C. Castellon1, M. Medrano1, L. F. Cabeza1*, M. E. Navarro2, I. Fernandez2, A. Lazaro3, B. Zalba3

1 GREA Innovacio Concurrent, Edifici CREA, Universitat de Lleida, Pere de Cabrera s/n, 25001-Lleida (Spain)

Phone: +34-973 003576, Fax: +34-973 003575

2 Departamento de Ciencias de los Materiales e Ingenieria Metalurgica, Universitat de Barcelona, Marti i
Franques 1, 08028-Barcelona (Spain). Phone: +34-93 4021298, Fax: +34-93 40335438
3 Instituto de Investigation en Ingenieria de Aragon. I3A, Grupo de Ingenieria Termica y Sistemas Energeticos.
(GITSE) Dpto. Ingenieria Mecanica. Area de Maquinas y Motores Termicos. Universidad de Zaragoza. Campus
Politecnico Rio Ebro. Edificio “Agustin de Betancourt”, Maria de Luna s/n. 50018 Zaragoza

Telefono: 976762567, Fax: 976762616

Corresponding Author, lcabeza@diei. udl. cat

Abstract

An option in building materials is the sandwich panel, which offers excellent characteristics in a modular system. The use of these panels means an advance in the construction area and insulation of buildings, sports, industrial buildings surfaces, artificial drying places, etc. They integrate the functions of cladding, thermal insulation, watertightness, mechanical strength and aesthetic appeal. It is a product composed of a ribbed sandwich panel formed by two sheets metal and insulating polyurethane core injected.

The high insulating value of the polyurethane foam allows important savings in the energy consumption. The stability of the polyurethane, resistant to water and numerous chemical compounds, as well as its immunity to the attack by biological agents, guarantees the durability of the insulation level and the quality of the product.

The goal of this study was to demonstrate the feasibility to use the microencapsulate PCM (Micronal BASF) in sandwich panels to increase its thermal inertia, and therefore, reduce the energy demand of the final buildings.

To manufacture the sandwich panel with microencapsulated PCM, this was added a step before (test 1) and after (test 2) the injection of the polyurethane, test 3 was to mix microencapsulated PCM with one of the components of the poliurethane. The sandwich panel with PCM contains about 8% in weight of PCM mixed with the polyurethane. A sample without PCM, manufactured moments later, was kept as reference.

Keywords: sandwich panel, PCM, thermal energy storage, microencapsulation

Nowadays, reduce the energy consumption is important for existing buildings as well as for new buildings. The literature is full of extensive literature reviews and practical studies about this topic, which were carried out during the last decades [1-4]. These technical efforts concluded that it is necessary to develop materials and techniques to minimize the use of non-renewable energy for air conditioning purposes in buildings.

Phase Change Materials (PCMs) have been considered for thermal storage in buildings since before 1980. With the advent of PCM implemented in gypsum board, plaster, concrete or other wall covering material, thermal storage can be part of the building structure even for light weight buildings. In the literature, development and testing were conducted for prototypes of PCM wallboard and PCM concrete systems to enhance the thermal energy storage (TES) capacity of standard gypsum wallboard and concrete blocks, with particular interest in peak load shifting and solar energy utilization.

During the last 20 years, several forms of bulk encapsulated PCM were marketed for active and passive solar applications, including direct gain. However, the surface area of most encapsulated commercial products was inadequate to deliver heat to the building after the PCM was melted by direct solar radiation. In contrast, the walls and ceilings of a building offer large areas for passive heat transfer within every zone of the building [5]. Several researchers have investigated methods for impregnating gypsum wallboard and other architectural materials with PCM [6-9]. Different types of PCMs and their characteristics are described. Manufacturing techniques, thermal performance and applications of gypsum wallboard and concrete block, which have been impregnated with PCMs, are discussed in several references [10, 11 and 12].

The temperature inside a building depends, among other things, on the outdoor temperature and on the heat capacity of the construction material and other components in the building.

An option in building material is the sandwich panel, which offers excellent characteristics in one modular system. The use of these panels means an advance in the construction area and insulation of buildings, sports, industrial buildings surfaces, artificial drying places, etc. They integrate the functions of cladding, thermal insulation, watertightness, mechanical strength and aesthetic appeal. It is a product composed of a ribbed sandwich panel formed by two sheet metals and insulating polyurethane core injected.

The high insulating value of the polyurethane foam allows important savings in the energy consumption. The stability of the polyurethane, resistant to the water and numerous chemical compounds, as well as its immunity to the attack by biological agents, guarantees the durability of the isolation level and the quality of the product (Figure 1).

The goal of this study was to demonstrate the feasibility to use a microencapsulate PCM (Micronal BASF) in sandwich panels to increase its thermal inertia, and therefore, reduce the energy demand of the final building.

The experiment was performed in the company Europerfil. The conventional process of manufacturing sandwich panel is a continuous injection of insulating polyurethane core between two metal sheet of galvanized pre-lacquered steel.

Figure 1View of the sandwich panel

For the addition of PCM, two options were studied:

• Modifying the manufacturing process, with the addition of a new step to include microencapsulated PCM, this process have 2 options (test 1 or test 2)

• Without modify the standard manufacturing process, adding a mix of polyurethane and PCM denominated test 3.

Test 1, the PCM was added at the beginning of the process (before the injection of the polyurethane) (Figure 2), the second one (test 2), the PCM was added after the polyurethane (Figure 3).

Figure 2 Manufacture of the sandwich panel with PCM (Test 1)

Figure 3 Manufacture of the sandwich panel with PCM (Test 2)

Both options were tried manually in the company with the purpose of testing which was the best way to distribute the microencapsulated PCM in the sandwich panel. For each procedure, a reference sample was kept.

Test 3 consists in mix microencapsulated PCM with one of the liquid component of the polyurethane. This process was tested with collaboration of the company PLASFI, and was studied only with the insulating polyurethane (without including the metal sheet).

The sandwich panel with PCM contains about 8% in weight of PCM mixed with the polyurethane. Table 1 shows properties of microencapsulate PCM.

Table 1 Properties of Micronal BASF as given by the manufacturer MICRONAL BASF PCM Melting temperature ~26 °C Phase change enthalpy 100 kJ/kg Microcapsules size 5 pm

The samples were divided in sections and the following tests were carried out:

Distribution of the PCM: with the help of the stereoscope the distribution of the PCM in the samples were analyzed.

Adhesion test: in order to see if the values are within the limits established by the standard UNE 41950 (L. MAX > 0.10 MPa).

Thermal performance test: the measurements were performed in two experimental installations at the University of Zaragoza [13] (figure 4) and at the University of Barcelona. Here, the panel sandwich sample was insulated in all surfaces but one. The airflow collides on the free surface. Temperature sensors are connected on the front free surface and on the back surface of the sandwich panel. Airflow temperature is controlled during all the experiment. The temperature evolution during the experiment is measured for different samples (Figure 4).

X2, T2 X1, T1

Figure 4 Experimental installation to measure the temperature evolution in a solid sample (University of
Zaragoza). X1=free surface; X2= insulated surface

3. Results