5.1 The application of HFTs and temperature sensors to building envelopes provide in-situ data for evaluating the thermal performance of an opaque building component under actual environmental conditions, as described in Practices C1046 and C1155. These applications require calibration of the HFTs at levels of heat flux and temperature consistent with end-use conditions.

5.2 This practice provides calibration procedures for the determination of the heat flux transducer sensitivity, S, that relates the HFT voltage output, E, to a known input value of heat flux, q.

5.2.1 The applied heat flux, q, shall be obtained from steady-state tests conducted in accordance with either Test Method C177, C518, C1363, or C1114.

5.2.2 The resulting voltage output, E, of the heat flux transducer is measured directly using (auxiliary) readout instrumentation connected to the electrical output leads of the sensor.

Note 1: A heat flux transducer (see also Terminology C168) is a thin stable substrate having a low mass in which a temperature difference across the thickness of the device is measured with thermocouples connected electrically in series (that is, a thermopile). Commercial HFTs typically have a central sensing region, a surrounding guard, and an integral temperature sensor that are contained in a thin durable enclosure. Practice C1046, Appendix X2 includes detailed descriptions of the internal constructions of two types of HFTs.

5.3 The HFT sensitivity depends on several factors including, but not limited to, size, thickness, construction, temperature, applied heat flux, and application conditions including adjacent material characteristics and environmental effects.

5.4 The subsequent conversion of the HFT voltage output to heat flux under application conditions requires (1) a standardized technique for determining the HFT sensitivity for the application of interest; and, (2) a comprehensive understanding of the factors affecting its output as described in Practice C1046.

5.5 The installation of a HFT potentially changes the local thermal resistance of the test artifact and the resulting heat flow differs from that for the undisturbed building component. The following techniques have been used to compensate for this effect.

5.5.1 Ensure that the installation is adequately guarded (3). In some cases, an assumption is made that the change in thermal resistance is negligible, particularly for very thin HFTs with a large surrounding guard, or is incalculable (1).

5.5.2 For the embedded configuration, analytical and numerical methods have been used to account for the disturbance of the heat flux due to the presence of the HFT. Such analyses are outside the scope of this practice but details are available in Refs (4-8).

5.5.3 For the surface-mounted configuration, measurement errors have been quantified by Trethowen (9). Empirical calibrations have also been determined by conducting a series of field calibrations or measurements. Such procedures are outside the scope of this practice but details are available in Orlandi et al. (10) and Desjarlais and Tye (11).

1.1 This practice, in conjunction with either Test Method C177, C518, C1114, or C1363, establishes procedures for the calibration of heat flux transducers that are dimensionally thin in comparison to their planar dimensions.

1.1.1 The thickness of the heat flux transducer shall be less than 30 % of the narrowest planar dimension of the heat flux transducer.

1.2 This practice describes techniques for determining the sensitivity, S, of a heat flux transducer when subjected to one dimensional heat flow normal to the planar surface or when installed in a building application.

1.3 This practice shall be used in conjunction with Practice C1046 and Practice C1155 when performing in-situ measurements of heat flux on opaque building components. This practice is comparable, but not identical, to the calibration techniques described in ISO 9869-1.

1.4 This practice is not intended to determine the sensitivity of heat flux transducers used as components of heat flow meter apparatus, as in Test Method C518, or used for in-situ industrial applications, as covered in Practice C1041.

1.5 The text of this standard references notes and footnotes which provide explanatory material. These notes and footnotes (excluding those in tables and figures) shall not be considered as requirements of the standard.

1.6 Units—The values stated in SI units are to be regarded as standard. The values given in parentheses are provided for information only and are not considered standard.

1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.8 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.