Buildings account for a significant amount of global energy use and CO 2 emissions. Thermally Activated Building Systems (TABS) are a technology with potential for significantly reducing buildings energy use. TABS are heating and cooling systems that are integrated in the building structure. They mainly exchange heat through radiation and are able to store heat in the building thermal mass. TABS high thermal mass and their interaction with the building structure make their energy evaluation and design process difficult. Development of simulation models has been essential to study the design and control of TABS. Control of TABS is challenging due to the slow response time and storage capacity. A lot of research has been conducted to develop control strategies that fully exploit its energy saving potential and that maximise the use of renewable energies. This paper summarizes the main characteristics of TABS and presents the developed simulation models and control strategies.
As a key tool for decarbonization, thermal energy storage systems integrated into processes can address issues related to energy efficiency and process flexibility, improve utilization of renewable energy resources and thus reduce greenhouse gas emissions. However, integration of these systems is dominated by the variety of potential processes in which the storage technologies can be deployed as well as the various benefits they deliver. Therefore, the requirements for thermal energy storage systems vary greatly depending on the chosen application, just as the systems themselves have different capabilities depending on their technical principles. This paper addresses this issue by developing a systematic methodology that approaches the challenge of characterizing and evaluating thermal energy storage systems in different applications in three concrete steps. To begin, a set of guidelines for process analysis has been created to disclose process requirements for storage integration. The methodology continues by explicitly defining the system boundary of a thermal energy storage system, as well as addressing technical and economic parameters. Finally, the approach concludes by determining the benefit of an integrated thermal energy storage system to an application and examines how key performance indicators vary based on the perspectives of different stakeholders. Within this work, the methodology is then applied to two case studies of hightemperature storage in concentrating solar power and cogeneration plants. Also introduced are the concepts of retrofit and greenfield applications, which are used to clarify differences between integrated storage systems. The paper shows how such a systematic approach can be used to consistently analyse processes for storage integration, facilitate comparison between thermal energy storage systems integrated into processes across applications and finally grasp how different interests perceive the benefits of the integrated storage system. This type of systematic methodology for technology integration has not been previously developed and as such, is a novel and important contribution to the thermal energy storage community. In the long term, this work builds the basis for a discussion on benefits of thermal energy storage system integration with diverse stakeholders including storage system designers, process owners and policy makers.
The increase of the capacity factor of thermal processes which use renewable energies is closely linked to the implementation of thermal energy storage (TES) systems. Currently, TES systems can be classified depending on the technology for storing thermal: sensible heat, latent heat, and sorption and chemical reactions (usually known as thermochemical energy storage). However, there is no standardized procedure for the evaluation of such technologies, and therefore the development of performance indicators which suit the requisites of the final users becomes an important goal. In the present paper, the authors identified the energy density as an important performance indicator for TES, and evaluated it at both material and system levels. This approach is afterwards applied to prototypes covering the three TES technologies: a two-tank molten salts sensible storage system, a shell-and-tube latent heat storage system, and a magnesium oxide and water chemical storage system. The evaluation of the energy density highlighted the difference of its value at the material value, which presents a theoretical maximum, and the results at system level, which considers all the parts required for operating the TES, and thus presents a significantly lower value. Moreover, the proposed approach captured the effect of the complexity and overall size of the system, showing the relevance of this performance indicator for evaluating technologies for applications in which volume is a limiting parameter.
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A radiant wall heating system embedded in a heavy brickwork envelope and coupled to a ground source heat pump supplied has been experimentally tested under real outdoor conditions. This system was applied to a room sized cubicle built in Puigverd de Lleida (Spain) test-site, where it was studied in system vs. system analysis in comparison to a reference cubicle built with commercial available technologies (insulated alveolar brick wall and air-to-air heat pump). The results showed the potential of the radiant wall, which in continuous operation reached energy savings between 19.97 % and 40.72 % based on set-point temperature. Most important, the active thermal mass of radiant wall allowed operating in off peak periods. Otherwise, this peak load shifting ability was completely inexistent in the reference cubicle. However, the results show that the radiant cubicle was unsuited to operate in occupancy schedules due to its slow response time. Furthermore, the tests show that optimization of the radiant wall system requires a control strategy that takes in account the dynamics of the system.
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