commit 68b60841506e8731851e8cb6a8f817647dadc187
Author: omicron <omicron.me@protonmail.com>
Date:   Mon Jun 8 13:54:45 2026 +0200

    Early explorations of calculation primitives

diff --git a/coefficients.py b/coefficients.py
new file mode 100644
index 0000000..58f22b1
--- /dev/null
+++ b/coefficients.py
@@ -0,0 +1,21 @@
+# Thermal conductivity λ in W/(m·K) (min, max)
+THERMAL_CONDUCTIVITY = {
+    "brick": (0.22, 0.81),
+    "concrete": (1.3, 1.3),
+    "reinforced_concrete": (1.7, 1.7),
+    "plaster": (0.52, 0.52),
+    "pir": (0.021, 0.026),
+    "pur": (0.022, 0.028),
+    "xps": (0.028, 0.044),
+    "mineral_wool": (0.031, 0.044),
+}
+
+THERMAL_CONDUCTIVITY_LOW = {k: v[0] for k, v in THERMAL_CONDUCTIVITY.items()}
+THERMAL_CONDUCTIVITY_HIGH = {k: v[1] for k, v in THERMAL_CONDUCTIVITY.items()}
+
+
+# Surface resistances in m²K/W
+RSI_HORIZONTAL = 0.13
+RSI_UPWARD = 0.10
+RSI_DOWNWARD = 0.17
+RSE = 0.04
diff --git a/interfaces.py b/interfaces.py
new file mode 100644
index 0000000..23b7716
--- /dev/null
+++ b/interfaces.py
@@ -0,0 +1,44 @@
+from abc import ABC, abstractmethod
+from dataclasses import dataclass
+
+
+@dataclass
+class Layer:
+    thermal_coefficient: float
+    thickness: float
+
+    @property
+    def R(self):
+        return self.thickness / self.thermal_coefficient
+
+
+@dataclass
+class Interface(ABC):
+    name: str
+    area: float
+
+    @property
+    @abstractmethod
+    def U(self) -> float: ...
+
+
+@dataclass
+class LayeredInterface(Interface):
+    layers: list[Layer]
+    r_surface_1: float
+    r_surface_2: float
+
+    @property
+    def U(self) -> float:
+        R_layers = sum(layer.R for layer in self.layers)
+        R = self.r_surface_1 + R_layers + self.r_surface_2
+        return 1 / R
+
+
+@dataclass
+class FixedUInterface(Interface):
+    u_value: float
+
+    @property
+    def U(self) -> float:
+        return self.u_value