Metamorphic rock Metamorphic rock Metamorphic rocks arise from the transformation of existing rock types, in a process called metamorphism, which means "change in form". The original rock (protolith) is subjected to heat (temperatures greater than 150 to 200 °C) and pressure ( or more), causing profound physical or chemical change. The protolith may be a sedimentary, igneous, or existing metamorphic rock. Metamorphic rocks make up a large part of the Earth's crust and form 12% of the Earth's land surface. They are classified by texture and by chemical and mineral assemblage (metamorphic facies). They may be formed simply by being deep beneath
Ground heat exchanger Ground heat exchanger Ground heat exchangers (GHEs), which are also called geothermal heat exchangers, have emerged as a promising and globally accepted way of exploiting shallow geothermal energy, for example ground-coupled heat pumps, ground heat storage. A GHE is essentially a pipe (e.g., U-, W-, or helical-shaped) in a vertical borehole or a foundation pile of a building, in which a circulating heat-carrying fluid absorbs (or discharges) heat from (or to) the ground. GHEs can have various configurations. This article discusses two kinds of closed loop GHEs, i.e., borehole and foundation pile GHEs. The borehole type is the most common.