1. A method comprising: pairing manipulated variables and controlled variables in an HVAC system; perturbing an unpaired variable of the HVAC system; controlling the HVAC system to compensate for the perturbance of the unpaired variable by adjusting one or more of the manipulated variables to maintain the controlled variables in a comfort range; determining a state of the system based upon logged data relating to the manipulated, controlled, and perturbed variables; repeating the perturbing, controlling, and determining a state of the system; and deriving a model from the determined states of the system, wherein the model is derived by measuring multiple steady states by perturbing different unpaired variables of the system while maintaining the controlled variables in a comfort range.