Solar Driven Air Conditioning System Research Articles

Dynamic modelling of a ground-coupled solar ejector cooling system

ABSTRACT This work presents a solar-driven air conditioning system based on ejector technology with closed-loop vertical geothermal boreholes. Modeling and simulation are carried out using Dymola software for dynamic transient analysis, with the refrigerant R134a. Condenser temperature regulation produces a 267% improvement of performance compared to a solar-only configuration. Solar fraction increases with increasing solar collector area, which benefits the system up to the limit of 27 m2 for a cooling load of 9 kW. The reservoir volume ensuring high solar fraction is 14 m3. Optimal generator saturation temperature ensures a seasonal coefficient of performance value of 0.772 and a maximum overall efficiency of 39%. When the system encounters deviations from the optimum set point, the overall efficiency becomes 37.4%.

Optimization of the thermal storage system in a solar-driven refrigeration system equipped with an adjustable jet-ejector

The present paper shows a numerical research about the influence of different thermal storage capacities and thermal power consumption strategies in a solar-driven air-conditioning system operating with refrigerant R1234yf. The computational model is fed with hourly climatic data (solar irradiance and ambient temperature) of the typical meteorological year of a Mediterranean location. A special focus is put on the dynamic response of the refrigeration system, the solar collector, and the sensible heat storage tank. Since the refrigeration needs are nearly synchronized with the sunny hours, small tank volumes are the most convenient architecture to achieve a rapid heating-up after tank discharges. For a parabolic trough collector span of 7.1 m, 13.3 kW of thermal power consumption represents a reasonable trade-off between the main performance indicators, mainly, the refrigeration capacity, COPth (thermal coefficient of performance) and the system's capability to operate properly ensuring an adequate thermal level in the heat reservoir.

Special Issue “Thermochemical Conversion Processes for Solid Fuels and Renewable Energies”

The world society ratifies international measures to reach a flexible and low-carbon energy economy, attenuating climate change and its devastating environmental consequences. The main contribution of this Special Issue is related to thermochemical conversion technologies of solid fuels (e.g., biomass, refuse-derived fuel, and sewage sludge), in particular via combustion and gasification. Here, the recent activities on operational flexibility of co-combustion of biomass and lignite, carbon capture methods, solar-driven air-conditioning systems, integrated solar combined cycle power plants, and advanced gasification systems, such as the sorption-enhanced gasification and the chemical looping gasification, are shown.

A New Design of an Integrated Solar Absorption Cooling System Driven by an Evacuated Tube Collector: A Case Study for Baghdad, Iraq

The electrical power consumption of refrigeration equipment leads to a significant influence on the supply network, especially on the hottest days during the cooling season (and this is besides the conventional electricity problem in Iraq). The aim of this work is to investigate the energy performance of a solar-driven air-conditioning system utilizing absorption technology under climate in Baghdad, Iraq. The solar fraction and the thermal performance of the solar air-conditioning system were analyzed for various months in the cooling season. It was found that the system operating in August shows the best monthly average solar fraction (of 59.4%) and coefficient of performance (COP) (of 0.52) due to the high solar potential in this month. Moreover, the seasonal integrated collector efficiency was 54%, providing a seasonal solar fraction of 58%, and the COP of the absorption chiller was 0.44, which was in limit, as reported in the literature for similar systems. A detailed parametric analysis was carried out to evaluate the thermal performance of the system and analyses, and the effect of design variables on the solar fraction of the system during the cooling season.

Charging and discharging characteristics of absorption energy storage integrated with a solar driven double-effect absorption chiller for air conditioning applications

The operation of solar driven air conditioning systems is limited to the availability of solar radiation. Consequently, to achieve extended cooling period, energy storage is necessary. This study presents performance evaluation and charging and discharging characteristics of an absorption energy storage coupled with solar driven double-effect water-lithium bromide (H2O-LiBr) absorption system through thermodynamic modeling and simulation. The absorption energy storage stores the solar heat in the form of chemical energy during the day and discharges later for cooling application. The integrated system achieved effective cooling for about fourteen hours on daily basis. The results indicate an average coefficient of performance (COP) of 1.35 for the integrated absorption chiller-storage unit and exergy efficiency of 25%. Furthermore, the overall COP of the integrated solar cooling system is 0.99 and the overall exergy efficiency is 6.8%, while the energy storage density for typical climatic conditions of Dhahran, Saudi Arabia is found to be 444.3 MJ/m3. The energy storage density obtained from the integrated solar driven H2O-LiBr double-effect absorption system is found to be higher by 13–54% compared to other integrated systems based on single-effect configuration.

Comparison of two hygroscopic materials for a solar-assisted desiccant-based air handling unit

Solar-driven air-conditioning systems are an interesting solution to reduce greenhouse gas emissions as they are essentially powered with a renewable energy source. Among the solar heating and cooling systems, desiccant-based air handling units (AHUs) are a very promising alternative as they require low temperature thermal energy for operation in cooling mode. In this paper the experimental plant of University of Sannio (Benevento, Southern Italy), consisting of an AHU with a desiccant wheel using as hygroscopic material silica gel is coupled with solar thermal collectors. This AHU has been also simulated with a different material for the desiccant wheel, the MIL101@GO-6 (MILGO). It is a composite material, consisting of graphite oxide dispersed in the MIL101 metal organic framework network structure, that shows a better dehumidification effectiveness. The energy and environmental performance of a desiccant-based solar heating and cooling system with this new material have been evaluated with respect to the conventional AHU based on cooling dehumidification. Yearly based dynamic simulations of the plant serving a university classroom located in Benevento have been performed. Furthermore, a comparison with the air-conditioning system equipped the currently adopted material (silica gel) has been carried out too. The optimal plant configuration varying collector type (flat plate and evacuated tube), tilt angle and surface has been found.

Thermal performance of desiccant-based solar air-conditioning system with silica gel coating

In the present paper, a solar-driven air-conditioning system comprising silica gel-coated concentric tube heat exchanger is fabricated and analyzed experimentally. The setup consists of two concentric tube heat exchangers with silica gel coating to achieve continuous dehumidification of the humid air. Parabolic trough-type solar collector is used as air heater to supply hot air continuously to regenerate the silica gel. The system performance is measured in terms of dehumidification factor and cooling capacity. The performance parameters are plotted against the different values of the atmospheric air temperature, cooling water temperature, and specific humidity. It is observed that the dehumidification factor and cooling capacity depend on both the cooling water temperature and the conditions of ambient air. The maximum value of dehumidification factor and cooling capacity achieved are 11.05 g/kg and 5.748 kJ/min, respectively, for the ambient air temperature of 37.6 °C and specific humidity of 23.99 g/kg.

Dynamic simulation of an integrated solar-driven ejector based air conditioning system with PCM cold storage

The development of a dynamic model using the TRaNsient System Simulation program (TRNSYS) for the performance assessment of a solar-driven air conditioning system with integrated PCM cold storage is presented. The simulations were carried out for satisfying the cooling needs of a 140m3 space during the summer season in Tunis, Tunisia. The model is composed of four main subsystems including: solar loop, ejector cycle, PCM cold storage and air conditioned space. The effect of varying the solar collector area (Asc) and the hot storage capacity (Vhs) on the solar fraction are investigated. It was found that the application of a relatively small hot storage tank (700l) led to the highest solar fraction (92%). A collector area about 80m2 is needed to assure a solar fraction of 70%. Increasing Asc beyond this value has only a small effect on the overall system efficiency. The influence of applying cold storage is also investigated. The results without cold storage indicated that the comfort temperature was exceeded in more than 26% of the time. With cold storage the periods of high indoor temperatures reduced significantly. An optimal storage volume of 1000l was identified resulting in the highest cooling COP and excellent indoor comfort (95% of the time with a room temperature below 26°C). The maximum COP and solar thermal ratio (STR) were 0.193 and 0.097, respectively.

Solar Heating and Cooling in Buildings – How Sustainable?

Conventional heating and cooling systems are responsible for large amounts of carbon dioxide release to the environment, as well as for the use of harmful refrigerants regarding the greenhouse effect and the ozone depletion potential. Solar radiation is a clean form of energy, which is required for almost all natural processes on earth. In South Africa, the majority of produced electricity is generated from fossil fuels and the potential of renewable energy sources is vast, solar radiation in particular is in abundance. The upper limit for Global Horizontal Irradiance (GHI) in South Africa can be as high as 2 300 kWh/m2/a, whereas the Direct Normal Irradiance (DNI) value attains a maximum of 2 900 kWh/m2/a, which is significantly higher than it is in other regions worldwide. The global air conditioning systems market has been estimated to reach 78.8 million units by 2015 due to increasing living standards, comfort expectations and global warming. South Africa is not the best performer regarding renewable energy use among African countries and there is a long way to go to achieve a sustainable environment. This paper seeks to investigate the feasibility and the sustainability of solar driven air conditioning system in South Africa based on meteological weather data. Currently, renewable energy is a topic of interest in South Africa after the 2008 energy emergency when power outages were rolled out due to inadequate maximum load planning. Solar air conditioning technology remains an untapped technology in South Africa.

Solar driven air conditioning and refrigeration systems corresponding to various heating source temperatures

Solar driven air conditioning systems can cope with solar collectors working in a wide range of temperatures. Sorption systems, including absorption and adsorption refrigeration systems, are among the best choices for solar cooling. Five systems including modular silica gel–water adsorption chiller, single/double effect LiBr–water absorption chiller, 1.n effect LiBr–water absorption chiller, CaCl2/AC (activated carbon)–ammonia adsorption refrigerator, and the water–ammonia absorption ice maker with better internal heat recovery were presented. The above five sorption chillers/refrigerators work under various driven temperatures and fulfill different refrigeration demands. The thermodynamic design and system development of the systems were shown. All these systems have improvements in comparison with existing systems and may offer good options for high efficient solar cooling in the near future.

Solar Driven Air Conditioning System Integrated With Latent Heat Thermal Energy Storage

This work is to investigate and validate of solar thermal storage system integrated with phase change material (PCM). The existing system is suggested to setup a Storage tank with phase change material (PCM), between the Solar concentrate dishes and Vapour absorption machine (VAM). The storage tank was used instead of an Electrical AC compressor, by which the renewable energy can be utilized to its full extent. Numerical Simulation is done and the Total Heat output, Temperature distribution along the bed, Pressure, charging time, discharging time, Mass flow rate are calculated. The storage system contains Erythritol as PCM in HDPE spherical capsule, having the storage capacity 345,121 KJ/hr (for the storage tank capacity) considering the latent heat and sensible heat of the Heat transfer fluid. Solar Driven Air Conditioning System Integrated With Latent Heat Thermal Energy Storage A. Ponshanmugakumar1*, M. Sivashanmugam1 and S. Stephen Jayakumar2 1 AMET University,Chennai,India; shnmgkmr8@gmail.com 2 VOLTAS India Ltd, Chennai, India Keywords: Vapour Absorption Machine (VAM), Phase Change Materials (PCM), Erithritol, Storage Tank, Numerical Simulation.

Solar Driven Air Conditioning System Integrated With Latent Heat Thermal Energy Storage

This work is to investigate and validate of solar thermal storage system integrated with phase change material (PCM). The existing system is suggested to setup a Storage tank with phase change material (PCM), between the Solar concentrate dishes and Vapour absorption machine (VAM). The storage tank was used instead of an Electrical AC compressor, by which the renewable energy can be utilized to its full extent. Numerical Simulation is done and the Total Heat output, Temperature distribution along the bed, Pressure, charging time, discharging time, Mass flow rate are calculated. The storage system contains Erythritol as PCM in HDPE spherical capsule, having the storage capacity 345,121 KJ/hr (for the storage tank capacity) considering the latent heat and sensible heat of the Heat transfer fluid.

A CFD analysis of the flow structure inside a steam ejector to identify the suitable experimental operating conditions for a solar-driven refrigeration system

This paper presents a numerical study of a steam ejector using CFD with the objective of identifying suitable experimental conditions that allows for a reliable ejector cycle operation. The flow structure and the mixing process inside the ejector were assessed for a range of operating conditions typical for a solar driven air conditioning system. The effect of varying the condenser pressure was studied. It was found that for relatively low condenser pressures (<2.5 kPa), two distinct shock waves occurred in the diffuser section resulting in a reduced re-compression efficiency, although it did not have a direct impact on the entrainment ratio. The effect of generator pressure was also studied. It was found that the entrainment ratio showed a maximum for constant condenser conditions. A near optimal condition of 70 kPa generator and 3 kPa condenser pressures were identified and tested in a preliminary experiment carried out with the solar driven ejector system installed in Tunis.

A Solar-Driven Ejector Refrigeration System for Mediterranean Climate: Experience Improvement and New Results Performed

The need for air-conditioning in the Mediterranean countries is higher and higher due to the effects of global warming. This paper deals with an investigation of a high performance, solar-driven air-conditioning system, the project entitled “Mediterranean AIRCOND”, is funded by the European Community under the „Community Activities in the Field of the specific program for RTD and demonstration on “Energy, Environment and Sustainable Development”. “AIRCOND” aims to study and investigate performances of advanced solar driven air conditioning system; the field system is composed of three sub systems: the heating loop, the ejector cycle and the cold storage-air handling units: The heating loop is composed of a solar array of 60 square meters evacuated tube solar collectors; installed at a tilt angle of 45o and facing to south, a 3000 L tank which is used as hot water storage in order to cover the required energy by the ejector cycle. The cold water produced by the ejector cycle will be then transferred in a 900L cold storage tank filled with 800L micro-encapsulated phase change material (MEPCM) for cold storage. It is designed to meet the dynamic cooling load. The ejector was tested at the School of the Built Environment in the University of Nottingham in UK and then transferred to Tunisia for field evaluation. Many previous theory studies have been fulfilled on this technology but never been performed experimentally at this level. This paper presents the research effort made and the experience gained during the implementation of the whole system: Different operation strategies were followed during more than one year to make the ejector cycle functional. The whole procedure has turned out to be very difficult; it was particularly difficult to obtain a deep vacuum and to ensure a good vacuum quality; this is a necessary working condition for the ejector cycle. Successful ejector tests were obtained during 8min, 15min and 40min, after many investigations; later experiments led to 3hours of continuous working. Results are very promising; the installation is still under tests in order to obtain a whole day permanent working of the ejector cycle and so of all the solar installation.

Performance and Operational Experiences of Solar Driven Cooling Plant after Five Years in Operation

 Abstract— The main aim of this study is to report the performance evaluation as well as the gained operational experiences of a solar- driven cooling plant after 5 years in operation, in addition, based on the gained experiences, a suggestion for an appropriate small- scale solar-driven cooling plant for hot arid areas. The plant performance results indicate: instead small solar energy values at the plant location, the daily solar fraction ranged from 0.33 to 0.41, and for the duration from August 2002 to November 2007 the total solar energy supplied to the chiller is 53914 kWh and the total external energy (gas energy) supplied to the chiller is 35249 kWh and their percentage are about 60% and 40%, respectively. The collectors' filed instantaneous mean efficiency value is about 0.63, the monthly average value varies from 34.1 % up to 41.8 %, with a five-year average value of 28.3 %, respectively and the daily chiller COP varies from 0.37 to 0.81, respectively. The gained from the operational experiences are: in hot arid areas, the water normally is rare, thus the re-cooling system should be designed based on dry re-cooling techniques. Moreover, based on the total initial capital cost of the entire solar cooling system, adsorption- cooling technology for small-scale solar-driven air-conditioning systems is the most appropriate. This is because these chillers can be driven by a low temperature energy source that can be obtained from flat plate collectors where, costs are a bit lower for flat plate collectors with liquid heat transfer carrier. Keywords—Solar cooling; Absorption chillers; Lithium bromide- water; operational experiences

Thermal conductivity measurement of two microencapsulated phase change slurries

This paper presents results of a thermal conductivity test carried out on microencapsulated phase change materials, to be used as a cooling storage and transport medium in a solar-driven air conditioning system. The microencapsulated slurries can be used not only as an energy storage medium but also as an energy transport medium, and this helps the system to be designed as compact as possible. The test has been carried out on two recently developed microencapsulated phase change materials. A convenient measurement system using transient line heat source technique is introduced, and the results of these measurements are presented in this paper. Copyright , Manchester University Press.

Solar-Driven Air-Conditioning Cycles: A Review

Most conventional cooling/refrigeration systems are driven by fossil fuel combustion, and therefore give rise to emission of environmentally damaging pollutants. In addition, many cooling systems employ refrigerants, which are also harmful to the environment in terms of their Global Warming Potential (GWP) and Ozone Depletion Potential (ODP). Development of a passive or hybrid solar-driven air-conditioning system is therefore of interest as exploitation of such systems would reduce the demand for grid electricity particularly at times of peak load. This paper presents a review of various cooling cycles and summarises work carried out on solar-driven air-conditioning systems.