diff --git a/Buildings/Fluid/SolarCollectors/ASHRAE93.mo b/Buildings/Fluid/SolarCollectors/ASHRAE93.mo
index f519b75a3b6..c4df93e5eec 100644
--- a/Buildings/Fluid/SolarCollectors/ASHRAE93.mo
+++ b/Buildings/Fluid/SolarCollectors/ASHRAE93.mo
@@ -180,6 +180,13 @@ capacity of copper.
 </html>", revisions="<html>
 <ul>
 <li>
+December 11, 2023, by Michael Wetter:<br/>
+Corrected implementation of pressure drop calculation for the situation where the collectors are in parallel,
+e.g., if <code>sysConfig == Buildings.Fluid.SolarCollectors.Types.SystemConfiguration.Parallel</code>.<br/>
+This is for
+<a href=\"https://github.com/lbl-srg/modelica-buildings/issues/3597\">Buildings, #3597</a>.
+</li>
+<li>
 September 16, 2021, by Michael Wetter:<br/>
 Changed <code>lat</code> from being a parameter to an input from weather bus.<br/>
 This is for
diff --git a/Buildings/Fluid/SolarCollectors/BaseClasses/PartialSolarCollector.mo b/Buildings/Fluid/SolarCollectors/BaseClasses/PartialSolarCollector.mo
index 1ead7210c59..e0ce5ff9bcd 100644
--- a/Buildings/Fluid/SolarCollectors/BaseClasses/PartialSolarCollector.mo
+++ b/Buildings/Fluid/SolarCollectors/BaseClasses/PartialSolarCollector.mo
@@ -3,7 +3,7 @@ model PartialSolarCollector "Partial model for solar collectors"
  extends Buildings.Fluid.Interfaces.LumpedVolumeDeclarations;
   extends Buildings.Fluid.Interfaces.TwoPortFlowResistanceParameters(final dp_nominal = dp_nominal_final);
   extends Buildings.Fluid.Interfaces.PartialTwoPortInterface(
-    final m_flow_nominal=perPar.mperA_flow_nominal*perPar.A);
+    final m_flow_nominal=m_flow_nominal_final);
 
   constant Boolean homotopyInitialization = true "= true, use homotopy method"
     annotation(HideResult=true);
@@ -125,9 +125,14 @@ protected
     "Partial performance data"
     annotation(choicesAllMatching=true);
 
-    Modelica.Blocks.Interfaces.RealInput shaCoe_internal
+  Modelica.Blocks.Interfaces.RealInput shaCoe_internal
     "Internally used shading coefficient";
 
+  final parameter Modelica.Units.SI.MassFlowRate m_flow_nominal_final(
+      displayUnit="kg/s") = if sysConfig == Buildings.Fluid.SolarCollectors.Types.SystemConfiguration.Parallel
+     then nPanels_internal*perPar.mperA_flow_nominal*perPar.A else perPar.mperA_flow_nominal*perPar.A
+    "Nominal mass flow rate through the system of collectors";
+
   final parameter Modelica.Units.SI.PressureDifference dp_nominal_final(
       displayUnit="Pa") = if sysConfig == Buildings.Fluid.SolarCollectors.Types.SystemConfiguration.Series
      then nPanels_internal*perPar.dp_nominal else perPar.dp_nominal
@@ -242,6 +247,13 @@ CEN 2006, European Standard 12975-1:2006, European Committee for Standardization
 revisions="<html>
 <ul>
 <li>
+December 11, 2023, by Michael Wetter:<br/>
+Corrected implementation of pressure drop calculation for the situation where the collectors are in parallel,
+e.g., if <code>sysConfig == Buildings.Fluid.SolarCollectors.Types.SystemConfiguration.Parallel</code>.<br/>
+This is for
+<a href=\"https://github.com/lbl-srg/modelica-buildings/issues/3597\">Buildings, #3597</a>.
+</li>
+<li>
 September 16, 2021, by Michael Wetter:<br/>
 Changed <code>lat</code> from being a parameter to an input from weather bus.<br/>
 This is for
diff --git a/Buildings/Fluid/SolarCollectors/EN12975.mo b/Buildings/Fluid/SolarCollectors/EN12975.mo
index 90413faec95..3bc2a59fb08 100644
--- a/Buildings/Fluid/SolarCollectors/EN12975.mo
+++ b/Buildings/Fluid/SolarCollectors/EN12975.mo
@@ -108,6 +108,13 @@ capacity of copper.
 </html>", revisions="<html>
 <ul>
 <li>
+December 11, 2023, by Michael Wetter:<br/>
+Corrected implementation of pressure drop calculation for the situation where the collectors are in parallel,
+e.g., if <code>sysConfig == Buildings.Fluid.SolarCollectors.Types.SystemConfiguration.Parallel</code>.<br/>
+This is for
+<a href=\"https://github.com/lbl-srg/modelica-buildings/issues/3597\">Buildings, #3597</a>.
+</li>
+<li>
 September 16, 2021, by Michael Wetter:<br/>
 Changed <code>lat</code> from being a parameter to an input from weather bus.<br/>
 This is for
@@ -134,7 +141,7 @@ First implementation.
 </html>"),
       Icon(coordinateSystem(preserveAspectRatio=false, extent={{-100,-100},{100,
             100}}),
-         graphics={
+      graphics={
         Rectangle(
           extent={{-84,100},{84,-100}},
           lineColor={27,0,55},
diff --git a/Buildings/Fluid/SolarCollectors/Examples/Tubular.mo b/Buildings/Fluid/SolarCollectors/Examples/Tubular.mo
index 28466b74b87..7e2f37e7649 100644
--- a/Buildings/Fluid/SolarCollectors/Examples/Tubular.mo
+++ b/Buildings/Fluid/SolarCollectors/Examples/Tubular.mo
@@ -38,14 +38,15 @@ model Tubular "Example showing the use of Tubular"
   Modelica.Blocks.Sources.Sine sine(
     f=3/86400,
     offset=101325,
-    amplitude=-1.5*solCol.dp_nominal)
+    amplitude=-0.1*solCol.dp_nominal)
     annotation (Placement(transformation(extent={{-100,-20},{-80,0}})));
   Buildings.Fluid.Sources.Boundary_pT sou(
     redeclare package Medium = Medium,
     T=273.15 + 10,
     nPorts=1,
     use_p_in=true,
-    p(displayUnit="Pa")) "Inlet for water flow"                                annotation (Placement(
+    p(displayUnit="Pa")) "Inlet for water flow"
+    annotation (Placement(
         transformation(
         extent={{10,-10},{-10,10}},
         rotation=180,
@@ -92,6 +93,14 @@ equation
 revisions="<html>
 <ul>
 <li>
+December 11, 2023, by Michael Wetter:<br/>
+Changed design flow rate. This is due to correction for the
+implementation of the pressure drop calculation for the situation where collectors are in parallel,
+e.g., if <code>sysConfig == Buildings.Fluid.SolarCollectors.Types.SystemConfiguration.Parallel</code>.<br/>
+This is for
+<a href=\"https://github.com/lbl-srg/modelica-buildings/issues/3597\">Buildings, #3597</a>.
+</li>
+<li>
 September 16, 2021, by Michael Wetter:<br/>
 Removed parameter assignment for <code>lat</code>.<br/>
 This is for
diff --git a/Buildings/Resources/ReferenceResults/Dymola/Buildings_Fluid_SolarCollectors_Examples_Tubular.txt b/Buildings/Resources/ReferenceResults/Dymola/Buildings_Fluid_SolarCollectors_Examples_Tubular.txt
index cc63d3f6594..c4ec08a5124 100644
--- a/Buildings/Resources/ReferenceResults/Dymola/Buildings_Fluid_SolarCollectors_Examples_Tubular.txt
+++ b/Buildings/Resources/ReferenceResults/Dymola/Buildings_Fluid_SolarCollectors_Examples_Tubular.txt
@@ -1,4 +1,4 @@
-last-generated=2021-09-16
+last-generated=2023-12-11
 statistics-simulation=
 {
   "linear": " ",
@@ -7,7 +7,7 @@ statistics-simulation=
   "numerical Jacobians": "0"
 }
 time=[0e+00, 8.64e+04]
-solCol.vol[3].T=[2.931499938964844e+02, 2.919305419921875e+02, 2.91035888671875e+02, 2.910977783203125e+02, 2.914320983886719e+02, 2.916263122558594e+02, 2.917364501953125e+02, 2.918013000488281e+02, 2.918355712890625e+02, 2.918450317382812e+02, 2.918268737792969e+02, 2.917788696289062e+02, 2.916997985839844e+02, 2.915844421386719e+02, 2.914170837402344e+02, 2.911626892089844e+02, 2.907439270019531e+02, 2.897762451171875e+02, 2.854419555664062e+02, 2.830054931640625e+02, 2.828385925292969e+02, 2.828497009277344e+02, 2.828634033203125e+02, 2.828759155273438e+02, 2.82886962890625e+02, 2.8289599609375e+02, 2.829056396484375e+02, 2.829205627441406e+02, 2.82935546875e+02, 2.829435119628906e+02, 2.829380493164062e+02, 2.829585266113281e+02, 2.831075439453125e+02, 2.838595275878906e+02, 2.861387023925781e+02, 2.908436584472656e+02, 2.985640258789062e+02, 3.022300415039062e+02, 3.037222900390625e+02, 3.049939575195312e+02, 3.062251281738281e+02, 3.074563598632812e+02, 3.087409362792969e+02, 3.100741882324219e+02, 3.114456481933594e+02, 3.128721313476562e+02, 3.144710083007812e+02, 3.163765258789062e+02, 3.192970275878906e+02, 3.240956726074219e+02, 3.330659484863281e+02, 3.345177001953125e+02, 3.048251037597656e+02, 2.967297973632812e+02, 2.947060241699219e+02, 2.936444702148438e+02, 2.929769287109375e+02, 2.925689697265625e+02, 2.924362182617188e+02, 2.924761657714844e+02, 2.92646484375e+02, 2.927496948242188e+02, 2.927188720703125e+02, 2.925965576171875e+02, 2.925583190917969e+02, 2.927740173339844e+02, 2.930754699707031e+02, 2.964302978515625e+02, 3.034049072265625e+02, 2.996808776855469e+02, 2.931159973144532e+02, 2.920925903320312e+02, 2.92120849609375e+02, 2.921827392578125e+02, 2.92224365234375e+02, 2.922430419921875e+02, 2.92237060546875e+02, 2.922110290527344e+02, 2.921666564941406e+02, 2.921014709472656e+02, 2.920101623535156e+02, 2.918832397460938e+02, 2.916912841796875e+02, 2.913562927246094e+02, 2.899408874511719e+02, 2.847178955078125e+02, 2.832078857421875e+02, 2.831043090820312e+02, 2.830921325683594e+02, 2.830996704101562e+02, 2.831146545410156e+02, 2.831254577636719e+02, 2.831221618652344e+02, 2.831068115234375e+02, 2.830870361328125e+02, 2.830640258789062e+02, 2.830382385253906e+02, 2.830082397460938e+02, 2.829681091308594e+02, 2.829047546386719e+02, 2.82763427734375e+02]
-solCol.vol[6].T=[2.931499938964844e+02, 2.919840393066406e+02, 2.917291870117188e+02, 2.920128479003906e+02, 2.921851196289062e+02, 2.922786865234375e+02, 2.923347778320312e+02, 2.923680419921875e+02, 2.92384765625e+02, 2.923871459960938e+02, 2.923722839355469e+02, 2.923392944335938e+02, 2.922866516113281e+02, 2.922095642089844e+02, 2.9209423828125e+02, 2.919091796875e+02, 2.915714721679688e+02, 2.906121215820312e+02, 2.885163879394531e+02, 2.843773193359375e+02, 2.826753540039062e+02, 2.82561767578125e+02, 2.825846252441406e+02, 2.826091918945312e+02, 2.826311950683594e+02, 2.82649658203125e+02, 2.826675415039062e+02, 2.8269482421875e+02, 2.827247314453125e+02, 2.827445373535156e+02, 2.827411193847656e+02, 2.827639465332031e+02, 2.8295263671875e+02, 2.838497314453125e+02, 2.862701721191406e+02, 2.934894409179687e+02, 2.977778930664062e+02, 2.988129577636719e+02, 2.995441589355469e+02, 3.002586975097656e+02, 3.009594421386719e+02, 3.016759033203125e+02, 3.02432373046875e+02, 3.032225036621094e+02, 3.040422668457031e+02, 3.049123229980469e+02, 3.059262390136719e+02, 3.071897277832031e+02, 3.092953796386719e+02, 3.130213928222656e+02, 3.213198852539062e+02, 3.429164428710938e+02, 3.382171630859375e+02, 3.14322021484375e+02, 3.066818542480469e+02, 3.040908203125e+02, 3.026192626953125e+02, 3.017124633789062e+02, 3.013418579101562e+02, 3.013551635742188e+02, 3.016401062011719e+02, 3.018568725585938e+02, 3.018363037109375e+02, 3.015976867675781e+02, 3.014117431640625e+02, 3.015606079101562e+02, 3.018356323242188e+02, 3.045715026855469e+02, 3.04002227783203e+02, 2.944256591796876e+02, 2.925515441894531e+02, 2.925135192871094e+02, 2.925572204589844e+02, 2.925914611816406e+02, 2.926131286621094e+02, 2.926210327148438e+02, 2.926143493652344e+02, 2.925963439941406e+02, 2.925669860839844e+02, 2.925239868164062e+02, 2.924629211425781e+02, 2.923750610351562e+02, 2.922315368652344e+02, 2.919439697265625e+02, 2.910379028320312e+02, 2.884861145019531e+02, 2.842343444824219e+02, 2.831340026855469e+02, 2.830425720214844e+02, 2.830471801757812e+02, 2.830741577148438e+02, 2.830981140136719e+02, 2.830985717773438e+02, 2.8307275390625e+02, 2.830362243652344e+02, 2.829933471679688e+02, 2.82945556640625e+02, 2.828917846679688e+02, 2.828245239257812e+02, 2.827292175292969e+02, 2.825635070800781e+02]
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diff --git a/Buildings/Resources/Scripts/BuildingsPy/conf.yml b/Buildings/Resources/Scripts/BuildingsPy/conf.yml
index ec05fd48020..cb8395e4b3f 100644
--- a/Buildings/Resources/Scripts/BuildingsPy/conf.yml
+++ b/Buildings/Resources/Scripts/BuildingsPy/conf.yml
@@ -423,6 +423,10 @@
   openmodelica:
     comment: Timeout on travis, https://app.travis-ci.com/github/lbl-srg/modelica-buildings/jobs/604300629#L376
     simulate: false
+- model_name: Buildings.ThermalZones.Detailed.Validation.BESTEST.Cases9xx.Case995
+  openmodelica:
+    comment: Timeout on travis, https://app.travis-ci.com/github/lbl-srg/modelica-buildings/jobs/614899187
+    time_out: 600
 - model_name: Buildings.ThermalZones.EnergyPlus_9_6_0.BaseClasses.Validation.FMUZoneAdapterZones1
   dymola:
     comment: Requires docker update to Ubuntu 22.04 due to libgc.
diff --git a/Buildings/package.mo b/Buildings/package.mo
index 19bd0761054..780b107c754 100644
--- a/Buildings/package.mo
+++ b/Buildings/package.mo
@@ -308,12 +308,16 @@ The following <b style=\"color:red\">critical errors</b> have been fixed (i.e.,
 that can lead to wrong simulation results):
 </p>
 <table class=\"releaseTable\" summary=\"summary\" border=\"1\" cellspacing=\"0\" cellpadding=\"2\" style=\"border-collapse:collapse;\">
-<tr><td colspan=\"2\"><b>xxx</b>
+<tr><td colspan=\"2\"><b>Buildings.Fluid.SolarCollectors</b>
     </td>
 </tr>
-<tr><td valign=\"top\">xxx
+<tr><td valign=\"top\">Buildings.Fluid.SolarCollectors.ASHRAE93<br/>
+                       Buildings.Fluid.SolarCollectors.EN12975
     </td>
-    <td valign=\"top\">xxx.
+    <td valign=\"top\">Corrected implementation of pressure drop calculation for the situation where the collectors are in parallel,
+                       e.g., if <code>sysConfig == Buildings.Fluid.SolarCollectors.Types.SystemConfiguration.Parallel</code>.<br/>
+                       This is for
+                       <a href=\"https://github.com/lbl-srg/modelica-buildings/issues/3597\">Buildings, #3597</a>.
     </td>
 </tr>
 </table>

xxx +
Buildings.Fluid.SolarCollectors
xxx +
Buildings.Fluid.SolarCollectors.ASHRAE93 + Buildings.Fluid.SolarCollectors.EN12975	xxx. +	Corrected implementation of pressure drop calculation for the situation where the collectors are in parallel, + e.g., if `sysConfig == Buildings.Fluid.SolarCollectors.Types.SystemConfiguration.Parallel`. + This is for + Buildings, #3597.