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The negative environmental impacts of burning fossil fuels have forced the energy research community seriously to consider renewable sources, such as naturally available solar energy. Thermally powered refrigeration technologies are classified into two categories: thermo-mechanical technology and sorption technology (open systems or closed systems). This paper provides a detailed review of the solar closed sorption (absorption and adsorption) refrigeration systems, which utilise working pairs (fluids). After an introduction of the basic principles of these systems, the history of development and recent advances in solar sorption refrigeration technologies are reported. The adsorption cooling typically has a lower heat source temperature requirement than the absorption cooling. Based on the coefficient of performance (COP), the absorption systems are preferred over the adsorption systems, and the higher temperature issues can be easily handled with solar adsorption systems. The thermodynamic properties of most common working fluids, as well as the use of ternary mixtures in solar-powered absorption systems, have been reviewed in this study. The paper also refers to new approaches to increase the efficiency and sustainability of the basic adsorption cycles, such as the development of hybrid or thermal energy storage adsorption systems. This research shows that solar-powered closed sorption refrigeration technologies can be attractive alternatives not only to serve the needs for air-conditioning, refrigeration, ice making, thermal energy storage or hybrid heating and cooling purposes but also to meet the demands for energy conservation and environmental protection. [ABSTRACT FROM AUTHOR]

The primary aim of this study is to assess thermal comfort based on the predicted mean vote (PMV) and predicted percent dissatisfied (PPD) indices using subjective and experimental measurements in two air conditioned classrooms at a university, where the air-exchange rate is assured by natural ventilation. The indoor environmental conditions were satisfactory, and all situations fit within the comfort limits. The mean value of the PMV index ranges from 0.55 to −0.69 during both seasons, and the mean value of the PPD index ranges from 11.66 to 15.04%.The influence of the air conditioning system and ventilation provided by manually operated windows during the cooling season on thermal comfort parameters and CO 2 concentration are also investigated by in situ measurements. In the absence of a cooling system and the ventilation rates, the air temperature exceeds the maximum comfort limit of 27 °C. Additionally, the PMV and PPD indices have the values of 0.87 and 21%, respectively and the CO 2 concentration increases above the admissible limit, reaching a value of 2400 ppm. By manually opening the windows, the CO 2 concentration decreases significantly to 1500 ppm. Thermal comfort is notably improved (PMV = −0.34, PPD = 7.4%) when the cooling system is running in the room. The secondary aim of this paper is to develop a prediction model of the academic performance during the cooling season. Application of this model indicates that the indoor environmental conditions can strongly affect student performance. Finally, a simulation model on the Transient System Simulation (TRNSYS) program of the PMV-PPD indices and heating/cooling energy demand for an amphitheatre with natural ventilation is proposed. [ABSTRACT FROM AUTHOR]

The ground-coupled heat pump (GCHP) system used to provide space heating for an office room is a renewable technology with a high performance. The experimental measurements are used to test the performance of a GCHP system integrated with the radiator or radiant floor heating system for an office room. A comparative analysis of the main performance parameters (energy efficiency and CO 2 emissions) is performed for the two heating systems. Additionally, two numerical simulation models of useful thermal energy and the system coefficient of performance (COP sys ) in heating mode are developed using the TRNSYS (Transient Systems Simulation) software. Finally, the simulations obtained using TRNSYS software are analysed and compared to the experimental data, resulting in good agreement and thus the simulation models are validated. [ABSTRACT FROM AUTHOR]

The ground-coupled heat pump (GCHP) system is a type of renewable energy technology providing space heating and cooling as well as domestic hot water. However, experimental studies on GCHP systems are still insufficient. This paper first presents an energy-operational optimisation device for a GCHP system involving insertion of a buffer tank between the heat pump unit and fan coil units and consumer supply using quantitative adjustment with a variable speed circulating pump. Then, the experimental measurements are used to test the performance of the GCHP system in different operating modes. The main performance parameters (energy efficiency and CO 2 emissions) are obtained for one month of operation using both classical and optimised adjustment of the GCHP system, and a comparative analysis of these performances is performed. In addition, using TRNSYS (Transient Systems Simulation) software, two simulation models of thermal energy consumption in heating, cooling and domestic hot-water operation are developed. Finally, the simulations obtained using TRNSYS are analysed and compared to experimental data, resulting in good agreement and thus the simulation models are validated. [ABSTRACT FROM AUTHOR]

The paper presents a review on recent development of possible substitutes for non-ecological refrigerants from HVAC&R equipment based on thermodynamic, physical and environmental properties and TEWI (Total Equivalent Warming Impact) analysis. This review contains a good amount of information regarding the environmental pollution produced by the working fluids of the air-conditioning, heat pump and commercial refrigeration applications and the ecological refrigerant trend. Overall, it is useful for those readers who are interested in current status of alternative refrigerant development related to vapour compression-based refrigeration, air-conditioning and heat pump units. The study describes the selection of refrigerants adapted to each utilisation based on the thermodynamic, physical and environmental properties and explores the studies reported with new refrigerants in domestic refrigerators, commercial refrigeration systems, air-conditioners, heat pumps, chillers and in automobile air-conditioners. Additionally, a comparative analysis of the TEWI for possible substitutes of refrigerant R22 used in various air-conditioning, heat pump and refrigeration systems is performed. [ABSTRACT FROM AUTHOR]

Abstract: This paper deals with the method of decreasing the size of heat exchanger surfaces by increasing the heat transfer coefficients and the importance of heat transfer enhancement for vaporization. We report an experimental study on surfaces modified by passive methods applied to heat transfer surfaces mechanically processed, covered with sleeves made by metallic tissues or covered with metallic porous layers performed using welding procedures. Experiments are made to investigate the heat transfer coefficient on copper tubes with a 22mm external diameter using heat from inner source to outer vaporizing liquid. There are developed specific heat transfer correlations for each group of enhanced surfaces. The experimental data and new proposed correlations are compared with well known correlations. The results are in best agreement with the Cornwell–Houston correlation. [Copyright &y& Elsevier]

Highlights: [•] We provided a detailed review of different solar refrigeration technologies. [•] Theoretical basis and practical applications for cooling systems were presented. [•] Different working pairs were illustrated by their COPs and maximum temperatures. [•] It was explored solar hybrid cooling systems with heterogeneous composite pairs. [•] A comparison of various solar cooling systems and some use suggestions were given. [ABSTRACT FROM AUTHOR]