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Development and Experimental Validation of a Dynamic Model for a Fresnel Solar Collector
Abstract
this paper presents a lumped parameter dynamic model of a Fresnel collector field of a solar refrigeration plant. The plant is located in the Escuela Superior de Ingenieros of the University of Seville. The dynamic model parameter model developed can be used as a control model or as a simulation tool to test controllers. The lumped parameters have been determined by using real data from the plant in different operating conditions. The model has been validated against a data validation set obtained from the plant. The model has shown to reproduce the system behavior with a good compromise in accuracy and model complexity.
... The solar field consists of 11 rows of mirrors which focus the direct solar radiation on a metal tube of 64 m long whereby the water is circulating. A more complete description can be found in [19]. ...
... The modeling of the Fresnel field is developed using similar equations to the case of parabolic trough fields modeling [24], but differ in the way of calculating the geometric efficiency, the shade factor and the thermodynamic properties of the fluid. The LFC system can be modeled using two different approaches: i) the concentrated parameter model used in control applications because its simplicity [19,20,22] and ii) the distributed parameter model which takes into account the spatial distribution of the system providing a more precise description [6,10,5]. The distributed parameter model is used for simulation purposes. ...
... beam and the shade factor [19]. The distributed parameter model is solved with an integration time of 0.25 s, dividing the tube into 64 segments of 1 m each. ...
... Con respecto al modelo matemático, se pueden usar dos enfoques: el modelo de parámetros concentrados y el modelo de parámetros distribuidos. El modelo de parámetros concentrados proporciona una descripción puntual del captador Fresnel [14]. Es una descripción más simple que el modelo de parámetros distribuidos. ...
... Cuadro 1: Descripción de los parámetros del modelo de forma, etc. La eficiencia geométrica depende deĺ angulo de incidencia del sol y el factor de sombra [14]. ...
... La razón de incluir un controlador feedforward es que ayuda al rechazo de perturbaciones [25]. El feedforward se calcula usando el modelo de parámetros concentrados como sigue [14]: ...
... Con respecto al modelo matemático, se pueden usar dos enfoques: el modelo de parámetros concentrados y el modelo de parámetros distribuidos. El modelo de parámetros concentrados proporciona una descripción puntual del captador Fresnel [14]. Es una descripción más simple que el modelo de parámetros distribuidos. ...
... Cuadro 1: Descripción de los parámetros del modelo de forma, etc. La eficiencia geométrica depende deĺ angulo de incidencia del sol y el factor de sombra [14]. ...
... La razón de incluir un controlador feedforward es que ayuda al rechazo de perturbaciones [25]. El feedforward se calcula usando el modelo de parámetros concentrados como sigue [14]: ...
Uno de los recursos m�as importantes para mejorar
la e�ciencia en los sistemas de energ��a solar, es
el control avanzado. En general, con el uso de estrategias
de control convencionales no se obtienen
buenos desempe~nos en todo el rango de operaci�on
debido a la din�amica fuertemente no lineal de este
tipo de sistemas, as�� como las m�ultiples fuentes de
perturbaciones. En este trabajo se desarrolla un
control predictivo basado en el espacio de estados
para controlar un captador solar tipo Fresnel. Su
comportamiento es analizado sobre el modelo de
par�ametros distribuidos no lineal de dicho captador.
... El sistema consiste en un tubo de metal de 64 metros de longitud, por el cual circula agua a presión [6]. La radiación solar incide sobre la superficie de espejos y ésta es concentrada en el tubo, el cual transmite el calor al fluido. ...
... La eficiencia geométrica está formada por tres partes: el factor de sombra, la cantidad de irradiación que se pierde por no ser el espejo perpendicular al vector radiación, y la parte del tubo que queda en sombras. Cada una de estas partes involucra complejos cálculos trigonométricos, así como hacer uso de un modelo 2D y 3D de la planta [6]. Con respecto al término de la eficiencia óptica influyen varios factores también: la limpieza de los espejos la cual influye en su reflectividad, la limpieza de los reflectores primarios y secundarios, la absortancia del tubo de metal, así como otros factores que son difíciles de modelar. ...
... Para una descripción más detallada del desarrollo de un modelo de parámetros concentrados del captador solar consultar [6]. ...
En este artículo se presenta el modelado matemático,
así como algoritmos de control de un captador solar
tipo Fresnel que pertenece planta de refrigeración
solar situada en la Escuela Superior de Ingenieros
de la Universidad de Sevilla. Se va a desarrollar un
modelo de parámetros distribuidos, ajustando los
parámetros del mismo con datos tomados del sistema
real y comparando la respuesta del modelo con la
salida del sistema. Por último, se implementará una
estrategia de control clásica, un PID con un
compensador de perturbaciones de tipo feedforward
paralelo, cuyo desempeño será validado mediante
simulación usando el modelo de parámetros
distribuidos.
... This paper presents a control scheme designed for the Fresnel collector field which is a part of the solar cooling plant located at the Engineering School (ESI) of Seville [9,10]. This plant consists of a Fresnel collector field, a double-effect LiBr+ water absorption chiller and a storage tank. ...
... The solar field orientation is East-West, and the sun-tracking system modifies the inclination of every row to concentrate the sun beam onto the metal tube. To do this, the sun-tracking system computes the solar vector by using the well-known formulas for solar azimuth and solar height [1], and then calculates the desired inclination of every row using the relative position between the row and the tube as explained in [10]. ...
... Its computation involves complex trigonometric formulas. These are well explained in [10]. ...
Model predictive control has been demonstrated to be one of the most efficient control techniques for solar power systems. An incremental offset-free state-space Model Predictive Controller (MPC) is developed for the Fresnel collector field located at the solar cooling plant installed on the roof of the Engineering School of Sevilla. A robust Luenberger observer is used for estimating the states of the plant which cannot be measured. The proposed strategy is tested on a nonlinear distributed parameter model of the Fresnel collector field. Its performance is compared to that obtained with a gain-scheduling generalized predictive controller. A real test carried out at the real plant is presented, showing that the proposed strategy achieves a very good performance.
... One of the application of solar energy is solar cooling systems. In recent years there has been substantial growth in the requirements of cooling systems in commercial and industrial buildings in order to provide greater comfort when thermal load due to the extensive use of personal computers and the use of lighting is dramatically increased, [4]. The coincidence between peak demand and peak production (solar maximum) is a remarkable advantage of the solar cooling plants compared to other applications of solar energy. ...
... In general, two approaches to model such a system are classified as the concentrated parameter model and the distributed parameter model. The concentrated parameter model provides a lumped description of the Fresnel collector field, [4]. The variation in the internal energy of the collector can be described as, [7] ...
... quires the knowledge of multiple factors such as the mirror reflectivity, the metal tube absorbance, the shape factor etc. The computation of the geometric efficiency n o is performed using complex mathematical formulas described in [4]. The PDE system can be solved by dividing the metal and fluid into 64 segments measuring 1 m long. ...
This paper addresses the design of an explicit model predictive controller for the outlet water temperature control of a solar cooling plant system that uses a field of Fresnel collectors. Solving multi-parametric quadratic programs~(mpQP) to obtain explicit solutions to constrained model predictive control~(MPC) problems enables the off-line design before the MPC controller is implemented, e.g., on a standard programmable logic controller. The simulation result shows the feasibility of the proposed control design for such a system. This is implementable on industrial application-based hardware platforms where computational and memory resources are limited
... Robledo et al. [32] develop a phenomenological lumped parameter dynamic model considering the optical and thermal models and an ordinary differential equation. The authors used least-squares methods to identify the model's parameters. ...
... It is worth noting that this paper proposes a third-order heat loss polynomial function to describe the heat losses coefficient, Eq. (10), instead of fourth and second-order polynomials that are typically used [32,33]. The third-order polynomial is employed because it becomes possible to change the sign oḟof Eq. (10), and consequently, the heat losses term of Eq. (8). ...
This work develops digital entities of a commercial Fresnel Solar Collector (FSC) installed in an absorption cooling plant. The objective is to create and validate models that describe the FSC dynamics across its whole operation range during the day and the night. Thus, the temperatures range between operation temperature of 180 °C and almost ambient temperature due to overnight heat losses. In the same sense, the flow range between zero to 13m³/h. The idea is that the digital twin will aid start-up and shut-down optimization and control design reliability. The paper employs two modeling approaches, then evaluates their twinning/adaptation time and performance validation. One model uses phenomenological modeling through Partial Differential Equations (PDE) and parameters identification, and another uses a data-driven technique with Adaptive Neuro-Fuzzy Inference Systems (ANFIS). The available measurement data sets comprise 25 days of operation with a sampling time of 20 s which, after outlier removal, filtering and treatment, resulted in 108416 samples. The validation considers six separate operating days. Results show that both models can twinning/adapt considering measured data. The models present pretty good results and are suitable for control and optimization. Besides, this is the first paper considering the FSC mirror defocus action on dynamic modeling and validation.
... The computation of geometric efficiency, which takes into account the effect of the cosine of the incidence angle of the solar beam and the shade factor, involves complex trigonometric formulas. These formulas are explained in [38]. ...
... The concentrated parameter model provides a lumped parameter description of the whole field. The variation in the internal energy of the fluid can be described by the equation [38]: ...
One of the ways to improve the efficiency of solar energy plants is by using advanced control and optimization algorithms. In particular, model predictive control strategies have been applied successfully in their control.
The control objective of this kind of plant is to regulate the solar field outlet temperature around a desired set-point. Due to the highly nonlinear dynamics of these plants, a simple linear controller with fixed parameters is not able to cope with the changing dynamics and the multiple disturbance sources affecting the field.
In this paper, an adaptative model predictive control strategy is designed for a Fresnel collector field belonging to the solar cooling plant installed at the Escuela Superior de Ingenieros in Sevilla. The controller changes the linear model used to predict the future evolution of the system with respect to the operating point.
Since only the inlet and outlet temperatures of the heat transfer fluid are measurable, the intermediate temperatures have to be estimated. An unscented Kalman filter is used as a state estimator. It estimates metal-fluid temperature profiles and effective solar radiation.
Simulation results are provided comparing the proposed strategy with a PID + feedforward series controller showing better performance. The controller is also compared to a gain scheduling generalized predictive controller (GS-GPC) which has previously been tested at the actual plant with a very good performance. The proposed strategy outperforms these two strategies.
Furthermore, two real tests are presented. These tests show that the proposed controller achieves adequate set-point tracking in spite of strong disturbances.
... In this subsection, the mathematical model of the Fresnel collector field is presented. Two approaches are usually considered in this kind of systems: the lumped parameter model (developed in [22]) and the distributed parameter model (described in [23]). In this paper, a distributed parameter model has been used. ...
... The heat transfer coefficient depends on the segment temperature and the water flow [26]. As far as the thermal losses coefficient is concerned, it was obtained using experimental data from the collector field [10,22]. Figures 4 and 5 show a comparison between the model and the real plant evolution in two different days (in October and June). ...
Solar energy for cooling systems has been widely used to fulfill the growing air conditioning demand. The advantage of this approach is based on the fact that the need of air conditioning is usually well correlated to solar radiation. These kinds of plants can work in different operation modes resulting on a hybrid system. The control approaches designed for this kind of plant have usually a twofold goal: (a) regulating the outlet temperature of the solar collector field and (b) choosing the operation mode. Since the operation mode is defined by a set of valve positions (discrete variables), the overall control problem is a nonlinear optimization problem which involves discrete and continuous variables. This problems are difficult to solve within the normal sampling times for control purposes (around 20–30 s). In this paper, a two layer control strategy is proposed. The first layer is a nonlinear model predictive controller for regulating the outlet temperature of the solar field. The second layer is a fuzzy algorithm which selects the adequate operation mode for the plant taken into account the operation conditions. The control strategy is tested on a model of the plant showing a proper performance.
... The CSP power plant is dedicated to the production of electricity, only (LFSC) technology can directly generate steam; its use varies at different scales from 10 kW to hundreds of MW [4] . In addition, it can be applied for the application in medium temperature range (100-250 °C) [5] . In this case, direct solar radiation (DNI) is considered as the main energy resource. ...
Drying is an energy intensive process, which requires a high amount of thermal and electrical energy. To respond to that challenge, this paper proposes an innovative phosphate dryer environment friendly. The idea is to exploit the Linear Fresnel Solar Collector (LFSC) in the drying process. A laboratory scale prototype was designed and constructed based on a detailed theoretical and optical study. The numerical results prove that the designed prototype admits a significant optical efficiency which can reach values higher than 0.7 from May to July. An adjustment of LFSC prototype mirrors by laser beam allows good optical performances suitable for phosphate drying. The experimental results showed that the residual humidity of the dried phosphate was in the order of 0.02 kg water/kg dry matter in the LFSC process and 0.07 kg water/kg dry matter in the open air process, after 04 h 40 min. The drying process using LFSC has reached international phosphate marketing standards. Based on 100 m2 LFSC aperture area, the yearly provided thermal energy was 59,766 kWh, the largest quantities of dried phosphate are obtained during the summer with a maximum of 43 tons in July and the dodged CO2 emissions are about 38,255 kg.
... P r e p r i n t n o t p e e r r e v i e w e d technology can directly generate steam; its use varies at different scales from 10 kW to hundreds of MW. In addition, it can be applied for the application in medium temperature range (100-250°C) [4]. In this case, direct solar radiation (DNI) is considered as the main energy resource. ...
... Multi-linear regression methods permit to better approximate the quasi-dynamic behaviour of receivers [19,20]. Other models consider the internal energy variation in the absorber [21,22]. Many of the aforementioned models consider both linear and quadratic heat losses; however, [23] also considers the bi-quadratic heat losses factor. ...
The modelling of Linear Fresnel Collectors (LFCs) is crucial in order to predict accurate performance for annual yields and to define proper commands to design the suitable controller. The ISO 9806 modelling, applied to thermal collectors, presents some gaps especially with concentration collectors including LFCs notably due to the factorisation of the incidence angle modifiers and the fact that they are considered symmetric around the south meridian. The present work details the use of two alternative modellings methodologies based on recorded experimental data on the solar system installed at the Cyprus Institute, in the outskirts of Nicosia, Cyprus. The first modelling is the RealTrackEff, which is an improved ISO9806 modelling, and the second is constructed using the CARNOT blockset in MATLAB/Simulink. Both models include all the elements of the heat transfer fluid loop, i.e., mineral oil, with a tank and a heat-exchanger. First, the open loop’s studies demonstrated that the root mean square on temperature is 1 ∘C with the RealTrackEff; 2.9 ∘C with the CARNOT and 6.3 ∘C with the ISO9806 in comparison to the experimental data. Then, a PID control is applied on the experimental values in order to estimate the impact on the outlet temperature on the absorber and on power generation. Results showed that the error on the estimation of the heat absorbed reaches 32%.
... LFR was used in their system to supply the required heat at 200 • C and a cold temperature of -12 • C was also achieved. Robledo et al. (2011) developed a lumped parameter dynamic model of a LFR used in a refrigeration cycle. They considered their model as a control model or as a simulation tool for testing the controller's behavior. ...
Solar energy is the most sustainable and free source to manage the world energy demand. One aspect of solar-driven energy supply can be observed in cooling systems. Recently, solar energy-based cooling systems have received many attentions. Solar cooling systems utilizing solar collectors, as the renewable and sustainable-based solution, have the good potentials to overcome the challenges associated with consumption of fossil fuels. In this study, the recent advances about the potentials of dish collectors and linear Fresnel reflectors for the usage in the cooling systems are reviewed. In addition, the solar-powered conventional absorption chiller and cryogenic systems are investigated. Hybrid cooling solar systems and solar-based combined cooling, heating, and power systems are also studied. The hydrogen production in cooling integrated systems and cold thermal energy storage are discussed. In each section, in addition to general description of the system, some explanations about the thermodynamic and economic aspects of the systems are provided. Finally, the main results of the review are summarized and based on the available gaps between the literatures, some suggestions are provided for the future studies. It was found that using solar dish collectors in a hybrid system, designed for the freshwater and LNG production, causes carbon dioxide emissions reduction by 40%, and also increases freshwater and LNG production by 95% and 4.7%, respectively. In the hybrid trigeneration solar-biomass power plants, using the linear Fresnel reflector leads to 29% save in biomass and land.
... A concentrated parameter model provides a lumped description of the whole sector [38,39]. In this paper, this equation is used to model the dynamics of the whole sector, as explained above. ...
Competitiveness of solar energy is one of current main research topics. Overall efficiency of solar plants can be improved by using advanced control strategies. To design and tuning properly advanced control strategies, a mathematical model of the plant is needed. The model has to fulfill two important points: (1) It has to reproduce accurately the dynamics of the real system; and (2) since the model is used to test advanced control strategies, its computational burden has to be as low as possible. This trade-off is essential to optimize the tuning process of the controller and minimize the commissioning time. In this paper, the modeling of the large-scale commercial solar trough plants Mojave Beta and Mojave Alpha is presented. These two models were used to test advanced control strategies to operate the plants.
... Although filtering entails a loss of information, it is not considered critical since in this paper we try not to entirely replace the measure of the pyrheliometer but to obtain a fault tolerant system using an approximate measure of the irradiance. Moreover, in CSP plants temperature is not critical, strictly speaking, for the production of the plant because it can work in a wide temperature range, which does not happen in other processes where the operating temperature range is very narrow and critical to the proper functioning of the process [21]. ...
In this paper we propose an estimator of solar radiation and a heuristic radiation selector to design a solar radiation Fault Tolerant Model Predictive Control strategy for solar trough plants. The complete design of the control system proposed has been simulated using the model of ACUREX solar trough plant at the Plataforma Solar de Almería (PSA) using a Gain Scheduling Generalized Predictive Control(GS-GPC) control strategy. Simulation results (estimation/heuristic selector/GS-GPC) of the proposed scheme are compared with simulations of the same GS-GPC controller strategy when using only a pyrheliometer radiation measurement.
... The solar system is composed of a set of Fresnel solar collectors (Fig. 2), supplied by Industrial Solar (I.S.F.C, 2012) which concentrate solar radiation onto an absorption tube through which a heat transfer fluid circulates (in our case, pressurized water). The Fresnel collector is used in small plants due to the cost reduction and the minimization of the plant maintenance (Grena and Tarquini, 2011;Robledo et al., 2010). ...
Solar cooling plants can work in multiple operation modes. A numerical model of the whole plant can be used to choose the adequate operation mode and optimizing the energy production by using hierarchical control strategies. Simplified models are required for solving the control problem in a suitable time-window using systems such as Programmable Logic Controllers (PLCs) or microcontrollers. The storage system is an important component of a solar cooling plant. They are useful in solar systems for helping to satisfy the energy demand when solar energy is not available. Those based on phase change materials (PCMs) have the advantage of high storage density at a small temperature range. This paper presents a simplified model of a PCM storage tank placed at the solar cooling plant of the Escuela Superior de Ingenieros (ESI) in Seville, focusing on the parameter estimation algorithm.
... The solar system is composed of a set of Fresnel solar collectors (Fig. 2), supplied by Industrial Solar (I.S.F.C, 2012) which concentrate solar radiation onto an absorption tube through which a heat transfer fluid circulates (in our case, pressurized water). The Fresnel collector is used in small plants due to the cost reduction and the minimization of the plant maintenance (Grena and Tarquini, 2011;Robledo et al., 2010). ...
... En este trabajo se ha desarrollado un modelo de Eco- simPro del captador tipo Fresnel de una planta solar para la producción de frio [6]. Se estima que la re- ducción de costes, gracias al uso de la tecnología Fresnel, es de un 50%, si lo comparamos con otras técnicas, lo cual lo hace atractivo para su implanta- ción en edificios. ...
With the advancement of new technologies, power systems are increasingly equipped with more sensors and actuators, heightening the risk of failure. This fact, together with the vulnerability of solar plants \x96not only to internal faults but also to the action of the sun, rain, wind, and animals, among others\x96 gives rise to the need for detecting and identifying faults to deal with them. Methods that detect and diagnose faults play a crucial role in solar plants, allowing the systems to cope with them as soon as they occur and before they lead to large-scale problems. This work proposes using neural networks to detect and distinguish mirror and flow rate faults in a Fresnel plant. In addition, a defocusing stage is added to access hard-to-isolate faults, increasing the accuracy of 89.61% to 97.43%. These results contribute to the problem of isolability in thermal solar plants. The simulations for obtaining the neural networks and the results were conducted on a model of the Fresnel plant located at the Engineering School of Seville, Spain (ETSI).
Solar Radiation Concentrating Technologies use large mirrors to concentrate sunlight onto a relatively small-aperture receiver. Solar Radiation Concentrating Technologies use large mirrors to concentrate sunlight onto a relatively small-aperture receiver. Linear Fresnel Reflector Systems use long, narrow, flat or slightly curved mirrors that reflect Sun’s rays onto a fixed linear receiver mounted above and along them. Even in small scale, they usually adopt one-axis tracking mechanisms. Therefore, as incident solar rays are generally oblique, it is inevitable for these Systems to not have optical losses: cosine effect, end losses, shading or blocking effects. Thus, although they have some advantages compared with other technologies (simplicity, robustness and low capital cost), they also have important drawbacks and limitations that significantly limit their efficiency.
In this paper, a detailed case study of the control aspect of a solar cooling plant with a Fresnel collector system is considered. The control problem that is taken into account is to maintain the outlet temperature of pressurized water leaving the field through the update of water pump flow rate.
This paper presents the application of a predictive controller with simultaneous identification to a solar air conditioning plant. The time varying nature of the process makes necessary an adjustment of the controller parameters to the varying operational conditions. The main novelty with respect to classic adaptive MPC scheme is to penalize the identificationt error in the cost function used for control. The behaviour of the controller is illustrated by simulations and experimental results. The integration of identification and control avoids the tedious identification procedure that is necessary before the start-up of any predictive controller. This new adaptive MPC scheme shows its effectiveness in controlling the outlet temperature in the solar thermal plant.
Preface.- List of figures.- List of tables.- Nomenclature.- Introduction.- Description and dynamic models of the plant.- Basic control schema.- Basic structures of adaptive control.- Model-based predictive control strategies.- Frequency-domain control and robust optimal control.- Heuristic fuzzy logic control.- Summary and concluding remarks.- References.- Index.
Improvement of climatic conditions affects productivity and efficiency. Running of conventional air conditioners to produce climatic environment of greater productivity is a problem in arid and humid zones without adequate electricity supply, and unconventional means have to be employed. Application of solar radiation for drying or humidifying air for conditioning without intermediary machinery is one of these solutions for increasing productivity and efficiency. Solar air conditioning without intermediary machines is explained, and ways are described for practical execution of solar air conditioning.Solar refrigeration without intermediary machinery is a continuation of solar air conditioning. Drops in temperature of 30°F and more are possible by it. Lower temperatures require employment of ventilators and heat exchangers. Their use provides temperatures of 33° to 35°F within a moving air current which is today's limit in solar refrigeration. This cooling of an air current permits at least cold storage of any size with temperatures of 40° to 50°F.For lower temperatures, rational resorption is reviewed in regard to regeneration by collectors of solar heat. With the same solar heat quantity inserted for regeneration, rational resorption delivers 2.50 to 3.25 times more refrigeration performance than conventional absorption refrigeration.
The work presented in this paper exploits the transport characteristic of a solar plant where the transport velocity (a flow) is the manipulated variable, i.e. the control input. The solar field is modelled by a partial differential equation. A non-uniform sampling in time is performed in order to obtain a discrete linear model. Due to the transport dynamics of the plant the resulting transfer function has a finite impulse response and the optimal control derived from a black-box approach of such a systems yield pure feed-forward compensators. The main contribution of this paper is the use of a state-space description of the plant in conjunction with the nonuniform sampling that allows to introduce the feedback mechanism through the state observer. The controller results from the optimization of a multi-step quadratic cost function. Experimental results performed with the solar plant are shown.
A solar/gas cooling plant at the Engineering School of Seville (Spain) was tested during the period 2008–2009. The system is composed of a double-effect LiBr + water absorption chiller of 174 kW nominal cooling capacity, powered by: (1) a pressurized hot water flow delivered by mean of a 352 m2 solar field of a linear concentrating Fresnel collector and (2) a direct-fired natural gas burner. The objective of the project is to indentify design improvements for future plants and to serve as a guideline. We focused our attention on the solar collector size and dirtiness, climatology, piping heat losses, operation control and coupling between solar collector and chiller. The daily average Fresnel collector efficiency was 0.35 with a maximum of 0.4. The absorption chiller operated with a daily average coefficient of performance of 1.1–1.25, where the solar energy represented the 75% of generator’s total heat input, and the solar cooling ratio (quotient between useful cooling and insolation incident on the solar field) was 0.44.
In spite of the fact that Spain is one of the EU countries with the highest solar resource on annual basis, the huge seasonal variation in solar radiation availability and the relatively short period with heating demand, make it difficult to reach significant contributions of solar energy to the buildings heating energy demand. This compromises the economic viability of big solar collector areas per capita, and introduces technical difficulties for the dissipation of the excess solar energy available in the summer months. On the other hand, in a large part of the Spanish territory, in other to reach adequate comfort conditions in our buildings, the energy demand for cooling is more important or of the same order than the heating demand. Cooling energy demand is now experiencing a fast growing rate as this comfort requirement becomes internalized. Domestic air conditioning equipments based on vapour compression cycles are being used to reach comfort conditions in some of the rooms of buildings that were designed without taking into account cooling requirements. In spite of their so far small contribution to the total building sector energy demand, these equipments are already imposing important constraints on the environment and the electricity distribution system. Solar absorption cooling arises as an interesting alternative, which at the same time allows reaching a higher solar contribution to the heating demand. However, solar cooling installations present several peculiarities with respect to the more known DHW or even heating installations, which require to incorporate a more detailed approach and additional considerations in the design and performance evaluation processes. Besides, some limitations still persist in solar absorption systems, which could make them loose their market potential for the benefit of other solar cooling options. In this paper, we present some conclusions arising from the experience gained in detailed TRNSYS dynamical simulation of some of the first commercial solar heating and cooling installations recently implemented in Spain, and analyse their perspectives in comparison with other solar cooling options.
Summer air conditioning represents a growing market in buildings worldwide, with a particularly significant growth rate observed in European commercial and residential buildings. Heat-driven cooling technologies are available, which can be used in combination with solar thermal collectors to alleviate the burden caused by air conditioning on the electric utilities and the environment. Solar air conditioning has progressed considerably over the past years as a result of efforts toward environmental protection and new developments in components and systems, and significant experience has been gained from demonstration projects. The main obstacles for large scale application, beside the high first cost, are the lack of practical experience and acquaintance among architects, builders and planners with the design, control and operation of these systems.This paper describes the main results of the EU project SACE (Solar Air Conditioning in Europe), aimed to assess the state-of-the-art, future needs and overall prospects of solar cooling in Europe. A group of researchers from five countries has surveyed and analyzed over 50 solar-powered cooling projects in different climatic zones. The paper presents a short overview on the state-of-the-art and potential of solar-assisted cooling and air conditioning technologies. The results of the study, including a database of the surveyed projects, an evaluation of these projects on a uniform basis, an economic analysis tool, user guidelines and a multimedia tool—are presented. The potential energy savings and limitations of solar thermal air conditioning in comparison to conventional technologies are illustrated and discussed.
This paper presents the application of a Model Predictive Controller to the temperature control in a solar air conditioning plant. The controller uses a Smith Predictor and includes a feed-forward control action to reject disturbances caused by solar radiation and the auxiliary gas heater. The tuning procedure is simple and allows a good compromise between robustness and performance. The behaviour of the controller is illustrated by experimental results.
A self-tuning proportional-integral controller for a solar distributed collector field that is based on a pole-assignment approach employing serial compensation to cope with measurable external disturbances is presented. The scheme is compared with the more commonly adopted parallel feedforward approach by both simulation and implementation on the plant itself.< >
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