Heat Pump
Definition
A device that moves heat from cold to hot — a refrigerator run in reverse to heat your home efficiently.
Symbol: · Unit: dimensionless
Technical definition
A reversed heat engine using work input to transfer heat from a cold reservoir to a hot one. Coefficient of performance COP = Q_H/W can exceed 1 (typically 3–4) — it moves more heat than the electrical energy consumed, unlike resistive heating.
Example
A heat pump with COP 4 delivers 4 kWh of heat for every 1 kWh of electricity — 400% ‘efficient’ in heating terms, because it moves heat rather than making it.
Common confusion
COP > 1 does not violate energy conservation — heat pumps move existing heat, they do not create it. The ‘extra’ energy comes from the cold outdoor air (or ground), not from nothing.