Well-insulated buildings are a key factor to reduce CO2 emissions. Studies show that the energy consumption of correctly insulated buildings can be reduced by up to 60% . Governments set strict building insulation regulations in place to reduce carbon emissions. Consequently, there is a continued growth of the global insulation market and a rising demand for highly effective insulation materials.
In most applications, the primary property of a thermal insulation material is its capability to reduce heat transfer between a surface and its surroundings or between a surface and another surface. Generally, the lower the thermal conductivity of a material, the greater its ability to insulate for a given material thickness and conditions. Therefore, a measurement technique is needed that makes it possible to determine the heat transfer properties of insulation materials very accurately and precisely. The Heat
–Flow –Meter method (HFM) is one of the methods used to determine the thermal conductivity of insulation materials.
ASTM thermal insulation standards – tested product efficiency
A lot of effort goes into the engineering of materials with very low thermal conductivity to supply the market with even better thermal insulation materials. Thermal Insulation products already on the market, on the other hand, undergo regular testing to ensure quality and effectiveness. ASTM’s thermal insulation standards such as ASTM C518 are key for specifying and evaluating the materials and methods used to reduce the rate of heat transfer. These thermal insulation standards help laboratories and institutes, device and equipment manufacturers, construction companies, and industrial firms examine these materials for efficiency.
There is a large selection of thermal insulation materials
There is already a wealth of choice in building insulation materials. Starting with the more common materials like glass wool, rock wool, EPS (Expanded Polystyrene) and XPS (Extruded Polystyrene) to materials derived from nature like hemp, straw and linen, or on the high-tech end of the spectrum, materials like aerogels and VIPs (vacuum insulation panels).
The efficiency of all of these materials is being checked in accordance with the ASTM thermal insulation standards. This way, they can be specified, evaluated and controlled for their rate of heat transfer.
Thermal conductivity and influential factors
The thermal conductivity λ indicates the heat flow that passes through a 1m² and 1m thick layer of a material at a temperature difference of 1 Kelvin (K). The unit of thermal conductivity is W/(m×K). The smaller λ is, the better the insulating capacity of a building material.
The thermal conductivity of a material depends mainly on the following factors:
- Thermal conductivity of the base material
- Type, size and arrangement of the pores or cells
- Type and pressure of the gas filling in the pores
- Structure of the solid components (crystalline, glassy, fibrous)
- Bulk density
- Moisture content
The heat flow meter – Accurate and fast determination of thermal conductivity and thermal resistance
Heat flow meters (HFM), as described in the ASTM C518 thermal insulation standard, are widely used for testing low-conductive materials. The HFM instrument is easy to use, applicable to a wide range of specimens and measurement results can be obtained fast.
In an HFM, the test specimen is placed between two temperature-controlled plates (Figure 1). An internal thickness gauge measures the sample thickness. In case of compressible samples, the plates can be driven to the desired thickness. Calibrated heat flux transducers integrated in the plates measure the heat flow through the sample. After reaching thermal equilibrium, the test is done.
Things to keep in mind when measuring thermal conductivity
- Specimen size and thickness is important ‒ NETZSCH offers the new HFM 446 Lambda Eco-Line in 3 different sizes from small to medium to large
- Materials may dry out or acquire moisture and will no longer be representative
– make sure you store your samples correctly prior to measurement
- Compressible materials show different properties depending on the pressure/change of density they experience ‒ easily compressible materials need precise load and plate distance control
Figure 3 demonstrates the influence of a material’s density on the thermal conductivity of a glass-fiber material.
The new HFM 446 Lambda Eco-Line saves time and energy
The HFM 446 Lambda Eco-Line is the latest range of NETZSCH heat flow meters.
It comes with improved temperature control for faster measurements, energy saving Eco-Mode and better user experience all-over.
- New Eco-Mode for reduced energy consumption
- Easy and fast set up saving installation time (instrument comes pre-calibrated)
- Precise measurements on easily compressible samples using drive-to-thickness feature
- Possibility to combine individual heat flux calibrations using MultiCalibration for increased accuracy
- Compliance to standards made easy with Stability Configuration Management
- New User Interface for improved instrument handling and smoother workflows
- Compact stand-alone unit, no PC required
The efficient thermal insulation of buildings plays an essential part in the effort to reduce Co2 emissions. In search for even better thermal insulating materials, heat flow meters play an important role. They are also essential for making sure that products on the market stay in line with the communicated efficiency.
 FIW München Bericht 12/12: Technologien und Techniken zur Verbesserung der Energieeffizienz von Gebäuden durch Wärmedämmstoffe