Warmteretentie

Warmteretentie is the ability of a material or system to retain thermal energy, i.e., to store heat and release it later. In building physics it is closely related to the concepts of thermal mass and thermal inertia. The amount of sensible heat stored is proportional to mass, specific heat capacity and the temperature change, described by Q = m·c·ΔT. Materials with high density and high specific heat, such as concrete or water, store more heat for a given temperature change. Latent heat storage using phase-change materials adds additional capacity at a chosen temperature.

The degree of warmteretentie depends on temperature, material properties and geometry. Thermal mass is effective when temperature fluctuations are gradual, allowing stored heat to moderate indoor temperatures. Insulation and low overall heat transfer, often expressed as a low UA value, reduce heat loss and extend how long stored heat persists. Other influencing factors include moisture content, surface emissivity and the use of encapsulated phase-change materials.

Applications include enhancing indoor comfort and reducing heating demand in buildings, passive solar design, and solar-thermal or district heating systems where heat is stored for later use. It is also employed in thermal energy storage systems sometimes referred to as thermal batteries.

Measuring warmteretentie involves storage capacity (sensible and latent) and the time constant for heat loss. A common rough estimate for the time constant is τ ≈ (ρ·c·V)/(U·A), where ρ is density, c specific heat, V volume, and U and A the overall heat transfer coefficient and area. This topic intersects materials science, architectural design and energy systems.