Natural working fluids in cycles for surplus heat-to-power conversion – Perspectives and history from Trondheim

For decades, the refrigeration technology research groups at NTNU and SINTEF have been developing components, cycles and methodologies to promote attractive solutions using natural working fluids. The same values and vision were brought along when the same research groups branched out into industrial surplus heat-to-power conversion in the early 2000's, and concepts using natural working fluids is dominantly the basis of all research also in this field today. In this work, the recent history of surplus heat-to-power research at SINTEF and NTNU is summarized, and our considerations related to benefits and drawbacks of relevant fluids is discussed. A principal model-based performance comparison of natural vs. synthetic fluids indicates that there is no fundamental difference in cycle performance between these fluid classes. The optimal solution will be case specific, but a general conclusion is that between CO₂ and hydrocarbons, there should exist an attractive alternative with respect to performance compared to the best synthetic fluids.