ISO 15099:2003

Overview - ISO 15099:2003 (Thermal performance of windows, doors and shading devices)

ISO 15099:2003 provides detailed calculation procedures for the thermal and optical transmission properties of fenestration systems. The standard defines algorithms and methods to determine key performance metrics such as thermal transmittance (U‑value), total solar energy transmittance (Solar τ) and visible transmittance for windows, doors and shading devices. It covers single and multiple glazing, low‑emissivity and solar‑reflective coatings, gas fills, metallic and non‑metallic spacers, frames of any material, tilted products, projecting systems and slat‑type shading.

Key topics and technical requirements

• Detailed energy-balance models: Solves energy balance for each glazing layer and cavity to predict actual pane temperatures and heat flows (the standard notes this is the only ISO method that fully accounts for these interactions).
• Optical transmission calculations: Procedures for computing direct, diffuse and total solar and visible transmittance through multi‑layer glazing and shading devices.
• Frame and edge effects: Numerical methods for frame thermal transmittance, area and linear Ψ values, and meshing/geometric representation.
• Shading device models: Definitions and optics for slat‑type and other shading devices, including ventilation effects and combined thermal/solar impacts.
• Boundary conditions and heat transfer: Prescribed reference and general boundary conditions, convective and longwave radiative heat transfer, and combined convective-radiative approaches.
• Normative data and annexes: Includes gas property values, solution techniques for multi‑layer optics, and example calculations for shading optics.

Applications and who uses ISO 15099

• Window and door manufacturers - to model product thermal performance during design and to support datasheets.
• Building energy modelers and consultants - for accurate fenestration inputs in whole‑building simulations.
• Software developers - implementing detailed fenestration algorithms in thermal and energy simulation tools (standard intended for computer implementation).
• Testing laboratories and certification bodies - to compare calculated performance with hot‑box and other test methods and to produce standardized performance indices.
• Architects, facade engineers and regulators - when selecting glazing, low‑e coatings, frames and shading for energy compliance and daylighting.

Related standards

ISO 15099 references and complements standards such as ISO 9050 (glazing optical properties), ISO 10077‑2 (frame numerical methods), ISO 12567‑1 (hot box thermal transmittance) and standards on heat transfer and solar irradiance (e.g., ISO 7345, ISO 9845‑1). Use ISO 15099 when a detailed, physically consistent calculation of fenestration thermal and solar performance is required.