System Thermal Resistance Test Report
Determination of the Thermal Resistance of Thermally Insulated Building Envelope Systems using CBA Bricks in accordance with ASTM C 1363-05: Standard Test Method for Thermal Performance of Building Materials and Envelope Assemblies by Means of a Hot Box Apparatus.
TEST APPLICANT: Clay Brick Association of SA (Pty) Ltd
Thermal Test Laboratory CC has been retained by The AAAMSA Group to test and determine the Thermal Resistance of four different clay brick wall systems, of which some includes specific thermal insulation measures, by means of a Rotatable Guarded Hot Box (RGHB) and in accordance with ASTM C 1363-05.
- Standard Test Conditions
The standard test conditions for the RGHB tests were selected based on the requirements of ASTM C1058 – 03(2008): Standard Practice for Selecting Temperatures for Evaluating and Reporting Thermal Properties of Thermal Insulation. The standard test conditions used for these tests are as follows: Room side (metering box) Air temperature: 21 ºC (Cold climatic conditions) Flow velocity: 0.3 m/s downward Climate side: Air temperature: – 5.0 ºC (Cold climatic conditions) Flow velocity: 5.5 m/s upward Mean temperature of specimens for cold climatic conditions: 8.0 °C
- Test Apparatus
The RGHB constitutes an eight-sided prism lying on its side, and is rotatable around its axis. The metering box is mounted inside the one chamber, while the cooling box is mounted inside the other chamber. The RGHB is constructed as two chambers fitting on the two sides of a frame panel into which the specimen (dark blue) is mounted. The chambers can move horizontally to allow access to thespecimen or the baffle plates of the metering box and environment box.
The metering box is shown in the figure below mounted on the room side (left) of the specimen, while the cooling box is on the environment chamber, right of the specimen. The air in the metering box is circulated past the specimen in a downward direction (red arrows), while air in the environment box also flows past the specimen (blue arrows), but in an upward direction. Both flow directions are in the direction of natural convection. The guard chamber behind the metering box
includes a rear baffle around which the air in the guard chamber is circulated (green arrows).
Both the metering box and the guard chamber on the room side (left side in Figure 1) are designed to allow the circulating air to be heated, while the air in the guard volume can also be cooled to enable the temperature in the guard volume to be temperature controlled. The walls of the metering box is instrumented with a thermopile consisting of 38 thermocouple pairs to allow the heat loss/gain through the wall of the metering box to be controlled down to minimum. The size of the specimen aperture in the surround panel is nominally 1.2 m (w) x 1.5 m (h), while the metered area (the area enclosed by the metering box) is 2,831 m2. The original thickness of the surround panel is 135 mm, but for this series of tests, the thickness of the surround panel was increased to match that of the relative specimen.
DISCLAIMER: Test report and results only relate to product(s) or sample(s) submitted for testing as identified herein. It does not imply TTL approval of the quality and/or performance of the item(s) in question and the results do not apply to any similar item that has not been tested. The Test Report shall not be reproduced except in full, without written approval from TTL or AAAMSA Tests marked “Not SANAS accredited” in this report are not included in the SANAS Schedule of Accreditation for this laboratory. Opinion and interpretations expressed herein are outside the scope of SANAS accreditation.
- Overview of RGHB Building Envelope System Test Approach
Since the thermal resistance of the clay brick walls to be tested can only be determined in a system test, four test specimens of nominally 1.5 m (h) x 1.2 m (w) were constructed. The specimens were constructed in Supawood frames mounted inside adjustable steel frames (see Appendix A) to ensure that the dimensions of the specimens are within the required tolerance allowance. The specimens were allowed to dry for a period of 28 days. In preparation for testing, a test specimen is removed from the steel frame and mounted in the aperture of the surround panel in a vertical position. It is then instrumented with up to 28 calibrated thermocouples mounted at selected positions on both surfaces of the specimen.
An extruded polystyrene (XPS) probe, instrumented with 6 equi-spaced type T thermocouples mounted along its length, is then mounted near the centre of the test specimen. It is used for measuring the dynamic specimen core temperatures of the specimen to determine whether stable conditions have been reached. After setting the test parameters, the cooling system is started and the system is allowed to saturate and reach stable conditions where it has to stay for a period of at least four hours within very tight tolerances. The thermal resistance and thermal transmittance of the test specimen are then determined by analysing the recorded test data.
- Description of the Test Construction
The specimen dimensions are 1 185 mm (width) x 1 485 m (height) with the depth varying per
specimen. The clay brick specimens are built inside test frames made from 12 mm thick Supawood.
The following systems were tested:
• WALL 1: A double clay stock brick wall with 12 mm mortar joints and with 12 mm plaster on both sides (painted white), with single wall brickforce with galvanised ties
tying the skins together every fourth course.
• WALL 2: A double brick wall made from perforated clay stock brick on the room side and perforated face brick masonry units on the climate side with 12 mm mortar joints and with 12 mm plaster on only the room side, painted white. The specimen has single wall brickforce with galvanised ties tying the skins together every fourth course.
• WALL 3: A double brick wall made from clay stock brick on the room side and perforated face brick masonry units on the climate side with 12 mm mortar joints,
separated by 30 mm thick Isoboard insulation panels tied to the room side skin, with a resultant air cavity of 20 mm. The wall has 12 mm plaster on only the room side,
• WALL 4: A double brick wall made from clay stock brick on both the room side and the climate side and with 12 mm mortar joints, separated by a 30 mm Expanded
Polystyrene insulation panels tied to the room side skin. The wall has 12 mm plaster on both surfaces, painted white.
- Test Results
Due to stringent stability requirements, RGHB tests are usually very long, lasting typically a few days per test. The following RGHB data is sampled every second, averaged and recorded every minute:
• The temperature histories for the specimen for each test
• The air flow rates in the metering box and the climate side
• The area-weighted temperatures of both sides of the surround panel
• The spatial temperature distribution of the baffle surface in the metering box
• The spatial temperature distribution of the metering box air
• The output of the thermopile measuring the heat flow through the metering box walls
• The temperature increase of the metering box cooling loop and its flow rate
• The surface temperatures of the specimen
• The temperatures of the XPS probe
The RGHB test data is analysed to determine the air-to-air thermal resistance values of the various specimens. This analyses takes account of the Watts input into the metering box (for controlling the air and baffle surface temperatures), the net thermopile gain/loss, the heat gain/loss through the surround panel and all other losses (or gains) such as flanking losses and possible thermal bridging for which the RGHB has been calibrated in accordance with the requirements of both the
National Fenestration Rating Council (NFRC) and the South African National Accreditation System (SANAS).
In the case of this series of tests, there were no flanking losses due to the fact that the specimen thickness and surround panel thickness were adjusted to be the same. The current surround panel was designed not to include any thermal bridges. The data for correcting for the remaining heat losses/gains are discussed below. To illustrate the level of stability achieved for these tests, the following sample data excerpts are included. Although the allowable tolerance on the temperature variation around the average value during the four-hour stable period is ± 0.3 °C as per ASTM C1363, the measured variations for the CBA tests were generally much less (Figure 2).
Figure 2: The temperature difference between the average surface temperatures on the
two faces of Specimen 4 during testing
Similarly, the RGHB power input is also required to be very stable. The one hour averaged data for
a typical test (Specimen 1) is depicted in Figure 3 below, together with the trendline for the data.
* The RGHB is designed for these standard surface conductance values that are validated during
the calibration of the RGHB.
In summary, the measured airstream-to-airstream thermal resistances for the four specimens are
Figure 3: The results of the data analysis phase
- Discussion of results and conclusions
In summary, the first two wall systems (Wall 1 and Wall 2) had the same thickness and differed by the type of brick used (stock clay bricks versus perforated clay bricks) and their surface finish on the climate side (plastered and painted white, versus a face brick finish). Their test results (Rth,1 = 0.35 and Rth,2 = 0.37) differ by 5%. This implies that the type of brick and surface finish do not make a major contribution to the thermal resistance of the wall systems.
The measured thermal resistance for the third and fourth wall systems tested (Wall 3 and Wall 4) differ notably from wall systems one and two, but also from one another (Rth,3 = 1.1 and Rth,4 = 1.4). The physical differences between these two wall systems are in the bricks used for the external wall (perforated face bricks for wall system 3 versus plastered stock clay bricks for wall system 4), and the type of insulation material panels between the bricks. Wall system one contains a 30 mm
Isoboard insulation panel, while wall system 4 contains an expanded polystyrene insulation panel.
Both wall systems were specified to have the same 20 mm air gap (see Appendix B). The measured difference in the thermal resistance between these two specimens is more than what is expected from the above-mentioned differences.
Sample Conditioning: The test specimens were maintained at ambient conditions prior to testing. Test Procedure: Please refer to TTL document, RGHB/SOP/01 2009: RGHB Operating Procedures. For the RGHB testing the thermal resistance of the insulation system is determined from air stream to air stream. The airflow condition in the climate side is selected to simulate a 20 km/hr warm or cold wind. Deviations (if any) from ASTM C 1363-05: No deviations