Add boundary condition coefficient to Surface HT calculation

interfaces.py

@@ -19,9 +19,10 @@ class Interface(ABC):
 
 
 class Surface(Interface):
-    def __init__(self, name: str, area: float):
+    def __init__(self, name: str, area: float, b: float = 1.0):
         self.name = name
         self.area = area
+        self.b = b
 
     @property
     @abstractmethod
@@ -29,7 +30,7 @@ class Surface(Interface):
 
     @property
     def HT(self) -> float:
-        return self.U * self.area
+        return self.b * self.U * self.area
 
 
 class LinearThermalBridge(Interface):
@@ -61,8 +62,9 @@ class LayeredSurface(Surface):
         layers: list[Layer],
         r_surface_1: float,
         r_surface_2: float,
+        b: float = 1.0,
     ):
-        super().__init__(name, area)
+        super().__init__(name, area, b)
         self.layers = layers
         self.r_surface_1 = r_surface_1
         self.r_surface_2 = r_surface_2
@@ -75,8 +77,8 @@ class LayeredSurface(Surface):
 
 
 class FixedUSurface(Surface):
-    def __init__(self, name: str, area: float, u_value: float):
-        super().__init__(name, area)
+    def __init__(self, name: str, area: float, u_value: float, b: float = 1.0):
+        super().__init__(name, area, b)
         self.u_value = u_value
 
     @property