2.1. Validation test for both Types with laboratory data

To validate both Types the models are fed with the ILK test data at first. These data have been used to determine the performance data file for Type 307 as well as the parameters of the characteristic equations for Type 177. In Fig. 3 and Fig. 4 the simulated cooling capacities (QEsim) of Type 307 with PD1 and PD2 are plotted relative to the measured test data (QEILK).

Comparing both plots an apparently lower agreement of the simulation results can be observed when using the performance data PD2. Nevertheless PD2 is more realistic since with PD1 also the measurement scatter is interpolated instead of a continuously increasing cooling capacity. It is seen from Fig. 1 that e. g. the value at 85°C is fitted much better when a stepwise linear inter­polation between neighbouring points is performed with PD1 instead of a global interpolation over the full range 80<tGi<95°C as it is done with PD2. Since there is no physical reason for a steeper increase of Qe between 80°C and 85°C and a more modest increase between 85°C and 90° PD2 is the better model — physically, not numerically. As explained earlier, with PD2 also a quasi­extrapolation is possible, since indirectly a kind of characteristic equation method has been applied by the global interpolation procedure when preparing PD2.

Comparing the test data to those of Type 177 (cf. Fig. 5) significant higher deviations can be observed as in Fig. 5. The reason is that the PD2-method, allows the global slope of e. g. Qe = f(tGi=var, tACi=const) to increase and de­crease again, although tACi is continuously increasing or decreasing. Here the variation of slopes is more limited due to the combination of all three external temperatures in one value (AAt*). Although physically reasonable this reduces the possibility of numerical fitting.