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Refrigerant-free heat pump

Researchers at the Fraunhofer Institute for Applied Solid State Physics (IAF) in Germany are making significant progress in the development of electrocaloric heat pumps that offer a promising alternative to compressor technology, with the goal of increasing efficiency and offering a more eco-friendly alternative to refrigerants.

This type of heat pump utilises the unique properties of electrocaloric materials, which have change their polarisation or the alignment of their positive and negative charges when an electric field is applied, leading to a temperature increase.

To maintain a stable temperature, the resulting heat is then dissipated through a heat sink, causing the material to cool down and return to its initial temperature.

When the electric field is removed, the order within the material decreases, leading to further cooling in accordance with thermodynamics. At this point, the material can absorb thermal energy from a heat source.

Importantly, this process is reversible, allowing for a cycle to be established.

The electrocaloric heat pump can alternate between heating and cooling modes by applying and removing the electric field. 

Electrocaloric material heats up when an electric field is applied. When you dissipate the heat to the environment and then remove the field, the material cools down; it can now absorb heat. Built up cyclically, the electrocaloric effect can be used to create a heat pump or a cooling system.

This reversible cycle enables the electrocaloric heat pump to efficiently transfer heat, making it suitable for both heating and cooling applications.

Currently, conventional heat pumps operate at approximately 50 per cent of the Carnot limit, which represents the maximum theoretical efficiency for any heat engine or pump operating between extreme temperatures. 

Electrocaloric heat pumps have the potential to surpass this efficiency, reaching up to 85 per cent, although the overall efficiency is significantly influenced by their integrated electronic controllers.

IAF researchers have successfully developed an ultra-efficient circuit topology for voltage converters based on Gallium Nitride transistors, maximising the performance and functionality of the voltage converter in controlling the heat pump.

This resulted in an impressive electrical efficiency of more than 99.74 per cent, surpassing the previous record of 90 per cent.

This breakthrough not only sets a new global benchmark but also represents a significant milestone in the advancement of solid-state heat pump technology. “Our ultra-efficient power electronics make it realistic for the first time to achieve well over 50 per cent of the maximum theoretical coefficient of performance with electrocaloric heat pumps,” said IAF power electronics researcher Stefan Mönch.

Ongoing studies in this field are focused on enhancing the efficiency and performance of ceramic and polymer-based electrocaloric materials, with the goal of enabling their widespread adoption.

Fraunhofer Institute for Physical Measurement Techniques researcher Kilian Bartholomé said high efficiency in materials, electronics and heat transfer is essential to getting the most out if this technology. “If you get all this under control, electrocalorics has enormous potential.”

Electrocaloric materials are emerging as a promising and energy-efficient alternative to conventional cooling and heating methods with the potential to transform various applications such as refrigeration, air-conditioning and thermal management for hybrid and electric vehicles.

The global HFC phase-down’s collision with concerns over PFAS have made refrigerant-free alternatives increasingly appealing in heating and cooling applications.

“There is still a lot of research to be done, but in the future, this technology could become a more efficient and completely emission-free solution for heating and cooling,” said Dr Mönch.

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