This service offers precise in-situ measurement of thermal transmittance (U-value) and thermal resistance (R-value) for opaque and transparent building envelope components (e.g. walls, façades, windows), under realistic environmental conditions. The measurements are conducted in the NTUA LivingLab pilot facility, which simulates real-world building performance through controlled thermal zones and a modular, reconfigurable envelope system.

The U-value represents the overall heat transfer coefficient of a material or construction element, while the R-value indicates its thermal resistance. These are key indicators for energy performance assessments and building regulation compliance. Performing these measurements in-situ, as opposed to in a laboratory, provides more realistic and application-relevant results, especially for systems intended for on-site construction or prefabricated modules.

The service uses internationally standardized methods:

• ISO 9869 for steady-state in-situ measurements of thermal resistance and transmittance in building elements.

• ASTM C1155 for determining thermal resistance based on temperature gradients and surface heat flux data.

The procedure involves mounting heat flux sensors and temperature probes on the interior and exterior surfaces of the component being tested. Continuous data logging is performed over a period of several days (or longer) to capture variations caused by diurnal temperature changes and occupancy-related dynamics.

Both opaque walls and window systems can be tested, provided the component is installed into one of the dedicated modular wall or glazing sections of the LivingLab. The service is ideal for manufacturers, researchers, and product developers aiming to demonstrate the real-world thermal performance of their materials or systems, especially those seeking to validate performance claims or support TRL5 technology development.