Restricted ratio of flow rates

Buildings/Fluid/HeatExchangers/ThermalWheels/Latent/BaseClasses/Effectiveness.mo

@@ -69,13 +69,15 @@ protected
 
   Real rat
     "Ratio of the average operating air flow rate to the nominal supply air flow rate";
-  Real epsSenPL
+  Real ratRes
+    "Ratio of the average operating air flow rate to the nominal supply air flow rate, restricted to valid domain";
+  Modelica.Units.SI.Efficiency epsSenPL
     "Part load sensible heat exchanger effectiveness used for calculation";
-  Real epsSen_nominal
+  Modelica.Units.SI.Efficiency epsSen_nominal
     "Nominal sensible heat exchanger effectiveness used for calculation";
-  Real epsLatPL
+  Modelica.Units.SI.Efficiency epsLatPL
     "Part load latent heat exchanger effectiveness used for calculation";
-  Real epsLat_nominal
+  Modelica.Units.SI.Efficiency epsLat_nominal
     "Nominal latent heat exchanger effectiveness used for calculation";
 
 equation
@@ -87,7 +89,7 @@ equation
   rat = (VSup_flow + VExh_flow)/2/VSup_flow_nominal;
   // Check if the extrapolation goes too far
   assert(rat > 0.5 and rat < 1.3,
-    "In " + getInstanceName() + ": The ratio of the operating flow rate to the nominal supply flow rate should be in the range of [0.5, 1.3].",
+    "In " + getInstanceName() + ": The ratio of the operating flow rate to the nominal supply flow rate should be in the range of [0.5, 1.3]. Restricting value for effectiveness calculation.",
     level=AssertionLevel.warning);
   // Switch between cooling and heating modes based on the difference between the supply air temperature and the exhaust air temperature
   fraCoo = if (equSen_nominal and equSenPL and equLat_nominal and equLatPL) then 0.5 else Buildings.Utilities.Math.Functions.regStep(TSup-TExh, 1, 0, 1e-5);
@@ -99,8 +101,9 @@ equation
   epsLat_nominal = if equLat_nominal then epsLatCoo_nominal else fraCoo*epsLatCoo_nominal + (1-fraCoo) * epsLatHea_nominal;
 
   // Calculate effectiveness
-  epsSen =uSpe*(epsSenPL + (epsSen_nominal - epsSenPL)*(rat - 0.75)/0.25);
-  epsLat =uSpe*(epsLatPL + (epsLat_nominal - epsLatPL)*(rat - 0.75)/0.25);
+  ratRes = Buildings.Utilities.Math.Functions.smoothLimit(x=rat, l=0.5, u=1.3, deltaX=0.01);
+  epsSen =uSpe*(epsSenPL + (epsSen_nominal - epsSenPL)*(ratRes - 0.75)/0.25);
+  epsLat =uSpe*(epsLatPL + (epsLat_nominal - epsLatPL)*(ratRes - 0.75)/0.25);
   assert(epsSen >= 0 and epsSen < 1,
     "In " + getInstanceName() + ": The sensible heat exchange effectiveness epsSen = " + String(epsSen) + ". It should be in the range of [0, 1].
     Check if the part load (75% of the nominal supply flow rate) or nominal sensible heat exchanger effectiveness is too high or too low.",
@@ -122,16 +125,16 @@ under heating and cooling modes at different flow rates of the supply
 air and the exhaust air.
 </p>
 <p>
-It firstly calculates the ratio of the average operating flow rate to the nominal
-supply flow rate by:
+It calculates the ratio of the average operating flow rate to the nominal
+supply flow rate as
 </p>
 <pre>
-  rat = (VSup_flow + VExh_flow)/(2*VSup_flow_nominal),
+  rat = max(0.5, min(1.3, (VSup_flow + VExh_flow)/(2*VSup_flow_nominal))),
 </pre>
 <p>
-where <code>VSup_flow</code> is the flow rate of the supply air;
-<code>VExh_flow</code> is the flow rate of the exhaust air;
-<code>VSup_flow_nominal</code> is the nominal flow rate of the supply air; and 
+where <code>VSup_flow</code> is the flow rate of the supply air,
+<code>VExh_flow</code> is the flow rate of the exhaust air,
+<code>VSup_flow_nominal</code> is the nominal flow rate of the supply air, and
 <code>rat</code> is the flow ratio.
 </p>
 <p>
@@ -143,15 +146,15 @@ It then calculates the sensible and latent heat exchanger effectiveness by:
 </pre>
 <p>
 where <code>epsSen</code> and <code>epsLat</code> are the effectiveness
-for the sensible and latent heat transfer, respectively;
+for the sensible and latent heat transfer, respectively,
 <code>epsSen_nominal</code> and <code>epsSenPL</code> are the effectiveness 
-for the sensible heat transfer when <code>rat</code> is 1 and 0.75, respectively;
+for the sensible heat transfer when <code>rat</code> is 1 and 0.75, respectively,
 <code>epsLat_nominal</code> and <code>epsLatPL</code> are the effectiveness 
-for the latent heat transfer when <code>Rat</code> is 1 and 0.75, respectively;
+for the latent heat transfer when <code>Rat</code> is 1 and 0.75, respectively, and
 <code>uSpe</code> is the speed ratio of a rotary wheel.
 </p>
 <p>
-The parameters <code>epsSen_nominal</code>, <code>epsSenPL</code>, <code>epsLat_nominal</code>, and 
+The parameters <code>epsSen_nominal</code>, <code>epsSenPL</code>, <code>epsLat_nominal</code>, and
 <code>epsLatPL</code> have different values depending on if the wheel is in
 the cooling or heating mode.
 If the supply air temperature is greater than the exhaust air 
@@ -161,9 +164,9 @@ Otherwise, it operates under the heating mode.
 </p>
 <P>
 <b>Note:</b> 
-The value of the <code>rat</code> is suggested to be between <i>0.5</i> and <i>1.3</i>, 
+The value of the <code>rat</code> is suggested to be between <i>0.5</i> and <i>1.3</i> during normal operation
 to ensure reasonable extrapolation.
-Likewise, an unbalanced air flow ratio less than 2,  i.e., <code>VSup_flow/VExh_flow</code> &#62; <i>0.5</i> 
+Likewise, an unbalanced air flow ratio less than 2, i.e., <code>VSup_flow/VExh_flow</code> &#62; <i>0.5</i>
 and <code>VSup_flow/VExh_flow</code> &#60; <i>2</i>, is recommended.
 </P>
 <h4>References</h4>
@@ -174,6 +177,10 @@ U.S. Department of Energy 2016.
 </html>", revisions="<html>
 <ul>
 <li>
+April 24, 2024, by Michael Wetter:<br/>
+Restricted flow ratio to valid region.
+</li>
+<li>
 September 29, 2023, by Sen Huang:<br/>
 First implementation.
 </li>

Buildings/Fluid/HeatExchangers/ThermalWheels/Sensible/BaseClasses/Effectiveness.mo

@@ -53,9 +53,9 @@ protected
 
   Real rat
     "Ratio of the average operating air flow rate to the nominal supply air flow rate";
-  Real epsPL
+  Modelica.Units.SI.Efficiency epsPL
     "Part load sensible heat exchanger effectiveness used for calculation";
-  Real eps_nominal
+  Modelica.Units.SI.Efficiency eps_nominal
     "Nominal sensible heat exchanger effectiveness used for calculation";
 
 equation
@@ -67,14 +67,16 @@ equation
   rat = (VSup_flow + VExh_flow)/2/VSup_flow_nominal;
   // Check if the extrapolation goes too far
   assert(rat > 0.5 and rat < 1.3,
-    "In " + getInstanceName() + ": The ratio of the operating flow rate to the nominal supply flow rate should be in the range of [0.5, 1.3].",
+    "In " + getInstanceName() + ": The ratio of the operating flow rate to the nominal supply flow rate should be in the range of [0.5, 1.3]. Restricting value for effectiveness calculation.",
     level=AssertionLevel.warning);
   // Switch between cooling and heating modes based on the difference between the supply air temperature and the exhaust air temperature
   fraCoo = if equ_nominal and equPL then 0.5 else Buildings.Utilities.Math.Functions.regStep(TSup-TExh, 1, 0, 1e-5);
   epsPL = if equPL then epsCooPL else fraCoo*epsCooPL + (1-fraCoo) * epsHeaPL;
   eps_nominal = if equ_nominal then epsCoo_nominal else fraCoo*epsCoo_nominal + (1-fraCoo) * epsHea_nominal;
   // Calculate effectiveness
-  eps =uSpe*(epsPL + (eps_nominal - epsPL)*(rat - 0.75)/0.25);
+  eps =uSpe*(epsPL + (eps_nominal - epsPL)*(
+    Buildings.Utilities.Math.Functions.smoothLimit(x=rat, l=0.5, u=1.3, deltaX=0.01) - 0.75)/0.25);
+
   assert(eps >= 0 and eps < 1,
     "In " + getInstanceName() + ": The sensible heat exchange effectiveness eps = " + String(eps) + ". It should be in the range of [0, 1].
     Check if the part load (75% of the nominal supply flow rate) or nominal sensible heat exchanger effectiveness is too high or too low.",
@@ -92,29 +94,29 @@ under heating and cooling modes at different flow rates of the supply
 air and the exhaust air.
 </p>
 <p>
-It firstly calculates the ratio of the average operating flow rate to the nominal
+It first calculates the ratio of the average operating flow rate to the nominal
 supply flow rate by:
 </p>
 <pre>
-  rat = (VSup_flow + VExh_flow)/(2*VSup_flow_nominal),
+  rat = max(0.5, min(1.3, (VSup_flow + VExh_flow)/(2*VSup_flow_nominal))),
 </pre>
 <p>
-where <code>VSup_flow</code> is the flow rate of the supply air;
-<code>VExh_flow</code> is the flow rate of the exhaust air;
-<code>VSup_flow_nominal</code> is the nominal flow rate of the supply air; and 
+where <code>VSup_flow</code> is the flow rate of the supply air,
+<code>VExh_flow</code> is the flow rate of the exhaust air,
+<code>VSup_flow_nominal</code> is the nominal flow rate of the supply air and 
 <code>rat</code> is the flow ratio.
 </p>
 <p>
-It then calculates the sensible heat exchanger effectiveness by:
+It then calculates the sensible heat exchanger effectiveness as
 </p>
 <pre>
   eps = uSpe * (epsPL + (eps_nominal - epsPL) * (rat - 0.75)/0.25),
 </pre>
 <p>
 where <code>eps</code> is the effectiveness
-for the sensible heat transfer, respectively;
+for the sensible heat transfer, respectively,
 <code>eps_nominal</code> and <code>epsPL</code> are the effectiveness 
-for the sensible heat transfer when <code>rat</code> is 1 and 0.75, respectively.
+for the sensible heat transfer when <code>rat</code> is 1 and 0.75, respectively, and
 <code>uSpe</code> is the speed ratio of a rotary wheel.
 </p>
 <p>
@@ -123,15 +125,15 @@ have different values depending on if the wheel is in
 the cooling or heating mode.
 If the supply air temperature is greater than the exhaust air 
 temperature, the exchanger is considered to operate under
-the cooling mode;
+the cooling mode.
 Otherwise, it operates under the heating mode.
 </p>
 <P>
 <b>Note:</b> 
-The value of the <code>rat</code> is suggested to be between <i>0.5</i> and <i>1.3</i>, 
+The value of the <code>rat</code> is suggested to be between <i>0.5</i> and <i>1.3</i> during normal operation
 to ensure reasonable extrapolation.
 Likewise, an unbalanced air flow ratio less than 2,  i.e., <code>VSup_flow/VExh_flow</code> &#62; <i>0.5</i> 
-and <code>VSup_flow/VExh_flow</code> &#60; <i>2</i>, is recommended.
+and <code>VSup_flow/VExh_flow</code> &#60; <i>2</i> is recommended.
 </P>
 <h4>References</h4>
 <p>
@@ -141,6 +143,10 @@ U.S. Department of Energy 2016.
 </html>", revisions="<html>
 <ul>
 <li>
+April 24, 2024, by Michael Wetter:<br/>
+Restricted flow ratio to valid region.
+</li>
+<li>
 January 8, 2024, by Sen Huang:<br/>
 First implementation.
 </li>