Correct VAV maximum air flow fraction during reheat

NREL · Sep 24, 2024 · 90f2846 · 90f2846 · nrel-bot-2c · Sep 24, 2024
1 parent e7ecb2d
commit 90f2846
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Showing 2 changed files with 43 additions and 8 deletions.
diff --git a/src/EnergyPlus/SingleDuct.cc b/src/EnergyPlus/SingleDuct.cc
@@ -2877,8 +2877,10 @@ void SingleDuctAirTerminal::SizeSys(EnergyPlusData &state)
 
             CheckZoneSizing(state, this->sysType, this->SysName);
 
-            MaxAirVolFlowRateDes = max(state.dataSize->TermUnitFinalZoneSizing(state.dataSize->CurTermUnitSizingNum).DesCoolVolFlow,
-                                       state.dataSize->TermUnitFinalZoneSizing(state.dataSize->CurTermUnitSizingNum).DesHeatVolFlow);
+            Real64 heatingMaxFlow = (this->DamperHeatingAction == Action::ReverseWithLimits)
+                                        ? state.dataSize->TermUnitFinalZoneSizing(state.dataSize->CurTermUnitSizingNum).DesHeatVolFlowMax
+                                        : state.dataSize->TermUnitFinalZoneSizing(state.dataSize->CurTermUnitSizingNum).DesHeatVolFlow;
+            MaxAirVolFlowRateDes = max(state.dataSize->TermUnitFinalZoneSizing(state.dataSize->CurTermUnitSizingNum).DesCoolVolFlow, heatingMaxFlow);
 
             if (MaxAirVolFlowRateDes < SmallAirVolFlow) {
                 MaxAirVolFlowRateDes = 0.0;
@@ -2927,7 +2929,11 @@ void SingleDuctAirTerminal::SizeSys(EnergyPlusData &state)
             }
         } else {
             CheckZoneSizing(state, this->sysType, this->SysName);
-            MaxHeatAirVolFlowRateDes = state.dataSize->TermUnitFinalZoneSizing(state.dataSize->CurTermUnitSizingNum).DesHeatVolFlow;
+            if (this->DamperHeatingAction == Action::ReverseWithLimits) {
+                MaxHeatAirVolFlowRateDes = state.dataSize->TermUnitFinalZoneSizing(state.dataSize->CurTermUnitSizingNum).DesHeatVolFlowMax;
+            } else {
+                MaxHeatAirVolFlowRateDes = state.dataSize->TermUnitFinalZoneSizing(state.dataSize->CurTermUnitSizingNum).DesHeatVolFlow;
+            }
             if (MaxHeatAirVolFlowRateDes < SmallAirVolFlow) {
                 MaxHeatAirVolFlowRateDes = 0.0;
             }

diff --git a/tst/EnergyPlus/unit/SingleDuct.unit.cc b/tst/EnergyPlus/unit/SingleDuct.unit.cc
@@ -2737,23 +2737,52 @@ TEST_F(EnergyPlusFixture, VAVReheatTerminal_SizeMinFrac)
     EXPECT_TRUE(compare_err_stream(""));
 
     int SysNum = 1;
+    auto &thisSys = state->dataSingleDuct->sd_airterminal(SysNum);
 
     // First test -  design min flow < max flow
     state->dataSize->ZoneSizingRunDone = true;
     state->dataSize->CurZoneEqNum = 1;
     state->dataSize->CurTermUnitSizingNum = 1;
     state->dataSize->TermUnitFinalZoneSizing(1).DesCoolVolFlowMin = 0.5;
-    state->dataSingleDuct->sd_airterminal(SysNum).SizeSys(*state);
-    EXPECT_EQ(0.5, state->dataSingleDuct->sd_airterminal(SysNum).ZoneMinAirFracDes);
+    thisSys.SizeSys(*state);
+    EXPECT_EQ(0.5, thisSys.ZoneMinAirFracDes);
 
     // Second test -  design min flow > max flow
     state->dataSize->ZoneSizingRunDone = true;
     state->dataSize->CurZoneEqNum = 1;
     state->dataSize->CurTermUnitSizingNum = 1;
-    state->dataSingleDuct->sd_airterminal(SysNum).ZoneMinAirFracDes = AutoSize; // need to reset this so it sizes again
+    thisSys.ZoneMinAirFracDes = AutoSize; // need to reset this so it sizes again
     state->dataSize->TermUnitFinalZoneSizing(1).DesCoolVolFlowMin = 1.5;
-    state->dataSingleDuct->sd_airterminal(SysNum).SizeSys(*state);
-    EXPECT_EQ(1.0, state->dataSingleDuct->sd_airterminal(SysNum).ZoneMinAirFracDes);
+    thisSys.SizeSys(*state);
+    EXPECT_EQ(1.0, thisSys.ZoneMinAirFracDes);
+
+    // test Maximum Flow Fraction During Reheat for heating dominated
+    thisSys.MaxAirVolFlowRate = DataSizing::AutoSize;
+    thisSys.ZoneMinAirFracDes = DataSizing::AutoSize;
+    thisSys.MaxAirVolFlowRateDuringReheat = DataSizing::AutoSize;
+    thisSys.MaxAirVolFractionDuringReheat = DataSizing::AutoSize;
+    state->dataSize->TermUnitFinalZoneSizing(1).DesHeatVolFlow = 1.7;
+    state->dataSize->TermUnitFinalZoneSizing(1).DesHeatVolFlowMax = 1.6;
+    thisSys.SizeSys(*state);
+    Real64 expectedZoneMinAirFracDes = std::min(1.0, state->dataSize->TermUnitFinalZoneSizing(1).DesCoolVolFlowMin / thisSys.MaxAirVolFlowRate);
+    Real64 expectedMaxAirVolFractionDuringReheat = state->dataSize->TermUnitFinalZoneSizing(1).DesHeatVolFlowMax / thisSys.MaxAirVolFlowRate;
+    EXPECT_EQ(expectedZoneMinAirFracDes, thisSys.ZoneMinAirFracDes);
+    EXPECT_EQ(1.0, thisSys.MaxAirVolFractionDuringReheat);
+    EXPECT_EQ(expectedMaxAirVolFractionDuringReheat, thisSys.MaxAirVolFractionDuringReheat);
+
+    // test Maximum Flow Fraction During Reheat for cooling dominated
+    thisSys.MaxAirVolFlowRate = DataSizing::AutoSize;
+    thisSys.ZoneMinAirFracDes = DataSizing::AutoSize;
+    thisSys.MaxAirVolFlowRateDuringReheat = DataSizing::AutoSize;
+    thisSys.MaxAirVolFractionDuringReheat = DataSizing::AutoSize;
+    state->dataSize->TermUnitFinalZoneSizing(1).DesHeatVolFlow = 1.4;
+    state->dataSize->TermUnitFinalZoneSizing(1).DesHeatVolFlowMax = 1.3;
+    thisSys.SizeSys(*state);
+    expectedZoneMinAirFracDes = std::min(1.0, state->dataSize->TermUnitFinalZoneSizing(1).DesCoolVolFlowMin / thisSys.MaxAirVolFlowRate);
+    expectedMaxAirVolFractionDuringReheat = state->dataSize->TermUnitFinalZoneSizing(1).DesHeatVolFlowMax / thisSys.MaxAirVolFlowRate;
+    EXPECT_EQ(expectedZoneMinAirFracDes, thisSys.ZoneMinAirFracDes);
+    EXPECT_EQ(1.0, thisSys.MaxAirVolFractionDuringReheat);
+    EXPECT_EQ(expectedMaxAirVolFractionDuringReheat, thisSys.MaxAirVolFractionDuringReheat);
 }
 
 TEST_F(EnergyPlusFixture, setATMixerSizingProperties_Test)