Kokonaislämmönläpäisy

Kokonaislämmönläpäisy, often referred to as the U-value or overall heat transfer coefficient, is a measure of how effectively a building component or structure prevents heat flow. It quantifies the rate of heat transfer through a unit area of the component for a unit temperature difference between the two sides. A lower U-value indicates better thermal insulation, meaning less heat is lost or gained.

The U-value is the reciprocal of the total thermal resistance (R-value). Thermal resistance considers the insulating properties of all the layers within a building component, such as insulation materials, bricks, plaster, and air gaps. Each material has its own thermal conductivity, which determines how easily heat passes through it. By summing the thermal resistances of all layers, the total thermal resistance is obtained, and its inverse gives the U-value.

In building physics, kokonaislämmönläpäisy is a crucial parameter for assessing the energy efficiency of buildings. It is used in calculations to determine heating and cooling loads, estimate energy consumption, and compare the performance of different construction materials and designs. Building regulations often specify maximum allowed U-values for various building elements like walls, roofs, and windows to ensure a minimum level of thermal performance.

Factors influencing the U-value include the type and thickness of insulation used, the materials of the structural elements, the presence of thermal bridges (areas where insulation is interrupted, leading to increased heat transfer), and the performance of windows and doors. Accurate calculation and application of U-values are essential for creating comfortable and energy-efficient indoor environments, reducing greenhouse gas emissions, and lowering energy costs.