This paper presents an experimental investigation on a hybrid solar system, including a water-based photovoltaic (PV) solar module and a phase change material (PCM)-based cooling tower, for cooling of the module. Elimination of heat from the PV module was performed by the use of water in the back of the panel. The PCM-based cooling tower was used as a postcooling system. A composite oil consisting of 82 wt% coconut oil and 18 wt% sunflower oil has been used as a novel phase change material in the cooling tower. The helical tubes of the cooling tower were fabricated in two different curvature ratios of 0.054 and 0.032. The experiments were performed at three different water flow rates of 11.71, 16.13, and 19.23 mL/s. The cooling performance evaluation was carried out using the average surface temperature and output power of the photovoltaic panel. The results indicated that diminution of the average PV surface temperature relative to the reference temperature was 34.01 and 32.36 °C at a water flow rate of 19.23 mL/s for the cooling systems with helical tube curvature ratios 0.054 and 0.032, respectively. Furthermore, the highest electric output power was achieved for the cooling system with a helical tube curvature ratio of 0.054 at a water flow rate of 19.23 mL/s.

Solar electric power generation utilizing photovoltaic (PV) modules is associated with low electrical efficiency that substantially decreases as its surface temperature exceeds an appropriate limit, particularly in hot climate regions. Consequently, it is required to keep PV modules relatively under a condition of low temperature using a cooling system as possible. The present experimental study evaluates the performance of the combined photovoltaic thermal (PV/T) module employing a water cooling system attached to the back surface during June for the city of Sohag in Egypt. The experimental results show that utilizing a water cooling system decreases the average surface temperature of the PV module from 44.8 °C to 30.3 °C on the back side and from 46.6 °C to 36.9 °C on the front side. The maximum value of the thermal heat gain of the PV/T module that is maintained at noon equals 230 W, and the corresponding value of the electrical power output is 34.4 W. Furthermore, the electrical efficiency of the PV/T module is 8% higher than that of the PV module without a water cooling system. Finally, the maximum and average values of the overall efficiency of PV/T module are 76.4% and 68.9%, respectively.

A building energy simulation study is carried out to analyze the performance of a triple-hybrid single-effect vapor absorption cooling system (VACS) operated by solar, natural gas, and auxiliary electricity-based cogeneration. A high capacity small office building subjected to different climatic conditions is considered. The system is designed to continuously maintain a specified building comfort level throughout the year under diverse environmental conditions. Simulations are done at different generator temperatures to investigate the performance in terms of total annual electric energy consumption, heating energy, and the coefficient of performance (COP). The performance of the present VACS is compared with the conventional compression-based system, which demonstrates the electric energy and cost saving potentials of the proposed VACS. Simulation outcomes are well-validated against benchmark data from national renewable energy laboratory and energy conservation building code. Interestingly, it is found that beyond a certain collector area, surplus energy savings can be acquired with the present triple-hybrid VACS as compared to the compression-based cooling. Results also show that COP of the simulated system is in line with experimental values available in the literature. Finally, recommendations are given to operate the complete system on solar and biomass resources, which provide encouraging opportunity for agriculture-based countries.

The demand for affordable, environment-friendly, and reliable water conditioning systems has led to the introduction of several standalone and/or hybrid alternatives. The technology of desiccant evaporative cooling (DEC) has proven to be dependable and has gained success at places where initially it was deemed unfeasible. Today, a number of related technologies and configurations are available. Among them, solar-assisted desiccant cooling system (SADCS) offers a cheap eco-friendly alternative, especially in hybrid configurations. Most studies have investigated the performance of numerous SADCS configurations in specific climatic conditions; however, at the global- and system-level scale, no such study is available. The current study investigates five different SADCS configurations using equation-based object-oriented modeling and simulation approach in five different climatic conditions. The selected climatic conditions cover a wide range of global weather data including arid/semiarid (Karachi), dry summer tropical (Adelaide), and mesothermal (Sao Paulo, Shanghai) to continental conditions (Vienna). The performance of all selected SADCS configurations (ventilation cycle, recirculation and ventilated-recirculation cycles, dunkle and ventilated-dunkle cycle) is analyzed for specified cooling design day of the selected cities. A uniform system control strategy based on the idea of displacement distribution (ventilation) system is used for each configuration and climatic zone. By monitoring their performances based on the values of cooling capacity (CC) and coefficient of performance (COP), the best SADCS configuration is proposed for each considered climatic condition in the world. The results revealed that the climates of Vienna, Sao Paulo, and Adelaide favor the use of ventilated-dunkle cycle configuration with average COP of 0.36, 0.84, and 0.93, respectively, while ventilation cycle based on DEC configuration suits the climate of Karachi and Shanghai with an average COP of 2.32 and 2.90, respectively.

This study investigates the efficiency of application of phase change materials (PCMs) in a solar cooling system. The proposed system consists of an adsorption chiller and a latent heat storage unit (LHSU) containing PCMs. The PCM stores solar energy during daytime and at nighttime, the thermal energy stored in the PCM is utilized to drive the adsorption chiller. An auxiliary heater is also used to provide the required energy in addition to the LHSU. To verify the accuracy of the obtained results, the modeling of the solar adsorption system and the PCM unit are validated separately. Moreover, the whole system performance is verified by evaluation of the conservation of energy in the system. The performance of the system is compared with a similar solar adsorption chiller lacking LHSU. Also, the parameters which affect the performance of the LHSU are studied. It is found that application of LHSU decreases auxiliary energy consumption and increases solar fraction. Solar fraction goes up more if larger amount of PCM is used. However, there exists a maximum mass of PCM which can be charged during the sunshine hours. The maximum chargeable mass of PCM goes up by increasing the solar collector area, which leads to decreasing auxiliary energy consumption and increasing solar fraction. The results also show that enlargement of the hot water storage tank reduces auxiliary energy consumption and enhances solar fraction, but decreases thermal storage efficiency. In order to achieve higher thermal storage efficiency and also less auxiliary energy consumption, it is suggested to use average-sized hot water storage tanks.

In this paper, passive cooling strategies have been investigated to evaluate their effectiveness in reducing cooling thermal loads and air conditioning energy consumption for residential buildings in Kingdom of Saudi Arabia (KSA). Specifically, three passive cooling techniques have been evaluated including natural ventilation, downdraft evaporative cooling, and earth tube cooling. These passive cooling systems are applied to a prototypical KSA residential villa model with an improved building envelope. The analysis has been carried using detailed simulation tool for several cities representing different climate conditions throughout KSA. The impact of the passive cooling systems is evaluated on both energy consumption and electrical peak demand for residential villas with and without improved building envelope for five cities, representatives of various climate conditions in KSA. It is found that both natural ventilation and evaporative cooling provide a significant reduction in cooling energy use and electrical peak demand for the prototypical villa located in dry KSA climates such as that of Riyadh and Tabuk. Natural ventilation alone has reduced the cooling energy end-use by 22%, while the evaporative cooling system has resulted in 64% savings in cooling energy end-use. Moreover, the natural ventilation is found to have a high potential in all KSA climates, while evaporative cooling can be suitable only in hot and dry climates such as Riyadh and Tabuk. Finally, the analysis showed that natural ventilation provided the lowest electrical peak demand when applied into the improved envelope residential buildings in all five cities in KSA.

Solar cooling systems might represent a viable alternative for space cooling in residential buildings because the peak of cooling demand matches the availability of solar radiation. The use of adsorption chillers in this field gives another environmental benefit, since they employ natural refrigerants as water. However, the design of such systems is critical because it relates to several parameters and cannot be easily accomplished using traditional tools. In this work, a dynamic model for the simulation of a small solar cooling system employing adsorption chillers has been evaluated. The model, realized with the commercial software trnsys , has been implemented to quantify the effect of different operational and design parameters on the overall performances of solar cooling systems in three different Italian cities (Milan, Rome, and Messina). Particular focus was put on the comparison of different heat rejection systems, which was found to be a critical aspect in the design of such systems. In addition, an economic analysis has been performed for an optimized system, in order to evaluate the payback time of the systems compared to a traditional air conditioning system and provide indication on the possible outlooks by means of a sensitivity analysis.

A solar thermal cooling system using novel nontracking external compound parabolic concentrators (XCPC) has been built at the University of California, Merced and operated for two cooling seasons. Its performance in providing power for space cooling has been analyzed. This solar cooling system is comprised of 53.3 m2 of XCPC trough collectors which are used to power a 23 kW double effect (LiBr) absorption chiller. This is the first system that combines both XCPC and absorption chilling technologies. Performance of the system was measured in both sunny and cloudy conditions, with both clean and dirty collectors. It took, on average, about 2 h for the collector system to reach operating temperatures between 160 and 180 °C. When operated in this temperature range, the XCPC collector array collected solar energy with an average daily efficiency of 36.7% and reached instantaneous efficiencies up to 40%. The thermal coefficient of performance (COP) of the system (including thermal losses and COP of absorption chiller) averaged at 0.99 and the daily solar COP of the entire system averaged at 0.363. It was found that these collectors are well suited at providing thermal power to drive absorption cooling systems and that both the coinciding of available thermal power with cooling demand and the simplicity of the XCPC collectors compared to other solar thermal collectors makes them a highly attractive candidate for cooling projects. Consequently, the XCPC technology is currently being commercialized in the U.S. and India. The XCPC's numerous potential applications include solar heating, cooling, desalination, oil extraction, electricity generation, and food processing.

The installation rate of crystalline silicon photovoltaic (PV) modules worldwide is at an all-time high and is projected to continue to grow as the cost of PV technology is reduced. It is important to note that PV power generation is heavily influenced by the local climate. In particular, for crystalline silicon-based PV devices, as the operating temperature of the panel increases, the efficiency decreases. Higher operating temperatures also lead to accelerated material and mechanical degradation, potentially compromising system effectiveness over the lifetime of the panels. In addition, atmospheric pollution can cause particle deposition on the surface of PV modules (soiling), reducing the amount of solar irradiance that reaches the PV material and reducing panel efficiency. Various cooling and cleaning methods have been proposed in the literature to mitigate these problems. In this study, a uniform film of water was continuously recirculated by pumping over the surface of a solar panel using an emitter head attached to the top of the panel. The water cooling technique was able to maintain panel temperature below 40 °C while adjacent untreated panels were operating near 55 °C. Besides the efficiency improvements due to cooling, the film of water also kept the panels clean, avoiding any reduced power output caused by panel soiling. Additional studies were carried out with artificially chilled cooling fluid, insulating materials, and side mirrors to examine the cooling system performance under different installation scenarios. Water cooling is concluded to be an effective means of increasing the efficiency of monocrystalline silicon photovoltaic panels. Under normal operating conditions, the increased energy output from the panels is more than sufficient to compensate for the energy required to pump the water.

This work has been realized in the framework of the Elioslab project, financed by the Italian Ministry of Education, University and Research (MIUR), which aims to create a research platform in order to develop components and systems for the production and utilization of medium and high temperature heat using concentrated solar energy. As regards high temperature heat production, a 30 kW solar furnace that consists of a heliostat with flat mirrors and a parabolic concentrator with off-axis alignment is being realized in order to achieve a solar radiation concentration peak of about 2000 suns. The energy flux relative to the concentrated radiation will be converted to high temperature heat by a cavity receiver cooled with CO2, and finally transferred to a device operating at high temperature consisting in a thermochemical reactor for hydrogen production. Due to the intermittency of solar radiation, a high temperature (>800 °C) packed bed sensible heat storage system, with alumina balls as heat storage material, has been developed in order to provide continuity to the user operation. This paper focuses on the parametric analysis that has been carried out by means of numerical simulations to evaluate the set of variable parameters that maximize the efficiency of the heat storage system of the solar furnace. The charging and discharging phases of the heat storage tank have been numerically simulated by means of an analytical model that takes into account the conductive, convective, and radiative heat transfer as well as turbulent diffusion due to the solid–fluid interaction. The results of the numerical parametric analysis are presented together with the experimental validation of the adopted analytical model accomplished by using a reduced-scale high temperature storage system.

The Energy Information Administration of the United States Department of Energy projects that more than 80% of the energy consumption of the U.S. by 2035 will come from fossil fuels. This projection should be the fuel to promote projects related to renewable energy in order to reduce energy consumption from fossil fuels to avoid their undesirable consequences such as carbon dioxide emissions. Since solar radiation match pretty well building cooling demands, solar cooling systems will be an important factor in the next decades to meet or exceed the green gases reduction that will be demanded by the society and regulations in order to mitigate environmental consequences such as global warming. Solar energy can be used as source of energy to produce cooling through different technologies. Solar thermal energy applies to technology such as absorption chillers and desiccant cooling, while electricity from solar photovoltaic can be used to drive vapor compression electric chillers. This study focuses on the comparison of a solar thermal cooling system that uses an absorption chiller driven by solar thermal energy, and a solar photovoltaic cooling system that uses a vapor compression system (electric chiller) driven by solar electricity (solar photovoltaic system). Both solar cooling systems are compared against a standard air cooled cooling system that uses electricity from the grid. The models used in the simulations to obtain the results are described in the paper along with the parameters (inputs) used. Results are presented in two figures. Each figure has one curve for the solar thermal cooling system and one for the solar photovoltaic cooling system. One figure allows estimation of savings calculated based the present value of discounted energy consumption cost. The other figure allows estimating primary energy consumption reduction and emissions reduction. Both figures presents the result per ton of refrigeration and as a function of area of solar collectors or/and area of photovoltaic modules. This approach to present the result of the simulations of the systems makes these figures quite general. This means that the results can be used to compare both solar cooling systems independently of the cooling demand (capacity of the system), as well as allow the analysis for different sizes of the solar system used to harvest the solar energy (collectors or photovoltaic modules).

One of the unique features of photovoltaic (PV) modules is the power drop that occurs as the silicon temperature increases due to the characteristics of the crystalline silicon used in a solar cell. To overcome this reduction in power, module surface cooling using water circulation was employed. The model performance was then conceptually evaluated and experimentally verified. A transient model was developed using energy balances and heat and mass transfer relationships from various other sources to simulate the surface cooling system. The measurements were in good agreement with the model predictions. The maximum deviation between the measured and predicted water and silicon temperature differed by less than 4 °C. The maximum power enhancement in response to the cooling was 11.6% when compared with a control module. The surface cooling system also washed the module surface via water circulation, which resulted in an additional power up of the PV module in response to removal of the particles that interfere with solar radiation from the surface of the PV module. Accordingly, the cooling system could reduce maintenance costs and prevent accidents associated with cleaning. In addition, the increase in cooling water temperature can serve as a heat source. The system developed here can be applied to existing photovoltaic power generation facilities without any difficulties as well.

Data centers are facilities that primarily contain electronic equipment used for data processing, data storage, and communications networking. Regardless of their use and configuration, most data centers are more energy intensive than other buildings. The continuous operation of information technology equipment and power delivery systems generates a significant amount of heat that must be removed from the data center for the electronic equipment to operate properly. Since data centers spend up to half their energy on cooling, cooling systems becomes a key factor for energy consumption reduction strategies and alternatives in the data centers. This paper presents a theoretical analysis of an absorption chiller driven by solar thermal energy as cooling plant alternative for data centers. Source primary energy consumption is used to compare the performance of different solar cooling plants with a standard cooling plant. The solar cooling plants correspond to different combinations of solar collector arrays and thermal storage tank, with a boiler as source of energy to ensure continuous operation of the absorption chiller. The standard cooling plant uses an electric chiller. Results suggest that the solar cooling plant with flat-plate solar collectors is a better option over the solar cooling plant with evacuated-tube solar collectors. However, although solar cooling plants can decrease the primary energy consumption when compared with the standard cooling plant, the net present value of the cost to install and operate the solar cooling plants are higher than the one for the standard cooling plant.

The variable, uncertain nature of climate imposes risk in using solar and building technologies, such as natural ventilation (NV). To maximize the potential benefit from NV while reducing risk, a building could be designed for NV along with the “real option” to install mechanical cooling in the future, if needed. Traditional evaluation procedures use expected values, which fail to acknowledge the value of uncertainty when system performance is a nonlinear function of the uncertain variable. A real options methodology is proposed to evaluate the flexible building design under climate uncertainty. A building energy simulation is used to obtain probability distributions of the cost savings of the option-based NV strategy and of the time when (if) the mechanical cooling system is installed. A simplified stochastic temperature generator is used, and it may be used to evaluate real options for other technologies sensitive to future climate. The results of a real options analysis provide information to project investors on (a) the likelihood of exercising the option, and (b) the improved financial value of the technology when implemented with a flexible strategy.

Reported here is the development, using results of analysis and experiments, and optimization of a numerical model for a concentrated photovoltaic system. Models for the two major components of the system (cooling system and receiver) are developed separately from one another and then linked to simulate the performance for the entire system. The model is linked to yearly weather data and the optimization routines included in MATLAB are then used to select the input parameters (pump size, number of radiators, fan speed, etc.) which maximize the solar to electrical conversion efficiency of the system.

This paper provides an overview of research related to automated fault detection and diagnosis for chillers, packaged air conditioners, and other vapor compression cooling equipment. The paper discusses the benefits, constraints, and possible products for FDD applied in the HVAC&R industry, presents results of fault surveys for packaged air conditioners and chillers, outlines the general structure and elements of an FDD system for HVAC&R equipment, describes specific methods associated with different FDD elements, and presents results from some specific case studies. The paper also attempts to provide an assessment of the state-of-the-art in FDD for vapor compression equipment and to identify the steps necessary to achieve widespread application.

This paper presents field test of a hybrid solar liquid desiccant cooling system conducted at a test house at the University of Florida’s Energy Research and Education Park. These tests consisted of operating the air conditioning system at the test house in two configurations: the conventional vapor compression system and the hybrid desiccant system. Experiments were conducted to study the influence of the air mass flow rate, temperature of the inlet air, temperature of the desiccant, and desiccant mass flow rate on the performance of both system configurations. Based on the field test results, it was found that the hybrid desiccant system improves the air conditioning performance in the field test house by decreasing the outlet humidity and temperature of the air.

Experimental study of a double-glazed forced-convection solar collector/regenerator for absorption solar cooling is presented. The south facing experimental solar collector/ regenerator with 10 deg slope is located at Kaohsiung, Taiwan at 120°18′ E longitude and 22°34′ N latitude. The size of the collector is 1 m wide and 7 m long with an effective regeneration area of 0.9 m by 6 m. Previous study for single-glazed forced-convection solar collector/regenerator operated at the same location has shown to have a best day-average efficiency of 17 percent. In order to raise the system performance, a double-glazed collector/regenerator is constructed such that air can be preheated in the upper channel flow. The preheated air is then conducted into the lower channel where it contacts with the film flow of solar heated lithium-chloride solution and regenerates the solution by carrying out the evaporated water vapor. The preheated air has lower relative humidity but the same humidity ratio since it is sensibly heated. Therefore, the regeneration driving potential is increased. The present study shows that the best day-average efficiency can reach 20 percent which increases the feasibility of the open-cycle absorption solar cooling system. Effects of controlling parameters on the collector/regenerator performance are studied, and heat and mass transfer correlations are also presented for design purposes.

Desiccant cooling systems have the ability to provide efficient humidity and temperature control while reducing the electrical energy requirement for air conditioning as compared to a conventional system. Naturally, the desiccant air dehumidification process greatly influences the overall performance of the desiccant system. Therefore, the effects of variables such as air and desiccant flow rates, air temperature and humidity, desiccant temperature and concentration, and the area available for heat and mass transfer are of great interest. Due to the complexity of the dehumidification process, theoretical modeling relies heavily upon experimental studies. However, a limited number of experimental studies are reported in the literature. This paper presents results from a detailed experimental investigation of the heat and mass transfer between a liquid desiccant (triethylene glycol) and air in a packed bed absorption tower using high liquid flow rates. A high performance packing that combines good heat and mass transfer characteristics with low pressure drop is used. The rate of dehumidification, as well as the effectiveness of the dehumidification process are assessed based on the variables listed above. Good agreement is shown to exist between the experimental findings and predictions from finite difference modeling. In addition, a comparison between the findings in the present study and findings previously reported in the literature is made. The results obtained from this study make it possible to characterize the important variables which impact the system design.

A silica-base monolithic adsorbent was prepared by sol-gel synthesis with a corrugated ceramic fiber sheet as a matrix and assembled in an adsorptive dehumidifier of rotary type, which operates with a thermal regeneration cycle. High efficiency of dehumidification was confirmed at a regeneration temperature as low as 80°C when the rotation speed or cycle time was adjusted to the optimal value. A prototype air conditioning unit equipped with the balanced flow dehumidifier was examined in a direct pass ventilation mode. A satisfactory decrease in enthalpy of product air relative to room air was observed. Changes in the state of air during processing are discussed rather rigorously in terms of a humidity chart.