Composite Wall R-value / U-value Calculator mechanism

Model scope

The mathematical model is standard under the stated unit assumptions, but the specification needs an explicit input contract for conductivity-based layers versus direct insulation R-values, a q sign convention, and validation rules. The honest label should also state steady-state one-dimensional conduction, no thermal bridging, and whether contact resistances, moisture effects, thermal radiation within cavities, and temperature-dependent material properties are excluded.

• The formulas Rtotal=Σ(L/k)+Rfilms and U=1/Rtotal are standard for steady-state, one-dimensional conduction when all quantities use compatible units.
• The data specification mentions both material thermal conductivity k and insulation R-values, but does not define whether a layer may be entered as an R-value. If an insulation R-value is used, it must be added directly and must not also be calculated from L/k or double-counted.
• q=U·A·ΔT correctly gives signed heat-transfer rate in watts, but the required sign convention and whether the displayed result is signed heat flow or absolute heat loss/gain are unspecified.
• The specification does not state whether Rfilms means exactly one interior and one exterior surface resistance, nor whether contact resistances are excluded.

Units and conventions

• For SI calculations, layer thickness L is in metres, thermal conductivity k is in W/(m·K), film resistances and total R-value are in m²·K/W, U is in W/(m²·K), area A is in m², ΔT is in K or °C difference, and q is in W.
• A temperature difference of 1 K equals a temperature difference of 1 °C; absolute Celsius temperatures must not be substituted for ΔT.
• Thickness values supplied in millimetres must be converted to metres before dividing by k when k is in W/(m·K).
• Rfilms are assumed to be additive surface resistances in m²·K/W.

Inspectable vector

One of 4 source-bound review vectors:

{
  "inputs": {
    "layers": [
      {
        "material": "brick",
        "thickness": 0.1,
        "thickness_unit": "m",
        "k": 0.5,
        "k_unit": "W/(m·K)"
      },
      {
        "material": "mineral wool insulation",
        "thickness": 0.1,
        "thickness_unit": "m",
        "k": 0.04,
        "k_unit": "W/(m·K)"
      },
      {
        "material": "gypsum board",
        "thickness": 0.012,
        "thickness_unit": "m",
        "k": 0.12,
        "k_unit": "W/(m·K)"
      }
    ],
    "film_resistances": {
      "inside": 0.13,
      "outside": 0.04,
      "unit": "m²·K/W"
    },
    "area": 40,
    "area_unit": "m²",
    "delta_T": 25,
    "delta_T_unit": "K"
  },
  "expected_outputs": {
    "Rtotal": 2.97,
    "Rtotal_unit": "m²·K/W",
    "U": 0.3367003367,
    "U_unit": "W/(m²·K)",
    "q": 336.7003367,
    "q_unit": "W"
  },
  "working": "Brick: L/k = 0.1/0.5 = 0.2 m²·K/W. Insulation: 0.1/0.04 = 2.5 m²·K/W. Gypsum: 0.012/0.12 = 0.1 m²·K/W. Films: 0.13 + 0.04 = 0.17 m²·K/W. Rtotal = 0.2 + 2.5 + 0.1 + 0.17 = 2.97 m²·K/W. U = 1/2.97 = 0.3367003367 W/(m²·K). q = U·A·ΔT = 0.3367003367·40·25 = 0.3367003367·1000 = 336.7003367 W."
}

Failure boundary

BREAK_CLAIMED · SELF_FLAGGED

A zero thermal-conductivity input causes division by zero in L/k, producing undefined R-value, U-value, and heat flow. The instrument must reject k=0 rather than propagate a numeric result.

Other records

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json
• evidence-tranche4/tranche4-results.json
• BOUNDARY_HAZARD_CATALOG.json