Here is a quick look at the system properties using the tools provided in Control System Professional. Among the transfer-function matrix elements, there are a total of 12 stable poles with a very wide spread of time constants. | Out[2]= |  |
This is the ratio of the largest time-constant to the smallest time-constant in the system. | Out[4]= |  |
These are the variations in the top temperature (solid line) and the bottom temperature (dashed line) for separate unit-step changes applied to each input. 
While these plots confirm that the open-loop system is stable, with the individual loop responses behaving as expected from the poles of the transfer-function matrix model elements, an improvement in the speed of response of the top temperature would be beneficial. |
