Imagine if the energy that surrounds us — the heat of the earth, the air around us — could be used directly to heat our homes and offices. It almost sounds like magic, but in reality it is an advanced technology that is already available today: heat pumps. These devices have the remarkable ability to draw energy directly from our environment and could represent a revolution in how we think and use energy.

Heat pumps are devices that transport heat from a location with a low temperature to a location with a higher temperature and thus help to efficiently heat or cool buildings. Due to their ability to use heat from the environment and use it for the heating or cooling process, they represent an environmentally friendly alternative to conventional heating systems.

But how exactly does a heat pump work and what are the different types and operating modes? In this blog article, we want to take a closer look at how heat pumps work and take a closer look at the various options.

Renewable energy as a heat source: sustainable heat supply through heat pumps

The ever-growing concerns about climate change and the need to reduce CO2 emissions have intensified the search for sustainable energy solutions. One such solution is heat pump technology, which uses renewable energy from our immediate vicinity. But how does it compare with conventional heating systems and what influence does it have on the CO2 balance?

Comparison with conventional heating systems

Although conventional heating systems, such as those powered by oil or gas, are widely used, they have some disadvantages in terms of efficiency and environmental friendliness. Their mode of operation is based on the combustion of fossil fuels, which leads to high CO2 emissions and other pollutant emissions. An aging oil heating system with around 18,000 kWh of heating capacity per year produces around 4.8 tons of CO2 — a heat pump with comparable output can be almost CO2-neutral, depending on the power source. By way of comparison, 80 trees must be planted to bind a ton of CO2 (4.8 t CO2 = 384 trees) every year!

Heat pumps, on the other hand, use energy from the earth, air or water to generate heat for living spaces or water. They only need electricity to function — and this can increasingly be obtained from renewable sources. As a result, they are able to deliver more energy in the form of heat than they consume in the form of electricity, making them an extremely efficient heating method.

CO2 balance and sustainability

The combustion of any fuel, whether heating oil, coal, gas or wood, produces CO2 emissions. However, these emissions vary depending on the energy content of the respective fuel. For example, the ratio between calorific value and emitted CO2 is 0.266 kg/kWh less favourable compared to pellets 0.036 kg/kWh.

Wood is particularly important when it comes to climate neutrality: During its growth phase, a tree absorbs the amount of CO2 that corresponds to the amount released during combustion. However, burning pellets or entire logs in particular leads to considerable particulate matter emissions. In addition, it takes a certain amount of time before a burnt tree is compensated by subsequent generations.

The CO2 balance of heat pumps is significantly better than that of conventional heating systems. Even when you take into account the electricity consumption of a heat pump, its carbon footprint is often lower, especially when the electricity comes from renewable sources. In countries or regions with a high proportion of renewable energy in the electricity mix, heat pumps can enable almost CO2-neutral operation. If you generate this electricity yourself with solar panels, CO2 emissions are almost zero.

In addition, heat pumps are a long-term investment in sustainability. Since they do not rely on finite fossil fuels, they offer a future-proof heating solution that is in line with global emissions reduction goals.

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Nature as an energy source: an overview of heat pump types and their heat sources

Heat pumps represent a turning point in modern energy generation by using the regenerative forces of nature instead of relying on conventional fuels. They draw their energy directly from the environment, whether from air, water or soil, and convert this energy into heat. This approach is entirely in line with a sustainable future that reduces reliance on fossil fuels and other traditional energy sources. But which types of heat pumps are there and what differences are there to consider?

Air-water heat pump

The air-water heat pump extracts heat from the outside air and transfers it to the heating system. Depending on their design and purpose, we distinguish between:

• Low temperature air-water heat pump: This variant is designed to generate low flow temperatures and is therefore ideal for floor heating systems. Due to the low flow temperatures, it works particularly efficiently and can achieve excellent heating output in well-insulated buildings (energy efficiency class A++ and better). It usually reaches an annual performance factor (JAZ) of around 4 to 5, which means that it produces around 4 to 5 units of thermal energy for every unit of electrical energy consumed.
• High temperature air-water heat pump: In contrast to the low-temperature variant, this type of heat pump can achieve higher flow temperatures. This makes it ideal for classic radiator heating systems that require higher temperatures. It can also be used to provide hot water. The JAZ is usually slightly lower, approximately in the range of 3 to 4, i.e. in the range of the energy efficiency class of A+.
• Monoblock air-water heat pump: With this design, all important components of the heat pump are integrated in a single device. As a rule, the monoblock air-to-water heat pump is installed outside the building. This variant is particularly space-saving and easy to install. The efficiency depends on the exact design, but may be similar to the low-temperature variant.
• Split system air-water heat pump: In contrast to a monoblock heat pump, the outdoor and indoor units of the split system are separated. The refrigerant only circulates on the outside, which offers several advantages, such as a more flexible installation and less noise pollution indoors. The efficiency is comparable to the low-temperature variant.
• Air-to-air heat pump: This special type of heat pump extracts heat from the outside air and transfers it directly to the indoor air. It works in a similar way to an air conditioner, but can also be used for heating. Air-to-air heat pumps are efficient and are ideal for targeted heating of rooms. Their efficiency depends on the design, but is usually in the range of other air-to-water heat pumps.

Water to water heat pump

This specialized heat pump uses groundwater as a heat source. The special thing about groundwater is its constant temperature, which is greater than ten degrees Celsius throughout the year. This makes operation particularly efficient and reliable.

The heat pump works with two wells: a suction well and an absorption well. The suction well extracts the groundwater, which serves as an energy source, while the suction well returns the water back to the ground. Groundwater is used in the heat pump to generate heat, which is then fed into a building's heating system.

The efficiency of a water-to-water heat pump depends on several factors, including water composition and the amount of groundwater available. Careful planning and advice is required to ensure that this type of heat pump can be operated economically. An important aspect when planning a water-to-water heat pump is water protection, as certain conditions must be approved by the competent authorities. It is advisable to check with the relevant offices early on to ensure that all necessary permits can be obtained prior to purchase.

Brine water heat pump

Compared to air-water heat pumps, brine-water heat pumps generally achieve higher efficiencies. The soil from which brine water heat pumps extract heat provides a relatively constant and moderate temperature throughout the year. In contrast, the air temperature on which air-water heat pumps depend can fluctuate significantly and be significantly lower in cold winter months. An important indicator for the efficiency of a brine-water heat pump is the difference between the outlet temperature of the heat source and the flow temperature of the heating system. The lower this temperature difference, the more efficiently the heat pump works.

The efficiency of a brine-water heat pump can be predicted using VDI guideline 4650. This calculation method is based on the COP (Coefficient of Performance) of the heat pump and various system parameters. The annual performance figure (JAZ) is the sum of all COPs occurring within a year and is used to determine the actual efficiency of the plant.

The brine-water heat pump uses the ground as a heat source and offers various methods for extracting heat:

• Earth probe: The geothermal probe is a proven method for using geothermal energy for brine-water heat pumps. This method involves drilling deep into the soil, which can reach up to 100 meters deep. A special antifreeze circulates in these boreholes, which absorbs the heat stored in the ground. Since temperatures at this depth are relatively constant throughout the year, the geothermal probe can efficiently extract thermal energy from the ground. This method is particularly suitable for areas where there is little space for flat systems such as area collectors. However, due to the deep drilling, careful planning and, if necessary, regulatory approvals are required.
• Area collectors: The use of area collectors is another way of extracting heat from brine-water heat pumps. With this method, plastic pipes are laid at a shallow depth, approximately one to two meters below the ground surface. These pipes form a network and are able to absorb thermal energy from the surrounding soil. The efficiency of this method depends on the space available. Large plots of land are particularly suitable for area collectors, as they offer more space to install these pipe systems. The thermal energy generated by surface collectors mainly comes from solar radiation and rainwater, which is why the surfaces must not be sealed to ensure efficiency.
• Ring trench collectors: The ring trench collector is a hybrid solution that combines the advantages of both horizontal and vertical heat extraction. This method involves laying plastic pipes in an oblique or horizontal ring trench that is recessed into the ground. The ring trench collector offers the advantage that it requires less space than area collectors and is at the same time more efficient than purely horizontal systems. This makes it a good option for plots where space is limited. Ring trench collectors can generate thermal energy from various depths in the ground and are therefore versatile.

Also interesting: Although the purchase costs for a geothermal heat pump are comparatively high, the costs of the geothermal heat exchanger develop in proportion to the output of the heat pump. This means that, for the initial higher investment, costs can be saved on heating costs over time. In combination with its own photovoltaic system, a brine-water heat pump can help to heat a house almost autonomously and offers low heating costs in the long term.

Hot water heat pump

The hot water heat pump, also known as a domestic water heat pump, is specifically designed for heating hot water. These pumps extract around 3/4 of the required heat from indoor or outdoor air and cover the remaining energy requirement with electricity.

It can use both recirculated air and exhaust air as a heat source. When used with recirculated air, it can also contribute to dehumidifying rooms in addition to heating water and thus reduce the risk of mold formation. When connected to an existing air distribution system, the hot water heat pump can allow controlled ventilation of the rooms. However, this requires an active supply air line to avoid negative pressure.

• Operation with recirculating air: In this operating mode, the hot water heat pump uses the recirculated air as a heat source. It can be used, for example, in cellars which have a constant and relatively high temperature in the winter months. During operation, the temperature in the cellar room is cooled by about two to four degrees. At the same time, the cellar air is dehumidified, which helps to reduce the risk of mold formation.
• Operation with exhaust air: In this operating mode, the hot water heat pump uses the warm exhaust air from various rooms to heat the water. In this case, the top cover of the exhaust air heat pump is replaced by an exhaust air cover and the heat pump is connected to the existing air distribution system. The cooled exhaust air, which is produced when drinking water is heated, is led outside as exhaust air. To ensure that there is no negative pressure, the supply air is supplied via separate supply air elements. This operating mode allows not only hot water heating, but also controlled ventilation of the rooms.

Typically, hot water heat pumps for single-family homes have a heating capacity in the range of 1.5 to 2.5 kW. They are compact and quiet to operate. The capacity of the hot water tank can usually be read by the product name (often approx. 200 to 300 l).

Hybrid heat pump technology

The hybrid heat pump is a heating technology that consists of a heat pump and another heat source that are coordinated with each other. It can be installed in a compact unit or in the form of two separate heating systems. In so-called dual-mode mode, one of the two heating systems generates heat up to a predetermined point at which the second heat source is switched on. This point is known as the bivalent point. Modern hybrid heat pumps have intelligent controls that automatically select the most efficient mode of operation.

Hybrid heat pumps can be configured in various ways.

• Combination gas condensing boiler: The most common variant is the combination of a heat pump with a gas condensing boiler (gas hybrid heating). This combination is particularly widespread and efficient, as modern gas condensing boilers generally operate in a modulating manner and adapt to heating requirements. However, hybrid heat pumps can also be combined with existing gas condensing boilers, provided that both systems are well coordinated.
• Combination solar thermal system: Another option is to combine a hybrid heat pump with solar thermal systems. This can make water heating environmentally friendly and reduce the load on the heat pump. However, it is important to plan the system carefully, as using the solar thermal system can impair the efficiency of the heat pump. Detailed planning, including a solar storage system and professional coordination of both systems, is required.
• combo solid fuel boiler: The combination of a heat pump with solid fuel boilers, in particular log boilers, is technically possible, but has several disadvantages. Log boilers are only efficient under heavy load and have longer heating times. This can result in a loss of comfort. As a rule, the combination with pellet boilers is expensive. A hybrid heat pump can also be combined with ventilation systems with heat recovery, but is usually only suitable for water heating as the air volume is limited.

The advantages of a hybrid heat pump lie in the high efficiency and cleanliness of the heat pump technology. It enables efficient heat generation, even when the temperatures in the heating system are low. The purchase costs for hybrid heat pumps are generally higher than for individual heating systems, but can be reduced through government subsidies. Hybrid heat pumps are particularly useful in energy-saving new or old buildings that have large heating surfaces or panel heating.

Large heat pumps

Large-scale heat pumps have been specially developed for use in larger building complexes or entire settlements and meet high European standards. Various waste heat sources, soil, industrial process heat, groundwater or even an ice energy storage device can be used as heat sources. They have the potential to meet both heating and cooling requirements in high-volume buildings. Until now, such buildings have often relied on fossil fuels such as oil or gas and use chillers for cooling. Large-scale heat pumps offer the opportunity to replace these traditional methods while reducing costs and reducing environmental impact.

These heat pumps can heat in winter and cool in summer. This not only results in lower investment costs, but also lower energy costs. The investment in large heat pumps often pays off fairly quickly, as they provide low-temperature heating and cooling all year round and enable efficient energy management thanks to their automated operation, “smart” monitoring and low maintenance costs.

Special feature: Large-scale heat pumps in cooling mode can often operate with lower operating costs than conventional chillers.

Suitability of these sources in old and new buildings

The suitability of different types of heat pumps depends on various factors. In new buildings, heat pumps appear to be “ideal” due to their good insulation and low flow temperatures. However, there are often negative assumptions about the use of heat pumps in old buildings. From an energy point of view, an old building is considered to have insufficient thermal insulation and uses a heating system with high flow temperatures, such as radiators.

The efficiency of a heat pump depends primarily on the temperature difference between the heat source and the required flow temperature (delta). The type of building, insulation and hot water distribution play a subordinate role. To maximize efficiency, planning should aim to minimize this delta. This can also be achieved through adjustments on the heating circuit side, such as increasing the flow rate and optimising the hydraulics.

In addition, a low JAZ does not necessarily mean that operating a heat pump in an old building is uneconomical. Because even if the JAZ is not as high as in a new building, the use of other heating systems in an old building could also be cost-intensive. In order to generate the required heat energy, increased resources (e.g. logs or gas) must also be used with conventional heating methods.

Important: When planning heat pumps in old and new buildings, a precise analysis of heat demand and use is therefore crucial. This is where a heat load calculation in accordance with the standard and hydraulic balancing according to method B are appropriate to ensure the suitability of different types of heat pumps.

Technical aspects: The technology behind heat pumps

The basic idea behind a heat pump is amazingly simple and is based on the principle of refrigerator technology. Heat pumps use the same technology as a refrigerator, only in the opposite direction. While a refrigerator takes heat from the inside and removes it to the outside, the heat pump extracts heat from the air, soil or groundwater from the environment in order to use it for heating purposes.

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The basic principle of a heat pump

The basic heat pump process can be divided into four main phases:

1. vaporization: In an evaporator, which is part of the heat pump, a refrigerant is evaporated at low pressure. During this evaporation process, the refrigerant absorbs heat from its environment, be it air, soil or groundwater. While the two media do not mix, the heat source releases its energy. This heat energy increases the temperature of the refrigerant and transforms it into a gaseous state. The ambient temperature of the evaporator must be higher than the boiling point of the refrigerant at low pressure so that heat transfer can take place.
2. compaction: The gaseous refrigerant vapor is then fed into the compressor (often a scroll compressor or reciprocating compressor), which acts like a compressor. Here, the pressure and temperature of the refrigerant are increased. This step requires energy, usually in the form of electricity. As pressure rises, so does the temperature of the refrigerant. The energy consumption of the compressor depends on the desired heating temperature.
3. liquefaction: The heated refrigerant is fed into the condenser, where it transfers heat to the heating system in the building. Here, the hot refrigerant vapor flows past the heating water, which transfers heat between the two media. The refrigerant releases energy, cools down and condenses back into its liquid form, while the heating water absorbs the heat and heats up.
4. Expansion: After the refrigerant has given off heat, it is passed through an expansion valve or throttle. This valve abruptly lowers the pressure of the refrigerant, which allows it to evaporate again. This allows the refrigerant to absorb heat again when it reaches the evaporator and the cycle starts all over again.

The efficiency of a heat pump depends heavily on the temperature of the heat source and the required heating temperature. The larger the temperature difference, the more energy is required for compression, which can affect overall efficiency.

Most heat pumps used in heating and cooling systems today are based on compression heat pump technology. These systems use an electrically operated refrigerant compressor, which plays a central role. Evaporation takes place in an evaporator, in which the environmental heat from the air, brine (soil) or groundwater is transferred to the liquid refrigerant. The gaseous refrigerant vapor is compressed by the compressor to increase its temperature before it transfers the heat to the heating system in the condenser.

For a heat pump to work effectively, various components are required, including the evaporator, compressor, condenser, and expansion valve. The entire process is repeated continuously, as a result of which the heat pump efficiently absorbs heat energy from the environment and uses it for heating purposes. Efficiency depends heavily on the temperature difference between the heat source and the heating system. The closer these temperatures are to each other, the more efficient the heat pump is.

Key terms in brief

COP (Coefficient of Performance)

The COP, or performance factor, is a decisive measure of the efficiency of a heat pump. It indicates how much heat energy the heat pump generates in relation to the energy supplied. For example, a COP of 3 means that the heat pump produces three units of heat energy while consuming one unit of electrical energy. The higher the COP, the more efficiently the heat pump works.

The average COP values for efficient heat pumps may vary depending on the type, model and specific operating conditions. Here are some rough averages that can be used as a reference:

1. air to water heat pumps: Efficient air-water heat pumps can achieve COP values of between 3 and 5 in typical heating applications. This means that they can generate 3 to 5 kilowatt hours of heat energy for every kilowatt hour of electrical energy used. Values below 3 may indicate an inefficient heat pump.
2. Geothermal heat pumps (geothermal heat pumps): Geothermal heat pumps often have an even higher COP value and can reach values of 4 to 6 or even more. This is because they can access a more stable and warmer heat source.
3. water to water heat pumps: Water-to-water heat pumps that use water as a heat source can also achieve very high COP values, often in the range of 4 to 6 or higher.

Manufacturers provide the COP value for their heat pump models. This value may vary depending on the temperature of the heat source and the flow temperature of the heater. The information is given in the form of letter + temperature/ letter temperature, where the first value represents the temperature of the heat source and the second value represents the flow temperature of the room heater at the measurement time.

The abbreviations A, B and W stand for various types of heat sources, namely air, earth and water (groundwater).

• A = air
• B = Earth
• W = water (groundwater)

example: Assume that the COP value of a heat pump is 4.2 and the COP figure is: A7/W35. This means that the heat source A = air and the heat pump achieves a performance factor of 4.2 at an outside temperature of 7°C and a flow temperature of 35°C.

In addition to the COP, the annual performance factor (JAZ) is an important parameter for the efficiency of a heat pump. While the COP is a snapshot of efficiency under laboratory conditions, JAZ measures performance over a longer period of time and takes into account the real conditions at the installation site. The JAZ is therefore a more reliable parameter for evaluating the efficiency of a heat pump in local operation.

CO2 emissions and GWP (Global Warming Potential)

Heat pumps are considered an environmentally friendly heating and cooling technology because they produce less CO2 emissions than fossil fuels. Global Warming Potential (GWP) is a key figure that indicates how much a greenhouse gas contributes to global warming. It is often expressed in terms of CO2. By way of comparison, the refrigerant R410A has a GWP value of 2088, while that of R290 is 3. This means that 1 kg R410A has an equivalent of 2088 kg CO2 emissions and 1 kg R290 of 3 kg CO2 emissions. Compared to conventional heating systems, heat pumps generally have a significantly lower GWP.

Definition of BTU (British Thermal Unit)

The BTU is a unit of thermal energy and is commonly used in the USA. 1 BTU is the amount of heat needed to heat 1 pound of water by 1 degree Fahrenheit. In SI units, this corresponds to approximately 1055 joules. The BTU is important for measuring and comparing heat outputs, particularly when it comes to heating or cooling capacities of heat pumps.

heating rod

A heating rod is a backup heating source in a heat pump. If the heat pump alone is not sufficient to maintain the desired room temperature, the heating element can be activated. This usually happens at extreme temperatures or when the heat pump is being serviced. The power of a heating rod may vary depending on the model and requirements. Typically, the power of a heating rod is between 3 and 15 kilowatts.

power modulation

Power modulation is a function that enables a heat pump to adjust its output to current requirements. This increases efficiency and ensures that the heat pump does not constantly switch on and off. Modern heat pumps can often continuously adjust their output between, for example, 20% and 100%. This modulation enables the heat pump to provide exactly the required heating or cooling capacity and thus optimize energy consumption.

Compactor

The compressor is the heart of a heat pump. It compresses the refrigerant, raises its temperature and drives the entire circuit. Modern heat pumps often use scroll or inverter compressors for better efficiency and output control. A common value for the output of a compressor is between 1 and 10 kilowatts, depending on the size of the heat pump.

Inverter

An inverter is an electronic controller that can continuously regulate the compressor's output. This allows the heat pump to react precisely to demand and keep the temperature in the building constant. Output control using an inverter makes it possible to optimize the energy consumption of the heat pump. The modulation can range from 20% to 100%, for example.

heating curve

The heating curve, also known as the heating curve, regulates how the flow temperature is adjusted depending on the outside temperature. When the outside temperature drops in winter, the heating curve increases the flow temperature accordingly. Precise adjustment of the heating curve is crucial for efficient operation of the heat pump.

Normally, the heating curve is pre-set by the installer when installing the heat pump. In practice, however, this setting must be adapted to actual heating and use conditions in order to optimally control the heat generation of the heat pump. This depends largely on the individual characteristics of the building and the heating heat distribution system.

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The slope of the heating curve shows by how many degrees the flow temperature of the heat pump should change when the outside temperature changes. While the steepness of the heating curve results from the combination of thermal insulation and heating distribution system, the parallel shift enables individual adjustment of the desired level of comfort. By adjusting the parallel shift, the room temperature can be easily raised or lowered as required.

Assuming that the desired room temperature is between 21 and 22 °C, this temperature must be provided automatically and without delay by the heat pump on both very cold and milder days. An adjustment of the heating curve is necessary if it is found that the heat pump heats too little or too much on some days. In such cases, the heating curve should be gradually adjusted via the heat pump control unit to ensure that the heat supply meets the actual requirements exactly. It is important that a single adjustment to the heating curve should only differ by 10% from the previous setting to avoid too much change.

heat pump control

The heat pump control unit controls all functions of the heat pump, including the compressor, power modulation and the heating curve. Precise control is crucial for efficiency and comfort when heating and cooling with a heat pump. Modern heat pump control systems use advanced algorithms and sensors to optimally adapt the output of the heat pump to current conditions and to minimize energy consumption.

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Operating modes of heat pumps: How heat pumps work

Heat pumps are true all-rounders when it comes to heating and cooling buildings. But how exactly are the devices operated? In this section, we will take a closer look at the various operating modes of heat pumps and understand how they efficiently adapt their performance to the respective requirements.

Monovalent operation

Monovalent operation is one of the basic operating methods of heat pumps. This is a mode in which the heat pump is solely responsible for providing heating or cooling energy. It only uses environmental heat as an energy source to maintain the desired temperature in the building.

example:

• A single-family home is solely heated by an air-water heat pump.

The monovalent operation is particularly environmentally friendly as it does not require the use of fossil fuels. However, it may not be sufficiently efficient in regions with extremely low temperatures, as environmental heat is limited in very cold weather.

In order to enable monovalent operation, a number of requirements must be met. First of all, the heat source must be able to cover the entire heating load of the building and the heating of drinking water without the assistance of an additional heat source. This requires that a constant heat source with stable temperatures is available.

The monovalent operation of a heat pump is often achieved using geothermal energy or groundwater. Special heat exchangers such as geothermal collectors or geothermal probes are used for this purpose. In addition, a monovalent system requires a heating system that can work with panel heating systems such as floor or wall heaters and fan convectors and supports low flow temperatures of around 40 degrees.

Using outside air as the sole heat source in monoval operation is often not recommended for economic reasons. That's because outdoor air has restrictions due to its temperature fluctuations and limited availability, particularly in very cold weather. In such situations, it is better to consider another mode of operation, such as monoenergetic or bivalent operation.

In practice, smaller brine/water heat pumps and water/water heat pumps are often used in monoval operation. These systems provide constant and sufficiently high source temperatures all year round so that the heat pump alone can cover the building's heating requirements. However, it is also possible to use the power of the heat pump in combination with other heat sources, depending on the specific requirements of the building and its environment.

Mono-energetic operation

Mono-energy operation is another important mode of operation of heat pumps. In this mode, the heat pump is used together with various heating sources, which, however, all use the same operating energy source (e.g. electricity). This operating mode is often used in combination with a heating rod to optimize efficiency and temperature control.

example:

• An air-to-water heat pump heats and cools a residential building all year round. During “cold peaks”, a heating element can be activated to maintain the desired temperature.

Mono-energy operation is often used for small air heat pumps in single-family homes that have an electric heating rod as a backup. When the outside temperature drops sharply in winter and the heat pump alone is not sufficient to generate enough heat, the heating element steps in. This rarely happens, around 5% of heating days, and has little effect on the efficiency of the heat pump. While air heat pumps often rely on the use of a heating rod, geothermal heat pumps usually do without this. The heat pump control makes it possible to activate or deactivate the heating element as required.

Extra: role of electric heating rod

The electric heating element, which is integrated in the buffer tank or in the heating flow, usually has an output of a few kilowatts (kW), typically between 2.5 and 10 kW. It can be useful in various situations, such as at very low outdoor temperatures, to support building drying in new buildings, for thermal disinfection of industrial water or as a safety measure when outside temperatures fluctuate strongly. In some cases, the heating element can also help to reduce purchase costs or to avoid frequent switching on and off of the heat pump during the transition period.

Dual mode

In dual-mode operation of heat pumps, an additional heat source is used in addition to the heat pump, which steps in when it is very cold outside and the heat pump alone cannot generate enough heat. This additional heat source can have various forms, such as gas, wood or oil boilers. If heat is not generated by electricity, this is known as a dual-mode heat pump operation. This approach is often used in older buildings where higher flow temperatures are required, or in larger systems where the exclusive use of the heat pump would not make economic sense.

example:

• A residential building uses an air-water heat pump in conjunction with a gas condensing boiler. The heat pump provides heating on mild days, while the gas condensing boiler steps in at extreme temperatures.

In dual-mode mode, the additional heat source takes over the heating from a specific point, the so-called bivalent point or dimensioning point. This approach is often used when upgrading existing buildings, particularly when higher system temperatures are required. Bivalent operation is normally only used in air heat pump systems and in drinking water heating systems in apartment buildings.

In order to keep operating costs low and maximize efficiency, it is important that the heat pump covers as much of the building's heating requirements as possible. Since the number of days with outdoor temperatures below -5°C is usually very limited, the bivalence point is often set or determined around this temperature. In such cases, the additional heating only accounts for a small percentage of the total heat required, for example around 1% at -10°C outside temperature and around 4% at -16°C outside temperature.

Bivalence point and its meaning:

The bivalence point is the temperature at which the heat pump and the alternative heating source can produce the same heating output. Defining the bivalent point or dimensioning point when designing an air heat pump is crucial, as the output of the heat pump decreases as outdoor temperatures decrease and the heating load of the building increases. The exact location of this point depends on the specific heat load of the building and is typically in the temperature range between -4 °C and -8 °C. Below this temperature, the heat pump can no longer operate efficiently, so it is normally operated in conjunction with other heating methods, such as gas, wood, solar thermal or geothermal energy.

Different types of bivalence: parallel, alternative and semi-parallel operation:

• Parallel operation: In bivalent parallel operation, the heat pump also alone carries the heat requirement up to the bivalent point. If this point falls below this point, the second heat source supports the heating operation of the heat pump. At low temperatures, the second heat source accounts for a higher share of the heat generation than the heat pump. However, both heat sources cover the heat requirement when the standard outside temperature is reached.
• In parallel operation, the heat pump and the alternative heating source work simultaneously to provide the required heating output.
• This is particularly efficient when the alternative heating source has a low flow temperature, meaning it can work efficiently at low temperatures.
• Alternative operation: In the bivalent alternative mode of operation, the heat pump alone bears the heat requirement until the bivalence point is reached. Below this point, the second heat source takes over the sole heating operation and the heat pump shuts off.
• In alternative mode, the heat pump is only switched on when the alternative heating source is insufficient to reach the desired room temperature.
• This minimizes the energy consumption of the heat pump, as it only works when needed.
• Partially parallel operation: The bivalent semi-parallel operation combines elements of bivalent parallel and bivalent alternative operation. The heat pump works alone up to the bivalence point and is then supported by the second heat source. When a further specified temperature is reached, the heat pump shuts off and the entire heat requirement is met by the second heat source alone. The planning must take into account when the heat pump is switched off and the second heat source takes over the sole heat generation.
• In partially parallel operation, the heat pump and the alternative heating source first work in parallel and then alone.
• For example, the heat pump can provide part of the required heating output, while the alternative heating source covers the rest.

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Other operating modes and technologies

In addition to the operating modes mentioned above, there are other technologies and operating modes that increase the efficiency and flexibility of heat pumps.

• Heat pump operation in cascade: The cascade method of heat pump operation involves connecting multiple heat pumps in series to increase overall efficiency. Each heat pump in the cascade has the task of further increasing the temperature of the refrigerant before it is transferred to the next unit. This approach is particularly advantageous in larger buildings, where different heating and cooling services must be covered efficiently and cost-effectively. Another advantage of this method is the increased security of supply, as if one unit fails, the others can continue to work smoothly.
• Modulating operation with inverters: Inverter-controlled heat pumps can continuously adjust their output to precisely meet current requirements. This results in a minimization of energy consumption and an increase in the annual efficiency of the heat pump. The inverter is at the heart of this variant and regulates output by adjusting the speed of the heat pump compressor. This prevents unnecessary switching on and off of the heat pump and reduces the load on its components.
• Hybrid operation of heat pumps: Hybrid systems combine heat pumps with other heating technologies, such as solar thermal energy or gas condensing boilers, to maximize overall efficiency. These systems consist of various types of heating, with the most common combination of gas heaters and air heat pumps. Depending on the selected operating mode, the controller controls when the heat pump is switched on and when the gas heating system is switched on. This can be based on defined goals, for example, such as achieving a specific performance factor (COP) or reducing CO2 emissions. Hybrid heat pumps are particularly useful in older buildings, where high flow temperatures in winter make using the heat pump alone uneconomical, while they can take full advantage of the heat pump in warmer months.

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Economic efficiency of heat pumps

When choosing a heat pump, profitability plays a decisive role. Efficiency and the associated savings depend heavily on the operating mode and individual circumstances.

Influence of operating mode on profitability

The economic efficiency of a heat pump is significantly influenced by its mode of operation. As mentioned above, there are various operating modes of heat pumps, including monovalent, monoenergetic and bivalent operation. Each of these operating modes has its own advantages and disadvantages in terms of profitability.

• Monovalent operation: This operating mode, in which the heat pump works alone without additional heating, is usually the most economical option when environmental conditions permit. The lower the required flow temperature is and the more constant the outdoor temperatures are, the more efficient this operating mode is. In regions with mild winters, monoval farming can deliver the best economic results.
• Mono-energetic operation: In mono-energy mode, the heat pump is used with various heating sources, which, however, all use the same operating energy source. Small air heat pumps in single-family homes often use a heating element as a backup, which is rarely used and has little negative effect on the annual performance factor. The use of an electric heating rod ensures that the heat pump can reach the desired temperature even under extreme conditions.
• Dual mode: Bivalent operation makes it possible to use multiple energy sources and is particularly relevant in regions with cold winters. Here, the heat pump can work efficiently up to a specific point and is then supported by an alternative heating source, such as a gas condensing boiler. The position of the bivalent point, at which the heat pump and the alternative heating source provide the same output, is decisive. With lower flow temperatures and higher heating loads, bivalent operation makes more economic sense.

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Cost-benefit ratio and potential savings

The cost-benefit analysis is an important step in evaluating the economic efficiency of heat pumps. Here, the investment costs for the purchase and installation of the heat pump are compared with the expected savings. The following factors should be considered:

Investment costs: The investment costs for heat pumps vary depending on the type and size of the system as well as the individual conditions of the location. Compared to conventional heating systems such as gas condensing boilers, the purchase costs for heat pumps can be higher. The costs of air heat pumps start at around 5,000 euros, while geothermal heating systems can cost up to 20,000 euros more due to additional drilling meters or a larger area collector.

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The higher investment costs for heat pumps are partly due to the need for modifications to the heating system, particularly in old buildings. In some cases, it may also be necessary to install an electric heating rod if the heat pump is operating in mono-energy mode. Despite these initial costs, the long-term benefits and savings must be considered.

operating costs: The operating costs of a heat pump consist of the energy costs for operating the heat pump and, if applicable, for the alternative heating source in dual mode. Heat pumps are known for their high energy efficiency, as they use heat from ambient air, water or soil. As a result, significant savings in energy costs can be achieved.

The annual performance factor (JAZ) is an important parameter that indicates the efficiency of the heat pump. The higher the JAZ, the more efficiently the heat pump works. Modern heat pumps can reach JAZ values of 4 or more, which means that they produce four times more heat than they consume in energy.

In old buildings, where higher flow temperatures are often required for heating, the JAZ may be slightly lower but still remains at an efficient level. The operating costs for a heat pump are therefore generally lower than those for conventional heating systems such as gas or oil heating systems.

Maintenance costs: Regular maintenance of a heat pump is crucial to ensure its efficiency and durability. Maintenance costs vary by manufacturer and model, but are usually in the range of 100 to 200 euros per year. Regular inspection and maintenance of the heat pump by a specialist ensures that it functions optimally and does not require expensive repairs.

Funding and financial incentives: The Federal Government recognizes the crucial importance of renewable energy and energy efficiency in the fight against climate change and has accordingly developed a range of funding programs to promote change in the building sector. The aim is to support the switch to heating systems, which are 65 percent based on renewable energy, through financial subsidies and cheap loans. From 2024, the federal government is funding the installation of environmentally friendly heating systems with basic funding of 30 percent of the total costs. This measure aims to strengthen climate protection and keep operating costs stable compared to fossil-powered heating systems.

For households with a total annual taxable income of up to 40,000 euros, there is an income-related bonus of 30 percent to offer low-income households in particular an additional incentive. By 2028, people who replace their outdated fossil heating systems (e.g. oil, coal, night storage or gas) with renewable energy sources will receive a speed increase of 20 percent. All of these bonuses can be combined but must not exceed 70 percent of the total costs. This represents significant financial support and makes investments in renewable energy extremely attractive.

The long-term savings achieved through lower operating costs and government funding can often offset and in many cases exceed the initial investment costs for a heat pump. It is therefore crucial to consider the total costs over the life of the plant and not just the initial expenditure.

Conclusion

In summary, it can be said that heat pumps offer an efficient way of extracting heat energy from renewable sources and using it in buildings for heating and water heating. From air-water heat pumps to geothermal heat pumps to hybrid heat pumps, there are various options available that are suitable for different requirements and circumstances. The selection of the optimal heat pump depends on various factors, including building size, regional climate conditions and individual needs.

Accurate heat load calculation and hydraulic balancing are crucial for choosing the right heat pump. In this context, software such as that from autarc can offer valuable support. AutArc's software for heat load calculation and hydraulic balancing makes it possible to determine the specific requirements of a building and to find the most suitable heat pump.

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