How do heat pump HVAC systems work to efficiently heat and cool a building?

Heat pump HVAC systems work by transferring heat between the inside and outside of a building using refrigerant. In heating mode, the system extracts heat from the outside air and transfers it inside. In cooling mode, it removes heat from inside and releases it outside. This process is efficient because it moves heat rather than generating it, making it a cost-effective way to heat and cool a building.