Geothermal Continued from page 52 “Based on the heat load, we recommended 16, 10-8-6
wells, each 1,500 feet deep,” said Orio. The term “10-8-6” stands for a 10-inch casing sealed into the bedrock, an 8- inch rock bore, and a 6-inch sleeve and pump. Each sub- mersible pump has a 10-hp motor to push water to the building’s mechanical room, and from there to all the heat pumps within the system. All 16 wells are located beneath the nursing home’s parking lot. Split up into two well fields, eight wells are
the water are all desirable, that test well becomes the first well on the field.” At this site, we found some of the best, mineral-free water we’ve ever seen, and the rock was also very stable.” The average water temperature across all the wells was 52 degrees.
System details “Each of the eight-well supply and return manifolds feed well water to a series of risers to the upper floors,”
A technician from Merrimack County Facility Maintenance conducts a diagnostics check on the geo-exchange system at the Merrimack County Nursing Home.
located under the upper parking lot, and eight below the lower, with the farthest well being 850 feet from point of entry into the building. Each eight-well field is piped to its own supply and return manifold. The caps are protected by manhole covers, and can be found in the green spaces between parking areas. Amherst, N.H.-based Skillings and Sons was the driller contracted for the MCNH job. The company had two of their four drilling rigs on the job, operated by five employees. “Each well took us about six days to drill,” said
President Roger Skillings. Drilling an eight-inch hole through 1500 feet of solid granite is no small task; it was a blessing in disguise, though. According to Skillings, the number-one enemy of a healthy standing column well is soft rock that cracks, collapses and caves in. “The first thing we do at any job that is to include a standing column well, is to drill a test well,” explained Skillings. “If the rock hardness, density, and the quality of
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explained Orio. “There are two of the big manifolds; each field feeds half of the building. We generally prefer to have no more than 10 wells, or 300-400 tons, on a given field. At MCNH, there’s a nominal 310 tons on each field.”
According to Orio, limiting the fields to 10 wells is for
ease of balancing. The well heads should be kept at the same elevation across the field. Since MCNH rests on a hill, the two fields are roughly five feet apart in elevation from each other. As customary for all standing column well systems, no circulators are used; there aren’t even any flow centers on the ClimateMaster units. Pressure at the mechanical room supply manifolds are maintained by the VFD-controlled submersible pumps, which operate in parallel. Pressure in the manifold that serves the upper field is kept at 52 psi, and at 55 psi for the
Continued on page 56 March 2011
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