A geothermal field that is believed to be among the largest in the U.S. is being installed during an expansion that will nearly double the size of the headquarters of medical software giant Epic Systems Corporation in Verona, WI, just south of Madison.
Approximately 1,800 employees now work in Campus 1 of Epic's headquarters, which was completed in 2005.
Another 1,400 Epic employees are currently spread around Madison in rented offices.
When Campus 2 is completed in January 2010, all 3,200 Epic employees will work at this one location.
J.P. Cullen & Sons, Inc. is the general contractor and construction manager building Epic's Campus 2 expansion, which includes a four-story underground parking ramp, three 150,000-square-foot office buildings, and one 177,000-square-foot office building.
In addition to providing office and meeting space, the 177,000-square-foot building, called Building K, will also hold all the mechanical equipment for Campus 2's four new buildings.
One of the unique features of the entire Epic headquarters complex is that all of its buildings except the learning center/auditorium will be heated and cooled entirely by a closed-loop geothermal system that uses 1,576 bore holes (commonly called "wells," even though there is no water in them), each drilled 300 feet deep into the earth.
Epic is so confident in geothermal climate control, notes J.P. Cullen Project Executive Jim Schumacher, that no natural gas is being provided for the Campus 2 buildings.
Epic's field of geothermal wells consists of two sections.
The first 576 wells were put in when Campus 1 was built from 2002 to 2005. That part of the system has already been operating for a few years.
The new geothermal system, being installed now as part of Campus 2 construction, contains 1,000 wells.
The system could also provide heating and cooling for the existing learning center/auditorium if Epic chooses to add it to the system.
In addition, the geothermal system and well field could accommodate yet another 1,000 wells if Epic decides to develop a Campus 3 on the site.
All of the wells in both sections of the geo field are identical. They measure just slightly less than 6 inches in diameter and plunge down 300 feet into the rock beneath the site.
Each of the 1,576 vertical bore holes holds a 600-foot loop of 1.5-inch-diameter SDR-9 polyethylene piping that is grouted in place and carries circulating water to exchange heat and coolness from the surrounding rock, which stays about 55 degrees Fahrenheit all year.
Even though the region's air temperature has varied from nearly 30 degrees below zero in the winter to more than 100 degrees above zero in the summer, the geothermal system will be able to heat and cool the buildings through all seasons.
Together, the 1,576 bore holes contain 179 miles of tubing — enough to stretch from Madison to the outskirts of Eau Claire, in northwestern Wisconsin.
Each of the bore holes is filled with a special thermal grout that seals the hole, holds the tubing in place, and also helps conduct heat and cold more efficiently between the rock and the tubing.
Groups of 10 bore holes are connected to form a local circuit, and 25 of the local circuits (250 bore holes' worth) connect to each central vault.
The previously completed field for Campus 1 has three vaults. The new field now being installed to support Campus 2 has four.
Campus 2's four vaults connect to a 28-inch-diameter main that carries heating and cooling water from the geo field to six Multistack chillers that exchange heat and cold between the external loop from the geo field and internal loops that will heat and cool the interiors of the four new buildings.
The heating/cooling water is circulated through the geothermal system by a 6,200-gpm pump.
The combined geothermal field for Campuses 1 and 2 covers 9.5 acres and generates enough thermal capacity to heat or cool the equivalent of 900 average-sized (2,200-square-foot) homes.
Professional Engineer Dan Rehbein of the geothermal system's designer, X-nth, Milwaukee, WI, says that the geothermal system is 250 to 300 percent efficient when it's in heating mode.
"A high-efficiency home furnace," says Rehbein, "does well to work at 90- to 95-percent efficiency. That means between 5 and 10 percent of its energy is not put to useful work."
"In contrast, this geothermal heating system gives back 2.5 to 3 times the energy put into it, so the user actually gains a great deal of heating efficiency."
The new geothermal heating system built for Campus 2 was designed by the Milwaukee office of the design engineering firm X-nth.
Bertram Drilling, Billings MT, bored the vertical wells, installed the vertical circulation tubing, and filled the wells with thermal grout.
G.O. Loop, Randolph, WI, installed well-field vaults and the piping that connects the wells to the vaults.
General Heating and Air Conditioning, Madison, WI, installed the geothermal system's mains, the six Multistack chillers, and internal heating and cooling pipes for the four new buildings.