The temperature underground, below some depth (depending on soil composition) is approximately constant throughout the year. A ground source (i.e., geothermal) heat pump takes advantage of this property by embedding its outdoor heat exchanger in the ground. This provides a lower heat sink temperature than the air in the cooling season and a higher heat source temperature in the warming season. For the horizontal ground source heat pump shown in the figure below, what is the minimum depth it can be buried such that the ground temperature is nearly constant throughout the year? Assume the material properties of the soil are: p 1300 kg m-, Cp = 1800 J kg- K-, k= 0.3 W m K-. = a.~10 cm b. ~1 m C. ~3 m d. ~30 m E Heat Pump Distribution System Heat Exchanger