Stability of Hydronic Networks With Independent Zone Controllers

Many heating, ventilation, and air conditioning systems are implemented using one heat source, the power of which is distributed to individual zones using a pipe network. Each zone can be independently controlled using its own zone controller. Due to the hydronic network interconnection, the zone controllers interact by pressure/flow changes. This brief addresses a question of when and under what conditions the overall system is a stable system. We use a simplified linearized model with linear heat exchangers (HXs) and linear hydraulic resistances. Moreover, all HXs are assumed to be the same. A closed-form formula for linearization of the interconnection is provided. Using these simplifications, we provide simple guidelines which the controller for each zone should satisfy. The main result is that from stability point of view, the interconnection does not bring any new design limitation. On the other hand, an improperly tuned controller can destabilize the interconnected system. An extensive simulation verification is provided.