Standard Test Method for Predicting Long-Term Thermal Resistance of Closed-Cell Foam Insulation
Rigid gas-filled closed-cell foam insulations include all cellular plastic insulations which rely on a blowing agent (or gas), other than air, for thermal resistance values. At the time of manufacture, the cells of the foam usually contain their highest percentage of blowing agent and the lowest percentage of atmospheric gases. As time passes, the relative concentrations of these gases change due primarily to diffusion. This results in a general reduction of the thermal resistance of the foam due to an increase in the thermal conductivity of the resultant cell gas mixture. These phenomena are typically referred to as foam aging.
For some rigid gas-filled closed-cell foam insulation products produced using blowing agent gases that diffuse very rapidly out of the full-thickness foam product, such as expanded polystyrene, there is no need to accelerate the aging process.
5.1.2 Physical gas diffusion phenomena occur in three dimensions. The one-dimensional form of the diffusion equations used in the development of this practice are valid only for planar geometries, that is, for specimens that have parallel faces and where the thickness is much smaller than the width and much smaller than the length.
Note 2—Please see Appendix X3 for a discussion of the theory of accelerated aging via thin slicing.
Note 3—Theoretical and experimental evaluations of the aging of insulation in radial forms, such as pipe insulation, have been made. (6) However, these practices have not evolved to the point of inclusion in the test standard.
The change in thermal resistance due to the phenomena described in 5.1 usually occurs over an extended period of time. Information regarding changes in the thermal resistance of these materials as a function of time is required in a shorter period of time so that decisions regarding formulations, production, and comparisons with other materials can be made.
Specifications C 578, C 591, C 1029, C 1126 and C 1289 on rigid closed-cell foams measure thermal resistance after conditioning at 23 ± 1°C (73 ± 2°F) for 180 ± 5 days from the time of manufacture or at 60 ± 1°C (140 ± 2°F) for 90 days. This conditioning can be used for comparative purposes, but is not sufficient to describe long-term thermal resistance. This requirement demonstrates the importance of the aging phenomena within this class of products.
The Prescriptive Method in Part A provides long-term thermal resistance values on a consistent basis for a variety of purposes, including product evaluation, specifications, or product comparisons. The consistent basis for these purposes is provided by a series of specific procedural constraints, which are not required in the Research Method described in Part B. The values produced by the Prescriptive Method correspond to the thermal resistance at an age of five years, which corresponds closely to the average thermal resistance over a 15-year service life (7, 8).
It is recommended that any material standard that refers to C 1303 to provide a product rating for long-term thermal resistance specify the Part A Test Method of C 1303.
The Research Method in Part B provides a relationship between thermal conductivity, age, and product thickness. The calculation methods given in Part B can be used to predict the resistance at any specific point in time as well as the average resistance over a specific time period.
Note 4—The 5-year aged values produced in Part A can be derived from the Part B data only if all other Part A requirements are met.
This test method addresses three separate elements relating to the aging of rigid closed-cell plastic foams.
Specimen Preparation—Techniques for the preparation of thin flat specimens, including their extraction from the “as manufactured” product, and the measurement of specimen thickness are discussed.
Measurement of the Thermal Resistance—Thermal resistance measurements, taken at scheduled times, are an integral part of the test method.
Interpretation of Data—Procedures are included to properly apply the theory and techniques to achieve the desired goals.
1.1 This test method covers a procedure for predicting the long-term thermal resistance (LTTR) of unfaced or permeably faced rigid gas-filled closed-cell foam insulations by reducing the specimen thickness to accelerate aging under controlled laboratory conditions (1-5) .
1.2 Rigid gas-filled closed-cell foam insulation includes all cellular plastic insulations manufactured with the intent to retain a blowing agent other than air.
1.3 This test method is limited to unfaced or permeably faced, homogeneous materials. This method is applied to a wide range of rigid closed-cell foam insulation types, including but not limited to: extruded polystyrene, polyurethane, polyisocyanurate, and phenolic. This test method does not apply to impermeably faced rigid closed-cell foams or to rigid closed-cell bun stock foams.
Note 1—See Note 7 for more details regarding the applicability of this test method to rigid closed-cell bun stock foams.
1.4 This test method utilizes referenced standard test procedures for measuring thermal resistance. Periodic measurements are performed on specimens to observe the effects of aging. Specimens of reduced thickness (that is, thin slices) are used to shorten the time required for these observations. The results of these measurements are used to predict the long-term thermal resistance of the material.
1.5 The test method is given in two parts. The Prescriptive Method in Part A provides long-term thermal resistance values on a consistent basis that can be used for a variety of purposes, including product evaluation, specifications, or product comparisons. The Research Method in part B provides a general relationship between thermal conductivity, age, and product thickness.
1.5.1 To use the Prescriptive Method, the date of manufacture must be known, which usually involves the cooperation of the manufacturer.
1.6 The values stated in SI units are to be regarded as the standard. The inch-pound values given in parentheses are for information only.
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 and health practices and determine the applicability of regulatory limitations prior to use.
1.8 Table of Contents:
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