Regression models
Table 3 presents the regression coefficients and standard errors
for both the low temperature models. Each of the coefficients indicates
the influence of each predictor variable (Ths,i, Ths,o and hp,e)
on the thermal efficiency. For example, the coefficient for the heat
source inlet temperature is lower for the simple ORC, indicating
that the benefit of increasing the heat source inlet temperature is
relatively smaller compared to the ORC. The standard errors of each
of the coefficients are the margins for the model output to remain
within a 95% confidence interval of the observed (simulated)
values. They are all seen to be minor compared to the coefficients.
Table 4 presents the regression model coefficients and the
associated statistics for the high temperature models. It is seen that the influence of Ths,i on the model output (thermal efficiency) is
again smaller for the simple ORC model. This is also the case for the
other variables Ths,o, Tc and DTpp, except the expander efficiency.
This suggests that the expander efficiency is more influential on the
simple ORC efficiency.
Consequently, the regression models for predicting the
maximum obtainable thermal efficiencies of the ORC are: