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Modelica Buildings library
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Incorrect hydronics in Experimental.DHC.Examples.Combined.ParallelConstantFlow #2967

Closed AntoineGautier closed 2 years ago

AntoineGautier commented 2 years ago

Simulating the model yields a negative ETS pump power due to incorrect hydronic principles. The model is indeed a blunt adaptation of SeriesConstantFlow to a two-pipe network, developed primarily to illustrate the use of Experimental.DHC.Networks.Combined.UnidirectionalParallel. However, the hydronic layout of the ETS (as presented in Sommer 2020) is suited for "passive networks" where the ETS is not exposed to a high differential pressure. For active networks (as it is the case here) a control valve should be used instead of a pump for the heat pump source circuits. In addition, as an ideal pump model is used (that takes mass flow rate as an input) the model logically computes a negative flow work and a negative power. I suggest removing that model from the library (as it may also be confused with the bidirectional network presented in Sommer 2020). Maybe an assert statement would also be useful in Fluid.Movers.FlowControlled_m_flow to generate a warning in case of a negative flow work.

mwetter commented 2 years ago

I agree that this is wrong and should be removed.

Adding an assertion to the pump would be good. We had a similar problem a few years ago where a pump ended up acting as a turbine because of a wrong hydraulic configuration.

mwetter commented 2 years ago

Todo:

AntoineGautier commented 2 years ago

Closed by PR #2974 and #2968.