Dynamic Simulation as a Tool for the Analysis of the Interactions Among the Controllers of HVAC Systems

During the last decade, the application of electronics to the different components of HVAC systems has offered new and sophisticated control systems able to adapt the behaviour of each single device and of the whole plant to design specifications. These sophisticated finely-tuned control systems are, in principle, able to play an im-portant role in reducing energy consumption and im-proving thermal comfort. At the same time, there has been a marked increase in the complexity of the HVAC plant layout. Combining the complexity of plants with that of the control systems and taking into account the possibility of equipping each component of the plant with its own control system, the result is a new genera-tion of energy systems with many possible interactions between controllers. Hence it becomes impossible for a designer to evaluate, in an easy way, the effects of such interactions. As a consequence, it is difficult to know, at the design-stage, how the overall control system will op-erate. Nowadays, dynamic simulation of the complete HVAC system makes it possible to emulate the system in which the controllers operate. In this paper, the dynamic model of a basic HVAC system involving a condensing boiler, radiators with thermostatic valves and an inverter driven hydraulic pump is presented. Each element of the circuit is equipped with its own control. The model of the system has been built by using a custom-made library of Simulink blocks specifically created for the dynamic sim-ulation of controlled HVAC systems. The dynamic model will be used in order to underline the strong influence of the control system on the HVAC energy efficiency and thermal comfort conditions. Specific design rules limiting the negative interaction among the activated control sys-tems are inferred by the results shown in this paper.