Phase change materials as smart nanomaterials for thermal energy storage in buildings

Abstract

Nowadays, energy production and consumption in buildings play an important role in the economic development of countries. For instance, buildings are central to the EU?s energy efficiency policy, as nearly 40% of final energy consumption and 36% of greenhouse gas emissions are attributable to houses, offices, shops, and other buildings. For achievement of highly energy-efficient buildings, significant paradigm shifts are necessary, particularly in the production requirements for cost-effective, durable, energy-efficient building envelopes. The application of phase change materials (PCMs) for thermal energy storage (TES) in building envelopes can assist the reduction of energy demands associated to the heating/cooling necessary to ensure adequate inner thermal comfort. PCMs are defined as a group of materials that can store/release relevant quantities of thermal energy upon a change in their physical phase (latent heat). In many applications, such storage of energy leads to energy conservation within the system (i.e. the building), thus resulting in improved energy efficiency. Heat is absorbed or released when the material changes from solid to liquid and vice versa. Therefore, PCMs readily and predictably change their phase with a certain input of energy and release this energy at a later time. PCMs must have a suitable phase change temperature range and the latent heat of fusion for the building environment. The optimal phase change temperature depends on the comfort temperature. Also, a PCM must have an adequate conductivity rate to be able to react fast to indoor temperature variations. However, the phase change temperature ranges of the typical PCMs used in buildings are limited, and their thermal conductivity is low. To further improve the efficiency of the energy saving with PCM, the possibility of using more than one type of PCM with distinct melting ranges and specific enthalpies (termed as hybrid PCM) is reported here. Furthermore, a numerical study is conducted to investigate the mixture of nanoparticles and PCM as alternative way to enhance the thermal properties of PCM. On the basis of knowledge acquired here, concept of nanoparticle with PCM system can be employed to scopes of energy-efficient residential and commercial buildings.