Understanding and improving the efficiency of heat pumps

Effizienz von Wärmepumpen mit x-change dynamic eco

The efficiency of a heat pump is a decisive factor in how climate-friendly and cost-saving heating can be. Modern systems get an astonishing amount of heat out of little electricity and can significantly outperform other heating technologies under optimal conditions. It is not only the technical details of the heat pump, but also the building and your own settings that make the difference. Many efficiency factors are directly in your hands.

At a glance

What does efficiency mean? An efficient heat pump provides a lot of heat with little electricity input.
Efficiency indicators: COP, JAZ, SCOP and ETAs make efficiency measurable and comparable. The higher the values, the more efficient the heat pump.
Important influencing factors: Efficiency depends not only on the technology of the heat pump, but also on the general conditions in the house.
Efficiency of heat pump types: brine / water heat pumps are particularly efficient. Air-to-water models are easier to install and are becoming more and more technically efficient.
Flow temperature as an efficiency factor: Heat pumps work most efficiently with low flow temperatures. Large heating surfaces, good insulation and ventilation with heat recovery help to reduce the flow temperature.
Optimisation options: Efficiency can be further increased through hydraulic balancing, correct controller settings, smart controls, regular maintenance and combination with a PV system.

Briefly explained: How does a heat pump work?

The heat pump extracts heat from the environment - i.e. from the air, the ground or the groundwater.
This environmental heat is absorbed by a refrigerant inside the heat pump.
A compressor compresses the refrigerant, causing its temperature and pressure to rise.
The heat generated is then transferred to the home's heating system via a heat exchanger.
The heat pump requires electrical energy, ideally from renewable sources, primarily to operate the compressor.

Find out more about how a heat pump works.

What does efficiency mean for heat pumps?

Basically, the less electricity a heat pump uses for heat generation, the higher its efficiency. Efficiency is therefore indicated using various key figures such as the COP or the JAZ, which represent the ratio between the electricity used and the heat generated.

A high value indicates a high level of efficiency. This not only has a positive effect on electricity costs, but also reduces the environmental impact.

Find out more about the electricity consumption and operating costs of heat pumps now.

Key figures for comparing the efficiency of heat pumps

In order to be able to assess and compare the efficiency of heat pumps before purchase as well as in later, real-life use, you should know and understand various key figures: COP, JAZ, SCOP and ETAs (_ηs).

COP (Coefficient of Performance)

The COP (coefficient of performance) describes the ratio of heat generated and electricity used. For example, a COP of 4 means that 4 kWh of heat is generated from 1 kWh of electricity. However, this value always refers to a defined operating point with specific flow and outside temperatures and is determined under test conditions. In reality, however, the conditions vary throughout the year and differ from building to building.

For this reason, the COP primarily provides an initial impression of the performance of heat pumps and makes them fundamentally comparable: A high COP value basically stands for an efficient system. However, it is not sufficient on its own to assess efficiency over the entire year - the JAZ, SCOP or ETAs values are usually also used for this.

What does the suffix A2/W35 in the COP value mean?The COP also specifies the conditions under which the respective value is achieved. These include

the heat source - here "A" stands for air (Air), "B" for brine (Brine) and "W" for water - and its temperature.
the flow temperature (W) of the heating system, for example "W35" for 35 degrees Celsius.

For example: COP 4.96 (A2/W35) means that at an air temperature of 2 degrees Celsius and a flow temperature of 35 degrees Celsius, one kilowatt of electricity generates 4.96 kilowatts of heat.

JAZ (anuual COP)

The COP (annual coefficient of performance) calculates the ratio between the total amount of heat generated and the amount of electricity required for this in actual operation. For example, a seasonal performance factor of 3 means that the heat pump in the building under consideration could generate an annual average of three kilowatts of heat with one kilowatt of electricity under real conditions of use.

Unlike the COP, the SPF therefore takes into account the real conditions on site, such as fluctuations in outside temperatures, user behaviour and building insulation. This makes the SPF much more meaningful for the actual operating costs and the environmental balance of a heat pump. The same basic principle applies here: The higher the SPF, the more economical and environmentally friendly the system is in everyday operation.

What is a good SPF for heat pumps?A value of at least 3.5 is generally considered a good seasonal performance factor.If the annual COP is higher, the heat pump consumes less electricity and therefore works more efficiently. For example, a COP of 4 or 5 is very good. The following average annual COPs can usually be achieved by the different types of heat pumps:

Air heat pumps approx. 3.5
Geothermal and water heat pumps approx. 3.8 to 4.5

You can use the JAZ calculator to individually calculate and compare the annual COP of a heat pump for your home.

SCOP (Seasonal Coefficient of Performance)

The SCOP (Seasonal Coefficient of Performance) indicates how efficiently a heat pump works on average over a complete heating period. As an extension of the COP, this value takes into account the fact that different outside temperatures prevail throughout the year, for example. Several operating points are therefore taken into account when determining the SCOP. These are based on the average seasonal temperatures and their frequency.

In contrast to the JAZ, which is calculated individually for each system and each building in actual operation, the SCOP is a standardised comparative value for different heat pump models. This means that the SCOP makes it easy to recognise which heat pump is particularly efficient under real conditions when comparing models.

What is a good SCOP for heat pumps? A heat pump is considered efficient if it has an SCOP of at least 4. This means that on average over the entire heating period, the system generates four kilowatts of heat with one kilowatt of electricity. If the SCOP is even higher, the heat pump consumes correspondingly less electricity and is therefore particularly economical. Very good appliances achieve SCOP values of 4.5 or more.

ETAs (seasonal space heating energy efficiency)

The ETAs value (_ηs, seasonal space heating energy efficiency) shows what percentage of the energy used actually arrives in the house as usable heat on an annual average. This takes into account the real operating conditions with regard to the changing seasons and climate zones. For example, if the ETAs value is 150 %, the heat pump generates 1.5 times as much heat per year from a given amount of electricity. The SCOP is used to calculate the ETAs value.

The big advantage: ETAs values are also given for other heat generators using suitable calculation methods. In principle, the auxiliary energy requirement and, by means of its primary energy factor, the climate balance of the energy source are also taken into account. In this way, this indicator also makes it possible to compare different heating systems and forms the basis for the energy label. The ETAs values for heat pumps are also decisive for subsidies today.

How do heat pumps compare in terms of ETAs?

In a direct comparison of ETAs values, heat pumps often score well because, unlike heating systems using fossil fuels, they achieve values of over 100 per cent. A value of around 130% is considered solid for heat pumps. Values from 150% to over 200% represent very efficient systems that consume particularly little electricity and operate economically.

What factors influence efficiency?

The efficiency of a heat pump depends on numerous factors. Not only is the technology of the heat pump itself decisive, but the conditions on site also play a role, for example the building and its equipment. A basic distinction is therefore made between two areas:

Technical factors of the heat pump

General conditions at the house

Type of heat pump: The type of heat pump - i.e. whether it is an air-to-water, brine / water heat pump or water-to-water heat pump - has a significant influence on efficiency. Differences arise due to the location, temperature of the heat source and range of applications.
Quality, efficiency and age: Modern, high-quality appliances generally offer better efficiency than older models, which are often less efficient.
Correct dimensioning and design: For the system to run optimally, it must be sized to suit the size of the building and the actual heat demand; professional planning and sizing by an expert are essential for this.
Setting and control: Efficiency can be significantly increased if the operating parameters - such as the lowest possible flow temperature - are optimised. Hydraulic balancing also ensures that all heating surfaces are supplied with heat evenly and according to demand. Intelligent control systems, smart home solutions and temperature sensors also help to continuously optimise operation.
Maintenance and care: Regular maintenance, inspections and necessary updates are important to ensure that the heat pump continues to operate smoothly and efficiently.

Building insulation and insulation standard: High-quality insulation of the walls, roof and basement ceiling ensures that as little heat as possible is lost. This significantly increases the efficiency of the heat pump.
Window type and airtightness: Modern, well-insulated windows and an airtight building envelope prevent draughts and reduce heat demand, which makes the operation of the heat pump more efficient.
Building size and required heating load: The size of the building and the resulting heat demand, also known as the heating load, largely determine how much energy needs to be used for heating. This has a direct influence on the design and efficiency of the heat pump.
Size of the heating surfaces and heating system: Large heating surfaces, such as underfloor or wall heating, enable low flow temperatures and are therefore particularly suitable for use with heat pumps. In contrast, older radiators usually require higher temperatures and work less efficiently.
User behaviour and actual heat demand: Individual user behaviour, i.e. how often and how intensively heating is used, has a noticeable influence on energy consumption. Personal preferences for room temperatures and hot water requirements also have a direct impact on the efficiency of the heat pump.

Which type of heat pump is the most efficient?

Air-to-water heat pump	Brine / water heat pumps	Water-to-water heat pump
Lowest efficiency in comparison, especially at low outside temperatures. However, modern appliances are increasingly achieving higher efficiency values.	Higher efficiency due to constant geothermal temperature all year round.	Highest efficiency of all types, as a constantly high groundwater temperature is utilised.
COP/JAZ usually lower than with other systems.	COP/JAZ usually higher than with air-to-water heat pumps.	Very high COP/JAZ values possible.
Very simple and quick installation, no ground or well construction required.	Requires earthworks for geothermal probes or collectors.	Access to suitable groundwater and official authorisation required.
Most common type on the market due to ease of installation	Particularly economical in regions with cold climates.	Installation and maintenance are particularly complex.
Particularly suitable for retrofitting and old buildings.	Installation more complex than with air-water models.	Particularly worthwhile for permanently high heat demand.
	Official authorisation required

Water and geothermal heat pumps usually achieve the highest efficiency, but require significantly higher installation costs and official authorisation. Air source heat pumps, on the other hand, are particularly easy and flexible to use, but sometimes have an efficiency disadvantage, especially in cold conditions. However, modern air-to-water models are becoming increasingly efficient thanks to further technical developments and can now keep up with the other systems in many applications.

Find out more about the different types of heat pumps now.

Flow temperature as the end of the spanner for optimum efficiency

The flow temperature is a decisive factor for the efficiency of a heat pump. It describes the temperature of the heating water that is fed from the heat pump into the heating system - for example, into a radiator or underfloor heating system.

To generate the required flow temperature, the heat pump utilises the heat from the energy source and brings it to the desired temperature level. The greater the temperature difference between the heat source and the heating flow, the more electricity the heat pump needs for the compression process.

While the temperature of the heat source - such as the outside air or the ground - cannot be influenced, the flow temperature can be actively reduced by taking certain measures. And lower flow temperatures increase the efficiency of the heat pump.

How can the flow temperature be reduced?

Optimise heating surfaces:
By using larger or more efficient heating surfaces, such as floor, wall or modern radiators, the heating system can be operated at lower temperatures.
Insulate the building envelope:
A well-insulated building envelope brackets the heat in the building, helping to ensure that the desired room temperature is already achieved with a lower flow temperature.
Ventilation with heat recovery:
The use of residential ventilation with heat recovery reduces additional heat losses and thus ensures that the heating system can cope with lower temperatures.

Tip: Increase efficiency without underfloor heating

Underfloor heating systems work with low flow temperatures and are therefore ideal for the efficient operation of a heat pump. However, it is not always possible to retrofit panel heating in existing buildings. Fortunately, a heat pump radiator can also be used to increase the efficiency of the heat pump.

Particularly practical: heat pump radiators take up no more space than the old radiators. Compared to conventional steel panel radiators, they can emit significantly more heat - a model such as the x-flair even achieves up to 80 % more output for the same size (type 33). This creates the best conditions for efficient heat pump operation and reduces your energy costs in the long term.

How to optimise the efficiency of the heat pump

10 effective measures

Insulate buildings well: Insulate the façade, roof, basement ceiling and windows sufficiently
Increase heating surfaces: Use panel heating (e.g. underfloor or wall heating) or larger radiators
Use special heat pump radiators: If space is a problem, use radiators that work efficiently even at low flow temperatures
Carry out hydraulic balancing: Allow heating surfaces to be supplied with heat optimally and evenly
Set the heating curve as flat as possible: Check the heating curve regularly and set it as low as possible
Use modern control/regulation: Use weather-compensated control, smart thermostats and smart home systems if necessary
Optimise room temperature and heating times: Choose room temperature sensibly; adjust heating times to actual demand
Regular maintenance/cleaning: Have the system checked, maintained and cleaned regularly
Professional dimensioning/adjustment: Adapt the heat pump and system to the building and requirements; have all components optimally adjusted
Use electricity from renewable sources: If possible, choose a green electricity tariff or use your own PV system

FAQs

What is the difference between COP and anuual COP?

The COP (coefficient of performance) indicates how much heat a heat pump delivers per amount of electricity used under defined test conditions. It is a laboratory value that is measured for certain outdoor and flow temperatures. The annual COP, on the other hand, describes the actual efficiency of the heat pump in real operation in a building over a whole year. It takes into account fluctuations in weather, user behaviour and building insulation. So while the COP is a theoretical comparative value for different devices, the COP shows how efficiently a heat pump actually works in everyday use. The higher both values, the more efficient the heat pump is.

What factors influence the efficiency of a heat pump?

The efficiency of a heat pump is determined by several factors. On the one hand, the technical properties of the system, such as the type of heat pump, its quality and the correct dimensioning, are decisive. On the other hand, the conditions in the house play a major role: good insulation, modern windows, large heating surfaces and a low flow temperature support economical operation. User behaviour - such as desired room temperatures and heating times - also has a direct impact on efficiency. Regular maintenance and an intelligent control system also help to keep the heat pump's performance high in the long term.

How does the flow temperature affect the efficiency of a heat pump?

The flow temperature is a decisive factor for the efficiency of a heat pump. The lower the temperature of the heating water that is fed into the heating system, the less electricity the heat pump requires. Systems with large heating surfaces such as underfloor or wall heating or with special heat pump radiators are particularly efficient, as they provide the desired thermal comfort with low flow temperatures. If, on the other hand, the heating water has to be heated to a high temperature, electricity consumption increases significantly and the efficiency of the heat pump decreases. A difference of just a few degrees is noticeable in terms of energy requirements.

Which type of heat pump has the best efficiency?

Water-to-water heat pumps generally achieve the highest efficiency as they utilise the constantly warm groundwater as an energy source all year round. Brine / water heat pumps, which use geothermal energy, also work very efficiently due to the constant temperature in the ground. Air-to-water heat pumps are the easiest to install, but usually achieve slightly lower efficiency values, especially at low outside temperatures. However, modern air-to-water models are increasingly catching up thanks to technical developments and in many cases can keep up with the other systems in terms of efficiency. Which type is the best choice ultimately depends on the conditions at the location and the individual requirements.

How efficient is a heat pump with radiators?

Heat pumps work most efficiently with large heating surfaces such as underfloor or wall heating, as these enable low flow temperatures. Conventional radiators often require higher temperatures, which increases the heat pump's power consumption and reduces efficiency somewhat. Special heat pump radiators, on the other hand, are a good alternative if underfloor heating is not possible: they emit a lot of heat even at low flow temperatures thanks to integrated fans, enabling the heat pump to operate efficiently.

Buy a KERMI heat pump

We attach great importance to the highest quality and flawless installation of our products. That is why we sell KERMI heat pumps exclusively via the three-stage sales channel. This ensures that you not only receive a premium product, but also benefit from the best possible advice, planning and professional installation. Your qualified local specialist partner is your direct contact and ensures the optimal integration of our efficient and sustainable heating solutions into your home.

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