Overview
EN ISO 8990:1996 (ISO 8990:1994) - published by CEN/ISO - specifies principles and minimum requirements for laboratory determination of steady‑state thermal transmission properties of building and similar industrial components using a calibrated hot box or a guarded hot box. The standard describes apparatus design principles (without mandating a single design), measurement techniques, calibration and performance evaluation, and required data reporting. It is primarily intended for laboratory testing of large, often inhomogeneous specimens (walls, floors, ceilings, full‑scale components) and excludes tests involving mass transfer through the specimen during the test.
Key topics and technical requirements
- Scope and purpose: Measure total heat transfer through a specimen under steady‑state conditions to derive thermal transmittance (U‑value) and thermal resistance (R‑value) for prescribed boundary conditions.
- Apparatus principles: Two alternative methods - guarded hot box (GHB) and calibrated hot box (CHB) - both reproduce hot and cold environments on either side of the specimen; the standard lays down minimum design, metering/guard box functions, specimen frames and chambers.
- Measurement elements: Steady‑state air and surface temperatures, power input to the hot side, and corrections for box wall losses, flanking losses and peripheral losses. The standard explains environmental temperature concepts combining radiant and air temperatures.
- Calibration & performance: Calibration specimens and procedures are required to quantify measurement accuracy and to evaluate imbalance resolution and box wall losses. Typical achievable accuracy for homogeneous specimens is on the order of ±5%, but each apparatus must be evaluated individually.
- Limitations: Not applicable where mass transfer (moisture migration) occurs during the test; results depend on specimen geometry, boundary conditions, temperatures, air velocities and humidity and must reflect intended application conditions.
Applications and users
- Who uses it: Accredited test laboratories, manufacturers of building envelope products (walls, roofs, windows), building physicists, R&D centres, regulatory bodies and consultants verifying thermal performance or compliance with regulations.
- Practical uses: Determining U‑values for compliance, validating thermal models, comparing insulation systems, product development and quality control for components that are large or non‑homogeneous and where whole‑assembly thermal behaviour is required.
Related standards
- ISO 8990 references other measurement standards (e.g., ISO 7345) for definitions and physical quantities. EN ISO 8990:1996 is the CEN adoption of ISO 8990:1994 and should be used alongside applicable national and international standards for testing, calibration and reporting.
Keywords: EN ISO 8990:1996, calibrated hot box, guarded hot box, thermal transmission properties, steady‑state, U‑value, thermal resistance, laboratory measurement, building components.
