ASTM C1784-13

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 product containing PCM or composite (such as micro- or macro-encapsulated PCM); or as a system, comprising arrays or assemblies of PCM products.

5.6.1 PCM Active Range, that is temperatures over which the phase transitions occur, for both melting and freezing of the PCM product or composites containing PCMs.

5.6.2 Specific heat of the fully melted and fully frozen product, defined outside the PCM Active Range.

5.6.3 Enthalpy change as a function of temperature, h(T), including both sensible and latent components.

5.6.4 Enthalpy plot—a histogram or table that indicates the change in enthalpy associated with incremental temperature changes that span the tested temperature range.

5.6.5 Enthalpy of phase transition during the PCM melting and freezing processes in materials and composites containing PCMs.

5.7.1 Imprecise PCM Active Range—PCMs in general do not have precise melting or freezing temperatures, and the entire active temperature range, from the beginning to the end of phase transitions, must be determined.

5.7.3 Sub-cooling—Occurs when the specimen cools below its nominal freezing temperature before it actually begins to freeze, thus exhibiting an unusual enthalpy-temperature curve. Solid-liquid and solid-solid phase changes are often dependent on heating and cooling rate.

5.7.4 Hysteresis—Occurs when a specimen heated from one temperature to another, and then returned to the original temperature, absorbs more (or less) heat at any particular temperature during the heating stage than it releases during cooling.

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.

1.5 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 enthalpy 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 enthalpy 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 enthalpy stored within the plate heat flux transducers and any material placed between the test specimen and the HFMA plates must be performed following 1.8 This test method applies to PCMs and composites, products and systems incorporating PCMs, including: 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 and health practices and determine the applicability of regulatory limitations prior to use.