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The present paper aims to evaluate the performance of a solar district cooling system in typical Middle East climate conditions. A centralized cooling station is supposed to distribute chilled water for a residential compound through a piping network. Two different solar cooling technologies are compared: two-stage lithium-bromide absorption chiller ( 2sABS ) driven by Parabolic Trough Collectors ( PTCs ) vs. single-stage lithium-bromide absorption chiller ( 1sABS ) fed by Evacuated Tube Collectors ( ETCs ). A computer code has been developed in Trnsys® (the transient simulation software developed by the University of Wisconsin) to simulate on hourly basis the annual operation of the solar cooling system, including building thermal load calculation, thermal losses in pipes and control strategy of the energy storage. A solar fraction of 70% was considered to size the solar field aperture area and the chiller capacity, within a multi-variable optimization process. An auxiliary compression chiller is supposed to cover the peak loads and to be used as backup unit. The two different solar cooling plants exhibit strongly different performance. For each plant configuration, the model determined the optimal size of every component leading to the primary cost minimization. The solar district cooling configuration based on 2sABS and PTCs shows higher performance at Riyadh (KSA) climate conditions and the overall cost is 30% lower than the one of the single-stage absorption chiller plant. [ABSTRACT FROM AUTHOR]

Abstract: Growing energy demand and global climate change are compelling reasons to look for effective utilisation of waste thermal energy and renewable energy resources. Fifteen percent of the electricity produced in the whole world is employed for refrigeration and air-conditioning processes of various kinds. Low-temperature heat operated environment-friendly adsorption cooling systems are emerging as viable alternatives to electricity-driven vapour compression refrigeration systems. Comparatively bigger sizes of adsorption based cooling units, due to their low specific cooling power, are preventing successful commercialization of the technology. Efforts are on to enhance the performance of adsorption systems through improvements in adsorbents properties, use of advanced cycles, etc. Recent application of nano-technology in the development of adsorbent material may be a big step forward towards making this technology competitive with available technologies in the market. This paper traces the evolution of the technology and analyses the obstacles to wide spread use of adsorption chillers. [Copyright &y& Elsevier]

Abstract: In cooling buildings, the use of solar energy can save around 50% of primary energy. Many studies have demonstrated the interest of such systems. However, developing and improving reliability of new components, design, control, and implementation remain a major concern. The performances of solar cooling systems are greatly influenced by climatic conditions. Indeed they affect both the driving energy of the chiller and the heat rejection. It is important to mention that internal loads and control strategy also have an impact on energy performances. Therefore, assessing the energy performance during the design phase is a key point in evaluating the economic interest of an installation. Moreover, once the commissioning of the installation is accomplished, there is a need to follow through and ensure its performance, since a large number of malfunctions can affect the quality of the system. Actual performances can be very different from those calculated in the design phase. With this aim, the present article deals with the development of an absorption chiller model used in an existing solar cooling system. This installation includes a single effect absorption chiller with a nominal chilling capacity of 30kW (EAW LB30 chiller functioning with water and lithium bromide), and it cools four classrooms of a University building in Reunion Island which is situated under a tropical climate. This pilot plant is very good monitored and can thus be used to develop and validate the absorption chiller model. The present paper first recalls the absorption principle and presents the pilot plant, the metrology, and the control strategy. Secondly, the experimental results are analysed and the steady state chiller model and also the identification method are developed. Thereafter, the simplex method is used to determine the design parameters of the machine. Finally, the simulation results are presented. The good agreement between the prediction and the experimental results allows the use of the model not only to design an installation but also to follow and control its performances. [Copyright &y& Elsevier]

Abstract: Since July 2008, a Solar Desiccant Evaporative Cooling (DEC) system has been operating as a test plant at the solar laboratory of the Dipartimento di Energia (ex DREAM) of the University of Palermo. The system is composed of an air handling unit (AHU) designed for ventilation of the laboratory coupled with a radiant ceiling that provides most of the required sensible cooling/heating energy. Flat plate collectors deliver part of the regeneration heat of the desiccant wheel during the summertime and are used for space heating during the wintertime. The system was designed for high humidity loads because of the typical climate conditions at the site and the need to support a radiant ceiling for sensible cooling. A hybrid configuration was chosen that uses two auxiliary cooling coils fed by a conventional compression chiller. One coil is used for pre-dehumidification. The other coil controls the air temperature if the desired supply temperature cannot be reached through indirect evaporative cooling alone. A specific feature of the system is the use of the heat rejected by the chiller to preheat regeneration airflow. The plant was monitored continuously after installation and start up phases were completed. This paper presents instantaneous, daily and monthly energy performance indicators for five summer months and three winter months. Monthly results are also presented and elaborated upon according to a monitoring procedure developed in the framework of the International Energy Agency (IEA) Task 38 “Solar Air Conditioning and Refrigeration” of the Solar Heating and Cooling Programme. Seasonal performance indicators such as electric and thermal COP and primary energy savings for cooling and heating operation are presented. It was found that about half of the total cooling energy delivered by the AHU was covered by the DEC process. Primary energy savings in summer, in comparison to a conventional AHU, came up to nearly 50%. The recovery of the heat rejected by the refrigerator was found as a good solution, permitting to reduce solar collector area in the design phase. Finally, main issues arisen from plant monitoring and possible solutions to enhance its energy performances are discussed. [Copyright &y& Elsevier]