Mathematical modeling of gas-fired combi boilers

The demanding demands of technology and governments are constantly shaping the water heating sector, resulting in a broad product portfolio of new, high-efficiency combi boilers. In this study, mathematical modeling of dual-function heating devices used for both central heating and domestic hot water heating was performed for both steady-state and transient conditions. LMTD and e-NTU techniques were used in the steady-state analyses, and the effects of different Nusselt number correlations on the model were investigated. In the transient analyses, five different partial differential equations modeling the heat transfer behavior of the system were discretized and solved using the finite differences method. The results were monitored through an interface developed in MATLAB. This mathematical model enabled the creation of two different digital twins of the physical combi boiler system. Furthermore, two different control algorithms, Proportional Integrative Derivative Control and Model Predictive Control, were integrated into the model, and these algorithms were optimized, and their performances were compared. The developed mathematical model was validated experimentally. As a result of the validation study, the total heat transfer deviation was calculated as 1.64% for the steady state and 0.7% for the unsteady state.