The forced air heat pump has proven to be the energy and cost efficient means of maintaining the atmosphere in a household to the comfort level most people desire. This by no means was an accident. The engineers that developed this system had this goal in mind when these were developed in the early 1990s.
One of the leading reasons for the different approach to heating and cooling units was the need to reduce the use of chlorofluorocarbons, like Freon (R-12) was needed. The new replacement was R-134a, R-717 (ammonia), R-744 (carbon dioxide), and still in use is R22.
The main principle behind the heat pump is the exploitation of the heat sink. In both theory and in applications, heat will travel to a place that is cooler by nature. For this reason, it takes less energy to help this natural process than to create it artificially.
The reversal of which way the heat transfer is being conducted is with the reversing valve. This allows the user to decide which of the two ends will be the heat sink.
When the first heat pumps were introduced, they were severely hammered in their production of heat for homes due to the difficulty of extracting heat from the outside air in the winter months. In time, a solution was devised. This was when the geothermal heat pumps were introduced.
The temperature variance between the surface air and the temperature underground is sufficient to make this an optimized heat exchange unit. The portion that is placed underground is only 4 to 6 feet deep. But that is deep enough to make a significant difference and make the forced air heat pump use less energy to operate.