Final answer:
A heat pump is a device that uses work to transport thermal energy from a colder to a warmer environment, essentially operating as a reversed heat engine. It works by applying external work to move thermal energy against its natural flow, with efficiency measured by its coefficient of performance (COP) or Heating Seasonal Performance Factor (HSPF) for heating applications.
Step-by-step explanation:
What is a Heat Pump?
A heat pump is a device that uses work to transfer energy by heat from a colder environment to a warmer environment, effectively reversing the natural flow of thermal energy. Unlike a heat engine which generates work from thermal energy, a heat pump uses work to 'push' thermal energy in the opposite direction of its spontaneous flow. This uses the principles of thermodynamics where a small amount of input energy is required to move a larger amount of thermal energy.
Reversing Thermal Flow
Heat pumps are essentially heat engines operated backwards. In natural conditions, heat flows from a hot environment to a cold one. Heat pumps reverse this by extracting energy from a cold source, such as the outside air in winter, and releasing it into a warmer interior space. To achieve this, work, typically from an electrical source, is applied to drive the thermal energy uphill.
An example of a heat pump is a refrigerator. The refrigerator extracts heat from its interior (which is maintained at a lower temperature than the room) and expels it to the surrounding environment.
Coefficient of Performance
The efficiency of a heat pump is measured by its coefficient of performance (COP), which is the ratio of heat energy transferred to the work input required. Again, taking a refrigerator as an example, its COP would be calculated based on the amount of heat extracted from inside (Qc) versus the electrical work (W) put into the system. For heating applications, the COP formula is also used, often represented by a specific term known as the Heating Seasonal Performance Factor (HSPF).