Comparison of thermal-hydraulic network control strategies

A dynamic thermal-hydraulic analysis of strategies used for the control of hydronic piping and heat exchanger networks is carried out. Three common temperature control methods are analysed and compared using a mathematical model. For this purpose a general thermal network with a primary loop, a secondary loop and a bypass that has the three control systems as special cases is proposed. The primary loop includes a chiller, while the secondary has a water-air cooling coil which serves as a thermal load. Integral controllers are used to vary the valve settings to control the air temperature leaving the cooling coil. The system responses for each of the three control schemes as a function of the thermal load are then compared to assess their relative merits using the temperature drop in the chiller as a criterion.