When the Watershed Committee of the Ozarks (WCOTO) designed its new educational facility, The Watershed Center, located at the beautiful Valley Water Mill Park, a ground source heat pump system (GHSP) was selected to handle the heating and cooling chores. As an environmental and educational organization, the WCOTO recognized the many benefits of utilizing a GSHP system. A competitive bid process was conducted, and Sunbelt Environmental Services Inc. (SES), Springfield, Mo., was awarded the contract to conduct a thermal conductivity test and install 19 6-inch diameter boreholes to 300 feet of total depth.
Valley Water Mill is located in Springfield in a karst geology area. At the park, two caves, numerous springs and a major fault system are present, adding to the unique drilling challenges that are common in southern Missouri. SES was no stranger to drilling at the Valley Water Mill property, having previously installed two monitoring wells as part of the United States Geological Survey (USGS) Ozark Aquifer Study. One well was installed to monitor the depth to water in the shallow or upper Springfield Plateau Aquifer that is present from the surface to the top of the Ozark Confining Unit at a depth of 225 feet. The other well was installed below the Ozark Confining Unit into the Ozark Aquifer to a depth of approximately 350 feet. Both wells contain dataloggers that transmit real-time data that can be accessed via the Internet.
On this particular GSHP project, SES worked with a local heating and cooling mechanical contractor to establish a grid for the ground source heat loops on 20-foot centers. Because the boreholes were in excess of 200 feet deep, a variance was required and obtained from the Missouri Department of Geology and Land Survey.
The first borehole was advanced to 300 feet, and a 1-inch diameter loop was installed. The specifications for grouting called for a full-length thermal grout with a thermal conductivity (k) value of 0.85 Btu/(hr*ft*F°). One 50-pound bag of Baroid Barotherm grout was mixed with 200 pounds of silica sand to provide a calculated k value of 0.88, with a permeability of 1 x 10-7 cm/sec. SES mixed the grout and then placed it, utilizing a specialty grout pump equipped with a 500-foot reel, thereby ensuring a grout seal that provided proper thermal characteristics and low permeability for ground water protection.
A 48-hour thermal conductivity test then was conducted on the newly installed GSHP loop. The results of the testing indicate a k value of 2.35 Btu/(hr*ft* F°), which validated the preliminary design of the heat-loop field based on the proposed building’s heating and cooling loads. Prior to initiating drilling, SES installed a shallow trench to prevent run-off during drilling from entering the Valley Water Mill Park lake, located adjacent to the drilling site. To complete the loop field, SES installed an additional 18 300-foot borings – complete with heat loops and full-length grouting – utilizing SES’s two air-rotary rigs.
At the Watershed Center, there will be myriad opportunities to see, feel and touch water protection demonstrations, discuss aspects of sustainable design and living, work with other people who care about water, examine working examples of water conservation and green building features, and learn how every person can take responsibility as a curator of our precious water supply.