Gesamtwärmedurchgangskoeffizient

GesamtWärmedur... is a term used in building physics to denote the overall thermal transmittance of a building component or of an entire building envelope. It describes how much heat passes through the structure from inside to outside for a given temperature difference. The concept is typically expressed as a U value in W/(m²·K) and serves as a single metric that aggregates the insulating properties of materials, layers, interfaces, and, in some approaches, thermal bridges.

Calculation starts from basic thermal resistance. For a multilayer element, the total thermal resistance is the sum of the internal surface resistance, the resistances of each material layer, and the external surface resistance: R_total = R_si + ΣR_layer + R_se. The overall transmittance is then U = 1 / R_total. For assemblies composed of multiple components, the weighted average U value is used: U_bar = Σ(U_i · A_i) / ΣA_i, where A_i is the area of each component. The heat loss through the envelope under a given ΔT is Q̇ = U · A · ΔT, with A being the component’s area.

Applications include energy performance assessments, building energy certificates, and designing renovations to meet efficiency targets. The concept also underpins calculations that balance heating and cooling needs across climates and building types. It is important to account for thermal bridges, air leakage, and moisture effects, which may require separate corrections or advanced modeling.

Standards and practices typically reference DIN EN ISO 6946 for calculating component thermal resistance and DIN EN ISO 10211 for linear thermal bridges, among other national and regional guidelines. The term emphasizes a holistic view of heat transfer but may simplify complex, dynamic behavior in real buildings. Related concepts include the U value, heat transfer coefficients, and thermal bridging considerations.