The heat distribution system using air to distribute the heat/cooling in the house – blown or forced air through ducts or grilles or wall hung a/c units.

Heat pump unit with the refrigeration cycle contained within one unit 'monobloc' which is then connected by piping to the heat distribution system. No refrigerant flows outside of the monobloc casing – just water, making installation possible by a plumber.

Heat pump unit with the entire refrigeration cycle being 'split' between separate outdoor and indoor units – which are connected using piping filled with refrigerant. Installation requires a refrigerant engineer.

Uses heat from the ambient air, they may be monobloc units or split. Air/water systems are always connected to a hydronic heat distribution by definition.

Air-to-air heat pumps use air for both the heat source and the heat sink. They are either developed from traditional air-conditioners extended to provide also heating functionality or they are optimized for heating and can then also be used for cooling. They are always split systems with a separate outdoor and indoor unit connected by pipes contain [..]

The COP is the ratio of useful heat produced to drive energy of the heat pump.

A compressor that can only run with one speed and thus constant capacity. To vary the capacity over time, the compressor is switched on or off (on-off operation).

The compressor speed can be controlled (varied) to change the heating capacity of the system. The main types used are inverter compressors, digital scroll compressors and multiple compressors:

Exhaust air heat pumps use energy from indoor air to provide heating, sanitary hot water. They can either use indoor air or be connected to a forced ventilation system. Most often, these systems are used for sanitary hot water preparation, not heating, due to limited heating capacity, but increasingly being marketed as a heating solution.

Uses heat from the ground, either via drillings (vertical) or via horizontal collector. Either pure water or brine (water-glycol mixture) is circulated in the heat exchanger. Naming variation depend on the medium used for energy dissemination including ground-to-water, or ground-to-air heat pumps. Direct expansion systems (DX) circulate a refrigera [..]