Electrically driven high-temperature heat pumps are a promising technology to replace fossil-fuel driven boilers used in industry. The impact is huge considering that around 20% of the global primary energy need is associated to industrial heating. If heat pumps could have output temperatures up to 200°C a large share of the need could be covered. To achieve high COP, the system should be coupled to low temperature waste heat or renewable energy sources (e.g solar or geothermal).
State of the art commercial heat pumps can attain temperatures around 100°C. Going higher results in many additional challenges. Many of these can be traced back to the heart of the system, the compressor. Normally the compressor is lubricated with oil. Not only does the oil lubricate the bearings, it also forms a mixture with the refrigerant and seals possible leakage paths in the compressor. In case of high temperatures (> 100°C) the oil used typically starts to disintegrate or the viscosity becomes too low. Going to oil-free compressors is possible but is very expensive and affects the performance.
First, we want to identify which oil/refrigerant mixture has potential in high temperature heat pumps going up to 200°C. The focus is on refrigerants with low global warming potential (either synthetic HFOs or natural refrigerants). There is limited prior research available on this topic up to temperatures of 150°C.
Secondly, the oil/refrigerant mixtures need to be tested in a small scale dedicated test-rig. This test-rig needs to be designed and constructed. The set-up will incorporate a viscosity flow meter, a volumetric pump, an injection device for adding refrigerant in a controlled manner and a temperature controller. Chemical stability will be tested on individual samples extracted after the experimental runs. The research contributes to a key challenge in getting high temperature heat pumps to the market.
This topic will contribute to Sustainable Development Goal 7: Affordable and clean energy