Optimum Heating Pattern of a Ground Source Heat Reference Map

A ground source heat reference map (GSHRM) shows the minimum necessary thermal performance of the ground heat exchanger (GHE) of a ground source heat pump (GSHP) system. Thermal performance depends on thermal properties of the ground, the ground temperature profile, heat advection by groundwater flow, and the GHE operating pattern. This study modeled optimum heating and cooling modes for a GSHRM. First, continuous and intermittent operation modes were compared, and a standard operation time was defined. In a standard household GSHP system, the quantity of heat transferred from the ground depends on household energy demand, which is relatively constant. Once the demand is known, an operation mode is selected that can meet it. Continuous operation increased the total amount of heat exchanged over a period of time but lowered the heat flux at the GHE, whereas intermittent operation with relatively long stopped periods decreased the total amount of heat but did not greatly decrease the heat flux at the GHE. Second, energy-saving efficiency and cost factors were compared among intermittent operation modes. Operation costs consist of the electrical energy supplied to the heat and circulation pumps. At a given operation time, the energy supplied to the heat pump depends on its coefficient of performance (COP), whereas that supplied to the circulation pump depends on its pressure loss, hence on the GHE length. A long GHE has a higher initial cost. Thus, the optimum heating pattern must consider the configuration of the GSHP system, including energy-saving efficiency and cost factors.