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The object of the present study is a natural refrigerant base (propane) heat pump system with a dual source/dual sink heat exchanger (air or ground-based) which is integrated into a centralized tri-generation system with PV and battery for a multi-family building located in Spain. To evaluate the performance of this complex system, a simulation environment was developed, connecting different software. The main program is TRNSYS, with the python package pytrnsys used to create the models and run the simulations, while a model predictive controller is externalized in a separate optimization software. The co-simulation environment enables to couple both software and operate the models in the simulation with the decisions made by the external controller. This environment was used to evaluate the considered system for three separate weeks of the year, each representative of the heating/cooling/DHW demands in winter, summer and intermediate seasons. For each of these weeks, the simulation was run once with a reference rule-based controller, and once with the advanced model predictive controller, to evaluate the additional benefits brought by the later strategy. The results were then extrapolated to the whole year, and revealed that the model predictive controller was able to provide cost savings of 12 to 20% (depending on the consideration or not of the cooling season which gave unexpectedly adverse results). This controller operated the heat pump more efficiently thanks to its prior knowledge of the best source to use at each moment (air or ground). It also managed the battery in a more economical way thanks to its prior knowledge of the time-varying electricity price, thus charging always at the cheaper hours of the day, and demonstrating the advantages of using forecasts and predictive optimization for HVAC control., CLIMA 2022 conference, 2022: CLIMA 2022 The 14th REHVA HVAC World Congress

The goal of the project TRI-HP is to develop systems based on electrically-driven natural refrigerant heat pumps coupled with photovoltaics to provide heating, cooling and electricity to multi-family buildings with an on-site renewable share of 80 %. The implementation of different energy sources for such a system often leads to a complex architecture of the overall system. The performance evaluation of such systems is not trivial and cannot be done via steady-state measurements of individual components. Instead, dynamic measurements using the hardware-in-the-loop approach are performed to test the performance of the newly developed systems. A method called concise cycle test (CCT) has been developed for this purpose. This method was adapted to the systems to be tested and applied in different versions. The CCT method is based on the selection of several representative periods of the year, and shows the behaviour of a complete system for heating and cooling under relevant conditions in these periods, enabling then to extrapolate the results for a whole year operation. Two different approaches were used to select the test sequence. For the measurement of a dual source/sink system, the annual weather data were divided into four clusters, from each of which representative days were selected. For the solar-ice-slurry system, a single, contiguous test cycle of typical days from throughout the year was selected. This allows both, to test the functionality of the ice-slurry storage and the advanced energy management strategies by performing experiments only on selected days. For the tests, the complete system including a heat pump and thermal and electrical storages are installed on a test rig. The test rig emulates a building, including the space heating and cooling distribution system, the domestic hot water draw offs, the solar collector field or ground heat exchanger depending on the system tested and the photovoltaic installation. The system tested must act completely autonomously to cover the demand for heating and cooling of the building and the draw-offs during a test cycle. In this work, the methodology has been applied to two different cases of complete systems adapted to different climates (Switzerland and Spain)., CLIMA 2022 conference, 2022: CLIMA 2022 The 14th REHVA HVAC World Congress

Energy flexibility of a building is really not a new concept. It originates from the demand side management regime, which for decades has been applied by the designers and operators to foster stable and bottleneck-free operation of the electrical energy systems. However, as the transition of both the demand and supply side of the energy system imposes new challenges to the management of the whole energy system, such as the variability and limited control of energy supply from renewables or the increasing load variations over the day, the energy Flexible Building concept has gained more international attention. However, despite the given attention, a uniform understanding and a commonly accepted definition is still not in place for this building concept. The lack of a clear international framework for the requirements and properties of energy Flexible Buildings leads to numerous definitions that are being developed in parallel and are applied to specific cases when evaluating and/or quantifying energy flexibility. Although the concept of energy flexibility of buildings is relatively simple to understand, its application in reality can be complex and difficult to explain in simple terms. This complexity is not helped by the myriad of ways in which energy flexibility can be achieved or the wide range of stakeholders involved; especially when many stakeholders have very little understanding, or interest, in the supply and demand of energy in buildings. There was, thus, a need for increasing knowledge on, and demonstration of, which services energy flexibility buildings can provide to the energy networks. At the same time, there was a need for identifying critical aspects and possible solutions to manage this energy flexibility, while maintaining the comfort of the occupants and minimizing the use of non-renewable energy. Based on the above the Executive Committee of the IEA Technical Collaboration Programme (TCP) Energy in Buildings and Communities (EBC) decided to initiate Annex 67 Energy Flexible Buildings in June 2015 with an end date of November 2019. The objectives were: - development of a common terminology, a definition of ‘energy flexibility in buildings’ and a classification method, - investigation of user comfort, motivation and acceptance associated with the introduction of energy flexibility in buildings, - analysis of the energy flexibility potential in different buildings and contexts, and development of design examples, control strategies and algorithms, - investigation of the aggregated energy flexibility of buildings and the potential effect on energy grids, and - demonstration of energy flexibility through experimental and field studies. The work of IEA EBC Annex 67 has been documented in 7 deliverables reports; the titles of these reports are: - Principles of Energy Flexible Buildings (the present report) summarizes the main findings of Annex 67 and targets all interested in what energy flexibility in buildings is, how it can be controlled, and which services it may provide. - Characterization of Energy Flexibility in Buildings describes the terminology around energy flexibility, the existing indicators used to evaluate the flexibility potential and how to characterize and label energy flexibility. - Control strategies and algorithms for obtaining Energy Flexibility in buildings reviews and evaluates control strategies for energy flexibility in buildings. - Experimental facilities and methods for assessing Energy Flexibility in buildings describes several test facilities including experiments related to energy flexibility and draws recommendations for future testing activities. - Stakeholder perspectives on Energy Flexible buildings considers the view point of different types of stakeholders towards energy flexible buildings. - Examples of Energy Flexibility in buildings summarizes different examples on how to obtain energy flexible buildings. - Project Summary Report contains a very brief summary of the outcome of Annex 67. The main findings of the five key deliverables are included in chapters 3-7 of the present report. The five key deliverables are: Characterization of Energy Flexibility in Buildings; Control strategies and algorithms for obtaining Energy Flexibility in buildings; Experimental facilities and methods for assessing Energy Flexibility in buildings; Stakeholder perspectives on Energy Flexible buildings; and Examples of Energy Flexibility in buildings. The third chapter of the present report unfolds the characterization methodology, terminology and definition developed by the Annex and the possible application of the methodology. The fourth chapter is devoted to the control of energy flexible buildings, which is the core of this concept. It demonstrates which control strategies and algorithms can provide energy flexibility from buildings and identifies critical aspects and possible solutions to manage energy flexibility. The fifth chapter gives the overview of the existing test facilities located in Belgium, Canada, Denmark, Finland Germany, Norway, Spain and Switzerland, which are designed and constructed to test different control strategies and combination of components, and thus evaluate the energy flexible building under realistic conditions. The sixth chapter provides the feedback on energy flexible buildings from the perspective of nine types of stakeholders. It presents and discusses their roles, motivations, and potential barriers to energy flexible buildings. The chapter closes with recommendations for how the different types of stakeholders should be approached and motivated in order to become an active part of the energy flexible concept The seventh chapter summarizes the good examples of energy flexibility collected during Annex 67. It describes the scope and focus of the examples, followed by a more detailed description of a sample of specific examples that describe the different sources of flexibility. It ends by evaluating the statistical range of the described examples. It is hoped that the present report will not only provide an impression of what energy flexibility in buildings is and how it can be obtained, but also be a source of inspiration for future research and development in this area.

Tesis llevada a cabo para conseguir el grado de Doctor por la Universidad Politécnica de Cataluña.--2020-01-24, Urgent actions are required to mitigate climate change and global warming. Decarbonizing our energy systems represents an important step in that direction. For the power grid, this means integrating larger share of renewable sources (RES), such as solar and wind power. Due to their variability and unpredictability, these sources however pose some challenges to the grid if they constitute the main electricity supply: possible supply-demand mismatch, consequent necessity to curtail RES production or to use peak fossil-fueled plants, grid congestions due to prosumers and decentralization, inviability of the other peak power plants without subsidies. Demand-side management (DSM), which consists in increasing the flexibility of the demand-side, constitutes a promising set of solutions to help manage the operation of the grid with high shares of RES. In particular, buildings and their embedded thermal mass can be regarded as thermal storage, and heat pumps represent one of the most ideal means to couple such storage with the power grid and cover the heating, cooling and hot water loads in a more flexible manner. Smart controls for heat pumps are required to harness the full energy flexibility potential of building thermal loads. A thorough literature review revealed that most strategies used for this purpose can be classified in two categories: rule-based control (RBC) and model predictive control (MPC). RBC is made of simple rules of the form ”if a condition is verified, then take an action”. MPC is a more advanced strategy that makes use of models and forecasts the behaviour of the systems in the near future in order to find the optimal plan of action. It requires the prior development of models, and the solving of an optimization problem at regular time intervals. For this reason, its development and operating costs are higher, although it outperforms RBC strategies in most cases. Both RBC and MPC can use external signals (named penalty signals in this thesis) to prompt their actions. The price of electricity is most often used for this purpose, leading to strategies that aim to reduce the costs. It was suggested to use also other signals, for this purpose a CO2 emissions signals was developed and used. This signal was derived from a new methodology presented in this work, and represents the marginal emissions of the grid (MEF): it thus gives a more accurate estimation of the potential impacts of DSM actions in terms of carbon footprint. In the mark of this thesis, both an RBC and an MPC controllers were developed as supervisory controls for an air-to-water heat pump supplying the heating, cooling and hot water needs of a residential building. The RBC strategy consists in modulating the set-points in the indoor space and in a hot water tank, using the penalty signal as trigger for the modulation. The MPC strategy consists in minimizing the overall summed penalties due to the heat pump use, while balancing with comfort constraints and a proper operation of the systems. Two versions of these controllers were produced: one using the electricity price as penalty signal, the other using the marginal emissions. The MPC controller in particular required the development of a simplified model of the building envelope (resistance-capacitance grey-box model) and of the heat pump performance, both adjusted differently for heating or cooling operation. The MPC included several novelties in its configuration, such as the mixed-integer formulation, the heat pump simplified model based on experimental data and the consideration of its computational delay.

PhotoVoltaic/Thermal (PV/T) panels were used for cooling water through the principle of nocturnal radiative cooling. This water was utilised for discharging Phase Change Material (PCM) which was embedded in ceiling panels in a climate chamber. Three different sets of flow rates were examined for the solar and the PCM loops, for five days each. The highest examined water flow rate (210 l/h) in the PCM loop provided the best thermal environment in the climate chamber, namely 92% of the occupancy time was within the range of Category III of Standard EN 15251. Although the lowest examined water flow rate (96 l/h) in the solar loop provided the highest average cooling power, due to the significant variations in the weather conditions during the three experimental cases, made it impossible to determine to which extent the difference in the cooling power is due to the different water flow rate. The percentage of electrical energy use that could be covered from the PV/Ts on site was 71.5% for Case 1, 68.3% for Case 2 and 86.8% for Case 3. In any case, the PV/T panels proved to be an efficient solution for the production of electrical energy, heated and chilled water.

The paper presents the analysis of energy retrofitting, integration of renewable energy and activation of energy flexibility in a cluster of buildings in the surroundings of a port on the Mediterranean Sea in Southern Italy, with the aim of checking the potential for it to achieve the status of positive energy district (PED). The objective of this study is to improve the contemporaneity between local energy generation and energy demand and reduce CO2eq emissions by considering signals that reflect the environmental variability of the electricity grid, through flexibility solutions applied to the HVAC system. The proposed scenarios are based on the dynamic simulation of the district and analyze the effect of actions that activate the energy flexibility of buildings through advanced control strategies of the air conditioning system. The results show that the joint action of energy efficiency strategies, integration of solar energy and energy flexibility improves the environmental sustainability of the district and the balance of energy flows. Specifically, the activation of energy flexibility contributes to a 10% reduction in operational CO2eq emissions and increases in self-consumption of energy per year. The operational emissions of the district vary from the base value of 33.37 tons CO2eq/y to 19.52 tons CO2eq/y in the scenario based on the integration of solar energy systems and energy efficiency measures, and to 17.39 tons CO2eq/y when also the demand-side energy flexibility is activated.