feat: Begins thermal balance point

Sources/Routes/Models/HeatingBalancePoint.swift

@@ -1,6 +1,11 @@
 public enum HeatingBalancePoint {
 
+  public static let description: String = """
+  Calculate the heating balance point.
+  """
+
   public enum Mode: String, CaseIterable, Codable, Equatable, Sendable {
+    case economic
     case thermal
   }
 
@@ -13,14 +18,14 @@ public enum HeatingBalancePoint {
       public let capacityAt47: Double?
       public let capacityAt17: Double?
       public let heatingDesignTemperature: Double
-      public let buildingHeatLoss: Double
+      public let buildingHeatLoss: HeatingBalancePoint.HeatLoss
 
       public init(
         systemSize: Double,
         capacityAt47: Double? = nil,
         capacityAt17: Double? = nil,
         heatingDesignTemperature: Double,
-        buildingHeatLoss: Double
+        buildingHeatLoss: HeatingBalancePoint.HeatLoss
       ) {
         self.systemSize = systemSize
         self.capacityAt47 = capacityAt47
@@ -47,4 +52,15 @@ public enum HeatingBalancePoint {
       }
     }
   }
+
+  public enum HeatLoss: Codable, Equatable, Sendable {
+
+    public enum Mode: String, CaseIterable, Codable, Equatable, Sendable {
+      case estimated
+      case known
+    }
+
+    case known(btu: Double)
+    case estimated(squareFeet: Double)
+  }
 }