Heat pumps are considered an efficient and sustainable heating technology. But not every heat pump works the same way. The way it is operated can determine efficiency, costs and deployment options. But which operating modes exist — and what makes them different from one another? You'll find out in this article.

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What are the operating modes of heat pumps?

There are six different operating modes for heat pumps: monovalent, monoenergetic, bivalent alternative, bivalent parallel, bivalent partially parallel and multivalent. It is highly dependent on the type of heat pump.

The mode of operation of a heat pump determines how it provides heat and whether additional heat sources are used. Depending on the type of building, heating load and desired efficiency, a certain mode of operation may make more sense than another. The following overview shows the most important variants and their features.

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Monovalent operation: When does it make sense?

In monovalent operation, the heat pump covers the entire heating requirement alone — without additional heating systems. To do this, the heat pump must be dimensioned in such a way that it can deliver enough heat even at the lowest expected outside temperature. The dimensioning point is based on the standard outdoor temperature of the respective location, often between -10 °C and -15 °C. This mode of operation is particularly suitable for new buildings with surface heating systems such as floor or wall heating systems.

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The advantage of monovalent operation is maximum efficiency, as no additional energy sources are required. In addition, operating costs are usually lower. However, the heat pump must be large enough so that it can deliver sufficient power even on very cold days.

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Mono-energetic mode: heat pump with additional electrical heating

In mono-energy operation, the heat pump covers almost all heating requirements and is supported by an additional electric heater when required. Air heat pumps in particular are equipped with a heating element as standard. This only kicks in at extremely low outdoor temperatures or during peak load periods. As a result, the system remains compact and does not require a second heat source such as a gas or oil heater. This mode of operation is particularly suitable for energy-efficient old buildings or new buildings in cold regions.

The biggest advantage of mono-energy operation is independence from additional heating systems — they heat completely without fossil fuels. There are also no maintenance costs for a second heating system. However, when used frequently, the heating element can result in increased electricity costs if the heat pump is not optimally dimensioned or parameterized. Careful planning and adjustment of the control system is therefore crucial.

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Dual mode alternative mode: combination with other heating

In dual-mode mode, the heat pump operates alone up to a specific outside temperature. Does the temperature drop below these specified Bivalence point, a second heat source, such as gas, oil or wood heating, switches on and completely takes over the heat supply. As a result, the heat pump can be made smaller. This mode of operation is particularly suitable for existing buildings, e.g. when the heat pump cannot cover the heat demand alone or existing heating systems should continue to be used.

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A major advantage of this mode of operation is the higher efficiency, as the heat pump mainly operates in its optimum output range. In addition, investment costs remain lower, as no oversized heat pump is required. The disadvantage lies in the dependence on the second heating system, which often works with fossil fuels and requires additional maintenance. This can make it more expensive to operate in cold winters.

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Dual mode parallel operation: Two systems at the same time

In bivalent parallel operation, the heat pump works together with a second heat source. In contrast to bivalent alternative operation, both systems can run at the same time. The heat pump covers heating requirements up to a specific outside temperature. When it gets colder, the second heat source — usually a gas or oil heating system — switches on and covers the remaining heat demand. This mode of operation is particularly suitable for existing buildings with high heating requirements and classic radiators that require higher flow temperatures.

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The advantage of dual-mode parallel operation lies in flexibility: The heat pump can efficiently cover a large part of the heating season, while the second heater is only switched on at very low temperatures. This reduces operating costs and reduces the burden on the environment. However, the higher maintenance costs for two heat sources and the complex regulation of the system are disadvantageous.

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Multivalent operation: independence through renewable energy

In multivalent operation, the heat pump is combined with at least one additional heat source. In particular, EE hybrid heating systems, which combine heat pumps with photovoltaic or solar thermal energy, enable maximum use of renewable energy.

• A heat pump with PV, for example, can use its own solar power for operation, which reduces electricity costs.
• The combination with solar thermal energy ensures that the heat pump has to work less, as the solar thermal system provides some of the heat — especially for hot water heating in summer. This increases the efficiency of the entire system and reduces the power consumption of the heat pump.

The major advantage of multivalent operation is independence from fossil fuels and rising energy prices. In addition, the heat pump can be made smaller, as other energy sources support the heating system. This lowers investment costs and improves efficiency. However, a multivalent system requires precise planning and coordination. Acquisition costs are also higher. Nevertheless, this combination pays off in the long term, particularly in single-family homes with a high share of self-consumption.

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Which factors determine the operating mode of the heat pump?

The operation of a heat pump is influenced by several factors:

• Building type and insulation standard: Well-insulated new buildings enable monovalent operation as the heating load is low. In older, poorly insulated buildings, bivalent systems often make more sense.
• Heat source: The type of heat source influences efficiency and mode of operation. Air-water heat pumps work depending on temperature and often require additional heating when it is extremely cold. Groundwater and groundwater heat pumps have more consistent performance and are better suited for monovalent operation.
• Type of heating distribution: Floor and wall heating systems operate with low flow temperatures and enable monovalent operation. Classic radiators require higher temperatures, which often requires a bivalent or monoenergetic solution.
• Standard outdoor temperature at the location: The lowest average winter temperature determines whether the heat pump can be operated alone (monovalent) or with assistance (bivalent, monoenergetic). In very cold regions, additional heating is often unavoidable.
• Heat pump sizing: A heat pump that is too small often requires additional heating. A heat pump that is too large often switches on and off, which reduces efficiency. The correct power adjustment is crucial for optimal operation.
• Use of renewable energy: A photovoltaic system can cover the heat pump's electricity requirements and enables more efficient operation. Solar thermal energy can support water heating and reduce the running time of the heat pump.

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How can I optimize the operation of my heat pump?

The efficiency of a heat pump depends heavily on how it is operated. Targeted optimizations can reduce power consumption, extend lifespan and reduce heating costs. You can optimally operate the heat pump by taking the following measures:

• Lower flow temperature: A lower flow temperature reduces power consumption. Ideally, it is 30 to 35 °C. This is achieved with surface heating systems (e.g. floor heating) or low-temperature radiators.
• Set the heating curve correctly: The heating curve determines how the flow temperature adapts to the outside temperature. A heating curve that is too steep leads to unnecessarily high temperatures and thus to higher energy consumption. Optimizing the heating curve saves electricity and ensures consistent heat.
• Use heat storage: A buffer tank can absorb excess heat when the heat pump is running particularly efficiently, e.g. when electricity prices are low. This avoids short cycle times and increases efficiency.
• Perform hydraulic adjustment: Hydraulic balancing ensures that all heating surfaces are evenly supplied with heat. Without this adjustment, the heat pump must provide unnecessarily high temperatures, which increases electricity consumption and costs.
• Perform regular maintenance: A dirty evaporator, incorrect pressure values or faulty control can significantly reduce the efficiency of the heat pump. An annual inspection by a specialist company ensures that the plant is running optimally.
• Combine photovoltaics to use your own electricity: A PV system can partially cover the heat pump's electricity requirements. This lowers electricity costs and makes operations more sustainable.
• Integrate smart home control: An intelligent controller can automatically adjust the heat pump to outdoor temperatures, electricity prices or self-consumption of PV power. This prevents inefficient operating phases and maximizes savings.

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Which mode of operation is the best?

The best way to operate a heat pump depends on the type of building, insulation and heating technology. Monovalent operation is ideal for new buildings with floor heating, as it offers the highest efficiency. In existing buildings with higher heating loads, bivalent or multivalent systems are often the better choice, as they offer flexibility and can absorb peak loads. The combination with renewable energies such as PV or solar thermal energy further optimizes operation and makes the heat pump more independent of rising electricity prices.

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