Abstract

Net zero energy buildings (nZEB) require the development of innovative technologies such as the use of phase change materials (PCMs) in walls for the energy requalification of low inertia buildings. The presence of a PCM layer in the external building wall, due to the effect of storage and release of latent energy phenomena, modifies the energy behavior, both during the summer and winter periods. This paper addresses the problem of the definition of the energetic behavior of a layer subject to phase change with periodic non-sinusoidal boundary conditions, characterizing the external walls of air-conditioned buildings. In such conditions, the layer is the site of the formation of one or more bi-phase interfaces, which originate on the boundary surfaces, or are always present and fluctuate within the layer. It is also possible that the layer does not undergo any phase change. The study has been developed by a finite difference numeric calculation model which explicitly determines the number and the position of the bi-phase interfaces that originate in the layer and the temperature and the heat flux fields. The surface heat fluxes are used to evaluate the PCM layer energetic behavior in terms of energy transferred through the boundary surfaces and of stored energy in sensible and latent form. The proposed method employs the characteristic day that it is periodically repeated for all the days of the considered month. The use of the characteristic days drastically reduces the computational burden of the numerical calculation and it allows to obtain guidance on the behaviour of the PCM throughout the year, in accordance with the variability of external climatic conditions, in order to select the PCM with the most suitable thermophysical properties. The methodology developed is applied to PCM layers with different melting temperatures and subject to climatic conditions of two locations, one with a continental climate and the second one with a Mediterranean climate. The results obtained allowed us to identify which PCM is more suitable in improving the energetic performances of building walls in the heating or cooling period during the year. In particular, the energy analysis highlighted that, in both localities, during the winter period: the lowest energy exiting from the indoor environment is ensured by a PCM with a melting temperature of 15 °C; the highest contribution of energy entering the indoor environment, mainly due to solar radiation, is recorded for a PCM with a melting temperature of 26 °C. During the summer period: the lowest value of energy entering the indoor environment is obtained by a PCM with melting temperature of 26 °C; the highest value of energy exiting from the indoor environment is ensured by a melting temperature equal to 20 °C. In both locations, a PCM with a melting temperature intermediate between those of the winter and summer set points of the indoor environment is the best compromise between winter and summer energy needs for an air-conditioned environment, as it allows obtainment of the highest values of the yearly total stored energy.

Highlights

  • Thermal energy storage (TES) technologies, such as phase change materials (PCMs), are considered one of the proper materials for achieving Net zero energy buildings (nZEB) targets

  • The procedure is used in order to evaluate, for each month during the year, upon variation of the PCM melting temperature and of the climatic conditions, the number of bi-phase interfaces which are formed in the layer, the monthly and the seasonal values of the transferred energy, and the monthly and the yearly values of the stored energy in latent and sensible form

  • Regarding the different PCMs and for the two locations: Section 4.1 shows, for each month, the number of bi-phase interfaces which are formed in the layer, the values of the total, latent and sensible stored energy and of the transferred energy on the two boundary surfaces, and explanations of the observed phenomena; Section 4.2 shows the seasonal values of the transferred energy on the two boundary surfaces and the yearly values of the total, latent and sensible stored energy

Read more

Summary

Introduction

Thermal energy storage (TES) technologies, such as phase change materials (PCMs), are considered one of the proper materials for achieving nZEB targets. The recent reviews of Souayfane et al [1] and of Zhou et al [2] highlight that, in recent decades, different passive and active technology systems with PCM were realized to improve the energy efficiency in the building envelope and to contain the temperature fluctuations in the indoor environment within a specific comfort range. PCMs are incorporated in a building construction material such as plaster, gypsum plasterboards, bricks, concrete and panels, or are blended with thermal insulations. Some other panels, such as PVC panels, CSM panels, plastic and aluminium foils are used to encapsulate PCMs. In the second case, the component can be manufactured before the building is being constructed and have a particular design. In contrast to previous passive systems, PCM active systems lead to a better heat transfer coefficient by replacing free convection by forced convection, with the help of small fans, to complete the solidification of the PCM

Methods
Results
Conclusion
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call