U = L2D/H
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Pick a preset or draw a shape. Then paint boundary conditions and Solve.
RESULTS
R total
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L2D
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heat flow Φ
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fRsi
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min surf °C
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Press ▶ SOLVE in the Solve tab to compute. Results appear here.
SYMBOLS — what these mean
- U
- thermal transmittance, W/m²K — heat lost per m² of element for each 1 K of inside-to-outside temperature difference. Lower is better.
- R
- total thermal resistance, m²K/W — the insulating value of the build-up, R = 1/U. Higher is better.
- L2D
- thermal coupling coefficient, W/m·K — the full 2-D heat flow per metre of section length per 1 K (EN ISO 10211): L2D = Φ / |ΔT|. U follows as U = L2D/H, where H is the section height (the dimension across the heat flow). This is the whole-section average U; for a plain layered wall it equals the hand-calculated 1-D value.
- Φ (phi)
- heat-flow rate, W/m — total heat crossing the section per metre of its run (always reported as a magnitude).
- ΔT
- driving temperature difference, K — taken from the boundary conditions you actually painted on edges, not from unused presets in the library. U uses its magnitude, so a warm-exterior (summer) case gives a positive U just like winter — only the flow direction reverses.
- probe U vs panel U
- the ⊥ probe reports a local 1-D value along one cut, R = Σ(d/λ) + Rsi + Rse (surface films included). The panel U = L2D/H is the 2-D average. They match for an unbridged wall; across a bridge the panel value is the one to quote for the whole element.
- Ψ (psi)
- linear thermal bridge (linear thermal transmittance), W/m·K — the extra heat flow per metre of a junction beyond the plain elements it connects, Ψ = L2D − Σ(Ui·bi) (EN ISO 10211).
- fRsi
- temperature factor, 0–1 — the coldest inner-surface temperature expressed as a fraction of the full inside-to-outside drop. ≥ 0.75 keeps the surface clear of the mould / condensation risk threshold.
- min surf
- coldest temperature on the inner surface, °C — where condensation would first appear.
METHOD & THEORY
3-D · VOXEL SOLVE