Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus

Importancia y uso:

4.1 This test method provides a rapid means of determining the steady-state thermal transmission properties of thermal insulations and other materials with a high level of accuracy when the apparatus has been calibrated appropriately.

4.2 Proper calibration of the heat flow meter apparatus requires that it be calibrated using specimen(s) having thermal transmission properties determined previously by Test Methods C177, or C1114.

Note 1: Calibration of the apparatus typically requires specimens that are similar to the types of materials, thermal conductances, thicknesses, mean temperatures, and temperature gradients as expected for the test specimens.

4.3 The thermal transmission properties of specimens of a given material or product may vary due to variability of the composition of the material; be affected by moisture or other conditions; change with time; change with mean temperature and temperature difference; and depend upon the prior thermal history. It must be recognized, therefore, that the selection of typical values of thermal transmission properties representative of a material in a particular application should be based on a consideration of these factors and will not apply necessarily without modification to all service conditions.

4.3.1 As an example, this test method provides that the thermal properties shall be obtained on specimens that do not contain any free moisture although in service such conditions may not be realized. Even more basic is the dependence of the thermal properties on variables, such as mean temperature and temperature difference. These dependencies should be measured or the test made at conditions typical of use.

4.4 Special care shall be taken in the measurement procedure for specimens exhibiting appreciable inhomogeneities, anisotropies, rigidity, or especially high or low resistance to heat flow (see Practice C1045). The use of a heat flow meter apparatus when there are thermal bridges present in the specimen may yield very unreliable results. If the thermal bridge is present and parallel to the heat flow the results obtained may well have no meaning. Special considerations also are necessary when the measurements are conducted at either high or low temperatures, in ambient pressures above or below atmospheric pressure, or in special ambient gases that are inert or hazardous.

4.5 The determination of the accuracy of the method for any given test is a function of the apparatus design, of the related instrumentation, and of the type of specimens under test (see Section 10), but this test method is capable of determining thermal transmission properties within ± 2 % of those determined by Test Method C177 when the ambient temperature is near the mean temperature of the test (T (ambient) = T (mean) ± 1°C), and in the range of 10 to 40°C. In all cases the accuracy of the heat flow meter apparatus can never be better than the accuracy of the primary standards used to calibrate the apparatus.

4.5.1 When this test method is to be used for certification testing of products, the apparatus shall have the capabilities required in A1.7 and one of the following procedures shall be followed:

4.5.1.1 The apparatus shall have its calibration checked within 24 h before or after a certification test using either secondary transfer standards traceable to, or calibration standards whose values have been established by, a recognized national standards laboratory not more than five years prior to the certification date. The average of two calibrations shall be used as the calibration factor and the specimen(s) certified with this average value. When the change in calibration factor is greater than 1 %, the standard specimen shall be retested and a new average calculated. If the change in calibration factor is still greater than 1 % the apparatus shall be calibrated using the procedure in Section 6.

4.5.1.2 Where both the short and long term stability of the apparatus have been proven to be better than 1 % of the reading (see Section 10), the apparatus may be calibrated at less frequent intervals, not exceeding 30 days. The specimens so tested cannot be certified until after the calibration test following the test and then only if the change in calibration factor from the previous calibration test is less than 1 %. When the change in calibration is greater than 1 %, test results from this interval shall be considered void and the tests repeated in accordance with 4.5.1.1.

4.5.2 The precision (repeatability) of measurements made by the heat flow meter apparatus calibrated as in Section 6.6 normally are much better than ±1 % of the mean value. This precision is required to identify changes in calibration and is desirable in quality control applications.

Subcomité:

C16.30

Referida por:

D7425_D7425M-13R19, C1937-24A, C1071-19, D5930-17, C0800-19, F0433-02R20, C0665-23, C1859-23, D3748-14R19, C1045-19, C0209-20, C1393-19, E1591-20, C0728-17AR22, C1676_C1676M-23, C0726-24, C1427-21, E1530-19, C0549-23, E2336-20, C1014-17, D6744-23, C1290-16R21, C0610-17R23, C0552-22, C0449-07R24, E1091-21, C1667-15R23, C0592-22A, C1482-24E01, C0516-19, C0764-19, E1231-24, C1484-10R18, C1847-21, E0861-13R21, C0553-13R19, C1512-10R20, D4612-16, C0653-24, C0656-17R23, C1126-19, C0739-24, D3575-20, C1534-24, C0196-00R19, C1289-23A, C1470-20, E1730-19, C0591-22, C1149-23, C1046-95R21, C0240-21, C0991-23, C0612-14R19, C0447-15R22, C1558-24, C1224-22, C1410-17R23, C1728-23, C1902-22A, C0533-17R23, D4819-13R21E01, C1086-20, C0534_C0534M-23, C1029-20, C0578-23, C1594-23, C0195-07R24, C1373_C1373M-23, C1058_C1058M-10R23, C0687-18, D5364-14R24, C1617-24, E2684-17, C0680-23A, C1044-24, C0335_C0335M-23, C1130-24, C1114-06R19, C1774-24, C1919-22, C1363-24, C0177-19E01, C1696-20, C1784-20, C1199-22, C1303_C1303M-23

Volúmen:

04.06

Número ICS:

91.120.10 (Thermal insulation of buildings)

Palabras clave:

calibration; error analysis; heat flow meter apparatus, thermal resistance; heat flux; instrument verification; thermal conductivity; thermal testing;