Hydrodynamics and Control in Thermal-fluid Networks

by Walfre Franco Theoretical, numerical and experimental studies of hydraulic, thermal and control aspects in fluid networks are presented. First, a one-dimensional differentialalgebraic nonlinear model, based on first principles, representing the time-dependent behavior in networks is developed. A thermal-hydraulic analysis of a small network with three common control strategies for heating and cooling of buildings is carried out. PID controllers are used to respond to changes in the thermal load. The temperature difference between the chiller supply and return water is used as a criterion for comparison. Next, an experimental hydronic network featuring these control methodologies is used to complement the theoretical study by including all the complexities of the problem, such as valves hysteresis, dynamic time constants, imperfect actuators and imperfect sensors. Stability and reachability issues arise during the control process as a consequence of changing the thermal load. The importance of location and selection of the hardware used for control becomes evident. Control hardware placement is addressed next. The discrete space of possible locations for a specific layout is explored in order to find the best configuration. The hardware elements are a control valve and two booster pumps. Pumping action is divided among the two pumps to be able to look at different combinations. The