Where a product is already subject to a product specification that describes procedures for the measurement of the aged 90/90 fractile thermal conductivity or thermal resistance of the c
Terms and definitions
For the purposes of this document, the terms and definitions given in EN ISO 7345, EN ISO 9288,
EN ISO 9229 and the following apply
3.1.1 declared thermal performance value of thermal performance, declared by a manufacturer, which is derived from measured values under the specified conditions and rules given in this standard
3.1.2 indentation concave depression in the surface of the facing (foil) such that shallow air pockets are created when the surface is in contact with a smooth flat plate
The core thermal resistance of the product is defined as the thermal resistance measured from one face to the other at the specified thickness, without accounting for the effects of any low emissivity outer surfaces or adjacent air spaces.
3.1.4 emissivity ratio of the energy radiated by a surface relative to the energy radiated by a blackbody at the same temperature
3.1.5 reflective surface low emissivity surface surface which has a low emissivity at the appropriate wavelength within the temperature range found in building elements
3.1.6 reflective insulation insulation product which has one or both external face(s) comprising a reflective surface
Note 1 to entry It is a measure of a material's ability to radiate heat.
Symbols and units
For the purposes of this standard, the following symbols and units apply
U sensor signal V ε emissivity - λ thermal conductivity W/(mãK) Φ heat flow rate W Ψ linear thermal transmittance W/(mãK) Δθ temperature difference K
90 % fractile with a confidence level of 90 %"
Product classification
This clause outlines the different generic product types referenced by the standard, with product type defined specifically for selecting the most suitable test method It is important to note that the product type number does not indicate a generic species of product To assign a product to a specific type, one must follow the flow charts provided in Annexes A, B, and C, in conjunction with sections 4.2, 4.3, and 4.4.
In sections 4.2, 4.3, and 4.4, the product type is identified based on its compressibility to ensure flat parallel surfaces, which necessitates the elimination of measurable air gaps between the specimen and the hot and cold plates of the testing apparatus without significantly reducing the specimen's overall thickness According to the weighted plate method outlined in EN 823:1994, it is essential to have no residual air spaces between the weighted plate and the specimen surface The weight of the plate used for thickness measurement must be the minimum required to eliminate air gaps, and the thickness measured under this plate will be utilized for assessing the core thermal resistance, as documented in the test report.
Product Type 1
A product is classified as Type 1 if it features regular geometry with parallel faces or is compressible, allowing it to fit between the hot and cold plates of the apparatus without significantly altering its core thermal properties This classification is applicable when the product's surfaces are smooth and flat, exhibiting no noticeable depth of pattern or indentation.
Examples of insulation materials include foam insulation with aluminum foil on both sides, mineral wool faced with aluminum foil, and multi-foil insulation products that are stitched or seamed only at the edges, featuring substantially flat and parallel faces.
2 low emissivity surface or surfaces
NOTE The emissivity of each of the outer surfaces can be different or the product can be faced on only one side
Figure 1 — Example of insulation material with reflective facing on each side
Product Type 2
A product is classified as Type 2 if it features regular geometry with parallel faces or is compressible, allowing it to fit between the hot and cold plates of the test apparatus without altering its core thermal properties The surfaces must not be flat and smooth, and can include indentations of less than 5 mm in depth, measured using the pin and plate method outlined in EN 823:1994, subclause B.1, or an equally accurate alternative The pin should be positioned at the lowest point of any indentation without penetrating the surface.
NOTE If the indentations are 5 mm or greater, it is product Type 3
EXAMPLES Including, but not limited to, some types of bubble foil insulation with reflective surfaces (see Figure 2)
Figure 2 — Example of bubble foil insulation with reflective surfaces
Product Type 3
A product is classified as Type 3 if it features irregular thickness geometry, lacks flat parallel faces, or cannot be compressed to achieve flat and parallel faces without altering its core thermal properties Additionally, Type 3 products are not measured using a guarded hot plate or heat flow meter apparatus.
NOTE 1 Its surfaces might or might not have indentations, the depth of which is not limited to any specific value
Stitched multi-foil reflective insulation products often feature seams or sealed pockets made from reflective foil sheets, as illustrated in Figure 3.
1 insulation layer(s) between foil – such as foam or wadding
2 welded or stitched fabrication feature
3 low emissivity external surface or surfaces
Figure 3 – Example of stitched multi-foil insulation
Product Type 4
Product Type 4 is a thin film or sheet, measuring less than 2 mm in thickness, that can be utilized alone or in multiple layers It features a low emissivity surface designed to enhance the thermal resistance of surrounding or enclosed air spaces, although it does not possess significant thermal resistance on its own.
Left picture: 2-layer foil system (1 and 2) with one air layer in-between
Right picture: 3-layer foil system (foil layers 1, 2 and 3) with two air layers in between
Figure 4 – Example of multiple layers of product Type 4 under flooring
General
In addition to the general requirements for testing thermal performance in accordance with EN 12664,
The thermal performance measurement of reflective insulation products, including Type 1, Type 2, and Type 3, must adhere to the specific mounting requirements outlined in sections 5.4 to 5.8 of EN 12667 and EN ISO 8990 Additionally, it is essential to measure the thickness of the specimens during this process.
Thickness measurement
For products with a nominal declared thickness exceeding 2 mm, thickness must be determined according to the procedures outlined in EN 823, utilizing the lowest weight of plate allowed by the test method to minimize air gaps; however, the minimum weight of plate can be adjusted from 50 Pa to 25 Pa In contrast, the thickness of thin films and sheets with a nominal declared thickness of less than 2 mm does not require measurement.
5.3.1 Size and number of specimens
The specimen size must be suitable for the apparatus used In cases where harmonised product specifications are not available, a minimum of three samples from at least three different production batches should be tested to allow for statistical analysis of thermal performance If a harmonised product specification is available, the guidelines from that standard should be adhered to.
All test specimens, except for emissivity measurements which have specific conditioning requirements, must be stored for a minimum of 6 hours at a temperature of (23 ± 5) °C In the event of a dispute, the specimens should be stored at (23 ± 2) °C and (50 ±).
5) % relative humidity for the time specified in any relevant harmonized product standard, or for a minimum of
Note 5.7.2 outlines the procedure for conditioning specimens intended for Hot Box measurements, particularly when the emissivity of the facing may be affected by aging Additionally, section 5.9 and Annex D detail the specific conditioning and aging requirements necessary for accurate emissivity measurement.
For products supplied in compressed form, it is essential to allow the material to fully recover for at least 6 hours, or longer if the manufacturer recommends it, before conditioning for testing In the event of any disputes, the procedure outlined in EN 823:1994, Annex A must be adhered to.
Determination of thermal resistance – outline
This standard outlines four distinct methods, each suited to various types of reflective insulation materials detailed in Clause 4 The performance measured by these methods yields comparable values, ensuring consistency across different approaches.
Of the four methods, three provide a measurement of thermal resistance as follows:
— METHOD A: Guarded Hot Plate Apparatus meeting the requirements of ISO 8302, EN 1946-2, EN 12664 and EN 12667;
— METHOD B: Heat Flow Meter Apparatus meeting the requirements of ISO 8301, EN 1946-3, EN 12664 and EN 12667;
— METHOD C: Hot Box Apparatus meeting the requirements of EN ISO 8990 and EN 1946-4 (see 5.7) and the fourth method is based upon the measurement of surface emissivity:
— METHOD D: Measurement of emissivity and calculation
The appropriate method for each product type is detailed in sections 5.5 to 5.8, along with flow charts in Annexes A, B, and C To identify the correct product type and testing method, the material's surface must be evaluated as outlined in Clause 4, and this information will be included in the test report.
The declared thermal resistance, R D, must be specified as limit values that encompass at least 90% of production, calculated with a 90% confidence level in accordance with the guidelines outlined in EN ISO 10456.
Determination of core thermal resistance of Product Type 1
5.5.1 Product thickness greater than 20 mm
5.5.1.1 Thermal resistance expected to be greater than 0,5 m²ãK/W
— METHOD A: Measure in a guarded hot plate apparatus, or
— METHOD B: Measure in a heat flow meter apparatus
5.5.1.2 Thermal resistance expected to be 0,5 m²ãK/W or less
— METHOD A: Measure in a guarded hot plate apparatus, or
— METHOD B: Measure in a heat flow meter apparatus
In each case thermocouples shall be attached to the specimen surface (using the procedures specified in
5.5.2 Product thickness less than or equal to 20 mm
5.5.2.1 Thermal resistance expected to be greater than 0,5 m²ãK/W
— METHOD A: Measure in a guarded hot plate apparatus using thermocouples embedded in the hot and cold plates, or
— METHOD B: Measure in a heat flow meter apparatus using the “dummy specimen” technique given in Annex E
5.5.2.2 Thermal resistance expected to be 0,5 m²ãK/W or less
— METHOD A: Measure in a guarded hot plate apparatus using thermocouples attached to the specimen surface (the procedures specified in EN 12664 shall be used), or
— METHOD B: Measure in a heat flow meter apparatus using the “dummy specimen” technique given in Annex E
If thermocouples are to be fixed to aluminium or other metal foil, the bare thermocouple wire shall be electrically isolated from the foil by a strip of thin adhesive tape
5.5.3 For all thicknesses and nominal thermal resistances
As an alternative to the options described in 5.5.1 and 5.5.2 above, any Type 1 product may also be measured using the procedure described as METHOD C in 5.7 below.
Determination of core thermal resistance of Product Type 2
5.6.1 Product Type 2 with surface indentations less than 2 mm in depth
Treat as Product Type 1 (see 5.5 to select appropriate methodology depending upon thickness and expected thermal resistance)
5.6.2 Product Type 2 with surface indentations greater than or equal to 2 mm, but less than 5 mm in depth
Use METHOD A or METHOD B: Measure in a guarded hot plate apparatus or heat flow meter apparatus using thermocouples attached to the specimen surface (using the procedures specified in EN 12664)
To prepare the specimen, fill the indentations with an aqueous gel and apply a thin layer of a low conductivity film, like polyethylene Subsequently, treat the specimen as Product Type 1 to assess core thermal resistance, following the methodology outlined in section 5.5.
5.6.3 Product Type 2 with surface indentations 5 mm in depth or greater
Where the surface indentations are 5 mm in depth or greater, the product shall be treated as if it were Product Type 3 (see 5.7)
5.6.4 For all thicknesses and/or nominal thermal resistances
As an alternative to the options described in 5.6.1 to 5.6.3, any Type 2 product may also be measured using the procedure described as METHOD C in 5.7.
Determination of core thermal resistance of Product Type 3 (METHOD C)
The thermal resistance of an air cavity insulated with a centrally mounted product is measured using a hot box apparatus that meets EN ISO 8990 standards By calculating the thermal resistance of the two air cavities and subtracting this from the total measured thermal resistance, the core thermal resistance of the product is determined.
5.7.2 Determination of the need for specimen conditioning a) Measure the emissivity of the facing "as received" and after conditioning (ageing) using the procedure in Annex D
According to EN 16012:2012+A1:2015 (E), if the difference between two measurements is 0.02 or less, the ageing is deemed negligible, allowing the use of the material as supplied for the hot box test without further ageing Conversely, if the difference in emissivity between the "as received" and aged specimens exceeds 0.02, the insulation material must undergo conditioning before being tested in the hot box.
!D.5.3", taking care not to damage the test specimen
5.7.3 Air cavity and specimen installation
Measure the thermal resistance of an air cavity insulated with a specimen that is representative of the test product including any stitching or welding in the body of the material
4 thermocouples measuring the INSIDE surface temperature of the cavity walls
5 thermocouples measuring the surface temperature of the specimen
Figure 5 — Typical test element used to measure the thermal resistance of an insulated air cavity
This arrangement effectively measures the thermal resistance of an insulated air cavity without requiring the core thermal resistance of the material, emissivity, or cavity geometries Key conditions include using suitable dry materials like plywood or MDF for external walls, ensuring the test specimen and air cavity dimensions are no less than 1 m × 1 m, and maintaining a minimum air cavity depth of 25 mm Expanded polystyrene pillars, with a cross-section of 20 mm × 20 mm and thermal conductivity below 0.04 W/(m·K), should be placed between the plywood and the product to preserve air cavity depths The product must be secured to the surrounding panel with low emissivity tape as per manufacturer recommendations, avoiding overlapped joints Additionally, at least nine thermocouples should be installed in the centers of equal area squares on the inside of each cavity wall.
The thermal resistance of the walls is not included in the measured value A minimum of five thermocouples must be securely attached to each side of the product using low emissivity tape For products with metallic surfaces, thermocouples should be placed on a layer of thin adhesive tape to prevent electrical connection Additionally, the surround panel must have a thickness ranging from 100 mm to 300 mm and be constructed from a material with thermal conductivity less than 0.04 W/(m·K).
The surround panel, featuring air cavities, must be installed between the warm and cold chambers of the hot box apparatus, allowing for the correct specimen orientation and the desired temperature difference To accurately measure the thermal performance of products, specimens should be positioned vertically with horizontal heat flow, under test conditions that create a temperature difference of (10 ± 1) K across the air cavity This temperature difference is monitored using thermocouples on the internal cavity wall surfaces, with a mean test temperature maintained at (15 ± 2) °C.
NOTE Other specimen orientations may be used to obtain information on the performance of products in various building applications
Cavity orientation and heat flow direction shall be specified in the test report
5.7.5 Allowance for heat transfer around the specimen (Edge surround)
When assessing a test element within a surround panel, it is essential to consider the minor additional heat transfer occurring around the specimen's perimeter through the surround panel.
Figure 6 — Heat transfer around the specimen perimeter
The linear thermal transmittance, Ψ e, represents the additional heat flow related to the test element and surrounding panel, with its value available in Table 1 The boundary heat flow, Φ e, is calculated using the formula: \$$Φ e = Ψ e P Δ θ\$$.
P is the perimeter of the air cavity, in m; Δθ is the air temperature difference between warm and cold chambers, in K
The heat flow through the test element shall be corrected for this boundary heat flow when calculating the thermal resistance of the air cavity from the measured data
Table 1 — Linear thermal transmittance for insulated cavity in a surround panel
Hot side reveal depth mm Ψ e
W/(mãK) λsur = 0,035 W/(mãK) λsur = 0,040 W/(mãK)
Values of Ψe for intermediate values λsur can be obtained by linear interpolation
NOTE 1 The linear thermal transmittance values shown in Table 1 have been calculated assuming the following:
− the reflective insulation product is in the centre of the cavity;
− there is a 30 mm air cavity each side of the product under test;
− the emissivity of the external surfaces of the product under test is 0,05;
− the effective thermal conductivity of the product under test is 0,032 W/(mãK);
− the effective thickness of the product under test is 30 mm;
− the walls of the cavity are made from 17 mm thick plywood;
− the thermal conductivity of the plywood is 0,16 W/(mãK);
− the insulated cavity is mounted vertically with horizontal heat flow
For a cavity measuring 2 m x 1 m within a surround panel that is 2.4 m x 2.4 m and 200 mm thick, with a thermal conductivity of 0.035 W/(m·K), the boundary loss (Φe) is approximately 1.6% of the total power entering the hot box.
To calculate the core thermal resistance of the product, follow the procedures outlined in EN ISO 6946, utilizing the measured temperatures to determine the thermal resistance of each air cavity The emissivity for the plywood or similar material walls should be assumed to be 0.9, as specified in section 5.9.2 and Annex D Next, derive the thermal resistance of the fully insulated air cavity using data from the hot box Finally, calculate the core thermal resistance of the product by combining the results from the previous steps.
Determination of the thermal performance of Product Type 4
The core thermal resistance of Product Type 4 is considered negligible The thermal performance of the specified system or installed product will be assessed using METHOD D The surface emissivity will be measured according to section 5.9.2, and the product's thermal performance, along with any airspaces, will be calculated in accordance with EN ISO 6946 at a nominal mean temperature of 15 °C and a temperature difference of 10 K across the total air cavities.
NOTE Specific designs and installations of Product Type 4 materials can be tested using METHOD C, the hot box
Emissivity
The emissivity of reflective surfaces is crucial for determining the thermal resistance of adjacent airspaces This parameter can change over time due to factors such as oxidation, corrosion, UV exposure, and temperature fluctuations The long-term effectiveness of low emissivity surfaces is closely tied to their resistance to these ageing processes While bright aluminum foil surfaces without protective coatings are particularly susceptible to corrosion, reflective materials with minimal surface protection can also experience ageing effects.
This standard does not cover the effects of aging on protected foils from UV light exposure However, this factor is significant for applications where products may be exposed to sunlight It is advisable to consult the manufacturer for more information regarding this property.
In specific applications, dust accumulation on upward-facing surfaces may diminish the advantages of low emissivity surfaces; however, this issue is not covered in this standard due to its application-specific nature.
The ageing of low emissivity surfaces due to oxidation or corrosion is significant for various applications and should be included in relevant European product standards However, in the absence of harmonized measurement procedures, emissivity testing must be conducted on specimens that have been conditioned according to section 5.9.2.3 and Annex D.
The materials and protective surfaces used in reflective insulation products vary widely in specifications and properties, making it challenging to determine surface emissivity and the effects of aging without direct measurement Consequently, providing universal tabulated or default values is not feasible due to the numerous variations Additionally, identifying the actual facing and coating, as well as their aging resistance, becomes increasingly difficult once the product is on the market Therefore, relying on default values is not advisable; accurate measurement remains the only reliable method.
Emissivity must be measured using the apparatus specified in Annex D or alternative equipment that provides equivalent accuracy and has been validated against the total hemispherical integrative sphere method, which serves as the fundamental physical reference procedure.
5.9.2.2 Size and number of specimens
Before testing, it is essential to carefully remove the outer low emissivity facing of composite products, ensuring that it does not get damaged, as this facilitates easier emissivity measurement If removal is not feasible, special precautions must be implemented to avoid overheating the specimen during the test, as outlined in D.6 of Annex D.
In the absence of specified ageing conditions in a European Technical Specification for the product type, each specimen intended for emissivity measurement must undergo conditioning as outlined in Annex D To prevent moisture ingress, the edges of each specimen should be sealed with self-adhesive waterproof aluminium foil tape before the conditioning process.
General
The measurement standards ISO 8301, ISO 8302, EN ISO 8990, and EN 1946 (Parts 1 to 4) play a crucial role in determining measurement uncertainties Additionally, the accreditation standard ISO 17025 mandates the use of methods outlined in the ISO Guide to Uncertainty in Measurements (GUM).
The following subclauses identify the additional sources of measurement uncertainty that will be associated with the measurements specified in this standard.
Thickness measurements
To accurately measure thermal resistance, it is essential to determine the thickness of the product and the spacing of the plates in hot plate measurements The procedure outlined in EN 823:1994 should be followed; however, manufacturers may need to collaborate to establish the optimal load for these measurements It is important to note that this measurement process may introduce additional errors, which must be evaluated by the individuals conducting the measurements.
Use of surface thermocouples on thin samples in a guarded hot plate or in heat flow
Surface thermocouples are recommended for specimens with a thermal resistance below 0.5 m²·K/W, although this method may introduce additional measurement errors that must be assessed.
Use of dummy insulation specimens
The measurement error of the dummy specimens, as detailed in Annex E, must be combined with the measurement uncertainty of the test method, following the procedures outlined in ISO/IEC Guide 98-3.
Derivation of the core resistance of a Type 3 Product from hot box measurements
Each step in the measurement process involves various uncertainties, including the standard measurement uncertainty from the hot box assessment of the insulated air cavity, the depths of the air cavity, and the emissivity values of both test material surfaces Additionally, uncertainties arise from the emissivity of the internal cavity walls, the temperature difference between the cold face of the test element and the internal cold face of the cavity, the temperature difference between the warm face of the test element and the internal warm face of the cavity, and the calculated thermal resistance of the cold side air cavity.
Each of these possible sources of uncertainty shall be evaluated and combined in accordance with GUM, and the range of uncertainty included in the report
Results derived from hot plate and emissivity measurements (Products Type 1 & 2)
The thermal performance must be established based on a minimum of three test results, calculated using the 90/90 fractile rules as per EN ISO 10456 This includes the 90/90 fractile value of the core's thermal resistance, rounded down to the nearest 0.01 m²·K/W, and the emissivity of the surface(s), expressed to two decimal places Additionally, depending on the application, it may also include the 90/90 fractile value of the core's thermal resistance combined with that of one or two adjacent vertical airspaces, rounded down to the nearest 0.05 m²·K/W.
1) Calculating the thermal resistance of the air cavities adjacent to the product using standardized calculation procedures specified in EN ISO 6946;
2) Using the emissivity of the surfaces from the procedure specified in 5.9;
3) Using the core thermal resistance determined from the procedures specified in 5.5 or 5.6;
When comparing products, a temperature difference of 5 K across each air cavity can be utilized for calculations Alternatively, the thermal resistance of the air cavity can be determined using a temperature difference that is appropriate for the specific application It is essential to clearly state the temperature difference used alongside the declared thermal resistance.
This calculation does not consider the impact of product overlap, specifically when the foil surface on the cold side is directly transferred to the warm side.
Results derived from hot box and emissivity measurements (Product Types 1, 2 & 3)
The thermal performance must be established based on a minimum of three test results, calculated using the 90/90 fractile rules as per EN ISO 10456 This includes the 90/90 fractile value of the thermal resistance of the core and the vertical air space(s), rounded down to the nearest 0.05 m² K/W, along with the specification of the air space(s) Additionally, it requires the 90/90 fractile value of the measured emissivity of the surfaces, expressed to two decimal places, and the 90/90 fractile value of the thermal resistance of the core, rounded down to the nearest 0.01 m² K/W.
Results derived from emissivity measurements only (product Type 4)
!The thermal performance determined in accordance with this standard shall be established using a minimum of 3 test results and calculated using the 90/90 fractile rules according to EN ISO 10456 as:
The EN 16012:2012+A1:2015 (E) standard requires the reporting of the 90/90 fractile value of the measured emissivity of surfaces, expressed to two decimal places Additionally, it mandates the calculated thermal resistance of the associated vertical air spaces, rounded down to the nearest 0.05 m²·K/W, along with the specification of these air spaces, the temperature differences applied, and the calculation method utilized.
The report must detail the product description, including its name, types of facing, and printing degree; identify the manufacturer or supplier; specify the product type (1, 2, 3, or 4); outline the test method and conditions, such as hot and cold face temperatures and heat flow direction; state the thickness and weight of the plate used in the test; declare the thermal performance as per Clause 7 for the relevant product type; provide the test date; and indicate the range of uncertainty for the test result.
Figure A.1 - Decision making flow chart for identification of product types
Figure C.1 - Selection of the measurement technique for product type 2
Measurement of emissivity using a Thermal Infra-Red apparatus
Principle of the hemispherical blackbody radiator
The hemispherical radiator (half sphere) in the form of a blackbody uses the thermal infra-red radiation principle (TIR-principle) The temperature of the blackbody is set and controlled at 100 °C
The hemispherical shape of the radiator is essential for achieving uniform illumination of the measurement surface, enabling accurate measurement of emissivity for rough and structured surfaces Energy reflected and emitted by the specimen is directed through a small opening in the radiator and focused onto an infra-red sensor via an infra-red lens This sensor converts the incident thermal radiation into a broad band, linear voltage signal that is proportional to the reflected thermal energy According to Planck’s law, the spectral distribution of thermal radiation at a blackbody's temperature is defined, and the radiator is set to 100 °C, resulting in a peak wavelength of approximately 8 μm, with over 97% of radiant energy falling within the 2.5 μm to 40 μm range.
Figure D.1 — Schematic diagram of typical thermal infra-red apparatus
Description of suitable hemispherical blackbody radiator and specimen holder
In order to reduce errors related to the hemispherical blackbody radiator (henceforth referred to as
To minimize the apparatus, the half sphere must have a diameter of at least 70 mm, with the specimen surface positioned approximately 2 mm from the apparatus The axis of the infra-red sensor should align accordingly.
EN 16012:2012+A1:2015 (E) infra-red lens assembly shall point at the centre of the specimen and shall be between 70° and 80° to the specimen surface
To ensure accurate evaluation of measuring signals, it is essential to utilize an appropriate electronic method Additionally, to prevent overheating of the specimen, the measurement duration must be restricted to a maximum of 3 seconds.
The specimen holder must feature a solid flat front surface measuring at least 140 by 140 mm, with the method of securing the specimen tailored to the material being tested It is essential that the specimen remains flat and wrinkle-free across its entire surface For thin materials, wrapping around the edges of the holder and securing with magnetic strips is recommended In the case of metal foils, effective heat-sink coupling is crucial, necessitating the use of heat conductance paste and a substantial aluminum plate as a heat sink For thicker and stiffer materials, the fixing method should be determined individually, utilizing clamps or hooks as needed During measurement, the specimen must be kept parallel to the apparatus, with a predefined distance of 2 mm maintained by spacers to prevent any rocking.
Figure D.2 — Arrangement of thermal infra-red apparatus and specimen
Calibration standards
The apparatus must be calibrated using precisely defined low and high emissivity standards, with low emitting surfaces having emissivity values between 0.01 and 0.02, and high emitting surfaces requiring values greater than 0.94 It is essential to base the calibration on recommended reference standards.
— low emissive standard: polished aluminium surface;
— high emissive standard: black light trap surface
Calibration standards must be certified either by the manufacturer of the equipment or by an independent institute, along with a certificate that indicates the measured emissivity Additionally, these calibration standards should be recertified or replaced with new certified standards at a minimum interval of every two years.
Calculation of the emissivity
Emissivity is calculated by comparing the measured results of a specimen with two calibration standards Using the sensor signals (U, UH, and UL) and the known emissivities of the calibration standards (εL and εH), the emissivity of the specimen (ε) can be determined using the formula: \$$ε = ε_H - (ε_H - ε_L) \times \frac{(U_H - U)}{(U_H - U_L)}\$$
The apparatus has a measurement range confined to the values of the two calibration standards, specifically within an emissivity range of 0.02 to 0.94 It is important to note that there are practical limitations when measuring very low emissivity values, as errors become significantly larger when emissivity falls below 0.05.
Sampling and preparation of the test specimens
Sampling
A sample of an undamaged reflective insulation product shall be selected at random from a batch of production material or from product placed on the market.
Dimensions and numbers of specimens
To ensure a representative analysis of the product, a minimum of three specimens must be collected, covering the length and width, including any relevant printing or perforation areas If the product has differing faces, at least three specimens should be taken from each face The size of the specimens should be adjusted according to the specimen holder and its fixing system, but must be no smaller than 250 mm by 250 mm.
Conditioning of specimens for ageing
The specimens will be placed in a climatic chamber at 90% relative humidity and 70 °C for 28 days To prevent moisture ingress, self-adhesive aluminum foil tape will be applied around the edges of each specimen Following the conditioning period, the specimens must stabilize for at least two hours at a temperature of (23 ± 2) °C and relative humidity of (50 ± 20) %.
Procedure for measurement of specimens
The apparatus must be powered on at least 2 hours prior to calibration and measurements It should be securely installed in a fixed position without any movement during the measurement process To ensure accuracy, calibration standards, specimens, and the apparatus must reach equilibrium under identical climatic conditions Additionally, it is essential to prevent air currents and draughts in the measurement area.
The specimen must be positioned vertically against the spacers surrounding the measuring window of the apparatus before activation for measurement Emissivity will be assessed at five different locations on each specimen To prevent temperature fluctuations during measurement, the time the specimen remains in the measuring position should be minimized, ensuring that the interval between positioning and the start of measurement does not exceed a specified limit.
To ensure accurate measurements, a second must pass without interruption If the measurement is disrupted or needs to be repeated, the specimen must be removed from the apparatus until it cools to laboratory temperature While rapid movement of the specimen during measurement is feasible, it is essential to couple the specimen to a substantial aluminum block for optimal results.
EN 16012:2012+A1:2015 (E) specific heat capacity of the material, the longer the specimen will need to cool down to laboratory temperature
To minimize measurement variability related to the laboratory, specimens, and apparatus, it is essential to recalibrate the equipment using two calibration standards at least once every hour of operation.
To achieve the highest possible repeatability in measurements, it is essential to follow specific guidelines: tests should be conducted by the same individual, the apparatus must be recalibrated for each specimen, and heat conductance paste along with a substantial aluminum heat sink should be utilized Only reflective sheets should be measured, avoiding any additional wadding or materials between the foil and the heat sink Additionally, the measurement time should not exceed 1.5 seconds, and the apparatus should be allowed to heat up for approximately 2 hours before testing begins.
Expression of results
The emissivity of the specimen must be reported to two decimal places Any single measurements yielding an emissivity below 0.02 or above 0.94 should be adjusted to 0.02 or 0.94, respectively, as per the apparatus's measurement range The test report must include the mean emissivity value, all individual values for the specimen, and the standard deviation of the results The mean emissivity value should also be rounded to two decimal places.
To determine the mean value from a sample, at least three specimens must be tested, with five measurements taken for each specimen The declared product value should be based on a minimum of three test results, ideally from three different production batches, following the 90/90 fractile rules outlined in EN ISO 10456 Manufacturers have the option to include more test results in their calculations If the mean value is below 0.05, it is reported as 0.05.
“Dummy specimen” technique for the heat flow meter apparatus
Principle
To ensure accurate thermal resistance measurements in heat flow meter apparatus, calibration with reference materials that have similar thermal performance is essential Since most apparatus are not calibrated with thin materials (less than 20 mm thick), this article introduces the "dummy specimens" method to align measurements with ISO 8301 standards.
Procedure
This method involves using two "dummy specimens," each with a minimum thickness of 10 mm, to create a composite specimen that matches the thickness of the reference samples used for calibrating the heat flow meter apparatus Measurements will be taken using the specimen arrangements shown in Figures E.1 and E.2.
1) using only the two dummy specimens, to determine their combined thermal resistance;
2) with the specimen under test sandwiched between the two dummy specimens
To ensure accurate measurements, the thickness of the test specimen must be preserved using appropriate low conductivity spacers These spacers should be adjusted to match the measured thickness of the test specimen and positioned between the dummy specimens outside the metering area.
The thermal resistance of the tested material is determined by calculating the difference in thermal resistance between the results of the second and first measurements.
Figure E.2 — Schematic diagram of dummy specimen arrangement with specimen under test
Specimens of low thermal resistance
In the case where the test specimen (excluding the dummy specimens) is expected to have a thermal resistance of less than 0,5 m 2 K/W, surface thermocouples shall also still be used.
Calibration
Achieving a temperature difference of 10 K across the test specimen necessitates an overall temperature difference of about 50 K across the entire stack Consequently, a distinct calibration file must be created to account for this temperature difference in the reference specimen.
[1] EN 15976:2011, Flexible sheets for waterproofing - Determination of emissivity