.Buildings.Airflow.Multizone.BaseClasses.powerLaw05

Information

This model describes the mass flow rate and pressure difference relation of an orifice in the form

V̇ = C sign(Δp) |Δp|^m

where V̇ is the volume flow rate, C > 0 is a flow coefficient Δ p is the pressure drop and m =0.5 is a constant flow coefficient. The equation is regularized for |Δp| < Δp_t, where Δp_t is a parameter.

The model is used for the interzonal air flow models. It is identical to Buildings.Airflow.Multizone.BaseClasses.powerLawFixedM but it is optimized for the common case of m=0.5.

Implementation

For |Δp| < Δp_t, the equation is regularized so that it is twice continuously differentiable in Δp, and that it has an infinite number of continuous derivatives in k.

If m, and therefore also a, b, c and d, change with time, then it is more convenient and efficient to use Buildings.Airflow.Multizone.BaseClasses.powerLaw.

If m is constant but different from 0.5, use Buildings.Airflow.Multizone.BaseClasses.powerLawFixedM.

Interface

function powerLaw05
  extends Modelica.Icons.Function;
  input Real C "Flow coefficient, C = V_flow/ sqrt(dp)";
  input Modelica.Units.SI.PressureDifference dp(displayUnit = "Pa") "Pressure difference";
  input Real a "Polynomial coefficient";
  input Real b "Polynomial coefficient";
  input Real c "Polynomial coefficient";
  input Real d "Polynomial coefficient";
  input Modelica.Units.SI.PressureDifference dp_turbulent(min = 0) "Pressure difference where regularization starts";
  input Modelica.Units.SI.PressureDifference sqrt_dp_turbulent(min = 0) "Square root of dp_turbulent (exposed as it usually is a parameter expression)";
  output Modelica.Units.SI.VolumeFlowRate V_flow "Volume flow rate";
end powerLaw05;

Revisions

• September 19, 2025, by Michael Wetter:
  First implementation.
  This is for IBPSA, #2043.