Dynamic Modeling and Control of a Hybrid Hydronic Heating System

A dynamic model of a hybrid hydronic heating system has been developed. Simulations of the control strategies and the model-based energy analysis for the overall system have been presented in this thesis. The hybrid hydronic system is composed of a conventional natural gas fired boiler hot water heating and a ground source heat pump system. The overall system consists of several components such as a boiler, a heat exchanger, a ground loop heat pump, a ground loop heat exchanger, baseboard heaters, and radiant floor hydraulic piping systems. The system model was described by nonlinear differential equations, which were programmed and solved using MATLAB. Two control strategies for improving the overall system performance were explored: (i) a conventional PI control, and (ii) an adaptive gain control. The simulation results subject to set-point changes showed that the performance of the adaptive controller is better than the fixed gain PI controller in disturbance rejection and stability. Energy simulations under three different operating strategies were conducted: (i) a conventional fixed set-point PI control, (ii) an outdoor air temperature reset control, and (iii) an optimal set-point PI control. It was shown that the outdoor temperature reset strategy can save 4.5% and 19.9% energy under cold day and mild day conditions compared to the conventional fixed set-point PI control strategy. In addition, the iv implementation of the optimal PI control strategy result in higher energy savings 6.6% and 22% as compared to the base case under cold and mild day conditions, respectively