13Energy consumed by heating, ventilation and air conditioning systems (HVAC) in 14 buildings represents an important part of the global energy consumed in Europe. 15 Thermal energy storage is considered as a promising technology to improve the energy 16 efficiency of these systems, and if incorporated in the building envelope the energy 17 demand can be reduced. Many studies are on applications of thermal energy storage in 18 buildings, but few consider their integration in the building. The inclusion of thermal 19 storage in a functional and constructive way could promote these systems in the 20 commercial and residential building sector, as well as providing user-friendly tools to 21 architects and engineers to help implementation at the design stage. The aim of this 22 paper is to review and identify thermal storage building integrated systems and to 23 classify them depending on the location of the thermal storage system. 24 25 26 Keywords: thermal energy storage (TES), building integration, active system, phase 27 change materials (PCM), thermal mass 28 29 30 35Solar applications, including those in buildings, require storage of thermal energy for 36 periods ranging from very short duration (in minutes or hours) to seasonal storage. The 37 main advantage of using TES in solar systems for buildings is the success of converting 38 an intermittent energy source in meeting the demand, which may be intermittent and/or 39 have a time shift [2]. TES can also be used for free-cooling of buildings. The advantage 40 here is the use of a natural resource for air conditioning in buildings. 42Advantages of using TES in an energy system are the increase of the overall efficiency 43 and reliability, but it can also lead to better economic feasibility, reducing investment 44 and running costs, and less pollution of the environment and less CO 2 emissions [3]. 45 Thermal energy can be stored using different methods: sensible heat, latent heat and 46 thermochemical energy storage [1,2,3]. 48Sensible storage is the most common method of heat and cold storage. Here energy is 49 stored by changing the temperature of a storage medium (such as water, air, oil, rock 50 beds, bricks, concrete, or sand). The amount of energy stored (Eq. 1) is proportional to 51 the temperature difference, the mass of the storage medium, and its heat capacity:where Cp is the specific heat of the storage material (J/kg·°C), ΔT the temperature 56 gradient (°C), m the mass of storage material (kg). 57 58 Latent heat storage is when a material stores heat through a phase transition. Usually the 59 solid-liquid phase change is used because of its high enthalpy and lack of pressure 60 problems. Upon melting, as heat is transferred to the storage material, the material 61 maintains a constant temperature constant at the melting temperature, also called phase 62 change temperature. The amount of heat stored can be calculated by Eq. 2. 63 64 3 h m Q    (Eq. 2) 65 66 where Δh is the phase change enthalpy, also called as melting enthalpy or he...

a b s t r a c tEnergy consumption trends in residential and commercial buildings show a significant increase in recent decades. One of the key points for reducing energy consumption in buildings is to decrease the energy demand. Buildings envelopes are not just a structure they also provide protection from outdoor weather conditions always taking into account the local climate. Thermal energy storage has been used and applied to the building structure by taking advantage of sensible heat storage of materials with high thermal mass. But in recent years, researchers have focused their studies on the implementation of latent heat storage materials that if well incorporated could have high potential in energy demand reduction without occupying the space required by sensible storage. The aim of this study is to review the thermal energy storage passive systems that have been integrated in building components such as walls, ceilings or floors, and to classify them depending on their component integration.

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