Fix for Defect #10508

Fixes the defect with a solution suggested in GitHub which includes the following:
1. Calculates average multiplier regardless of system operation (now simply calculates it every time)
2. Uses the limit of 30 as a warning threshold but does not eliminate the value (previously set to 1 so that it wouldn't affect the average)
These items have been accomplished through the creation of a new subroutine that controls the calculation limits and calculates the sum, count, and average.

src/EnergyPlus/ZoneTempPredictorCorrector.cc

@@ -5149,7 +5149,6 @@ void InverseModelTemperature(EnergyPlusData &state,
 
     // HM calculation only HM calculation period start
     if (state.dataEnvrn->DayOfYear >= hybridModelZone.HybridStartDayOfYear && state.dataEnvrn->DayOfYear <= hybridModelZone.HybridEndDayOfYear) {
-        Real64 HMMultiplierAverage(1.0);
         Real64 MultpHM(1.0);
 
         thisZoneHB.ZT = zone.ZoneMeasuredTemperature; // Array1D<Real64> ZT -- Zone
@@ -5248,31 +5247,15 @@ void InverseModelTemperature(EnergyPlusData &state,
                                                              thisZoneHB.airHumRat) *
                            Psychrometrics::PsyCpAirFnW(thisZoneHB.airHumRat)) *
                           (state.dataGlobal->TimeStepZone * Constant::SecInHour); // Inverse equation
-                if ((MultpHM < 1.0) || (MultpHM > 30.0)) {                        // Temperature capacity multiplier greater than
-                                                                                  // 1 and less than 30
-                    MultpHM = 1.0;                                                // Default value 1.0
-                }
             } else {
                 MultpHM = 1.0; // Default value 1.0
             }
 
-            zone.ZoneVolCapMultpSensHM = MultpHM; // For timestep output
+            processInverseModelMultpHM(
+                state, MultpHM, zone.ZoneVolCapMultpSensHMSum, zone.ZoneVolCapMultpSensHMCountSum, zone.ZoneVolCapMultpSensHMAverage, ZoneNum);
 
-            // Calculate the average multiplier of the zone for the whole running period
-            {
-                // count for hybrid model calculations
-                if (MultpHM > 1.0) {
-                    zone.ZoneVolCapMultpSensHMSum += MultpHM;
-                    zone.ZoneVolCapMultpSensHMCountSum++;
-                }
+            zone.ZoneVolCapMultpSensHM = MultpHM; // For timestep output
 
-                // Calculate and store the multiplier average at the end of HM
-                // simulations
-                if (state.dataEnvrn->DayOfYear == hybridModelZone.HybridEndDayOfYear && state.dataGlobal->EndDayFlag) {
-                    HMMultiplierAverage = zone.ZoneVolCapMultpSensHMSum / zone.ZoneVolCapMultpSensHMCountSum;
-                    zone.ZoneVolCapMultpSensHMAverage = HMMultiplierAverage;
-                }
-            }
         } // Hybrid model internal thermal mass calcualtion end
 
         // Hybrid model people count calculation
@@ -5346,6 +5329,43 @@ void InverseModelTemperature(EnergyPlusData &state,
     state.dataHeatBalFanSys->PreviousMeasuredZT1(ZoneNum) = thisZoneHB.ZT;
 }
 
+void processInverseModelMultpHM(EnergyPlusData &state,
+                                Real64 &multiplierHM, // Hybrid model thermal mass multiplier
+                                Real64 &multSumHM,    // Sum of Hybrid model thermal mass multipliers
+                                Real64 &countSumHM,   // Count of number of points in sum
+                                Real64 &multAvgHM,    // Average of hybrid model mass multipier
+                                int zoneNum           // Zone number for the hybrid model
+)
+{
+    Real64 constexpr minHMMultValue = 1.0;
+    Real64 constexpr maxHMMultValue = 30.0;
+
+    auto &zone = state.dataHeatBal->Zone(zoneNum);
+    auto &thisZoneHB = state.dataZoneTempPredictorCorrector->zoneHeatBalance(zoneNum);
+
+    // Apply limits and generate warnings as needed
+    if (multiplierHM < minHMMultValue) { // don't allow this to be less than minimum (potential for instability)
+        multiplierHM = minHMMultValue;
+    } else if (multiplierHM > maxHMMultValue) { // as per suggestions in Defect #10508, only warn if greater than the max
+        if (thisZoneHB.hmThermalMassMultErrIndex == 0) {
+            ShowWarningMessage(state, format("Hybrid model thermal mass multiplier higher than the limit for {}", zone.Name));
+            ShowContinueError(state, "This means that the ratio of the zone air heat capacity for the current time step to the");
+            ShowContinueError(state, format("zone air heat storage is higher than the maximum limit of {:.1R},", maxHMMultValue));
+        }
+        ShowRecurringWarningErrorAtEnd(
+            state, "Hybrid model thermal mass multiplier limit exceeded in zone " + zone.Name, thisZoneHB.hmThermalMassMultErrIndex);
+    }
+
+    // Update running totals (but only when there is a valid multiplier, i.e. multiplier is greater than min but not higher than the max)
+    if (multiplierHM > minHMMultValue) {
+        multSumHM += multiplierHM;
+        countSumHM++;
+    }
+
+    // Calculate average (always so that it does get calculated)
+    if (countSumHM >= 1) multAvgHM = multSumHM / countSumHM;
+}
+
 void InverseModelHumidity(EnergyPlusData &state,
                           int const ZoneNum,                   // Zone number
                           Real64 const LatentGain,             // Zone sum of latent gain

src/EnergyPlus/ZoneTempPredictorCorrector.hh

@@ -221,6 +221,7 @@ namespace ZoneTempPredictorCorrector {
         Real64 tempDepLoad = 0.0;
         Real64 airRelHum = 0.0;   // Zone relative humidity in percent
         Real64 AirPowerCap = 0.0; // "air power capacity"  Vol*VolMult*rho*Cp/timestep [W/degK]
+        int hmThermalMassMultErrIndex = 0;
 
         virtual ~ZoneSpaceHeatBalanceData() = default;
 
@@ -338,6 +339,14 @@ namespace ZoneTempPredictorCorrector {
                                  Real64 AirCap                  // Formerly CoefAirrat, coef in zone temp eqn with dim of "air power capacity"rd
     );
 
+    void processInverseModelMultpHM(EnergyPlusData &state,
+                                    Real64 &multiplierHM, // Hybrid model thermal mass multiplier
+                                    Real64 &multSumHM,    // Sum of Hybrid model thermal mass multipliers
+                                    Real64 &countSumHM,   // Count of number of points in sum
+                                    Real64 &multAvgHM,    // Average of hybrid model mass multipier
+                                    int zoneNum           // Zone number for the hybrid model
+    );
+
     void InverseModelHumidity(EnergyPlusData &state,
                               int ZoneNum,                   // Zone number
                               Real64 LatentGain,             // Zone sum of latent gain