Freiburg-based start-up Qurie GmbH, a spin-off from the Fraunhofer Institute for Physical Measurement Techniques IPM, is developing a solid-state heat pump that operates without conventional compressors or refrigerants.

Unlike today’s vapor-compression systems, which rely on refrigerant cycles and mechanical compressors, Qurie’s technology uses the temperature change of electrocaloric materials under an applied electric field to drive a thermal cycle. According to the company, this approach could achieve significantly higher theoretical efficiencies of over 70%, compared to around 50% for conventional heat pumps, potentially reducing electrical energy demand by up to 30%. 

A key innovation of the system is a patented heat management concept based on active electrocaloric heat pipes. These systems enable rapid latent heat transfer via evaporation and condensation of a working fluid such as ethanol or water, allowing higher operating frequencies and improved thermal transport without complex mechanical components.

“Vapor compression systems have a number of disadvantages,” the company’s co-founder and managing director, Christian Vogel, told pv magazine. “Many of the best refrigerants are either already banned or will be phased out, mainly because they contributed either to ozone depletion or have a high global warming potential. Natural refrigerants are a good alternative, but they come with their own limitations. Some are flammable and therefore unsuitable for certain applications, while others like CO₂ carbon dioxide require very high operating pressures, which makes small systems expensive and complex.”

The proposed heat pump system is based on an electrocaloric cycle, where a solid-state material is used. “There are two main classes of materials that exhibit this effect: ceramics and polymers,” Vogel explained. “We work with both ceramic materials and polymer-based systems, particularly polyvinylidene fluoride (PVDF), a so-called electroactive polymer.”

The key principle is that the material changes temperature when an electric field is applied. It is typically placed between two electrodes, like a capacitor. “When the electric field is switched on, the internal electric dipoles in the material become more ordered,” the managing director said. “This increase in order reduces the material’s entropy. Because the system tends to maintain overall entropy, the decrease in internal entropy is compensated by an increase in thermal energy, so the material heats up.”

This heat can then be removed using a heat sink. When the electric field is switched off, the dipoles return to a more disordered state, entropy increases again, and the material cools down back toward its original temperature.

“What makes this effect particularly interesting is its high degree of reversibility,” Vogel said. “Traditional vapor compression systems suffer from losses due to friction and other effects. When a gas is compressed, it heats up, and when it expands again it cools down, but it does not return perfectly to its original state. In electrocaloric materials, by contrast, the reversibility can be quite high in some cases.”

However, the key challenge is always heat transfer: adding and removing heat from the material is typically the slowest step in the cycle. This limits the achievable operating frequency. In conventional systems using liquid flow, the so-called active regenerators, the slowest step is the heat exchange between the solid material and the fluid. Many start-ups and research groups are working on magnetic, electric, and other caloric systems using this approach.

“The limitation is that these systems are often restricted to about one cycle per second, because heat transfer is too slow,” Vogel stressed. “Our approach replaces the continuous fluid flow with evaporation and condensation processes. Instead of circulating water over the material, we use a heat pipe chamber. A heat pipe is essentially a vacuum-sealed cavity containing a working fluid such as water, or ethanol or another alcohol for lower temperatures.”

When the electric field is applied, the material heats up and causes the working fluid to evaporate, increasing pressure. The vapor is then released through a pressure valve. When the field is switched off, the material cools, vapor condenses back onto it, and fresh fluid is drawn in from the opposite side at a lower temperature. “In this way, heat can be pumped across small temperature differences—slightly colder on the left, slightly warmer on the right,” he went on to say. “This process can run much faster than conventional systems. While liquid-based systems typically operate at around 1–2 Hz, we have already demonstrated operation at up to 20 Hz, meaning twenty condensation and evaporation cycles per second.”

By connecting multiple stages in series, each separated by one-way pressure valves, larger temperature lifts can be achieved. “This allows us to bridge temperature differences of several degrees, for example from 5 C up to 40 C in typical applications,” Vogel said.

The system consists of three main thermodynamic components: an evaporator, a condenser, and a valve—similar in principle to conventional refrigeration, but implemented in a solid-state-assisted cycle. “The system is assembled into modular segments, including custom-designed check valves that open at very low pressure differences while ensuring reliable closure,” the managing director added. “A four-stage cascade has already demonstrated 2 W of cooling power over a 2 Kelvin temperature lift.”

A dedicated power electronics system has also been developed to continuously charge and discharge the material, since every second element is charged while the others are not. This requires a relatively advanced driving circuit.

“In experiments, the system visibly ‘breathes,’ meaning it cycles through repeated evaporation and condensation within the chamber,” Vogel further explained. “This has been demonstrated in single-segment test rigs, with four segments already combined to achieve the current performance results.”

The path from here to a finished product is still ongoing. The next prototype will include around 20 segments, targeting a 20 Kelvin temperature span and approximately 100 W of cooling capacity. “The first commercial application will be control cabinet cooling and photonics or laser cooling,” Vogel stated. “These are niche markets where conventional refrigerants are often not suitable due to safety requirements such as ATEX explosion protection.” 

“We believe the technology could ultimately be around 20% more efficient than current vapor compression systems in the 100 W to 10 kW range. However, scaling becomes more difficult, as our system scales linearly with material usage, whereas compressors benefit from more favorable scaling effects,” Vogel concluded. “We therefore do not target very large systems such as hotel air conditioning, but rather applications below 10 kW, including residential-scale heat pumps.”

Initial customers are expected to come from industrial cabinet cooling manufacturers and laser cooling companies. These systems are currently often based on Peltier elements, which are inefficient, expensive, and have a coefficient of performance below one.

The company is backed by early-stage investors including the High-Tech Gründerfonds, the European Investment Fund via its TT49 technology transfer fund, and Aepikur GmbH. Development activities are also supported through a federal research program from Germany’s Federal Ministry for Economic Affairs and Energy.