Adding hinged windows in models (WindowOpening class)

cara/models.py

@@ -195,16 +195,40 @@ class WindowOpening(Ventilation):
     #: The length of the opening-gap when the window is open
     opening_length: float
 
+    #: The type of the window ('sliding' or 'hinged')
+    window_type: str = 'sliding'
+
+    #: The width of the window (used only to get cd_b of a hinged window).
+    window_width: float = None
+
     #: The number of windows of the given dimensions.
     number_of_windows: int = 1
 
     #: Discharge coefficient: what portion effective area is
-    #: used to exchange air (0 <= cd_b <= 1)
-    cd_b: float = 0.6
+    #: used to exchange air (0 <= cd_b <= 1). Overrides the value
+    #: obtained from the window parameters
+    cd_b: float = None
 
     #: Minimum difference between inside and outside temperature
     min_deltaT: float = 0.1
 
+    @property
+    def _cd_b(self):
+        if self.cd_b is not None:
+            return self.cd_b
+        elif self.window_type == 'sliding':
+            return 0.6
+        elif self.window_type == 'hinged':
+            window_ratio = self.window_width / self.window_height
+            M = (0.06 if window_ratio < 0.5 else 0.048 if window_ratio < 1 else
+                    0.04 if window_ratio < 2 else 0.038)
+            cd_max = (0.612 if window_ratio < 0.5 else 0.589 if window_ratio < 1
+                    else 0.563 if window_ratio < 2 else 0.548)
+            window_angle = np.arccos(1-self.opening_length**2/(2.*self.window_height**2))
+            return cd_max*(1-np.exp(-M*window_angle))
+        else:
+            raise ValueError("Unknown window type; please specify cd_b")
+
     def transition_times(self) -> typing.Set[float]:
         transitions = super().transition_times()
         transitions.update(self.inside_temp.transition_times)
@@ -228,7 +252,7 @@ class WindowOpening(Ventilation):
         temp_gradient = (inside_temp - outside_temp) / outside_temp
         root = np.sqrt(9.81 * self.window_height * temp_gradient)
         window_area = self.window_height * self.opening_length * self.number_of_windows
-        return (3600 / (3 * room.volume)) * self.cd_b * window_area * root
+        return (3600 / (3 * room.volume)) * self._cd_b * window_area * root
 
 
 @dataclass(frozen=True)