Guarded Hot Plate Thermal Conductivity Tester

Guarded Hot Plate Thermal Conductivity Tester – QualiGTX™ GHP

Guarded Hot Plate Apparatus for Insulation Boards and Mortars, 300 × 300 mm Specimen

The QualiGTX™ GHP Guarded Hot Plate Thermal Conductivity Tester determines the thermal conductivity (lambda value) of insulation materials using the steady-state guarded hot plate method. It covers a measurement range of 0.010 to 3.000 W/(m·K) and accommodates specimens measuring 300 × 300 mm. These measurements establish whether insulation materials satisfy specified thermal performance requirements for building applications. As a primary reference method, the guarded hot plate also provides the benchmark for calibrating comparative thermal conductivity instruments. The system delivers measurement accuracy within 2% and repeatability below 1%.

Designed for foam concrete, insulation mortars, and other comparable cast or molded materials, the apparatus tests specimens prepared using a corresponding 300 × 300 mm mold. Its automated loading and unloading system maintains consistent clamping pressure throughout testing. This is particularly important when evaluating rigid materials, where variations in specimen surface flatness and contact resistance at the plate interfaces can introduce measurement errors. Applying uniform pressure helps maintain consistent thermal contact conditions and improves repeatability between successive tests.

The temperature controls provide flexibility for testing under specified conditions, with the cold plate adjustable from 5 to 50 °C and the hot plate adjustable from ambient temperature to 80 °C. This allows laboratories to establish the required mean test temperature rather than relying on fixed operating conditions. The apparatus accepts specimens from 10 to 45 mm thick, with 25 mm identified as the preferred thickness. It operates on a single-phase power supply with a consumption of 2 kW. The equipment weighs 215 kg and measures 1600 mm in height, with a footprint of 800 × 600 mm. The specified operating environment is 10 to 40 °C, and installation in an air-conditioned laboratory is recommended.

Guarded Hot Plate Thermal Conductivity Tester – QualiGTX™ GHP Applications

Accurate thermal conductivity measurements support material selection, insulation performance assessment, building energy calculations, and the development of new construction products. The QualiGTX™ GHP provides laboratories and manufacturers with a primary-method solution for evaluating heat transfer through insulation and cement-based materials.

• Foam Concrete Manufacturing and Quality Control: Monitors thermal conductivity across production batches to identify changes associated with variations in mix density, foaming agent concentration, and curing conditions. This helps manufacturers maintain consistent insulation performance throughout production.
• Insulation Mortars and Thermal Render Evaluation: Measures the thermal properties of insulating plasters and render formulations intended for application to masonry and concrete surfaces, supporting material qualification and product performance assessment.
• External Wall Insulation Systems: Establishes thermal conductivity values for insulation materials used in external wall assemblies. These measurements provide essential input for calculating the thermal performance of complete wall systems.
• Rigid Insulation Board Assessment: Evaluates the thermal conductivity of rigid insulation boards and panels within the supported thickness range, providing measurement data for manufacturing quality checks and product acceptance.
• Building Energy Performance and Code Requirements: Determines declared lambda values used in thermal transmittance (U-value) calculations, supporting building energy assessments and regulatory documentation.
• Lightweight and Aerated Concrete Research: Helps researchers and manufacturers compare different concrete formulations during product development, particularly when reducing heat transfer is a key material design objective.
• Pavement and Subgrade Insulation Evaluation: Characterizes the thermal properties of insulating layers incorporated into road structures to limit frost penetration and support pavement construction requirements.
• Independent Construction Materials Testing Laboratories: Provides guarded hot plate measurement data for third-party testing, material certification, and product approval services where recognized primary-method results are required.
• Porous and Cellular Material Research: Supports investigations into the relationship between pore structure, material density, moisture content, and heat transfer behavior in porous and cellular materials.

Standards

The QualiGTX™ GHP is designed around the internationally recognized guarded hot plate procedure for determining steady-state thermal resistance and associated thermal properties of insulation materials.

• ISO 8302 – Thermal Insulation: Determination of Steady-State Thermal Resistance and Related Properties, Guarded Hot Plate Apparatus.

Guarded Hot Plate Thermal Conductivity Tester – QualiGTX™ GHP Key Features

The QualiGTX™ GHP integrates a guarded heating plate arrangement, automated specimen handling, and independently adjustable hot- and cold-side temperatures to support controlled steady-state thermal conductivity testing.

• Primary Guarded Hot Plate Method: Uses a separately controlled guard surrounding the central measuring area to minimize lateral heat transfer physically. This arrangement establishes the reference conditions required for primary-method thermal conductivity measurements.
• 300 × 300 mm Specimen Dimensions: Accommodates specimens prepared with a matching casting mold, allowing foam concrete and insulation mortar samples to be molded directly to the required test dimensions instead of being cut afterward.
• Automated Specimen Handling and Consistent Clamping: Automates specimen loading and unloading while maintaining uniform pressure across the test surface. Consistent plate contact helps control interface resistance and reduces variations between measurements.
• Wide Thermal Conductivity Range: Measures values from 0.010 to 3.000 W/(m·K), covering materials ranging from high-performance insulation products to denser cement-based construction materials.
• 10 to 45 mm Specimen Thickness: Supports a range of standard cast and board-type specimen thicknesses, with 25 mm recommended as the preferred testing dimension.
• Adjustable Cold Plate Temperature: Provides cold-side temperature settings from 5 to 50 °C, allowing laboratories to establish the required boundary conditions for measurements at specified mean temperatures.
• Adjustable Hot Plate Temperature: Operates from ambient temperature to 80 °C, supporting tests that require elevated mean temperatures above normal laboratory conditions.
• Measurement Accuracy Within 2% and Repeatability Below 1%: Provides the measurement consistency needed for determining declared thermal conductivity values and preparing product certification or approval documentation.
• Single-Phase 2 kW Power Requirement: Operates from a single-phase electrical supply while accommodating the equipment's heating and cooling requirements, without requiring a three-phase connection.
• Rigid 215 kg Construction: The substantial equipment frame provides mechanical stability and helps maintain plate alignment, supporting consistent contact conditions across the specimen.

Theory and Method

The guarded hot plate method determines thermal conductivity by measuring the heat passing through a material under stable temperature conditions. A specimen with known thickness and surface area is placed between heated and cooled plates. Once steady-state conditions are established, the apparatus measures the heat flow through the specimen and the temperature difference between its two faces. These values, together with the specimen dimensions, are used to calculate thermal conductivity. Although the calculation itself is straightforward, obtaining an accurate result depends on ensuring that the measured heat travels through the specimen rather than escaping through surrounding areas.

This is the central problem addressed by the guarded plate arrangement. Heat generated by a conventional heater naturally spreads in multiple directions. Some of this energy can travel sideways instead of passing through the designated measuring area. If this lateral heat loss is included in the measurement, the calculated thermal conductivity becomes higher than the actual value. The resulting error is particularly significant for highly insulating materials, where accurate heat flow measurement is essential.

To control this effect, the guarded hot plate places a separately powered guard ring around the central metered heating section. Both sections are maintained at the same temperature, eliminating the temperature gradient that would otherwise drive heat sideways between them. With lateral heat transfer suppressed, the energy supplied to the central measuring section passes through the specimen rather than escaping around its edges. This physical control of heat flow is what establishes the guarded hot plate as an absolute reference method. Heat flow meter instruments are consequently calibrated against measurements obtained using this technique.

Specimen thickness also influences measurement quality because it affects both temperature development and heat loss. With a thin specimen, the temperature difference across the material is relatively small, making the thermal resistance at the plate-to-specimen interfaces a more significant part of the overall measurement. Increasing specimen thickness produces a larger temperature difference, but also increases the potential for heat loss through exposed edges and extends the time needed to reach steady-state conditions.

A thickness of 25 mm provides a practical balance between these competing factors for most insulation materials. This explains why it is the preferred specimen dimension within the apparatus's supported range of 10 to 45 mm.

Laboratory temperature stability is equally important for reliable measurements. The guard system uses a control loop to maintain the temperature balance between the central measuring plate and the surrounding guard, while operating within the influence of the ambient environment. Fluctuations in room temperature place additional demands on this control process and can extend the time required to establish stable measurement conditions. Maintaining a consistent laboratory environment, preferably through air conditioning, therefore helps the apparatus achieve steady-state readings more efficiently.

Guarded Hot Plate Thermal Conductivity Tester - QualiGTX™ GHP Technical Specifications