A. Lazaro*, J. M. Marin, P. Dolado, B. Zalba

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
Phone: 976762566, Fax: 976762616
Corresponding Author, ana. lazaro@unizar. es

Abstract

Building applications of phase change materials (PCM) and its contribution to energy efficiency are being studied. One of the most promising applications of thermal energy storage with phase change is the inclusion of microencapsulated phase change materials into building materials. It could be for external enclosure (increasing thermal inertia) or other applications inside the building (walls or furniture). Objectives and effects are different in each case, and it should be tested in order to corroborate that the effect is as were designed. Some new products are being introduced into the market. Thermal studies are needed to test them and to design properly its applications.

At University of Zaragoza (Spain), an experimental setup based on energy balances used to measure stored energy in macroencapsulation of PCM was modified to measure thermal effect of phase change materials inclusion into different elements.

Those tests are based on transitory heat conduction analysis on samples. A new methodology of test combining heat capacity measurements and thermal effect tests and data analysis was developed to study thermal effect as a comparison between the same element with and without PCM. Some results are also presented in this conference [13].

Keywords: Phase Change Material, Thermal Energy Storage, Experimental, Buildings

1. Introduction

Thermal Energy Storage using phase change materials is being studied for building applications [1]. Some authors proposed the use of macroencapsulation of PCM in wallboards [2-4] or in Panel sandwich [5,6] to increase thermal inertia. Bentz et al. [7] proposed three different applications of PCM in concrete at different temperatures and Medina et al. [8] proposed the use of structural panels in combination to macroencapsulation of PCM. Recent years, microencapsulation of PCM has been proposed to solve problems of leakages and distribution in those kinds of applications. Schossig et al.

[9] and Cabeza et al. [10] have studied the addition of microencapsulated PCM in building materials to reduced energy consumption in buildings.

Depending on the application, the climate and the season, the effect of PCM in buildings could be satisfactory or not [11]. It is need to study thermal properties of PCM itself, to know the temperature range within the phase change takes place, enthalpy as a function of temperature to know the energy storage capability and thermal conductivity to study the heat transfer resistance. It is noteworthy that heat capacity and density could be estimated from proportional mass rules, but thermal conductivity depends on molecular contact between the components of the material and has to be studied together.

Thermal effects of PCM in building materials are two: it modifies the energy storage capability and the heat conduction coefficient. Therefore, thermal diffusivity of the sample becomes necessary to study transient heat conduction of the wall and to evaluate thermal effect of PCM addition in building materials. For example, regarding to external enclosure, thermal behaviour depends on global heat transfer coefficient (U) and thermal inertia, which provides deferment and diminish the amplitude of the heat-flow wave. The objective should be in this case to decrease thermal diffusivity.

There are not many commercial devices to study thermal diffusivity as a function of temperature. They use small samples and from some buildings materials is not possible to have a representative samples (for example concrete with PCM). The aim of the work at University of Zaragoza is to be able to evaluate two effects, thermal conductivity and energy storage capability as a function of temperature of building materials.