feat: Adds hydronic system pressure calculator.

Sources/ViewController/Extensions/String+units.swift

@@ -0,0 +1,3 @@
+public extension String {
+  static let fahrenheit = "°F"
+}

Sources/ViewController/HomePage.swift

@@ -61,6 +61,12 @@ struct HomePage: HTML, Sendable {
         svg: .droplets,
         route: .psychrometrics(.index)
       )
+      group(
+        label: "Hydronic System Pressure",
+        description: HydronicSystemPressure.description,
+        svg: .circleGauge,
+        route: .hydronicSystemPressure(.index)
+      )
     }
   }
 

Sources/ViewController/Live.swift

@@ -133,6 +133,15 @@ extension ViewController: DependencyKey {
           return HVACSystemPerformanceResult(response: response)
         }
 
+      case let .hydronicSystemPressure(route):
+        switch route {
+        case .index:
+          return request.respond(HydronicSystemPressureForm(response: nil))
+        case let .submit(request):
+          let response = try await request.respond(logger: logger)
+          return HydronicSystemPressureResponse(response: response)
+        }
+
       case let .moldRisk(route):
         switch route {
         case .index:

Sources/ViewController/Views/HydronicSystemPressure.swift

@@ -0,0 +1,74 @@
+import Elementary
+import ElementaryHTMX
+import PsychrometricClient
+import Routes
+import Styleguide
+
+struct HydronicSystemPressureForm: HTML, Sendable {
+  let response: HydronicSystemPressure.Response?
+
+  typealias Key = HydronicSystemPressure.Request.FieldKey
+
+  var content: some HTML {
+    FormHeader(label: "Hydronic System Pressure", svg: .circleGauge)
+
+    form(
+      .hx.post(route: .hydronicSystemPressure(.index)),
+      .hx.target("#result")
+    ) {
+      div(.class("space-y-6")) {
+        div(.class("grid grid-cols-2 gap-4")) {
+          LabeledContent(label: "Height (ft.)") {
+            Input(id: Key.height, placeholder: "Building height")
+              .attributes(.type(.number), .min("0.1"), .step("0.1"), .autofocus, .required)
+          }
+
+          LabeledContent(label: "Water Temperature (\(String.fahrenheit))") {
+            Input(id: Key.waterTemperature, placeholder: "Temperature (optional)")
+              .attributes(.type(.number), .min("32.0"), .step("0.1"))
+          }
+        }
+
+        Note {
+          """
+          Water temperature should be the coldest water temperature the system sees, which for boilers will be
+          when the system is filled with water.
+          """
+        }
+
+        div {
+          SubmitButton(label: "Calculate System Pressure")
+        }
+      }
+    }
+
+    div(.id("result")) {
+      if let response {
+        HydronicSystemPressureResponse(response: response)
+      }
+    }
+  }
+}
+
+struct HydronicSystemPressureResponse: HTML, Sendable {
+  let response: HydronicSystemPressure.Response
+
+  var content: some HTML {
+    ResultContainer(reset: .hydronicSystemPressure(.index)) {
+      ResultBox {
+        div(.class("grid grid-cols-2")) {
+          VerticalGroup(label: "Pressure", value: "\(double: response.pressure)", valueLabel: "psi")
+          VerticalGroup(
+            label: "Water Density",
+            value: "\(double: response.waterDensity.value)",
+            valueLabel: response.waterDensity.units.rawValue
+          )
+        }
+      }
+      WarningBox(warnings: response.warnings)
+      Note {
+        "Expansion tank pressure should match system fill pressure."
+      }
+    }
+  }
+}