(2) The zone outdoor airflow Voz 3. The ground loop heat exchanger consists of a 3/4 in DR 11 HDPE tube placed in a 5 in. diameter bore grouted with thermally enhanced sodium bentonite. The location of the U tube in a vertical borehole is B type as shown in Figure 3.5. The thermal conductivity of the grout is 0.8 Btu/h-ft-°F. The outside and inside diameters of the tube are 1.08 in. and 0.86 in. Determine the thermal resistance of the grout, Rg