# https://en.wikipedia.org/wiki/Thermal_conductivity

fn heat_transfer(λ: ThermalConductivity,
                 wall_area: Area,
                 thickness: Length,
                 temp_hot: Temperature,
                 temp_cold: Temperature) -> Power =
    λ × wall_area × (temp_hot - temp_cold) / thickness

let λ_concrete: ThermalConductivity = 0.92 W / (m · K)

print(heat_transfer(λ_concrete, 3 m × 2 m, 20 cm, from_celsius(20), from_celsius(0)))
