Critical Measurement of Well Thermal Properties to Support Design

For large tonnage (100 tons or greater) HVAC systems, it is imperative that a test well be drilled and that measurement of the thermal characteristics of the well (as representative) be undertaken prior to a final design. The defining thermal properties include: the "effective" thermal conductivity, K, of the formation surrounding the bore; the thermal diffusivity, a, and the characteristic thermal decay rate, r. Armed with this knowledge, the geothermal engineer can begin to specify the design (wetted feet per delivered ton) to meet a building heating or cooling load. This paper will demonstrate the measurement analysis and interpretation required to extract this information, using a number of geothermal installations to validate the approach