Much attention is focused on increasing the energy efficiency to decrease fuel costs and CO2 emissions
throughout industrial sectors. The ORC (organic Rankine cycle) is a relatively simple but efficient process
that can be used for this purpose by converting low and medium temperature waste heat to power. In
this study we propose four linear regression models to predict the maximum obtainable thermal efficiency
for simple and recuperated ORCs. A previously derived methodology is able to determine the
maximum thermal efficiency among many combinations of fluids and processes, given the boundary
conditions of the process. Hundreds of optimised cases with varied design parameters are used as observations
in four multiple regression analyses. We analyse the model assumptions, prediction abilities
and extrapolations, and compare the results with recent studies in the literature. The models are in
agreement with the literature, and they present an opportunity for accurate prediction of the potential of
an ORC to convert heat sources with temperatures from 80 to 360 C, without detailed knowledge or
need for simulation of the process.