When are infrared heaters an alternative to heat pumps?

14.07.2021 08:00 |Druckvorschau

Under certain conditions, well -thought -out concepts with direct current heating can be an alternative to heat pump solutions and save CO2.The prerequisite is a low heating energy requirement and the use of electricity from renewable energies.

Mit der beschlossenen Energiewende reagiert Deutschland auf den Klimawandel, der maßgeblich auf die CO₂-Emissionen zurückzuführen ist.In order to reduce this sustainably, the previously dominant fossil/atomic energy system must be completely replaced by renewable energy in the future.In most studies, wind power and photovoltaic systems are considered key technologies of future energy generation

The fossil energy industry is based on primary sources, through which the heat can be used directly (petroleum, natural gas, coal).However, the generation of electricity from these sources is associated with considerable conversion losses of up to 60%.With the increasing regenerative energy sources in the form of wind power and solar radiation, however, the proportion of electricity obtained in terms of climate increases.This can in turn be converted into gaseous or liquid energy sources via appropriate conversion systems, but now here at the price of considerable conversion losses.The boundary conditions therefore differ fundamentally in the two energy systems.

As a consequence, this means that in the case of a regenerative energy system, the direct use of electrical energy compared to gaseous or liquid energy sources has an advantage.The studies on future energy supply are therefore assuming massive electrification of all energy sectors.

The importance of electricity generation increases in all energy sectors

In the two most important sectors mobility and heat supply of buildings, the current developments already have a corresponding transformation: in the area of traffic, the trend clearly shows towards electromobility, in the area of heat generation, the heat pump as an electrical heat supplier is now the dominant heating system [2].This is also confirmed by the pilot projects as part of the Efficiency House Plus Initiative, of which four fifths via heat pump technology are heated [3].

Trend towards higher degrees of technology

Heat pumps use local environmental heat and thus achieve particularly high electrical efficiency.With an annual number of year (JAZ) of 3 to 5, 3 to 5 kilowatt hours of heat can be generated with one kilowatt hour of electricity.However, this proficiency gain is accompanied by a not inconsiderable material and financial effort.The use of local anergie requires a variety of components, such as

einen Wärmeerzeuger (Wärmepumpe),

eine Wärmequellenerschließung (Erdsonde, Erdkollektor, Luftwärmetauscher, Eisspeicher, usw.),

eine Wärmespeicherung (Pufferspeicher),

eine Wärmeübergabe (Fußbodenheizung, Heizkreisverteiler),

eine Regelung (Raumthermostate, Stellventile, WP-Regelung),

eine Messdatenerfassung zur Überprüfung der Effizienz und der Abrechnung und schließlich

einen Haustechnikraum

With increasing efficiency, the complexity of the system and thus also the susceptibility to errors in the interaction of the components, such as z, often increases with increasing efficiency.B.Ice storage, hybrid collectors or cold local heating networks.The heat supply systems also contribute significantly to the increase in construction costs.A research project from 2015 as part of the Future Building Initiative has shown that the costs for building technology (KG 400) have increased significantly more than the other construction costs in recent years

Infrared heaters as a low-tech alternative

Compared to the complex heat pump systems, direct electric heating proves to be extremely simplest type of spatial warming.Especially in housing construction, the so-called infrared heaters (IR heating) increased in recent years.An IR system essentially only consists of two components

einer Wärmeerzeugung (Infrarot-Heizelemente) und

einer Regelung (Raumthermostat).

Due to the low complexity (low-tech), the IR heating compared to classic heat pump variants has some advantages in ecological and economic terms:

Vergleichsweise sehr geringe Anfangsinvestitionskosten,

vergleichsweise sehr geringer Materialaufwand (Graue Energie),

kein Technikraum erforderlich,

keine Leitungs- und Speicherverluste,

kein Hilfsenergiebedarf,

geringer Energieaufwand für Installation, Wartung, Instandhaltung und Entsorgung,

geringe Störanfälligkeit (Resilienz),

lange Lebensdauer,

einfache Umbau-/Nachrüstbarkeit,

sehr flexible, schnelle und unmittelbare raum- oder zonenweise Regelung der thermischen Behaglichkeit durch den Nutzer und

keine Wärmemengenzähler, Messdatenerfassung und Abrechnung erforderlich.

Away from fossil fuels, instead electricity generation through photovoltaics

Dennoch konnten sich direktelektrische Heizungen in den vergangenen Jahrzehnten aufgrund hoher Wärmeverbräuche der Gebäude und damit verbundener Stromkosten und CO₂-Emissionen durch fossil erzeugten Strom nicht etablieren.In the meantime, however, the framework conditions - especially in the new building - have changed fundamentally:

Der Heizenergiebedarf für neu errichtete Gebäude ist dank Energieeinsparverordnungen und damit einhergehender besserer Gebäudedämmung massiv gesunken

Knapp die Hälfte der elektrischen Energie wird in Deutschland inzwischen mittels regenerativer Quellen erzeugt. Der Primärenergiekennwert ist dadurch von 3,0 im Jahr 2000 auf inzwischen 1,8 gesunken, die CO₂-Emissionen von 644 auf 401 g/kWh [7].

Mit den inzwischen deutlich günstigeren Photovoltaikanlagen lässt sich heute regenerativer Strom wirtschaftlich und langfristig lokal am Gebäude erzeugen [8].

A low heating requirement now meets a cost -effective and local regenerative current generation.Therefore, the question is particularly interesting for energy-efficient buildings, what potential simple and inexpensive infrared heating systems-especially in combination with local power generation via photovoltaics-have for the heat supply of buildings.

Comparison in the research project IR building

Previous studies on IR heaters have not produced any resilient foundations for planning in construction practice.Against this background, the Constance University of Applied Sciences decided to carry out the IR research project in cooperation with several project partners.Financial support came from the Innovation Program Future Construction of the Federal Institute for Building, Urban and Spatial Research [9].As part of the project, three heating systems-air heat pump with underfloor heating, electrical underfloor heating and infrared heating-were examined in terms of measurement technology.The aim was to determine how high the differences in electricity consumption in real operation are taking into account all components.Furthermore, the example of a pilot project ecological and economic comparison calculations in the form of an ecological balance and life cycle costs were created over 50 years.The full research report and the results of the supplementary laboratory measurements are available under bit.Ly/born.

Scientific accompanying research of a pilot project

The multi -family house K76 with 16 residential units in Darmstadt was planned with direct current heating and completed in 2017.Room heating is carried out via infrared heaters installed on the ceilings, the hot water is heated via local instantaneous water heaters.Each of the residential units has a decentralized ventilation system with heat recovery. Auf dem Dach ist eine 36,2-kW_p-PV-Anlage installiert.Planned and implemented the Werk project.The building cooperative K76 was around architects from Darmstadt, building owner and client.The approximately 1360m² living space is divided into 15 residential units with 50 to 120m² each.The pilot project was already published in Geb 07/08 2019 (in the stream of the heat turn) and described in detail.

The measurement results over two complete heating periods and the essential parameters were compared.A complementary social science user survey showed that the residents participating in the study are satisfied with the comfort and usability of the IR heating.

With the support of the project partner EE Concept, ecological and economic accounting was carried out for the pilot project K76 - not only in terms of the realized energy concept, but also with regard to an alternative possible heat pump solution.The period for the calculations was set to 50 years.The exchange of technical components and component layers also included the accounting due to age -related wear.For the ecological comparison, the life cycle modules production (A1-A3), maintenance (B1-B3) and operation (B6) were considered.

As far as the economic accounting for life cycle costs is concerned, the K76 project shows that the IR variant leads to a higher cash value despite the high savings on investment costs due to the higher consumption costs over the 50 years considered.However, the following aspect should be observed: The low investment costs are free to use the heat pump variant that cannot be used to finance regenerative electricity generation.The K76 project also decided to invest part of the saved technology costs in a PV system that has been installed on the roof.Such a variant-IR system with a PV system-showed cheaper values in a second view than in the heat pump variant if one calculated the financial equivalent of the generated solar power.

Comparison of the investment sums of heat pump systems compared to IR heating system

As a result, it can be more economical to attract electricity with a PV system than to invest in the additional costs for a heat pump system.However, overarching costs for electricity management are not taken into account.Of course, a heat pump concept can also be combined with a PV system.However, the differential costs and thus also the available budget for solar power in the IR variant increase again.The limiting factor can then be the available area for the expansion of photovoltaics.

The ecological accounting using the example of the K76 project shows that the lower expenses in the manufacture and maintenance of the IR system in operation are overcompensated by the higher power consumption and generate a value of around 50% higher.When taking the solar generation of electricity into account by the photovoltaic system analogous to the economic consideration, however, the total values and savings of approx..15%.

The building size is also crucial

In addition to the analysis of the multi -family house K76, a parameter study was examined to what extent different partial aspects influence the life cycle costs and the ecological balance.The building size and the resulting heating load or the resulting heating load or.The heat sales.The calculations assume that the total differential costs between heat pump and infrared variant will be invested in PV systems.As a result, the reduction of the building size has an advantageous effect on the IR system both in an economic and ecological point of view.One of the main reasons is that the investment costs of infrared heating in contrast to the heat pump solution almost linear to the building size or.Depict the heating load.

Obwohl Direktstromheizungen viele attraktive Eigenschaften aufweisen, sind sie gegenüber Wärmepumpensystemen bislang keine relevante Alternative für die Gebäudeheizung, weil sie höhere Stromverbräuche aufweisen und folglich bei fossiler Stromerzeugung mehr CO₂ emittieren.

However, the results summarized in this article form a new approach for the evaluation of direct current heating.If you couple the investment in a heat supply system with the generation of renewable energy, the question arises as to which concept - use of anergy or solar power generation - achieve the better parameters regarding life cycle costs and ecological balance. Unter der Voraussetzung, dass die eingesparten Herstellungskosten bei der Infrarot-Heizung in wirtschaftlich attraktive und CO₂-freie Stromerzeugung (insbesondere lokale solare Stromerzeugung) investiert werden, kann vor allem bei kleinen Gebäuden mit geringem Wärmeumsatz die Kombination Infrarot-Heizung und Photovoltaik vorteilhaft sein.In favorable boundary conditions, in this variant, the additional solar power generated significantly exceeds the additional consumption of the infrared system compared to the heat pump variant.

Solar power needs memory for buffing

The main disadvantage of this approach is the challenge that - unlike the anergie in the event of a heat pump solution - the solar power cannot cover the energy requirement for direct current heating at the same time.This requires intelligent solutions for electricity storage and network utilization, for which there are already different approaches.Finally, it can be said that direct current heating systems under certain boundary conditions - especially for small buildings with low heat sales - can be a sensible solution for the future heat supply of small buildings.If the saved capital is bindingly used for regenerative electricity generation, you can also make a contribution to the transformation of the energy supply within the meaning of the energy transition.

Follow-up project IR-BAU 2

At the end of 2020, the follow-up project IR-Bau 2 started with additional studies on the potential of IR heating systems.The question of how the material-specific and constructive properties of IR heating elements affect efficiency in the company.Furthermore, further building typologies are accompanied and analyzed.It should also be examined how the combination of an IR system with photovoltaics can be optimized, especially with regard to self-consumption-optimized regulation.The results of the examinations are documented in a guide for planners and builders.

This post by Prof.Dr.-Ing.Thomas Stark and Jan Heider M.A.was first published in Geb 1/2021.Stark has been teaching and researching in the field of energy -efficient construction at the HTWG Konstanz since 2008.In 2003 he founded the planning office EE-Plan, which went into EE Concept GmbH in 2008.Heider studied architecture at the HTWG Konstanz and worked between 2009 and 2018 in various offices with a focus on energy -efficient construction.From 2017 to 2019 he headed the research project "IR-Bau"