Heat pump glossary

The most important terms you will encounter during planning, quoting and operation, explained briefly and clearly.

A

Defrosting: During defrosting, an air-source heat pump removes frost and ice from its outdoor heat exchanger. This uses a little energy and is just part of winter operation.

Bivalence point: The bivalence point is the outdoor temperature below which the heat pump alone is no longer sufficient and a second heat generator helps out.
Domestic hot water heat pump: A domestic hot water heat pump only heats your hot water. It is usually mounted directly on a cylinder and uses the heat from the indoor or outdoor air.

COP (Coefficient of Performance): The COP indicates how much heat a heat pump generates from one kilowatt-hour of electricity: measured on a test bench, at a single operating point.

Efficiency class (ErP energy label): The EU energy label classifies heat pumps into efficiency classes. klimaaktiv recommends the highest available class at a 40 °C flow temperature.
Energieausweis (energy performance certificate) and heating demand (HWB): The Heizwärmebedarf (heating energy requirement) in the Energieausweis (energy performance certificate) shows how much heat your house theoretically needs. It is a good initial indication of whether a heat pump is suitable.

Surface heating (underfloor and wall heating): A surface heating system emits heat over large areas such as the floor or wall. It manages with low flow temperatures and is a good match for a heat pump.
Horizontal collector (ground collector): A horizontal collector is a pipe network just below the surface of the ground, through which a geothermal heat pump extracts heat from the garden. It requires a lot of space.

GWP (Global Warming Potential): The GWP value shows how much a refrigerant contributes to global warming if it escapes. CO2 has a value of 1; the lower, the better.

Heating curve: The heating curve determines how warm the heating water should be at a given outdoor temperature. Correctly adjusted, it saves electricity while maintaining the same level of comfort.
Heating load: The heating load is the output in kilowatts that your house needs on the coldest day. The heat pump is sized according to this, not according to the old boiler.
Heating element (electric auxiliary heater): The heating element is an auxiliary electric heater in the cylinder or appliance. It kicks in on very cold days, but only produces 1 kWh of heat from 1 kWh of electricity.
Hybrid heating system (heat pump with boiler): A hybrid heating system combines a heat pump with a second heat generator, such as a pellet boiler. This is particularly useful at high flow temperatures.
Hydraulic balancing: During hydraulic balancing, each heating circuit is adjusted so that it receives exactly the required amount of water. This allows for a lower flow temperature.

Inverter and power modulation: A modulating heat pump continuously adjusts its output to demand, usually via an inverter. This is more efficient than simply switching on and off.

Seasonal Performance Factor (SPF): The seasonal performance factor shows how much heat your heat pump delivers over the entire year per kilowatt-hour of electricity. It is the most important key figure.

Refrigerant: The refrigerant is the substance that evaporates and liquefies again inside the heat pump, thereby transporting the heat from the source into the house.

Legionella protection cycle: The anti-legionella cycle regularly heats the hot water cylinder to a higher temperature to kill off germs. You can clarify with your installer how often this is useful.
Air-to-water heat pump: The air-to-water heat pump uses the outdoor air as a heat source to heat the heating water. It is the easiest type of heat pump to install.

Monobloc heat pump: With a monobloc heat pump, the entire refrigerant circuit is located in the outdoor unit. Only water pipes lead into the house, not refrigerant lines.
Monovalent, monoenergetisch, bivalent: The operating mode indicates whether the heat pump heats alone, an immersion heater kicks in, or a second heating system such as a boiler assists.

Low-temperature radiator: Low-temperature radiators emit enough heat even at low flow temperatures. It is often sufficient to replace individual critical radiators.

Photovoltaic self-consumption with a heat pump: With a heat pump, you can use more of your own solar power yourself, especially for hot water. In the depths of winter, however, PV only covers a small portion.
Buffer tank: A buffer cylinder is a water tank for heating water. With modern, modulating heat pumps in detached houses, it is often not needed at all.

R290 (propane): R290 is propane used as a natural refrigerant. It has a very low global warming potential, but is flammable and therefore requires safety precautions.
Return temperature: The return temperature is the temperature of the heating water flowing back to the heat pump from the radiators or underfloor heating.

Sound pressure level: The sound pressure level is the volume that reaches a specific location, such as the property boundary. It decreases with distance from the heat pump.
Sound power level: The sound power level indicates how much noise the heat pump itself emits, regardless of the location. It is listed in the data sheet and is suitable for comparison.
SCOP (seasonal coefficient of performance): The SCOP is a standardised seasonal coefficient of performance for a standard climate. It is suitable for comparing devices, but does not tell you what your system will actually achieve.
SG-Ready: SG-Ready is a label for heat pumps with an interface through which they can process signals from the PV system, energy manager or grid.
Brine-to-water heat pump (geothermal energy): The brine-to-water heat pump extracts heat from the ground via probes or collectors. It is more efficient than an air-source heat pump, but more complex.
Grid operator blocking times: With an interruptible heat pump tariff, the grid operator is allowed to temporarily switch off the heat pump. The system must be able to bridge these pauses.
Split heat pump: A split heat pump consists of an outdoor and an indoor unit connected by refrigerant lines. Installation requires specialist knowledge of refrigeration technology.

Cycling: Cycling means that the heat pump frequently switches on and off for short periods. This reduces efficiency and lifespan, and often indicates that the unit is too large.
Deep drilling (geothermal probe): With deep drilling, a geothermal probe is inserted vertically into the ground. It requires little surface area and provides consistent heat all year round.

Flow temperature: The flow temperature is the temperature of the heating water on its way to the heating surfaces. The lower it is, the more efficiently the heat pump operates.

Heat meter: A heat meter measures how much heat your heat pump delivers. Together with the electricity meter, this allows you to determine the actual seasonal performance factor (SPF).
Heat pump tariff: A heat pump tariff is a dedicated electricity tariff for the heat pump, often via an interruptible metering point. Whether it is worth it is a matter of calculation.
Hot water cylinder (boiler): The hot water cylinder stores heated drinking water. It should be as large as necessary and as small as possible to keep heat losses to a minimum.
Water-to-water heat pump (groundwater): The water-to-water heat pump uses groundwater as a heat source. It is highly efficient, but requires wells and a water rights permit.