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Artificial intelligence techniques have been successfully applied to control dynamic systems looking for an optimal control. Among those techniques, reinforcement learning has been shown as particularly effective at reducing the dimensionality of some real problems and solving control problems by learning from experience. The use of thermal energy storage active systems in the building sector is identified as suitable option to reduce their energy demand for heating and cooling. However, these systems might be expensive and require appropriate control strategies in order to improve the performance of the building. In this paper a ventilated facade with PCM is controlled using a reinforcement learning algorithm. The ventilated facade uses mechanical ventilation during nighttime to solidify the PCM and releases this cold stored to the inner environment during the peak demand period. It is crucial to decide correctly the schedule of charge and discharge process of the PCM according to the weather and indoor conditions. An experimentally validated numerical model is used to test the performance of the control algorithm under different weather conditions. Important improvements on the energy savings due to the use of control strategies were found and supported by the data under the different tested climatic conditions. ; The work partially funded by the Spanish government (ENE2011-28269-C03-01, ENE2011-22722 and ULLE10-4E-1305). The authors would like to thank the Catalan Government for the quality accreditation given to their research group (2014-SGR-123). The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement #PIRSES-GA-2013-610692 (INNOSTORAGE). Alvaro de Gracia would like to thank Education Ministry of Chile for Grant PMI ANT1201.

The use of active thermal energy storage can provide energy savings, cost reduction and CO2 mitigation by reducing energy demand for heating and cooling, allowing the use of peak load shifting strategies and enhancing the introduction of renewable energies in the sector. The high investment cost of these systems makes mandatory an appropriate control in order to maximize the energy benefits during its operation. Within this context artificial intelligence techniques have been successfully used to control active thermal energy storage units. This paper uses an experimentally validated numerical tool to study the effect of different control strategies on the performance of one TES system applied to the building sector, a ventilated facade with PCM which uses free cooling. Three different strategies were designed to control the ventilated facade based on cost savings, energy reduction and CO2 mitigation, under different climatic conditions. Results show robust benefits in the three tested control strategies, achieving average savings in comparison to a manual operation of the system of 4.3%, 7.8%, and 16.7%. Moreover, the paper shows that when the control strategy is focused on optimizing cost, the other two benefits claimed by TES systems (energy and CO2 mitigation) are significantly reduced. ; The work is partially funded by the Spanish Government (ENE2015-64117-C5-1-R (MINECO/FEDER), ENE2015-64117-C5-3-R (MINECO/FEDER), TIN2015-71799-C2-2-P and ULLE10-4E-1305). The authors would like to thank the Catalan Government for the quality accreditation given to their research group (2014 SGR 123) and the city hall of Puigverd de Lleida. This project has received funding from the European Commission Seventh Framework Programme (FP/2007-2013) under Grant agreement N°PIRSES-GA-2013-610692 (INNOSTORAGE) and from the European Union's Horizon 2020 Research and Innovation Programme under grant agreement No. 657466 (INPATH-TES), and the fund received by the Royal Society of New Zealand. Alvaro de Gracia would like to thank Ministerio de Economia y Competitividad de España for Grant Juan de la Cierva, FJCI-2014-19940.

Nowadays, European policies are promoting low energy buildings because of the high amount of energy consumption of the building sector. Phase change materials (PCM) have been studied in building implementation as a passive system to reduce the energy demand. Based in the experience obtained in the experimental set-up of Puigverd de Lleida (Spain), this paper pretends to analyze experimentally the PCM performance in a scenario with internal thermal gains. The experiments were done in three different cubicles with the same internal dimensions. The selection of the constructive systems used in these three cubicles allows the authors to evaluate the impact of using PCM in a typical Mediterranean building. A domestic heat pump for summer and an electric radiator for winter were installed to control the internal temperature of the cubicles. The results of summer period experiments show that the PCM cubicle stored the heat produced by the internal loads limiting the heat dissipation to the outer environment. Therefore, the energy consumed by the HVAC system of the PCM cubicle during the cooling period is higher than that of the other cubicles that dissipated the thermal loads according to the thermal resistance of their envelopes. Therefore, the PCM selection should take into account not only the comfort temperature but also the activity and functionality of the building. ; The work partially funded by the Spanish government (ENE2011-28269-C03-01) and the European Union (COST Action COST TU0802). The authors would like to thank the Catalan Government for the quality accreditation given to their research group (2009 SGR 534) and the city hall of Puigverd de Lleida.

Thermal energy storage (TES) is a technology with a high potential for different thermal applications. It is well known that TES could be the most appropriate way and method to correct the gap between the demand and supply of energy and therefore it has become a very attractive technology. In this paper, a review of TES for cold storage applications using solid–liquid phase change materials has been carried out. The scope of the work was focussed on different aspects: phase change materials (PCMs), encapsulation, heat transfer enhancement, and the effect of storage on food quality. Materials used by researchers as potential PCM at low temperatures (less than 20 C) are summarized and some of their thermophysical properties are reported. Over 88 materials that can be used as PCM, and about 40 commercially available PCM have been listed. Problems in long term stability of the materials, such as corrosion, phase segregation, stability under extended cycling or subcooling are discussed. Heat transfer is considered both from theoretical and experimental point of view and the different methods of PCM encapsulation are reviewed. Many applications of PCM at low temperature can be found, such as, ice storage, conservation and transport of temperature sensitive materials and in air conditioning, cold stores, and refrigerated trucks. ; The work partially funded by the Spanish Government (ENE2008-06687-C02-01/CON and ENE2011-22722) and the European Union (COST Action COST TU0802 and project EFFIBUILDINGS – FP7-PEOPLE-2009-IIF-/-253914). The authors would like to thank the Catalan Government for the quality accreditation given to their research group (2009 SGR 534). Eduard Oró would like to thank the University of Lleida for his research fellowship.

Rural depopulation is a worldwide fact and has a domino effect on medium and small cities, which act as a nucleus of reference for small towns. Moreover, the United Nations (UN) stressed that disparities between rural and urban areas are pronounced and still growing over time. Globally, people in rural areas lack access to modern energy services, which affects productivity, educational and health services, exacerbating poverty, among other things. Given this reality, the following research questions arise: how can we act to reverse this reality? Are there examples of transformation in rural contexts where community empowerment is a key strategy? This paper aims at describing the transformation process of a small rural municipality towards a sustainable development, in parallel to the activation of the local productivity that helps to eliminate the effects of rural depopulation. Therefore, the project ALMIA was established as an example of a sustainable village that is Almatret (Catalonia-Spain). The backbone of such project is the commitment to community impowerment, where the main results are the generation of networks with experts and researchers to help the municipality's energy transition, the involvement of the local administration, the commitment to technological development, as well as the socio-community development. Moreover, the activities developed within the project ALMIA are aligned with the UNs Sustainable Development Goals, alignment that is analyzed in detail. Thus, this paper aims to further highlight existing sustainable development practices related to community empowerment in order to promote similar practices. ; This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 768824 and under the grant agreement No 723596. This work is partially supported by ICREA under the ICREA Academia programme. The authors would like to thank the Catalan Government for the quality accreditation given to their research group (2017 SGR 1537). GREiA is certified agent TECNIO in the category of technology developers from the Government of Catalonia. The authors would like to thank the Almatret municipality for their involvement in this challenging project.

Photovoltaic panels (PV) coupled to a heat pump supplying heat to a radiant wall is a system with potential to reduce the imported energy from the grid for heating and cooling of buildings. The radiant wall works as a thermal storage system (TES) allowing storage of the PV output and, thus, peak load shifting. However, the management of these technologies is complex due to the dynamics of the system. This paper presents several control concepts with different purposes such as shifting energy use to off-peak periods, maximizing self-consumption of PV output, and minimization of imported energy from the grid. An experimentally validated numerical model from previous research was used to investigate and compare the different proposed control concepts. Results showed that charging the wall with solar energy resulted in higher overall energy use of the heat pump, while the imported grid energy was significantly reduced, thanks to self-consumption. ; The authors acknowledge the South Australian Department of State Development who have funded this research through the Premier's Research Industry Fund - International Research Grant Program (IRGP 33). The work was partially funded by the Spanish government (ENE2015-64117-C5-1-R (MINECO/FEDER), ENE2015-64117-C5-3-R (MINECO/FEDER), and ULLE10-4E-1305). GREA is certified agent TECNIO in the category of technology developers from the Government of Catalonia. The authors would like to thank the Catalan Government for the quality accreditation given to their research group (2014 SGR 123) and the city hall of Puigverd de Lleida. This projects has received funding from the European Commission Seventh Framework Programme (FP/2007–2013) under Grant agreement Nº PIRSES-GA-2013-610692 (INNOSTORAGE) and from European Union's Horizon 2020 research and innovation programme under grant agreement Nº 657466 (INPATH-TES). Alvaro de Gracia would like to thank Ministerio de Economia y Competitividad de España for Grant Juan de la Cierva, FJCI-2014-19940.

Thermally activated building systems (TABS) can work as thermal energy storage (TES) systems, which are useful in shifting the energy use of space cooling and heating in buildings. The present study analyses and optimizes simple deterministic control concepts for radiant wall supplied by a heat pump for cooling purposes. First, the "solar" concept was studied, which was focused on exploiting the output of a photovoltaic (PV) array. Secondly, a "peak load shifting" concept exploiting the low electricity cost and high heat pump energy efficiency during night periods was evaluated. The results showed that the "solar" concept saved between 57% and 95% in comparison to a conventional control in different PV installed capacities. Moreover, the optimized "peak load shifting" concept had lower operation cost than the conventional control with most of the PV configurations proposed. Therefore, the study showed that the investment in the PV array was fully harnessed only with specific controls. Furthermore, the "solar" control concepts were found to help achieving the goals of net-zero energy buildings by maximising self-consumption of renewable energies in the building, as well as reducing the total imported/exported energy. ; The authors acknowledge the South Australian Department of State Development who have funded this research through the Premier's Research Industry Fund – International Research Grant Program (IRGP 33). The work was partially funded by the Spanish government (ENE2015-64117-C5-1-R (MINECO/FEDER), ENE2015-64117-C5-3-R (MINECO/FEDER), and ULLE10-4E-1305). GREA is certified agent TECNIO in the category of technology developers from the Government of Catalonia. The project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 712949 (TECNIOspring PLUS) and from the Agency for Business Competitiveness of the Government of Catalonia. The authors would like to thank the Catalan Government for the quality accreditation given to their research group (2017 SGR 1537) and the city hall of Puigverd de Lleida.

Thermally activated building systems (TABS) consist of pipes or ducts embedded in the building structure. This is a well-known technology for its capability to reduce energy use for cooling buildings. Additionally, TABS help integrating renewable energies, such as free-cooling with ground heat exchangers (GHE). However, TABS cooling load is sensitive to the internal load, and the use of GHE for free-cooling is limited to low energy buildings. In a previously published research, a radiant wall cubicle without internal gains demonstrated to achieve significant energy savings. However, the current research showed that under domestic and office scheduled internal gains equivalent to 42 W·m-2 the radiant cubicle increased its energy consumption for cooling more than the reference cubicle with air-to-air heat pumps. As a result, the radiant cubicle used around 20% more energy than the reference at air temperature set-point 24 ºC but saved around 20% compared to the reference at 26 ºC. Despite this, the radiant wall could still reduce the cooling cost through peak load shifting even though it showed to consume more energy than a conventional HP. ; The work was partially funded by the Spanish government (ENE2015-64117-C5-1-R (MINECO/FEDER), ENE2015-64117-C5-3-R (MINECO/FEDER), and ULLE10-4E-1305). GREA is certified agent TECNIO in the category of technology developers from the Government of Catalonia. The authors would like to thank the Catalan Government for the quality accreditation given to their research group (2014 SGR 123) and the city hall of Puigverd de Lleida. This projects has received funding from the European Commission Seventh Framework Programme (FP/2007–2013) under Grant agreement Nº PIRSES-GA-2013-610692 (INNOSTORAGE) and from European Union's Horizon 2020 research and innovation programme under grant agreement Nº 657466 (INPATH-TES). Alvaro de Gracia would like to thank Ministerio de Economia y Competitividad de España for Grant Juan de la Cierva, FJCI-2014-19940.

In Europe the building sector represents 41% of the final energy consumption and the 40% of the total GHG emissions of end-use sectors (Directive 2010/31/EU) [1]. Solar energy is one of the forms of renewable energy that has great potential to enable EU the ambition of 12% of heating coming from renewable sources by 2020 [2]. Within this context, the overall objective of the project Innovative Micro Solar Heat and Power System (Innova MicroSolar) is to develop a high performance and cost effective solar heat and power system, which consist in a novel flat Fresnel mirror solar concentrating collector and micro organic Rankine cycle plant combined with advanced phase change materials as thermal storage, all system managed by smart control units. This technology will be initially implemented in individual dwellings and small business residential buildings for on-site electricity and heat generation using solar thermal energy. ; This study has received funding from European Union's Horizon 2020 research and innovation programme under grant agreement Nº723596 (Innova MicroSolar) and Nº 657466 (INPATHTES), from the European Commission Seventh Framework Programme (FP/2007-2013) under grant agreement Nº PIRSES-GA-2013-610692 (INNOSTORAGE). The work is partially funded by the Spanish government (ENE2015-64117-C5-1-R (MINECO/FEDER) and ENE2015- 64117-C5-3-R (MINECO/FEDER)). GREA is certified agent TECNIO in the category of technology developers from the Government of Catalonia. The authors would like to thank the Catalan Government for the quality accreditation given to their research group (2014 SGR 123). Alvaro de Gracia would like to thank Ministerio de Economia y Competitividad de España for Grant Juan de la Cierva, FJCI-2014-19940.

Rapid expansion of solar thermal energy for increasing energy efficiency of buildings has been adopted in short/medium and long-term energy strategies of EU countries. This enhancement of energy efficiency in buildings is in line with regional actions with the European climate energy objectives as defined in the European Union's "20-20-20" targets and in the European Commission's Energy Roadmap 2050. Within this context, the overall objective of this work is to develop an innovative high performance and cost effective hybrid solar heat and power system, which consist in a novel flat Fresnel mirror solar concentrating collector and micro organic Rankine cycle plant combined with advanced phase change materials as thermal storage, all system managed by smart control units. The initial application is to be implemented in individual dwellings and small business residential buildings for on-site electricity and heat generation using solar thermal energy. It is estimated that the proposed technology will deliver 60% of domestic energy requirements and provide 20% reduction in energy costs and greenhouse gas emissions compared to the best existing low carbon energy technologies. To reach the main objectives, the first step consist in providing information on features of architecture of domestic and small business residential buildings and their annual energy demands for different countries such as: Spain, France Germany, Italy, and United Kingdom. This will include detailed building information of envelopes (walls, roof, lofts, etc.), structure, fabric, and results of energy demands (domestic hot water, space heating and electricity) for the abovementioned countries. This information will be used as input data during the development of this technology as it will point out the potential benefits of the system in different countries, climates, and building typologies. ; This study has received funding from European Union's Horizon 2020 research and innovation programme under grant agreement Nº723596 (Innova MicroSolar) and Nº 657466 (INPATH-TES), from the European Commission Seventh Framework Programme (FP/2007-2013) under grant agreement Nº PIRSES-GA-2013-610692 (INNOSTORAGE). The work is partially funded by the Spanish government ENE2015- 64117-C5-1-R (MINECO/FEDER), ENE2015-64117-C5-3-R (MINECO/FEDER) and (ULLE10-4E-1305). GREA is certified agent TECNIO in the category of technology developers from the Government of Catalonia. The authors would like to thank the Catalan Government for the quality accreditation given to their research group (2014 SGR 123). Alvaro de Gracia would like to thank Ministerio de Economia y Competitividad de España for Grant Juan de la Cierva, FJCI-2014-19940.

Solar thermal energy has been adopted in medium and long‐term energy strategies within EU countries for increasing the energy efficiency of buildings. In this context, the overall objective of this project consists in developing an innovative high performance and cost effective hybrid system (solar heat and electrical power). The initial application is to be implemented in residential buildings for on‐site electricity and heat generation using solar thermal energy. The proposed technology is expected to deliver 60% of domestic energy requirements (heating and domestic hot water) and provide 20% reduction in energy costs and greenhouse gas emissions compared to the best existing low carbon energy technologies. A benchmark on the energy demand for the different types of residential buildings in Europe serves as reference scenario to evaluate the potential applicability of the different existing renewable technologies and to establish a comparative framework in terms of quantitative values. Thus, the specific aim of this study consists in performing a state‐of‐the‐art on the different building typologies, which can host this technology, and their energy demands for heating and domestic hot water, as well as their associated CO2 emissions. ; This study has received funding from European Union's Horizon 2020 research and innovation programme under grant agreement Nº723596 (Innova MicroSolar) and Nº 657466 (INPATH‐TES). The work is partially funded by the Spanish government ENE2015‐64117‐ C5‐1‐R (MINECO/FEDER) and ENE2015‐64117‐C5‐3‐R (MINECO/FEDER). GREA is certified agent TECNIO in the category of technology developers from the Government of Catalonia. The authors would like to thank the Catalan Government for the quality accreditation given to their research group (2014 SGR 123). Alvaro de Gracia would like to thank Ministerio de Economía y Competitividad de España for Grant Juan de la Cierva, FJCI‐2014‐19940.

Cooling in the industry sector contributes significantly to the peak demand placed on an electrical utility grid. New electricity tariff structures include high charges for electricity consumption in peak hours which leads to elevated annual electricity costs for high-demanding consumers. Demand side management (DSM) is a promising solution to increase the energy efficiency among customers by reducing their electricity peak demand and consumption. In recent years, researchers have shown an increased interest in utilizing DSM techniques with thermal energy storage (TES) and solar PV technologies for peak demand reduction in industrial and commercial sectors. The main objective of the present study is to address the potential for applying optimization-based time-of-use DSM in the industry sector by using cold thermal energy storage and off-grid solar PV to decrease and shift peak electricity demands and to reduce the annual electricity consumption costs. The results show that when cold thermal energy storage and solar PV are coupled together higher annual electricity cost savings can be achieved compared to using these two technologies independently. Additionally, considerable reductions can be seen in electricity power demands in different tariff periods by coupling thermal energy storage with off-grid solar PV. ; The work partially funded by the Spanish government (ENE2015-64117-C5-1-R (MINECO/FEDER), ENE2015-64117-C5-3-R (MINECO/FEDER), and TIN2015-71799-C2-2-P). The authors would like to thank the Catalan Government for the quality accreditation given to their research group (2014 SGR 123) and the city hall of Puigverd de Lleida. This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 657466 (INPATH-TES). Alvaro de Gracia would like to thank Ministerio de Economia y Competitividad de España for Grant Juan de la Cierva, FJCI-2014-19940.

The building sector accounts for one third of the global energy consumption and it is expected to grow in the next decades. This evidence leads researchers, engineers and architects to develop innovative technologies based on renewable energies and to enhance the thermal performance of building envelopes. In this context, the potential applicability and further energy performance analysis of these technologies when implemented into different building typologies and climate conditions are not easily comparable. Although massive information is available in data sources, the lack of standardized methods for data gathering and the non-public availability makes the comparative analyses more diffcult. These facts limit the benchmarking of different building energy demand parameters such as space heating, cooling, air conditioning, domestic hot water, lighting and electric appliances. Therefore, the first objective of this study consists in providing a review about the common typologies of residential buildings in Europe from the main data sources. This study contains specific details on their architecture, building envelope, floor space and insulation properties. The second objective consists in performing a cross-country comparison in terms of energy demand for the applications with higher energy requirements in the residential building sector (heating and domestic hot water), as well as their related CO2 emissions. The approach of this comparative analysis is based on the residential building typology developed in TABULA/EPISCOPE projects. This comparative study provides a reference scenario in terms of energy demand and CO2 emissions for residential buildings and allows to evaluate the potential implementation of new supply energy technologies in hot, temperate and cold climate regions. From this study it was also concluded that there is a necessity of a free access database which could gather and classify reliable energy data in buildings. ; This study has received funding from European Union's Horizon 2020 research and innovation programme under grant agreement Nº723596 (Innova MicroSolar). The work is partially funded by the Spanish government (RTI2018-093849-B-C31). Julià Coma would like to thank Ministerio de Economía y Competitividad de España for Grant Juan de la Cierva, FJCI-2016-30345. José Miguel Maldonado would like to thank the Spanish Government for his research fellowship (BES-2016-076554). This work is partially supported by ICREA under the ICREA Academia programme.

Cool roof effectiveness in improving building thermal-energy performance is affected by different variables. In particular, roof insulation level and climate conditions are key parameters influencing cool roofs benefits and whole building energy performance. This work aims at assessing the role of cool roof in the optimum roof configuration, i.e., combination of solar reflectance capability and thermal insulation level, in terms of building energy performance in different climate conditions worldwide. To this aim, coupled dynamic thermal-energy simulation and optimization analysis is carried out. In detail, multi-dimensional optimization of combined building roof thermal insulation and solar reflectance is developed to minimize building annual energy consumption for heating-cooling. Results highlight how a high reflectance roof minimizes annual energy need for a small standard office building in the majority of considered climates. Moreover, building energy performance is more sensitive to roof solar reflectance than thermal insulation level, except for the coldest conditions. Therefore, for the selected building, the optimum roof typology presents high solar reflectance capability (0.8) and no/low insulation level (0.00-0.03 m), except for extremely hot or cold climate zones. Accordingly, this research shows how the classic approach of super-insulated buildings should be reframed for the office case toward truly environmentally friendly buildings. ; The work was partially funded by the Spanish government (RTI2018-093849-B-C31). This work was partially supported by ICREA under the ICREA Academia programme. Dr. Alvaro de Gracia has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 712949 (TECNIOspring PLUS) and from the Agency for Business Competitiveness of the Government of Catalonia. This publication has emanated from research supported (in part) by Science Foundation Ireland (SFI) under the SFI Strategic Partnership Programme Grant Number SFI/15/SPP/E3125.

A proper management of thermal energy storage (TES) charging and discharging processes allows the final users to optimize the performance of TES systems. In this paper, an experimental research is carried out to study how the percentage of charge in a latent heat TES system (partial load operating conditions) influences the discharge process. Several charging and discharging processes were performed at a constant heat transfer fluid (HTF) mass flow rate of 0.5 kg/s and temperature of 155 °C and 105 °C, respectively. High density polyethylene (HDPE) with a total mass of 99.5 kg was used as phase change material (PCM) in a 0.154m3 storage tank based on the shelland-tube heat exchanger concept. Five different percentages of charge have been studied: 58 %, 73 %, 83 %, 92 %, and 97 % (baseline test). Results showed that by modifying the percentage of charge, the time required for the charging process was reduced between 97.2% and 68.8% in comparison to the baseline case. However, the energy accumulated was only reduced a maximum of 35.1% and a minimum of 5.2%, while the heat transfer rates during the first 60 min of discharge were reduced a maximum of 45.8% and a minimum of 6%. Therefore, partially charging the TES system not lower than 85% of its maximum energy capacity becomes a good option if the final application accepts a maximum decrease of discharging heat transfer rates of 10% if compared to the fully charged system. ; The work was partially funded by the Spanish government (ENE2015-64117-C5-1-R (MINECO/FEDER), ENE2015-64117-C5-3-R (MINECO/FEDER), and ULLE10-4E-1305). The authors would like to thank the Catalan Government for the quality accreditation given to their research group (2014 SGR 123). GREA is certified agent TECNIO in the category of technology developers from the Government of Catalonia. This project has received funding from the European Commission Seventh Framework Programme (FP/2007-2013) under Grant agreement No. PIRSES-GA-2013-610692 (INNOSTORAGE) and from the European Union's Horizon 2020 research and innovation programme under grant agreement No. 657466 (INPATH-TES). Jaume Gasia would like to thank the Departament d'Universitats, Recerca i Societat de la Informació de la Generalitat de Catalunya for his research fellowship (2017 FI_B1 00092). Alvaro de Gracia would like to thank Ministerio de Economia y Competitividad de España for Grant Juan de la Cierva, FJCI-2014-19940. Simone Arena would like to thank the Department of Mechanical, Chemical and Materials Engineering of the University of Cagliari for funding his research grant.