours, where cooling hours significantly outweigh heating hours, a cooling tower could add even more to system efficiency or capacity. That’s something we didn’t include in our original plans, but today I would.”
Finally, he notes that there are numerous technical support assets available. “It is critically important to have a good design and good implementation.”
Sidebar: About the School
The Richard Stockton College is an award-winning, mid-sized liberal arts and sciences college located in the southeastern New Jersey pinelands area. Founded in 1971, today the college has an enrollment of 6,300 and annually graduates 1,500 students, nearly half of whom go on to graduate school.The school is part of the New Jersey Higher Education System and is recognized for its programs in natural sciences, physical therapy, and environmental and marine science education. Named for a New Jersey patriot and signer of the Declaration of Independence, the college is located 12 miles from Atlantic City on a rural campus that has been recognized for its harmonious fit with its pinelands setting.
Publication date: 10/08/2001
