EXPERIMENTAL INVESTIGATION ON THE THERMAL BEHAVIOR OF THREE DIFFERENT INSULATION MATERIALS: WOOD, POLYSTYRENE AND HEMP WOOL

Abstract— The aim of this work is to study experimentally the thermal behavior and the energetic efficiency of a homogeneous wall. The materials chosen are polystyrene such as organic insulation material, then wood and hemp wool such as ecological insulation materials. The work carried out consists of characterizing the thermal properties of these three materials and then, evaluating one by one the thermal performance of each material by applying three different fluxes with the variation of the material thicknesses from 2cm to 4cm, which allow us to evaluate their impact on the thermal ability of the wall.

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. Thermal Behavior Evaluation
After the characterization of our three insulating materials, we had studied their thermal behaviour. For this aim, a model house with replaceable side walls was used for determining the transient profile of the inside and outside temperatures of the wall which are measured at a constant interior and outer air temperature and then calculating the thermal resistance R.

II.B.1 Experimental device description  High insulation house
The high insulation house is a dimension casing of 400 mm × 400 mm × 400 mm, ground insulated through a 5 cm thick Styrofoam plate. It consists of a thermally insulated base rack with removable lid, measuring walls, exterior insulation and heating. Side walls are with square apertures (210 mm × 210 mm); and the measuring walls are set in from the inside and pressed by two screws against the aperture gasket. Each of the exterior walls carries a profile and a small eccentric plate to hold supplementary insulating material. Every angle pillar has a hole to introduce temperature probes. The hole is sealed off with foam material. The lid is insulated by a 5 cm thick Styrofoam plate, fixed to the angle pillars of the base rack with 4 knurled screws which cannot be lost.
 Thermal regulation The thermal regulation is ensured by a regulating unit in plastic casing with plug to connect heating and a knob for selection of temperature. Its maximum switching power is of 100 W, and its regulating accuracy is about ± 2°C. The unit is equipped with a connecting cable with 5 pole diode plug linked with a temperature probe (NTC resistance) in an open metallic protective tube.
 Heat transfer service unit H112 The bench mounted Hilton Heat Transfer Service Unit H112 contains a variable power supply with all associated electrical circuits protected by a residual current circuit breaker and overload cut outs. The rear panel contains a power socket for the optional units and access for the data acquisition system. Miniature type K thermocouple sockets allow the connection of up to 12 temperature sensors from the range of optional experimental units available. The unit has three digital displays on the front panel including a push button digital temperature indicator allowing all relevant parameters to be displayed. Parameters displayed on the Heat Transfer Service Unit H112 are temperature, voltage range 0-240 Vac and Current range 0-2 Aac.
 Data Acquisition HC113A The computerized Data Acquisition Upgrade HC113A consists of a 21 channel Hilton Data logger (D103), together with pre-configured, ready to use, Windows compatible educational software. Factory fitted coupling points on the H112 Options allow installation of the upgrade to the unit at any time in the machine's extensive life. The Hilton Data logger (D103) connects using the cable supplied to a standard USB port on the user supplied PC.
 HDL Software The pre-configured menu driven Software supplied with the computer Upgrade HC113A allows all recommended experiments involving the electronic transducers and instruments on the H112 options to be carried out with the aid of computerized data acquisition, data storage and on-screen data presentation.

II.B.2 Experimental procedure
We begun the experience by placing the material on the side that we choose to study, we should make sure that the other sides are perfectly insulated and we don't have any thermal bridge. Holes in the corner posts of the model house are used for the insertion of thermocouples -NiCr-Ni type K-to measure the interior and inside wall temperatures. The thermocouple used for measurement of the interior temperature is projected about 5cm into the house. For measurement of the wall temperatures, the tip of the thermocouple should be firmly secured at the level of the lateral holes and as close as possible to the perpendicular centerline of the wall.    If we compare the temperature's gradient between inside and outside surface, we can observe that it increases with the increase of the thickness of each insulating material and for all the heat flux density imposed. For the wood, the temperature's gradient between inside and outside surface varies from 1,73°C to 11,35°C for the three thicknesses investigated and for the three heat flux densities imposed. For the polystyrene, the variation is from 2°C to 12,4°C, and for the hemp wool, it's from 2,18°C to 12,45°C.    By calculating the thermal resistance [12] [13] (figure 15), we can see that, for each insulating material, it increases with the increase of the thickness [14].

B. Φ=40 W/m²
If we compare between the three insulating materials, it's clearly shown that we have a slight superiority for hemp wool followed by polystyrene and then by wood. These experimental results are in good agreement with literature because the increase of the thickness of an insulating materiel until reaching its critical thickness influences positively the thermal performances of walls [15], by increasing its thermal resistance first; and also by having influence of its thermal inertia, despite of the fact that an insulation material don't have a higher thermal inertia for the heat storage, its lower thermal inertia plays a crucial role for comfort by providing thermal phase lag, especially in summer [16].