Detecting State of Charge in PCMs - Experimental investigation of changes in chemical and physical properties during phase transitions

Abstract

The energy use in the residential sector has steadily increased during the last decades as a consequence of an increased demand for heating and cooling in buildings. One of the main problems when it comes to indoor climate control is that the energy is not used efficiently. For instance, energy is used to heat the building during cold nights and additional energy is used to cool the building during hot days. Ideally the excess energy generated during the day could be stored and then released into the building during the night, thus reducing the energy use and energy losses. This effect could be realized utilizing the potential of phase change materials (PCMs). A PCM is a material that is able to store and release large amounts of energy with respect to its volume through solid-liquid phase transitions. By introducing PCMs in building envelopes it is possible to reduce the energy demands for indoor climate control in the building up to 25 %. To facilitate implementation of PCM solutions in buildings it is important to be able to visualize that the material is active. This can be done by measuring the proportions of the material that is either in liquid or solid state, also called the state of charge (SOC) at any given time. The main purpose of this master’s thesis is to investigate non-destructive and quantitative methods to measure the SOC in order to support implementation of technical PCM solutions in the future. It is also important that the methods can be commercially suitable when it comes to economic, environmental and technical aspects. This has been done utilizing the fact that the physical, chemical and thermal properties of a material changes during phase transitions and could possibly be correlated to the SOC. Based on the results presented in this study, changes of certain properties correlate better to the SOC than others depending on the investigated PCM type (polymers, sugar alcohols and salt hydrates). The change in light transmittance as a PCM undergoes phase transition has seen to correlate well to the SOC for all of the investigated PCM types, additionally this method shows good commercial and technical implementation potential.