نشریه انرژی های تجدیدپذیر و نو
سال دوم شماره 2 (پیاپی 4، زمستان 1394)

In the present paper, the earth-air heat exchanger specification including system utilization methods, channels configuration as well the most important merits and demerits of this system has been assessed completely. Then, passive systems which can be integrated with the underground channels has been assessed. Eventually, the significant recent decades studies on earth-air heat exchanger has been evaluate in order to obtain the worth and weak points of the past researches as well as proposing the novel ideas and set the further studies policy. The former studies evaluation shows that the earth-air heat exchanger can be utilized in summer for cooling purpose and also it can be used as preheating system in winter. However, this system has higher performance as a cooling system. The results indicated that by considering the earth-air heat exchanger in the hybrid systems, the total system performance will be improved incredibly.

In the present paper, a hybrid cycle combing two novel technology of solid oxide fuel cell (SOFC) and micro gas turbine (MGT) to produce power in micro scale. The SOFC utilizes an external steam reformer to convert methane to hydrogen which is consumed as the SOFC main fuel. The fuel cell stack gas with high quality is used in a MGT to increase the cycle capability to produce more power. To analyze the cycle behavior a thermodynamic model is proposed and solved. In addition to make sure about the SOFC operation the cell voltage of the SOFC is calculated versus the current density and the calculated data is compared with experimental data presented by other researchers. The comparison shows a good agreement. To evaluate the cycle operation the impact of different parameters such as current density, cell working pressure and reforming temperature on the cycle performance criteria such as power generation by the SOFC, power generation by the MGT, cycle electrical efficiency, SOFC electrical efficiency, and SOFC working temperature are investigated. The results show that the fuel saving ratio of 45% in power production and overall electrical efficiency of 60% are achievable.

Nowadays, using the double skin facades has attracted the attention of many engineers because of its significant effects on the buildings’ energy consumption, beside of maximum absorption of solar renewable energy. The previous researches have shown that the double skin facades have an appropriate thermal performance in the cold season. However, using double skin façade may lead to increase the building’s energy demand in the warm season. Therefore, in the recent years, the idea of using double skin facades with phase change materials (PCM) has been proposed in order to decrease the summer energy consumption of buildings. In this study, a thermal performance analysis has been performed by considering a high-rise building with the phase change material double skin façade in Tabriz and Bandarabas climatic conditions. The results indicate that using the ordinary double skin façades in Tabriz climatic conditions can decrease the building’s energy consumption up to 20% in cold months of the year; but it can lead to increase the summer cooling load about 14%. However, by using double skin façades with the phase change material glazing, the building’s energy consumption in cold and warm seasons may decrease about 12.5% and 7%, respectively. Also, the double skin façades with the phase change material glazing shows a good performance in Bandarabas climatic conditions with cooling and heating load energy saving about 5.7 and 12.6%, respectively.

Energy consumption tendency in buildings and to find out the methods to manage and optimize it as audit or energy management methods are considered nowadays. Energy audit in every building is influenced by academic studies, experience and acquainting with new technologies of energy conservation. Renewable energies can play an important role in this way. Phase change materials (PCMs) are new substances with high heat of fusion. They absorb energy as latent heat until transformation in their phase. When the absorbed heat is needed, heat is extracted and material change to the primary condition. PCMs are very effective because they can be used in a variety of temperatures in cooling and heating. During the summer season, the benefits are a decrease in overall energy consumption and a time shift in peak load to off-peak hours that can decrease energy consumption cost. So, in this paper the role of PCMs in energy consumption management is considered.

In recent years saving energy has become of the most crucial topics in the entire energy industry. In the past several decades, by decreasing the fossil fuel sources, the energy crisis has become one of the most important issues of the world. Thermal integration in the plant is one of the methods that can be used for performance modification and energy saving in industrial units. Natural gas processing plants are one of the biggest industrial units. In these processes, a refrigeration system is used for the required. In current study, refrigeration system of propane facility of a typical gas refinery plant has been investigated using combined pinch and exergy method. The results show that, with correction of temperature levels of refrigeration systems, power consumption of system decreases about 16%.

Energy saving in building is one of the key issues in the sustainable energy development since in terms of primary energy consumption, buildings represent for more than 40% in most countries. Energy storage system is considered as an effective energy utilization method for buildings. In this paper, the phase change materials (PCMs) and their application in buildings have been introduced as a promising latent heat thermal energy storage method. The extensive melting temperature range in PCMs (from -100°C to 800°C and more) causes a strong inclination toward utilizing it for various applications. Using PCMs as a thermal energy storage system reduce the thermal energy demand of the building due to the time shifting in heat transfer phenomena from the heating and cooling energy source to the building. The PCMs can be usually used in form of microcapsule or flexible and rigid panels through the building envelope or double glazing windows. Based on the obtained results, the flexible and rigid panels are more cost effective than microcapsule PCMs. by selecting a proper PCM based on the corresponding thermal energy storage configuration, up to 30% energy saving can be achieved on the thermal energy utilization in the building.

Due to energy crisis and shortage of fossil fuels and emissions from those that have arisen serious concerns in relation to environmental issues, the use of renewable energy, especially solar energy has many attentions. A significant part of energy used in buildings is consumed by air conditioning systems. According to temperature of the generator, renewable and solar energy can be used as thermal driver in absorption refrigeration systems. In this study, two effects lithium bromide-water solar absorption cooling systems is simulated to be used in Tehran in summer. It is shown that coefficient of performance is increased by increasing temperature of high pressure generator until 130°C significantly and after that remain approximately constant. Since the high temperature generator has high energy consumption, temperature of 130 oC is recommended for high pressure generator. Collectors used in this system are fixed axis parabolic ones. Because the average heat absorbed by the collector varies each month, parallel arrangement are used. Required collector area is determined due to needed solar energy. For 20 kW cooling capacity, 52.5 m2 collector area is required with a 4 m3 storage tank.

Today, energy crisis is one of the most important problems in the world and to overcome, different countries apply various solutions. Non-renewable resources of energy such as fossil fuels are going to end rapidly. Applying of non-renewable resources causes to environmental pollution and sequent global warming. Therefore tendency to apply renewable energy resources such as wind, solar energy, geothermal, etc. is increased around the world and government interested to invest on these types of energy. This review paper introduces briefly about all types of energy and especially on solar energy as the most important renewable resources. In this paper, solar cells as photovoltaic devices that convert solar energy to electricity are introduced, also different types of solar cells, advantages and disadvantages of each group, performance mechanism and finally some progress in solar cell technologies, is considered.

The operation of a novel solar-energized long term storage system has been studied using computer simulation. The system uses a phase change material (PCM) consisting CaC12، 6H20 for short-term heat storage; crushed-rocks sensible heat storage bin with enclosed hot water tank and heat pump system for medium-term heat storage، and soil for long-term heat storage. Calculations indicate that this system will provide a higher heat gain than a single bin system studied earlier. The single bin system was studied analytically and theoretically، comparing the use of a PCM and crushed-rocks، and included a heat pump operating from the same bin. Due to analysis and design method of experiment، the effect of six variance factors on system performance for higher PCM efficiency was studied.