4.1 The use of heat flux transducers on building envelope components provides the user with a means for performing in-situ heat flux measurements. Accurate translation of the heat flux transducer output requires a complete understanding of the factors affecting its output, and a standardized method for determining the heat flux transducer sensitivity for the application of interest.

4.2 The sensitivity of the heat flux transducer is determined primarily by the sensor construction and temperature of operation and the details of the application, including geometry, material characteristics, and environmental factors.

Note 1-Practice C1046 includes an excellent description of heat flux transducer construction.

4.3 The presence of a heat flux transducer is likely to alter the heat flux that is being measured. To determine the heat flow that would occur in the absence of the transducer, it is necessary to either:

4.3.1 Ensure that the installation is adequately guarded (1).³

4.3.2 Adjust the results based on a detailed model or numerical analysis. Such analysis is beyond the scope of this practice, but details can be found in (2-6).

4.3.3 Use the empirically measured heat flux transducer sensitivity measured under conditions that adequately simulate the conditions of use in the final application.

4.4 There are several methods for determining the sensitivity of heat flux transducers, including Test Methods C177, C518, C1114, and C1363. The selection of the appropriate procedure will depend on the required accuracy and the physical limitations of available equipment.

4.5 This practice describes techniques to establish uniform heat flow normal to the heat flux transducer for the determination of the heat flux transducer sensitivity.

4.6 The method of heat flux transducer application must be adequately simulated or duplicated when experimentally determining the heat flux transducer sensitivity. The two most widely used application techniques are to surface-mount the heat flux transducer or to embed the heat flux transducer in the insulation system.

Note 2-The difference between the sensitivity under uniform normal heat flow versus that for the surface-mounted or embedded configurations has been demonstrated using multiple mathematical techniques (7-9).