kuumuskadu

Kuumuskadu is Estonian for heat loss and refers to the transfer of thermal energy from a warmer body or environment to a cooler one. In physics and building science, kuumuskadu describes the rate at which a system loses heat to its surroundings. It is typically quantified as a heat flow rate, Q̇, in watts, or as total energy loss, Q, over a period. For steady-state conditions, heat transfer through a boundary is often written as Q̇ = U A ΔT, where U is the overall heat transfer coefficient, A the surface area, and ΔT the indoor–outdoor temperature difference.

Kuumuskadu arises from conduction through solids, convection of air, and radiation between surfaces. In buildings, air leakage and ventilation can dominate loss in airtight designs, while insulation, wall and roof assemblies, and window performance determine other contributions. Thermal bridging, where heat bypasses insulation through structural elements, also adds to kuumuskadu.

Common indicators include the U-value (W/m^2 K) of components, the R-value (m^2 K/W), and the air change rate. The overall building heat loss is often expressed as a heat loss coefficient, in W/K, indicating the heat lost per degree of indoor–outdoor difference.

Mitigation focuses on reducing kuumuskadu and increasing efficiency: thicker or better insulation, sealing, high-performance windows, minimizing thermal bridges, and using heat recovery ventilation to reclaim exhaust heat.

See also: energy efficiency, thermal insulation, building envelope, HVAC, U-value.