.Buildings.Fluid.Actuators.Valves.TwoWayPressureIndependent

Information

Two way valve with a pressure-independent valve opening characteristic. The mass flow rate is controlled such that it is nearly equal to its set point y*m_flow_nominal, unless the pressure dp is too low, in which case a regular Kv characteristic is used.

Main equations

First the minimum pressure head dp_min required for delivering the requested mass flow rate y*m_flow_nominal is computed. If dp > dp_min then the requested mass flow rate is supplied. If dp < dp_min then m_flow = Kv/sqrt(dp). Transition between these two flow regimes happens in a smooth way.

Typical use and important parameters

This model is configured by setting m_flow_nominal to the mass flow rate that the valve should supply when it is completely open, i.e., y = 1. The pressure drop corresponding to this working point can be set using dpValve_nominal, or using a Kv, Cv or Av value. The parameter dpValve_fixed can be used to add additional pressure drops, although in this valve it is equivalent to add these to dpValve_nominal.

The parameter l2 represents the non-ideal leakage behaviour of this valve for high pressures. It is assumed that the mass flow rate will rise beyond the requested mass flow rate y*m_flow_nominal if dp > dpValve_nominal+dpFixed_nominal. The parameter l2 represents the slope of this rise: d(m_flow)/d(dp) = l2* m_flow_nominal/dp_nominal. In the ideal case l2=0, but this may introduce singularities, for instance when connecting this component with a fixed mass flow source.

Options

Parameter deltax sets the duration of the transition region between the two flow regimes as a fraction of dp_nominal or m_flow_nominal, depending on the value of from_dp.

Implementation

Note that the result in the transition region when using from_dp = true is not identical to the result when using from_dp = false.

Variables *_y1 and *_y2 serve a dual use. They are used to 1) compute the support points at *_x1 and *_x2, which should not depend on m_flow or dp and 2) to compute the flow functions when outside of this regime, which does depend on m_flow or dp. Min and max functions are therefore used such that one equation can serve both puroposes.

Revisions

• June 10, 2021, by Michael Wetter:
  Changed implementation of the filter and changed the parameter order to a constant as most users need not change this value.
  This is for #1498.
• August 7, 2020, by Ettore Zanetti:
  changed the computation of phi using max(0.1*l, . ) to avoid phi=0. See issue 1376.
• November 9, 2019, by Filip Jorissen:
  Guarded the computation of phi using max(0, . ) to avoid negative phi. See issue 1223.
• October 25, 2019, by Jianjun Hu:
  Removed icon graphics annotation. This is for #1225.
• April 14, 2017, by Filip Jorissen:
  Revised implementation using cubicHermite such that it does not have a local maximum and such that it is C2-continuous. See #156.
• March 24, 2017, by Michael Wetter:
  Renamed filteredInput to use_inputFilter.
  This is for #665.
• March 15, 2016, by Michael Wetter:
  Replaced spliceFunction with regStep. This is for issue 300.
• January 22, 2016, by Michael Wetter:
  Corrected type declaration of pressure difference. This is for #404.
• January 29, 2015, by Filip Jorissen:
  First implementation.