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Corrected implementation of dynamic flow regime #4491

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d0aa2c7
Corrected implementation of dynamic flow regime
mwetter Mar 7, 2026
c77ccba
Refactored to avoid use of when inside if
mwetter Mar 8, 2026
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75 changes: 54 additions & 21 deletions Buildings/Fluid/HeatExchangers/BaseClasses/PartialEffectivenessNTU.mo
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -53,6 +53,9 @@ model PartialEffectivenessNTU
final parameter Real NTU_nominal(min=0, fixed=false)
"Nominal number of transfer units";

Buildings.Fluid.Types.HeatExchangerFlowRegime flowRegime(fixed=false, start=flowRegime_nominal)
"Heat exchanger flow regime";

protected
final parameter Medium1.ThermodynamicState sta1_default = Medium1.setState_pTX(
T=Medium1.T_default,
Expand Down Expand Up @@ -85,8 +88,10 @@ protected
"Nominal temperature at port b2";
parameter Buildings.Fluid.Types.HeatExchangerFlowRegime flowRegime_nominal(fixed=false)
"Heat exchanger flow regime at nominal flow rates";
Buildings.Fluid.Types.HeatExchangerFlowRegime flowRegime(fixed=false, start=flowRegime_nominal)
"Heat exchanger flow regime";

parameter Real mPro_flow_nominal(unit="kg.kg/(s.s)") = m1_flow_nominal*m2_flow_nominal
"Product of nominal mass flow rates, used for scaling";

initial equation
assert(m1_flow_nominal > Modelica.Constants.eps,
"m1_flow_nominal must be positive, m1_flow_nominal = " + String(
Expand Down Expand Up @@ -156,25 +161,46 @@ initial equation
Z=Z_nominal,
flowRegime=Integer(flowRegime_nominal)) else 0;
UA_nominal = NTU_nominal*CMin_flow_nominal;
equation
// Assign the flow regime for the given heat exchanger configuration and capacity flow rates
if use_dynamicFlowRegime then
if (configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.ParallelFlow) then
flowRegime = if (C1_flow*C2_flow >= 0) then Buildings.Fluid.Types.HeatExchangerFlowRegime.ParallelFlow else Buildings.Fluid.Types.HeatExchangerFlowRegime.CounterFlow;
elseif (configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.CounterFlow) then
flowRegime = if (C1_flow*C2_flow >= 0) then Buildings.Fluid.Types.HeatExchangerFlowRegime.CounterFlow else Buildings.Fluid.Types.HeatExchangerFlowRegime.ParallelFlow;
elseif (configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.CrossFlowUnmixed) then
flowRegime = Buildings.Fluid.Types.HeatExchangerFlowRegime.CrossFlowUnmixed;
elseif (configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.CrossFlowStream1MixedStream2Unmixed) then
flowRegime = if (C1_flow < C2_flow) then Buildings.Fluid.Types.HeatExchangerFlowRegime.CrossFlowCMinMixedCMaxUnmixed
else Buildings.Fluid.Types.HeatExchangerFlowRegime.CrossFlowCMinUnmixedCMaxMixed;
else
// have ( configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.CrossFlowStream1UnmixedStream2Mixed)
flowRegime = if (C1_flow < C2_flow) then Buildings.Fluid.Types.HeatExchangerFlowRegime.CrossFlowCMinUnmixedCMaxMixed
else Buildings.Fluid.Types.HeatExchangerFlowRegime.CrossFlowCMinMixedCMaxUnmixed;
end if;
else
flowRegime = flowRegime_nominal;

flowRegime = flowRegime_nominal;

algorithm
// Assign the flow regime for the given heat exchanger configuration and
// mass flow rates

// ParallelFlow vs CounterFlow
when(use_dynamicFlowRegime and (configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.ParallelFlow) and
flowRegime==flowRegime_nominal and (m1_flow*m2_flow/mPro_flow_nominal < -0.001)) then
flowRegime := Buildings.Fluid.Types.HeatExchangerFlowRegime.CounterFlow;
elsewhen(use_dynamicFlowRegime and (configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.ParallelFlow) and
flowRegime==Buildings.Fluid.Types.HeatExchangerFlowRegime.CounterFlow and (m1_flow*m2_flow/mPro_flow_nominal > 0.001)) then
flowRegime := flowRegime_nominal;

// CounterFlow vs ParallelFlow
elsewhen(use_dynamicFlowRegime and (configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.CounterFlow) and
flowRegime == flowRegime_nominal and (m1_flow*m2_flow/mPro_flow_nominal < -0.001)) then
flowRegime := Buildings.Fluid.Types.HeatExchangerFlowRegime.ParallelFlow;
elsewhen(use_dynamicFlowRegime and (configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.CounterFlow) and
flowRegime == Buildings.Fluid.Types.HeatExchangerFlowRegime.ParallelFlow and (m1_flow*m2_flow/mPro_flow_nominal > 0.001)) then
flowRegime := flowRegime_nominal;

// have ( configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.CrossFlowStream1MixedStream2Unmixed)
elsewhen(use_dynamicFlowRegime and (configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.CrossFlowStream1MixedStream2Unmixed) and
flowRegime == flowRegime_nominal and (C1_flow < 0.95*C2_flow)) then
flowRegime := Buildings.Fluid.Types.HeatExchangerFlowRegime.CrossFlowCMinMixedCMaxUnmixed;
elsewhen(use_dynamicFlowRegime and (configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.CrossFlowStream1MixedStream2Unmixed) and
(flowRegime == Buildings.Fluid.Types.HeatExchangerFlowRegime.CrossFlowCMinMixedCMaxUnmixed and (C1_flow > 1.05*C2_flow))) then
flowRegime := flowRegime_nominal;
// have ( configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.CrossFlowStream1UnmixedStream2Mixed)
elsewhen(use_dynamicFlowRegime and (configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.CrossFlowStream1UnmixedStream2Mixed) and
flowRegime == flowRegime_nominal and (C1_flow < 0.95*C2_flow)) then
flowRegime := Buildings.Fluid.Types.HeatExchangerFlowRegime.CrossFlowCMinUnmixedCMaxMixed;
elsewhen(use_dynamicFlowRegime and (configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.CrossFlowStream1UnmixedStream2Mixed) and
(flowRegime == Buildings.Fluid.Types.HeatExchangerFlowRegime.CrossFlowCMinUnmixedCMaxMixed and (C1_flow > 1.05*C2_flow))) then
flowRegime := flowRegime_nominal;
end when;

if not use_dynamicFlowRegime then
assert(noEvent(m1_flow > -0.1 * m1_flow_nominal)
and noEvent(m2_flow > -0.1 * m2_flow_nominal),
"*** Warning in " + getInstanceName() +
Expand All @@ -187,6 +213,7 @@ equation
level = AssertionLevel.warning);
end if;

equation
// Effectiveness
eps = Buildings.Fluid.HeatExchangers.BaseClasses.epsilon_C(
UA=UA,
Expand Down Expand Up @@ -251,6 +278,12 @@ for <code>UA</code>.
</html>", revisions="<html>
<ul>
<li>
March 7, 2026, by Michael Wetter:<br/>
Corrected implementation of switch of flow regime.<br/>
This is for
<a href=\"https://github.com/ibpsa/modelica-ibpsa/issues/2086\">IBPSA, #2086</a>.
</li>
<li>
February 7, 2025, by Jelger Jansen:<br/>
Removed <code>import</code> statement.
This is for
Expand Down
86 changes: 51 additions & 35 deletions Buildings/Fluid/HeatExchangers/WetCoilEffectivenessNTU.mo
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,8 @@ model WetCoilEffectivenessNTU

parameter Buildings.Fluid.Types.HeatExchangerConfiguration configuration=
Buildings.Fluid.Types.HeatExchangerConfiguration.CounterFlow
"Heat exchanger configuration";
"Heat exchanger configuration"
annotation(Evaluate=true);
parameter Real r_nominal=2/3
"Ratio between air-side and water-side convective heat transfer coefficient";

Expand Down Expand Up @@ -77,6 +78,9 @@ model WetCoilEffectivenessNTU
Real dryFra(final unit="1", min=0, max=1) = dryWetCalcs.dryFra
"Dry fraction, 0.3 means condensation occurs at 30% heat exchange length from air inlet";

Buildings.Fluid.Types.HeatExchangerFlowRegime flowRegime(fixed=false, start=flowRegime_nominal)
"Heat exchanger flow regime";

protected
final parameter Modelica.Units.SI.MassFraction X_w_a2_nominal=w_a2_nominal/(1
+ w_a2_nominal)
Expand Down Expand Up @@ -219,8 +223,6 @@ protected
"Index of water";
parameter Buildings.Fluid.Types.HeatExchangerFlowRegime flowRegime_nominal(fixed=false)
"Heat exchanger flow regime at nominal flow rates";
Buildings.Fluid.Types.HeatExchangerFlowRegime flowRegime(fixed=false, start=flowRegime_nominal)
"Heat exchanger flow regime";

Modelica.Thermal.HeatTransfer.Sources.PrescribedHeatFlow preHea
"Prescribed heat flow"
Expand Down Expand Up @@ -281,6 +283,9 @@ protected
p=Medium2.p_default,
X=Medium2.X_default[1:Medium2.nXi]) "Default state for medium 2";

parameter Real mPro_flow_nominal(unit="kg.kg/(s.s)") = m1_flow_nominal*m2_flow_nominal
"Product of nominal mass flow rates, used for scaling";

initial equation
assert(m1_flow_nominal > Modelica.Constants.eps,
"m1_flow_nominal must be positive, m1_flow_nominal = " + String(
Expand Down Expand Up @@ -318,41 +323,45 @@ initial equation
configuration <= Buildings.Fluid.Types.HeatExchangerConfiguration.CrossFlowStream1UnmixedStream2Mixed,
"Invalid heat exchanger configuration.");
end if;
flowRegime = flowRegime_nominal;

equation
algorithm
// Assign the flow regime for the given heat exchanger configuration and
// mass flow rates
if use_dynamicFlowRegime then
if (configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.ParallelFlow) then
flowRegime = if (C1_flow*C2_flow >= 0)
then
Buildings.Fluid.Types.HeatExchangerFlowRegime.ParallelFlow
else
Buildings.Fluid.Types.HeatExchangerFlowRegime.CounterFlow;
elseif (configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.CounterFlow) then
flowRegime = if (C1_flow*C2_flow >= 0)
then
Buildings.Fluid.Types.HeatExchangerFlowRegime.CounterFlow
else
Buildings.Fluid.Types.HeatExchangerFlowRegime.ParallelFlow;
elseif (configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.CrossFlowUnmixed) then
flowRegime = Buildings.Fluid.Types.HeatExchangerFlowRegime.CrossFlowUnmixed;
elseif (configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.CrossFlowStream1MixedStream2Unmixed) then
flowRegime = if (C1_flow < C2_flow)
then
Buildings.Fluid.Types.HeatExchangerFlowRegime.CrossFlowCMinMixedCMaxUnmixed
else
Buildings.Fluid.Types.HeatExchangerFlowRegime.CrossFlowCMinUnmixedCMaxMixed;
else
// have ( configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.CrossFlowStream1UnmixedStream2Mixed)
flowRegime = if (C1_flow < C2_flow)
then
Buildings.Fluid.Types.HeatExchangerFlowRegime.CrossFlowCMinUnmixedCMaxMixed
else
Buildings.Fluid.Types.HeatExchangerFlowRegime.CrossFlowCMinMixedCMaxUnmixed;
end if;
else
flowRegime = flowRegime_nominal;

// ParallelFlow vs CounterFlow
when(use_dynamicFlowRegime and (configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.ParallelFlow) and
flowRegime==flowRegime_nominal and (m1_flow*m2_flow/mPro_flow_nominal < -0.001)) then
flowRegime := Buildings.Fluid.Types.HeatExchangerFlowRegime.CounterFlow;
elsewhen(use_dynamicFlowRegime and (configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.ParallelFlow) and
flowRegime==Buildings.Fluid.Types.HeatExchangerFlowRegime.CounterFlow and (m1_flow*m2_flow/mPro_flow_nominal > 0.001)) then
flowRegime := flowRegime_nominal;

// CounterFlow vs ParallelFlow
elsewhen(use_dynamicFlowRegime and (configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.CounterFlow) and
flowRegime == flowRegime_nominal and (m1_flow*m2_flow/mPro_flow_nominal < -0.001)) then
flowRegime := Buildings.Fluid.Types.HeatExchangerFlowRegime.ParallelFlow;
elsewhen(use_dynamicFlowRegime and (configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.CounterFlow) and
flowRegime == Buildings.Fluid.Types.HeatExchangerFlowRegime.ParallelFlow and (m1_flow*m2_flow/mPro_flow_nominal > 0.001)) then
flowRegime := flowRegime_nominal;

// have ( configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.CrossFlowStream1MixedStream2Unmixed)
elsewhen(use_dynamicFlowRegime and (configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.CrossFlowStream1MixedStream2Unmixed) and
flowRegime == flowRegime_nominal and (C1_flow < 0.95*C2_flow)) then
flowRegime := Buildings.Fluid.Types.HeatExchangerFlowRegime.CrossFlowCMinMixedCMaxUnmixed;
elsewhen(use_dynamicFlowRegime and (configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.CrossFlowStream1MixedStream2Unmixed) and
(flowRegime == Buildings.Fluid.Types.HeatExchangerFlowRegime.CrossFlowCMinMixedCMaxUnmixed and (C1_flow > 1.05*C2_flow))) then
flowRegime := flowRegime_nominal;
// have ( configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.CrossFlowStream1UnmixedStream2Mixed)
elsewhen(use_dynamicFlowRegime and (configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.CrossFlowStream1UnmixedStream2Mixed) and
flowRegime == flowRegime_nominal and (C1_flow < 0.95*C2_flow)) then
flowRegime := Buildings.Fluid.Types.HeatExchangerFlowRegime.CrossFlowCMinUnmixedCMaxMixed;
elsewhen(use_dynamicFlowRegime and (configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.CrossFlowStream1UnmixedStream2Mixed) and
(flowRegime == Buildings.Fluid.Types.HeatExchangerFlowRegime.CrossFlowCMinUnmixedCMaxMixed and (C1_flow > 1.05*C2_flow))) then
flowRegime := flowRegime_nominal;
end when;

if not use_dynamicFlowRegime then
assert(noEvent(m1_flow > -0.1 * m1_flow_nominal)
and noEvent(m2_flow > -0.1 * m2_flow_nominal),
"*** Warning in " + getInstanceName() +
Expand All @@ -365,6 +374,7 @@ equation
level = AssertionLevel.warning);
end if;

equation
connect(heaCoo.port_b, port_b1) annotation (Line(points={{80,60},{80,60},{100,60}},color={0,127,255},
thickness=1));
connect(heaCooHum_u.port_b, port_b2) annotation (Line(
Expand Down Expand Up @@ -650,6 +660,12 @@ Fuzzy identification of systems and its applications to modeling and control.
</html>", revisions="<html>
<ul>
<li>
March 7, 2026, by Michael Wetter:<br/>
Corrected implementation of switch of flow regime.<br/>
This is for
<a href=\"https://github.com/ibpsa/modelica-ibpsa/issues/2086\">IBPSA, #2086</a>.
</li>
<li>
February 7, 2025, by Jelger Jansen:<br/>
Removed <code>import</code> statement.
This is for
Expand Down