Question: A groundwater heat pump is a refrigeration device that rejects heat to the ground through buried pipes instead of to the local atmosphere. The heat rejection rate for such a machine at an Istanbul location is to be 22 kW in a location where the ground temperature at depth is 17 oC. The thermal conductivity of the soil at this location may be taken as 1.6 W/m oC. Water is to be circulated through a length of horizontal buried pipe or tube with the water entering at 29 oC and leaving at 23.5 oC. The convection coefficient on the inside of the pipe is sufficiently high that the inner pipe wall temperature may be assumed to be the same as the water temperature.

Select an appropriate pipe/tube material, size and length to accomplish the required cooling. You may choose standard steel and plastic pipe sizes.

Examine several choices (different sizes of steel and plastic pipe sizes) before making your final selection and give reasons for that selection.