Final answer:
Burying a heat exchanger underground for a heat pump is advantageous because the stable ground temperature increases the heat pump's efficiency, leading to more effective heating with less energy compared to using the fluctuating outside air temperatures. Geothermal heat pumps operate at higher efficiency and offer cost-effectiveness over time despite the higher initial investment and installation costs.
Step-by-step explanation:
It is worthwhile to bury the heat exchanger of a heat pump underground because the ground temperature a few meters below the surface is fairly constant and close to the average air temperature. This leverage of moderate-temperature ground provides a thermal reservoir which is more efficient than using the extreme outside air temperatures. As a result, geothermal heat pumps benefit from a smaller temperature difference (ΔT) and operate at a higher efficiency.
Heat pumps are an economical means for heating because they transfer more energy (heat) to a space than the electrical work (W) put into them. This is true especially where winter temperatures are mild and electricity is inexpensive compared to other fuels. Moreover, heat pumps are versatile in that they can cool spaces in summer, adding further to their utility and cost-effectiveness over time.
However, the initial cost of a heat pump, including installation especially underground, is greater than that of traditional furnaces, and electricity can be more expensive than burning fuels. Therefore, these pumps must have a longer operational life for the initial costs to be recouped.