Measuring the characteristics of thermal insulation · PDF fileMeasuring the characteristics...

Measuring the characteristics of thermal insulation materials

Insulation Testing equipment,

standards and procedures

1

Instruments to measure the thermal conductivity

2 © Claude-A. Roulet, Apples, 2015

Measurement principle

© Claude-A. Roulet, Apples, 2015 3

𝜅 =𝑞 · 𝑑

Δ𝑇

Density of heat flow rate

Temperature difference

Thickness

Measuring the density of heat flow rate

Guarded hot plate:

Instrument designed in such a way that all the power heating a hot plate flows in one direction through a known section of the sample.

Heat flow meter

The heat flows through a plane layer of known resistance. The temperature difference across it is proportional to the density of heat flow rate


Guarded hot plate aparatus Two samples


Sample 1

Sample 2

Cold plate

Cold plate

Hot plate Guard Guard

Guarded hot plate aparatus Single sample


Insulating material

Sample

Hot, guard plate, same temperature

Cold plate

Hot plate Guard Guard

Standards - GHP

• ISO 8302 - Determination of steady-state thermal resistance and related properties - Guarded hot plate apparatus

• ASTM C177 – 13: Standard Test Method for Steady-State Heat Flux Measurements and Thermal Transmission Properties by Means of the Guarded-Hot-Plate Apparatus.

• IS 3346:1980 - Method for the determination of thermal conductivity of thermal insulation materials (two slab, guarded hot-plate method).


Standards - GHP ISO and ASTM are equivalent (same requirements)

Tests according to ISO comply to ASTM and IS 3346 , providing that :

• 2 samples configuration

• Temperature unbalance across gap < 0.05 K

• Sample thickness measurement in the apparatus, accurate to within 0.5%

• Improved cooling power stability.

• Rigid specimens made flat to ±0.025% with faces parallel within 1% of thickness

• Include in the report the moisture content of the specimen as received, before, and after test


Heat flow meter apparatus


Test sample

Hot plate

Heat flow meter

Cold plate

Temperature

sensors

Example of heat flow meter


Thermoelectric legs

Metal connections

Heat flow meter configurations


Single specimen, one HFM

Single specimen, two HFM’s

Two specimens, one HFM

Standards

• ISO 8301:1991 - Determination of steady-state thermal

resistance and related properties - Heat flow meter

apparatus

• ASTM C 518-10: Standard Test Method for Steady-State

Thermal Transmission Properties by Means of the Heat

Flow Meter Apparatus.

• IS 9489:1980 - Method of test for thermal conductivity of

thermal insulation materials by means of heat flow meter


Standards - HFM ISO and ASTM are equivalent (same requirements). IS 3346 is based on ASTM C 518-10

Tests according to ISO comply to ASTM and IS 3346 , providing that :

• The moisture content of the specimen as received, before, and after test are included in the report


HFM calibration

• This instrument needs a periodical calibration

• A calibration specimen is used, with thermal resistance measured in a GHP apparatus

• Performed within 24 hours before or after the test

• If proven stable within 1% of reading, calibration interval can be longer

• However, no report is issued before the next calibration


Calibration

• Performed at temperatures T and thickness d close to those given with the calibration specimen.

• The calibration factor for the heat flow meter temperature TH is then:

𝑓(𝑇𝐻) = 𝜅𝑐∆𝑇

𝑒 𝑑𝑐1 −

𝛿𝑑

𝑑𝑐+

1

𝜆𝑐

𝑑𝜅𝑐

𝑑𝑇𝛿𝑇

• Keep a record of calibration factors


Measurement procedure

Characteristics to be measured

• Dimensions

• Density

• Moisture content as received, before and after the thermal conductivity test

• Thermal conductivity

16 © Claude-A. Roulet, Apples, 2015


Sampling

• Go to the factory or a delivery store

• Pick packages at random

• For declared values, get samples manufactured at various dates


Conditioning • In a climatic chamber or cabinet

• Until constant weight

• Possible conditions:



Temperature Relative humidity

23 ± 2 °C 50 ± 5 %

23 ± 2 °C Dry

27±2 °C 65±5 %


Side dimensions

Dimensions of products:

• ISO 29465:2008:Thermal insulating products for building applications -Determination of length and width.

Dimensions of test samples:

• ISO 29768:2008:Thermal insulating products for building applications -Determination of linear dimensions of test specimens



Side dimensions

Tools

• Flat table

• Metal rule or metal tape, graduated in millimetres and permitting reading to an accuracy of 0.5 mm



Side dimensions of products



Thickness

Products:

• ISO 29466:2008: Thermal insulating products for building applications - Determination of thickness.

Test samples:

• ISO 29768:2008: Thermal insulating products for building applications -Determination of linear dimensions of test specimens


Measurement procedure - Thickness

Conditioning light, compressed mats • Completely unroll the mat

• Cut into pieces 1-1,5 m long

• Hold the piece vertically in both hands by a long edge so that the other long edge is approximately 450 mm above the floor.

• Drop the piece once so that it strikes the floor.

• Repeat this on the opposite edge for all pieces.

• Wait at least 5 min for the pieces to reach a state of equilibrium before taking any measurements.



Thickness

Tools

• A hard, flat reference surface,

• A square, rigid plate 200 mm aside weighing 1020±20 g to exert a total pressure on the test specimen of 250 ± 5 Pa.

• A dial gauge, accuracy of at least 0.05 mm and mounted on a rigid frame fastened to a flat rigid base plate that is at least as large as the test specimen.




Thickness

Thickness Measurement


Table

Put at zero

Thickness Measurement



Density

ISO 29470:2008: Thermal insulating products for building applications -- Determination of the apparent density

Tool: Balance accurate to ± 0.5%


Density: procedure

• Samples as delivered or specimens for thermal conductivity

• Remove facings and coatings

• Measure all dimensions

• Weigh specimens to 0,5%


𝐷𝑒𝑛𝑠𝑖𝑡𝑦 = 𝐷𝑟𝑦 𝑤𝑒𝑖𝑔ℎ𝑡

𝑀𝑒𝑡𝑒𝑟𝑒𝑑 𝑣𝑜𝑙𝑢𝑚𝑒

Thermal conductivity - Procedure

Rigid materials shall be plane, flat, parallel


Test sample

Hot plate

Heat flow meter

Cold plate

Hot plate

Cold plate

Heat flow meter


Loose fill materials shall be “homogeneous»


Test sample

Hot plate

Heat flow meter

Cold plate

§

Hot plate

Cold plate

Heat flow meter

Hot plate


Loose fill materials

– in a shallow container

– thin, conductive, IR-emmitting covers

– place insulating spacers at the four corners

– weigh the container empty and filled



• Condition samples

• Determine weight and density

• Set test temperatures :


Mean

temperatures

Cold plate Hot plate

10 5 15

23 18 28

30 20 40

Dew point


0

5

10

15

20

10 15 20 25 30 35

Air tem

pera

true -

Dew

poin

t

Air temperature

30%

40%

50%

60%

70%

80%

90%

95%

HR


Wait for thermal equilibrium

• Time constant:


𝜏 = 𝜌𝑝 𝑐𝑝 𝑑𝑝 + 𝜌𝑠 𝑐𝑠 𝑑 𝑅

Hot plate Sample

Examples with heat flow meter (𝜌𝑝 𝑐𝑝 𝑑𝑝=0)

𝜏 = 20 · 1000 · 0.05 1.25 = 1250 𝑠

𝜏 = 100 · 1000 · 0.1 2.5 = 25′000 𝑠

Thermal conductivity - procedure

Wait for thermal equilibrium:

• Record heat flow density (or thermal resistance) every time constant

• Wait until 5 successive readings are within 1%

Alternative

• Record during 24 hours


Wait for thermal equilibrium


0

0.5

1

1.5

2

0 5 10 15

The

rmal

re

sist

ance

Time

±1%

Thermal conductivity - Interpretation

HFM

𝑅 =𝑇ℎ − 𝑇𝑐

𝑓 𝑒

f: calibration factor

e: reading

GHP

𝑅 =𝑇ℎ − 𝑇𝑐

𝑁 𝑃𝐴

A: metering area in m²

N: number of test samples

P: heating power in W


Mean apparent conductivity:

𝜅 =𝑑

𝑅

Reporting includes at least:

• Name and address of the laboratory

• Type of instrument used

• Date of the test

• Date of the last heat instrument calibration

• Type, or types, of calibration materials used.

• Identification of the material,

• Dimensions of test samples

• Method of specimen preparation for loose-fill materials,

thermal resistance of sheet material interposed between

the test sample and apparatus plates.

• Thickness as tested with uncertainty range, specifying if

this thickness is imposed or measured.


Reporting includes at least (ctd):

• Method, temperature and air humidity for the conditioning.

• Relative mass changes during conditioning with uncertainty

range.

• Density of the conditioned samples with uncertainty range

• Relative mass change during test with uncertainty range.

Observed thickness and volume changes during test.

• Hot and cold temperatures, temperature difference, and

mean test temperature, with uncertainty ranges.

• Density of heat flow rate through specimen at the

equilibrium, with uncertainty range.

• Thermal resistance of test samples, with uncertainty range.


Reporting includes at least (end):

• Where applicable, the thermal conductivity (with

uncertainty range) and range of thickness for which these

values have been measured or are known to apply.

• For direct-reading apparatus, the results of the calibration

of electronic circuitry and equipment, or a statement of

compliance including date, and a statement of compliance

on linearity requirements shall be included.

• Statement of compliance with the appropriate ISO and

possibly other standards with exceptions if applicable.

A reporting form is proposed in Appendix E


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