Alternatives to system identification

Salut,

I am currently attempting to model a plant using the sys iden. toolbox, however the models being formulated are very poor. It is monitoring temperature control using and on/off pump for a fermentation system.

If anybody has any useful books that would allow for the system to be modeled more accurately (i.e. by hand) or another program, please comment.

Maybe as an alternative, I am unsure as to whether changing the input from a pump on/off operation to something more tangible, maybe a heat transfer, however, still unsure how to perform that calculation with the system being 'uncertain'.

Help will be greatly appreciated.

Merci.