Myths and common misconceptions about heat pumps

In short
Modern heat pumps can be operated very well in houses with existing radiators and generally do not require any replacement of conventional radiators. Nevertheless, heat pumps are more efficient when used in combination with underfloor heating due to the associated lower flow temperatures and are therefore more economical than heat pumps with conventional radiators.

Video explanation

In detail
The main point of this issue concerns the flow temperature of the existing heating system, i.e. the temperature of the water when it leaves the heating unit and enters the heating circuit. For underfloor heating, the required temperature is typically 35 °C, whereas conventional radiators require higher temperatures of around 55 °C or more. Today's modern heat pumps can easily provide these high flow temperatures, so that the house is sufficiently warm even in combination with traditional radiators.

Generally speaking, however, the lower the flow temperature, the more efficient the heating system. As underfloor heating requires lower temperatures, a heat pump combined with underfloor heating is consequently more efficient and economical than one using conventional radiators.

However, it is also possible to replace existing radiators with low-temperature radiators in order to reduce the required flow temperature and make the entire heating system more efficient without installing underfloor heating. The achieved flow temperature should ideally be a maximum of 55°C to ensure good efficiency.


 

In short
Heat pumps can deliver high flow temperatures, but running them continuously at higher temperatures reduces their efficiency and increases energy costs. Modern heat pumps automatically adjust the flow temperature to the outside temperature in order to work as efficiently as possible.

Video expanation

In detail
Heat pumps typically supply flow temperatures of 55 °C, which is sufficient for many old buildings. There are also high temperature heat pumps that can achieve significantly higher flow temperatures. However, running heat pumps continuously at high flow temperatures reduces their efficiency, increasing both energy consumption and electricity costs. 

As a rule, heating systems are operated in accordance with outside temperatures, which means that the flow temperature is automatically increased in extremely cold weather and lowered again when the outside temperature rises. Modern heat pumps work using the same principle and regulate the flow temperature up to 55 °C if necessary.
 

In short
Modern heat pumps can also be used effectively in existing buildings with low insulation standards and with conventional radiators instead of underfloor heating. They are capable of generating high flow temperatures with good efficiency and are therefore also an interesting alternative in older constructions.

Video explanation

In detail
In existing buildings, the flow temperature of the heating system, i.e. the temperature of the water when it comes out of the heating system and enters the heating circuit, is particularly important. Underfloor heating generally requires 35 °C, while conventional radiators require flow temperatures of up to 55 °C or even higher, depending on the insulation level of the building.

As a rule, the lower the flow temperature, the more efficient the heating system. Consequently, a heat pump is less efficient in existing buildings with conventional radiators than in new constructions with underfloor heating.

Nevertheless, modern heat pumps can easily generate high flow temperatures at high efficiency and are therefore also an interesting alternative for existing buildings. If you want to operate a heat pump in existing buildings even more efficiently, you can take additional measures such as adapting and modernising the radiators, setting the correct flow temperature, or improving the building insulation to reduce energy consumption.
 

In short
Heat pumps do produce a certain amount of sound, but there are different types of devices and installation methods as well as additional sound insulation measures to keep the noise level below 40 dB(A) (maximum value in Luxembourg to be eligible for state subsidies and municipal authorisations). Sound insulation should therefore be taken into account during installation in order to avoid unnecessary noise pollution.

Video explanation

In detail
Sound insulation plays an important role for heat pumps in two respects: firstly, acoustic insulation in the house itself and secondly, external sound insulation in respect to neighbouring buildings.

Sound insulation should already be taken into account during installation for any type of heat pump. It is, for instance, possible to use elastic sound insulation mounts to prevent oscillations and vibrations being transmitted from the heat pump to the walls of the house and thereby generating unwanted sounds inside the house. These measures are easy to implement and are usually taken into account by the installer.

In the case of air-to-water heat pumps that extract heat from the air outside and where an outdoor unit is installed, it is particularly important to ensure adequate noise protection with respect to the neighbours. These outdoor units contain a fan that draws the air through a heat exchanger, and this fan is the main source of noise. Any sound generated by the outdoor units and/or the fan spreads through the air, and the distance to the outdoor unit affects how audible it is. In Luxembourg, 40 dB(A) must not be exceeded at the neighbour's boundary, which has to be proven in order to obtain state subsidies and municipal approval for a heat pump.

The national sound calculator, which can be found at www.schallrechner.lu, is used to verify the acoustic level at the neighbour's boundary. The installer can use this sound calculator to determine the level in advance so that the 40 dB(A) at the neighbour's boundary is not exceeded; it can simulate a range of heat pump variants, different installation options, possible additional soundproofing measures and much more. This makes it easier to select a suitable variant that complies with the threshold value.

It is important to discuss this issue with the installer as early as the initial quotation stage, as there are considerable differences between the various heat pumps in terms of noise emissions. At the same time, when submitting the offer, it should also be considered where the outdoor unit can be installed to comply with the noise threshold to the neighbour.

 

In short
In new buildings, it is possible to install a heat pump so that it always covers 100 % of the heat demand. In existing constructions, it is possible that the heat pump may not be able to cover 100% of the heat demand at outside temperatures below -2 °C. In this case, a second heating unit would cover the missing 2 to 5% (of the annual consumption). A lot of heat pumps are available as hybrid systems with an integrated electric heating element. A professional installation design is crucial in such a case. Hybrid solutions can also serve as a transition towards 100% reliance on renewable energies.

Video explanation

In detail
A lot of heat pumps are already available as hybrid systems (there is a second heat generator), usually with an integrated electric heating element. As energy levels vary with the outside temperature, an air-to-water heat pump can generate less energy at low outside temperatures than at higher temperatures. 

In new buildings, it is possible to design the heat pump so that it generates 100 % of the required energy even at low outside temperatures. Given that the number of cold days below -2 °C in Luxembourg is only around 3 weeks a year and that the power requirements are generally higher compared to new buildings, it is common practice to install heat pumps in existing buildings that do not cover 100 % of the energy requirement at very low outside temperatures, but instead use a backup heating element to generate the missing energy (2 % to 5 % of annual consumption).

To determine the optimum size of the heat pump, it is important to have the installation professionally designed. In isolated cases, it may make sense to opt for a hybrid solution in combination with other heating units, for instance if the existing oil or gas heating system is not that old or if it is unclear whether the radiators can operate efficiently with the provided flow temperature. Furthermore, a hybrid installation can also be used as a temporary solution to make the oil or gas heating system superfluous through subsequent insulation measures.
 

In short
Research shows that heat pumps can also be operated economically in existing buildings, especially if combined with solar power generation, hydraulic optimisation and, if necessary, structural adjustments. Although the initial investment is higher, the heat pump pays for itself over its lifespan due to lower operating costs, savings from using photovoltaic energy and state subsidies. Continuous monitoring and metering of energy consumption is essential to maximise efficiency and reduce operating costs.

Video explanation

In detail
Heat pumps are an ideal heating solution for new buildings as they are well insulated and have low flow temperatures. Nevertheless, studies have shown that heat pumps can also be operated cost-effectively in existing structures. The system can be optimised by combining it with a photovoltaic installation to autconsume electricity, by adjusting the hydraulics of the heating circuit and, if necessary, by making structural improvements.

Hydraulic balancing is indispensable to ensure that the flow temperature across all heating surfaces can be kept as low as possible. It may also be necessary to replace individual radiators with more efficient models.

Compared to conventional heating systems such as gas or oil boilers, the initial investment for a heat pump is admittedly higher, but this is relativised over the course of its lifespan due to their lower operating costs. A heat pump also makes it possible to utilise more electricity from your own photovoltaic system. In addition, there are national and municipal subsidy programmes that reduce investment costs and improve profitability.

To ensure that the system runs as cost-effectively as possible, it is important to continuously monitor and, if necessary, adjust the system. For this purpose, separate electricity meters should be installed on the electricity side upstream of the heat pump and heat meters on the heat supply side. The measured data is ideally stored and read from the meters in certain time intervals. The installer or the interested homeowner can use this data to optimise the system and continuously reduce operating costs.

 

In short
This assumption is generally incorrect. A heat pump provides more heat than it consumes in electricity. This also makes it more environmentally friendly than its fossil fuelled competitors, such as gas and oil boilers, as households in Luxembourg do not obtain coal-fired electricity but instead exclusively green electricity.

Video explanation

In detail
A heat pump draws heat from the surrounding environment and utilises it by raising it to a higher temperature level. An air source heat pump, for example, extracts heat from the outside air, while a geothermal system harnesses the subsoil as a heat source. This energy extracted from the natural surroundings is free and climate-neutral.

The correlation between the amount of heat generated and the electricity consumed depends on the temperatures that the heat pump has to deliver. In general, however, it can be said that the average heat pump produces around three times as much heat as the electricity it consumes. This is not the case with a gas or oil heating system. Here, the ratio between the heat output and energy input from the combustion of gas or oil is at most 1/1. In older heating units, this level of efficiency is even considerably lower, as all thermal installations have a certain degree of wastage. This applies to both heat pumps and conventional fossil-fuelled heating systems. A conventional heating system uses energy from gas or oil, while a heat pump uses a free and climate-neutral energy source from the environment in addition to electricity.

In Luxembourg, households do moreover not normally receive coal-fired electricity, but are supplied exclusively with green electricity. So the question doesn't even really apply here. By choosing your electricity product from your supplier, you can decide for yourself how many CO₂ emissions you take into account in your purchases. Regionally produced green electricity is not only good for your own carbon footprint, but also strengthens the local economy.
 

In short
Thanks to intelligent load projections, the heat pump load is currently matched to the existing grid capacity in line with demand. Moreover, the Luxembourg electricity grid is already undergoing extensive planning and work to prepare it for future demand.

Video explanation

In detail
In intelligent energy grids, heat pumps can communicate with the grid via modern communication technologies. This enables energy suppliers to create load forecasts and adapt the demand generated by heat pumps to the available grid capacity. This allows for a more effective integration and balancing of electricity demands on the grid. However, with the increasing number of heat pumps, a certain grid expansion may become necessary at the distribution level and corresponding planning and works are already being carried out on the Luxembourg power grid. According to the latest studies, this effort is both economically and technically justified and, in any case, necessary if the energy supply is to be transitioned to renewable energy.
 

In short
In a nutshell: Air-to-air heat pumps are designed to regulate indoor room temperatures as efficiently as possible and to continuously adjust their energy consumption. Their performance depends on various factors, such as room size, insulation or outside temperatures.

Video explanation

In detail
In detail: Air-to-air heat pumps, also known as split air conditioning systems, are designed to work as an active air conditioning system, extracting heat from the interior and releasing it into the outside air. They continuously adapt their output to the cooling requirement and only use as much energy as is necessary to effectively cool the room. The performance and efficiency of a heat pump for cooling depends on various factors, such as the size of the room, the outside temperature and the insulation of the building.

In contrast to active cooling, passive cooling, such as night cooling (cold outside air) or reversible geothermal heat pumps (cold from the ground), is always more energy-efficient, as no energy is required in the cooling process.

 

In short
Modern heat pumps are durable, reliable, and generally have a long lifespan, especially if they are installed, dimensioned, and maintained correctly.

Video explanation

In detail
Modern heat pumps are durable, reliable, and generally have a long lifespan, especially if they are installed, dimensioned, and maintained correctly. Maintenance can include, for example, cleaning the air heat exchangers, testing the refrigerant circuit for leaks, verifying the electrical connections and an overall inspection of the system. A well-maintained heat pump can have a prolonged service life of well over 20 years. It is important that the heat pump is installed and maintained by a qualified professional to avoid any potential problems and maximise the life span of the system.
 

In short
While it is true that heat pumps rely on liquid coolants to transport heat, these are contained in a closed system isolated within the appliance and are therefore not directly harmful to the environment. The standard for modern appliances is also moving towards more environmentally friendly alternatives.

Video explanation

En détail
Heat pumps use a refrigerant to "transport" the heat. The heat pump extracts the heat from the air or ground and then absorbs it with its refrigerant to raise it to a higher temperature level with help from the compressor. In this process, the refrigerant is not consumed but continues to flow in a closed circuit within the heat pump. The refrigerant is thus only used to transport the heat.

So why is the refrigerant harmful to the climate? The global warming potential (GWP) has been determined for each of these coolants in order to determine the extent by which a particular cooling agent contributes to climate change when it is released into the atmosphere. The benchmark is carbon dioxide (CO₂) with a GWP of 1. Over the years, refrigerants have progressively become less harmful. For example, modern heat pumps use the refrigerant R32 with a value of 675, while the latest models use R290, i.e. propane gas, with a value of only 3. It is important to know that R290 propane gas will in future be prescribed as the standard at EU level and many manufacturers are already adapting their devices accordingly. 

Furthermore, the refrigerant used in a heat pump is not inherently harmful to the environment, as it only causes harm if the coolant escapes from the closed circuit and is released into the atmosphere if the system is tampered with or leaks. For this reason, it is important that the installer checks the system for any potential leaks when installing or maintaining the system and during regular inspections.

 

In short
A heat pump that is appropriately dimensioned in conjunction with the heating surfaces (radiators, underfloor heating) does not need a buffer cylinder. Nowadays, almost all available models are equipped with the necessary technology and can operate on a modulated basis.

Video explanation

In detail
This assumption is based on older heat pump models and no longer corresponds to today's standards. With older heat pumps, the output could not be optimally adapted to the heat demand of the house.

To avoid constantly switching the system on and off, a buffer tank was installed for the hot water of the heating circuit, which became an integral part of the heating system. If more heat was produced than the house needed, the excess heat was stored in the buffer cylinder so that it could be fed back into the heating circuit later when required. The buffer cylinder ensured that the entire heating system worked more consistently and therefore more efficiently.

Nowadays, however, over 90 % of heat pumps are equipped with so-called "inverter" technology and can operate on a modulating basis. This means that the output of the heat pump adapts to the heat demand of the house and produces exactly the amount of heat required at that moment. This is the reason why most modern heat pumps no longer require a buffer tank and consequently run more efficiently than older systems.

 

In short
Heat pumps are available with a range of power capacities and can be installed and used efficiently in both apartment buildings and larger constructions. The key to efficiently utilising heat pumps in apartment buildings is a sensible integration into the domestic hot water system and a professional installation.

Video explanation

En détail
Heat pumps can also be very effective for heating apartment buildings. There are both centralised and decentralised systems that can either supply the entire building or just individual residential units with heat.

The right choice of the right heat pump and the correct dimensioning depend on various factors, such as the size of the property, the desired heat output and the thermal insulation. In many countries, heat pumps are already being successfully used in apartment blocks. The performance of heat pumps is not limited to a defined range or area and modern systems can be deployed efficiently and reliably in a variety of situations.

Heat pumps are available in different performance classes: Small heat pumps for small flats or detached houses (approx. 2 to 15 kW); medium heat pumps for larger residential and commercial buildings (approx. 15 to 50 kW); large heat pumps for larger commercial and industrial facilities (over 50 to several hundred kW); megawatt heat pumps, e.g. for industrial uses or heating networks (several megawatts). As well as providing high output, they can also generate high temperatures of up to 120 °C. 

The key to efficiently utilising heat pumps in apartment buildings is a sensible integration into the domestic hot water system and a professional installation.

 

In short
On the contrary: there are extensive subsidy programmes for heat pumps, as they are an energy-efficient heating technology and one of the few technologies that make a sustainable contribution to CO₂ reduction (decarbonisation of buildings).

Video explanation

En détail 
In order to be eligible for funding, various criteria must be met, such as the use of energy-efficient heat pumps, compliance with sound insulation thresholds and proof of hydraulic balancing. It should be noted that these criteria are to be understood in terms of consumer protection, i.e. the efficiency, cost-effectiveness and reliability of the subsidised heat pump must be guaranteed. There are a number of national and municipal subsidy programmes that offer financial incentives for the use of heat pumps. 

Klima-Agence provides a subsidy simulator on its website, which can be used to easily calculate available subsidies. We also offer free advisory sessions.

In short
Modern heat pumps have no problem working in colder environments. The key is to choose the right model and installation method for the given situation in order to optimise performance.

Video explanation

In detail
These days, many heat pumps are quite common in colder climates. More than half of all households in Norway are fitted with a heat pump. A clear demonstration that heat pumps also work in colder climates. 

Thanks to technological improvements, they can extract sufficient heat from the environment even at low outside temperatures. In some cases, they can be combined with other heat sources to support the heating in extreme temperatures. Good structural insulation and energy efficiency measures are also important to increase the cost-effectiveness of the heat pump in cold climates. Choosing the right type and size of heat pump are equally important.