Glossary

Air-based distribution system

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.

Air source (mono-bloc)

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.

Air source (bi-bloc or split)

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.

Air-to-water heat pump (ASHP)

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 / Reversible (AAHP)

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 containing refrigerant. Generally these systems have to be installed by qualified refrigeration engineers and are sold through a cooling/refrigeration channel.

Coefficient of Performance (COP)

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

Compressor (Fixed speed)

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).

Compressor (variable/modulating speed)

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:

  • Inverter compressors control the speed by changing the frequency of the power input.
  • Digital scroll compressors technology operates on the principle of loading and unloading of scrolls i.e. the scrolls are engaged and disengaged periodically to get durations of “full capacity” and “no capacity”. Time average of the loading and unloading state results in variable capacity output to vary the compressor speed.
  • multiple compressors can be used in to provide extended variable output. A stepwise capacity variation can be achieved by starting/stopping additional compressors.

Exhaust air heat pump

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.

Ground-to-x heat pump, geothermal heat pump (GSHP, closed loop)

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 refrigerant in the collector. Direct expansion-water units use a hydronic heat distribution system.

Hydronic (water based) distribution system

The heat distribution system is water based – e.g. the heat pump is connected to radiators, underfloor heating, fan convectors/fan coils.

Sanitary hot water heat pump (SHW)

Sanitary hot water heat pumps use mostly air to produce hot water (up to 65°C). They can use indoor or outdoor air to achieve this purpose. They are either built as compact units with an integrated tank or they are connected to an external hot water tank.
Alternative name: Domestic hot water unit

Seasonal Performance Factor (SPF)

The SPF is the average COP taken over a heating season.

Thermally driven heat pump

Heat pumps that come in different variations using gas as auxiliary energy. They can either use gas to run a gas motor (gas motor driven) and operate as conventional compression unit. They can also use a thermal process (adsorbtion or absorbtion) as an alternative to mechanical compression.

VRF systems (multi-split)

Air conditioning heating and cooling technology. One outdoor unit (condenser) connected to multiple indoor units, all of which may operate independently, i.e. providing heating and/or cooling at the same time. VRF systems are a more sophisticated version of the minisplit HVAC system used throughout the world. They distribute the refrigerant instead of piping hot water and chilled water to each fan coil unit (FCU) or air handling unit (AHU). By supplying different amounts of refrigerant to evaporators, the systems may provide simultaneous heating and cooling.

Water-to-water heat pump (WHSP, open loop)

Uses heat from a water source such as a well. Typically water is pumped from the source in an open system through the heat exchanger and returned to the source. In case of water-to-water heat pumps, they are often monobloc units with hydronic distribution. In case of water-to-air heat pumps, air is used as the heat distribution medium.