• Energy Research

The scope of this paper is to give a short overview of the state of the art regarding control strategies, identify the role of different operating conditions, and provide useful suggestions for the design and operation of a solar assisted absorption cooling system, in line to the European regulation as well as its directly related directives. The operation of a solar absorption cooling system under real conditions is subjected to various limitations regarding its ability to satisfy the required cooling demand, as well as to avoid certain internal conditions which would lead to problematic situations and jeopardize the smooth operation of the system - such as solution crystallization and water freezing. Thus, it is very important to define and refine new control operating strategies, from an internal and external perspective. Several control strategies are discussed, altogether with a new fuzzy logic approach, which shall be experimentally validated as future actions, due to its highly promising capability. Peer Reviewed

The scope of this paper is to give a short overview of the state of the art regarding control strategies, identify the role of different operating conditions, and provide useful suggestions for the design and operation of a solar assisted absorption cooling system, in line to the European regulation as well as its directly related directives. The operation of a solar absorption cooling system under real conditions is subjected to various limitations regarding its ability to satisfy the required cooling demand, as well as to avoid certain internal conditions which would lead to problematic situations and jeopardize the smooth operation of the system - such as solution crystallization and water freezing. Thus, it is very important to define and refine new control operating strategies, from an internal and external perspective. Several control strategies are discussed, altogether with a new fuzzy logic approach, which shall be experimentally validated as future actions, due to its highly promising capability. Peer Reviewed

The operation of a solar-driven H2O-LiBr Absorption Chiller (AbC) is subjected to various limitations regarding its ability to satisfy efficiently the required cooling demand while avoiding certain internal conditions, such as H2O-LiBr solution crystallization and water freezing. These circumstances would lead to problematic situations and jeopardize the continuous operation of the system. Thus, the development of accurate control strategies is an issue of interest. A new operational control strategy approach is introduced and tested through simulation studies, by employing a transient model of the entire solar cooling application. A prototype under development is used for the parametrization of the direct air-cooled AbC model used in the simulations. The developed control strategy aims to minimize the electrical consumption of the auxiliary components of the AbC (i.e., fan, pumps) during the partial load operation period, by using a fuzzy logic interference rule for determining the cooling capacity demand and then applying an optimization algorithm for determining the velocity of the auxiliary components. Within the proposed control strategy, a fast-calculation model is embedded, which predicts the chiller’s capacity under variable external conditions and partial load operation. The electrical COP is increased up to 2.2 times with respect to a baseline case, based on a basic two-step control strategy, while allowing the chiller to operate smoother, minimizing the crystallization and freezing risk. This project has received funding from SOLAR-ERA.NET Cofund 2 Joint Call undertaking under the European Union’s Horizon 2020 research and innovation program (ECOSUN project) . During the elaboration of the work, G. Papakokkinos held a Margarita Salas Grant of the Spanish Government and J. Zheng a China Scholarship Council Studentship with the Polytechnical University of Catalonia. Peer Reviewed

The operation of a solar-driven H2O-LiBr Absorption Chiller (AbC) is subjected to various limitations regarding its ability to satisfy efficiently the required cooling demand while avoiding certain internal conditions, such as H2O-LiBr solution crystallization and water freezing. These circumstances would lead to problematic situations and jeopardize the continuous operation of the system. Thus, the development of accurate control strategies is an issue of interest. A new operational control strategy approach is introduced and tested through simulation studies, by employing a transient model of the entire solar cooling application. A prototype under development is used for the parametrization of the direct air-cooled AbC model used in the simulations. The developed control strategy aims to minimize the electrical consumption of the auxiliary components of the AbC (i.e., fan, pumps) during the partial load operation period, by using a fuzzy logic interference rule for determining the cooling capacity demand and then applying an optimization algorithm for determining the velocity of the auxiliary components. Within the proposed control strategy, a fast-calculation model is embedded, which predicts the chiller’s capacity under variable external conditions and partial load operation. The electrical COP is increased up to 2.2 times with respect to a baseline case, based on a basic two-step control strategy, while allowing the chiller to operate smoother, minimizing the crystallization and freezing risk. This project has received funding from SOLAR-ERA.NET Cofund 2 Joint Call undertaking under the European Union’s Horizon 2020 research and innovation program (ECOSUN project) . During the elaboration of the work, G. Papakokkinos held a Margarita Salas Grant of the Spanish Government and J. Zheng a China Scholarship Council Studentship with the Polytechnical University of Catalonia. Peer Reviewed

Adsorption cooling systems (ACS) may contribute towards a sustainable way of satisfying the increasing cooling demand, as they utilize solar thermal energy and employ non-ozone-depleting substances. Apart from the intrinsic ACS performance, the successfulness of its operation depends on its integration within the entire thermal system (solar collectors, thermal storage and building), which is not straight-forward due to thermal inertia effects and its inherent cyclic operation. Numerical simulations can contribute in understanding the system behavior, its adequate dimensioning and the implementation of optimized control strategies. A computational model was developed, capable of performing conjugate, dynamic simulations of the entire thermal system. The influence of the control criteria is investigated and quantified through three simulation phases, conducted for various solar collectors areas and storage volumes. Higher solar fraction is achieved for lower auxiliary heater activation temperature and lower temperature difference activation of the solar pump. Subsequently, simulations with variable cycle duration were performed, using optimized cycle duration according to the instantaneous operating temperatures. This approach reduces significantly the auxiliary consumption or satifies the demand with less solar collectors. The potential CO2 emissions avoidance is calculated between 28.1-90.7% with respect to four scenarios of electricity-driven systems of different performance and CO2 emission intensity. Peer Reviewed