Estimating the outlet temperature of a plate heat exchanger: Application of bilinear observers

In this paper the application of bilinear observers is proposed to estimate the outlet temperature of the plate heat exchanger (PHEX) in gas combi boilers without using an additional sensor. To achieve this goal a physical model of the PHEX is derived guaranteeing adequate accuracy. This low order model unlike existing models enables the implementation on low performance microprocessors. The applicability of two proposed observer design approaches is verified by means of a stability analysis. The advantages of the bilinear over the linear design approach are pointed out using measurement data of the considered heating appliance.