Arne Hoeg interviewed on SUSHEAT Heat Shift
Why is decarbonising industrial heat above 150°C hard?
Decarbonising industrial heat above 150°C is technically possible today with electric boilers. As Enerin co-founder and CEO Arne Høeg explains, the problem is economics: gas is cheaper, and every megawatt of heat capacity from an e-boiler needs an equivalent megawatt of electricity generation and grid capacity. Heat pumps solve that problem, but conventional heat pumps face four challenges at these temperatures.
In Episode 4 of SUSHEAT's Heat Shift podcast series, The Future of Industrial Energy, project communication co-lead Tristan Bath talks to Enerin co-founder about one of the project's core technologies: Enerin's high-temperature Stirling heat pump. The upgraded heat pump will be validated in the lab, delivering 250°C alongside the other components on the test rig.
Answering the episode's key question of why delivering heat above 150°C is so challenging, Arne outlines four main hurdles and explains why the Stirling heat pump is different to conventional heat pumps.
Conventional heat pumps
1️⃣ Limited temperature lifts. Conventional heat pumps are typically able to lift temperatures by 60–80°C in one step. To reach 150°C and above, you need two or even three heat pumps in series, each feeding its heat to the next to deliver the target temperature.
2️⃣ Space. Putting heat pumps in series often means separate rooms and a lot of floor space.
3️⃣ Integration. Installing them often requires modifications to factory production lines, which can mean downtime and increased cost risks if factory equipment changes in the future.
4️⃣ Refrigerants. Some refrigerants are toxic, flammable, and bad for the environment. Is the refrigerant compatible with the factory's safety requirements and environmental rules, and will it be phased out due to its greenhouse gas emissions potential? Every refrigerant also has its own temperature window. Reaching high temperatures therefore means combining different heat pumps together, such as ammonia to propane to steam, each with its own operating challenges.
How the Stirling heat pump used in SUSHEAT gets around these challenges
♻️ More efficient at big lifts. Enerin's test data, compared with published figures for other heat pumps, indicates that Stirling heat pumps are more efficient for one-step temperature lifts above 100°C. Enerin’s Stirling heat pump can achieve a lift of up to 200°C in a single step.
♻️ Space. Enerin’s HoegTemp requires a footprint of roughly 5 by 6 metres — less real estate compared to other systems. It can be housed with existing boilers in the plant or mechanical room.
♻️ Integration. The HoegTemp heat pump is simple to integrate. It can be installed in existing and new plants. Connect it to the nearest steam line, power and any available cooling or liquid circuit as the heat source, or even ambient air. Multiple, modular machines can be combined for larger capacities and redundancy.
♻️ No evaporating or condensing of refrigerants. The gamma reverse Stirling cycle uses an inert gas like helium as its refrigerant, which stays in the gas phase, operating at all normal temperatures. The gas is compressed at high temperatures to deliver heat to the process via a water circuit, then expanded at low temperatures to extract heat from the source. This makes it highly flexible.
SUSHEAT is funded by CINEA, the European Climate, Infrastructure and Environment Executive Agency.