Abstract: Buildings are the largest end user of energy, since 40% of all energy is used in the residential/tertiary sectors. The energy demand for cooling or heating applications has been growing constantly over the past few years. One main reason for this development is that new buildings are often constructed by light materials and the lack of thermal storage capacity leads to fast overheating or subcooling of the building.
The need of thermal energy storage may often be linked to the following cases: there is a mismatch between thermal energy supply and energy demand; when intermittent energy sources are utilized; for compensation of the solar fluctuation in solar heating systems.
The use of thermal storage walls that serve both as solar collector and thermal storage is well known. The wall is usually composed of masonry or containers filled with water to provide sensible heat storage resulting from the specific heat capacity of a material as it increases in temperature.
Sensible heat energy storage has the advantage of being relatively cheap but the energy density is low and there is a gliding discharging temperature. To overcome these disadvantages phase change materials (PCMs) can be used for thermal energy storage.
PCMs are materials capable of increasing thermal inertia of buildings without increasing the thickness of walls, for instance. In comparison with other thermal storage materials, such as concrete or water, PCMs have a higher energy storage density. In that way, one can achieve the same goal with less material. On the other hand, PCMs also allow the storage and the release of thermal energy at an almost constant temperature.
A research group from "Constantin Brancusi" University from Targu-Jiu patented a new type of composite wall system incorporating PCMs and evaluated its potential for air conditioning/heating energy savings in continental temperate climate.
The novelty of the wall system consists of the fact that two PCM wallboards, impregnated with different PCMs are used. The structure of the new wall system is that of a three-layer sandwich-type insulating panel with outer layers consisting of PCM wallboards and middle layer conventional thermal insulation.
The PCM wallboard layers have different functions: the external layer has a higher value of the PCM melting point and it is active during hot season and the internal layer with a PCM melting point near set point temperature for heating is active during cold season. A year-round simulation of a room built using the new wall system was carried out and the effect of PCM presence into the structure of the wall system was assessed. It was found that the new wall system contributes to annual energy savings and reduces the peak value of the cooling/heating loads.

Brief Biography of the Speaker:
Mihai CRUCERU, born on 02.07.1967 in Targu-Jiu, Romania, graduated from Installations for Buildings Faculty, Technical University of Civil Engineering Bucharest (1991), where he obtained also his PhD (1998). He worked for one year as HVAC engineer and he joined in 1992 the Energy Department from "Constantin Brancusi" University Targu-Jiu where he is now professor of Heat Transfer and Energy Management. He was Dean, Head of Department for Education Quality, and now he is Vice-Rector for Education. His research is focused on Heat and mass transfer, Thermal equipment design and Energy efficiency. He is Energy auditor and Thermal equipment and fluid systems expert. He was involved, as director or researcher, in 18 national and international research projects. He published 11 books and more than 110 articles in relevant journals and conference proceedings.