ASTM C1784-20

5.3.1 Applications of PCM in building envelopes take multiple forms, including: dispersed in, or otherwise combined with, a thermal insulation material; a separate object implemented in the building envelope as boards or membranes containing concentrated PCM that operates in conjunction with a thermal insulation material. Both of these forms enhance the performance of the structure when exposed to dynamic, that is, fluctuating, boundary temperature conditions.

5.3.2 PCMs can be studied in a variety of forms: as the original “pure” PCM; as a composite containing PCM and other embedded materials to enhance thermal performance; as a 5.4 This test method describes a method of using a heat flow meter apparatus to determine key properties of PCM products, which are listed below. Engineers, architects, modelers, and others require these properties to accurately predict the in-situ performance of the products (2).

5.5 The objective is generally to conduct a test under temperature conditions that will induce a phase transition (for example, melting or freezing) in the PCM product during the course of the test.

5.6 Determination of thermal storage properties is the objective of this test method, and key properties of interest include the following:

5.7 PCM products often possess characteristics that complicate measurement and analysis of phase transitions during a test. Following are some of the known issues with PCMs:

5.8 The properties measured are determined by fundamental thermophysical properties of the constituent materials of the product, and are thus inherent to the PCM product. The desired thermal performance enhancement, however, will depend strongly on the particular environment, climate, and mode of the actual engineering application of the PCM.

1.2.1 The storage capacity of a PCM is well defined via four parameters: specific heats of both solid and liquid phases, phase change temperature(s) and phase change enthalpy 1.3 To more accurately predict thermal performance, information about the PCM products’ performance under dynamic conditions is needed to supplement the properties (thermal conductivity) measured under steady-state conditions.

1.4 This test method is based upon the HFMA technology used for Test Method C518 but includes modifications for specific heat and enthalpy change measurements for PCM products as outlined in this test method.

1.5 Heat flow measurements are required at both the top and bottom HFMA plates for this test method. Therefore, this test method applies only to HFMAs that are equipped with at least one heat flux transducer on each of the two plates and that have the capability for computerized data acquisition and temperature control systems. Further, the amount of energy flowing through the transducers must be measureable at all points in time. Therefore, the transducer output shall never be saturated during a test.

1.6 This test method makes a series of measurements to determine the thermal energy storage of a test specimen over a temperature range. First, both HFMA plates are held at the same constant temperature until steady state is achieved. Steady state is defined by the reduction in the amount of energy entering the specimen from both plates to a very small and nearly constant value. Next, both plate temperatures are changed by identical amounts and held at the new temperature until steady state is again achieved. The energy absorbed or released by the specimen from the time of the temperature change until steady state is again achieved will be recorded. Using a series of temperature step changes, the cumulative enthalpy stored or released over a certain temperature range is determined.

1.7 Calibration of the HFMA to determine the ‘correction factors’ for the energy stored within the plate heat flux transducers and any material placed between the test specimen and the HFMA plates must be performed following Annex A1. These correction factors are functions of the beginning and ending temperatures for each step, as described in Annex A1.

1.8 This test method applies to PCMs and composites, products and systems incorporating PCMs, including those with PCM dispersed in or combined with a thermal insulation material, boards or membranes containing concentrated or dispersed PCM, etc. Specific examples include solid PCM composites and products, loose blended materials incorporating PCMs, and discretely contained PCM.

1.9 This test method may be used to characterize material properties, which may or may not be representative of actual conditions of use.

1.10 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.11 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.

1.12 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.