The design of one secondary loop of a complex network often neglects the effect that its operation has on the others. The present is a study of hydrodynamic and thermal interaction between secondaries in a thermal-hydraulic network as the system goes from one steady state to another. Experimental results are related to those derived from a mathematical model. The network consists of a primary and three secondary loops. There is a water-to-water heat exchanger on each secondary, with the cooling coming from the primary and the heating from a separate loop. A step change is introduced by manually actuating a valve in one of the secondaries, resulting in changes in the other loops also. The response time of the temperature is found to be an order of magnitude higher than that of the flow rate, which is again an order of magnitude higher than the pressure difference. The steady-state results show that there is significant interaction, and that it is dependent on the initial operating condition. The hydrodynamic and thermal responses are found to be very different.

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