modelSingleMixing

Information

This model represents a heating system where the configuration Buildings.Fluid.HydronicConfigurations.ActiveNetworks.SingleMixing serves as the interface between a variable flow primary circuit at constant supply temperature and a constant flow secondary circuit at variable supply temperature. The primary pump is operated at constant speed so the operating point rides the pump characteristic as the three-way valve closes. The secondary supply temperature is reset with an open loop, representing for instance a reset logic based on the outdoor air temperature. Two identical terminal units are served by the secondary circuit. Each terminal unit has its own hourly load profile.

For this model to simulate properly the ratio of the Kvs coefficient between the bypass branch and the direct branch of the control valve (con.val.fraK) must be set to 1. Otherwise, if con.val.fraK=0.7 cavitation occurs when the secondary pump starts and the control valve is fully open, as the secondary pump head exceeds the primary pressure differential augmented by the pressure drop across the direct branch of the control valve. Alternatively, if the pump is sized with the pressure drop across the direct branch of the control valve (disregarding the higher pressure drop across the bypass) it cannot provide enough head at low supply temperature set point when the valve is partially closed.

Note that the load loa1 is not fully met at partial load (see plot #4 from 17 h in model time) due to the unbalanced bypass of the terminal unit control valves. See Buildings.Fluid.HydronicConfigurations.ActiveNetworks.Examples.DiversionOpenLoop for further details.

Parameters

Components

Revisions

• June 30, 2022, by Antoine Gautier:
  First implementation.