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Nowadays, air conditioning consumes, on average, around one-fifth of the total power used in buildings globally. The present paper aims to provide the present status on the employment of Earth-to-Air Heat eXchangers (EAHX) to contain the consumption of energy and to reduce the effect on the environment in response to the Montreal and Kyoto protocols in a way to achieve cleaner energy production with a low Global Warming Potential (GWP) and a low ozone depletion potential (ODP). Different peculiarities and applications (direct or hybrid) are critically analyzed and reviewed. Specifically, in this paper, the different hybrid applications presented in the literature, where the Earth-to-Air Heat eXchangers are coupled to advanced systems, are reviewed. Finally, an IoT-based EAHX control system plan is reported and discussed to optimize energy efficiency and thermal comfort to suit operating conditions under different time zones. [ABSTRACT FROM AUTHOR]

To further improve the stability and renewable energy utilization of the compound heat source heat pump system under complex operating conditions, a multi-mode solar heat pump system was proposed and a mathematical model was established in this paper. The accuracy of the model is verified by the experimental data, with the relative error within ±15%. The effects of the number of solar photovoltaic/thermal (PV/T) collectors (area), environmental parameters, and refrigerant flow rate on system performance are discussed separately for different models by the validated model. The results show that (1) PV/T-water source heat pump mode: the number of PV/T collectors in parallel (area) increases to 3 (3.84 m2), and the system performance improves the most, subsequently weakening; (2) PV/T-water and air composite heat pump model: When the refrigerant distribution ratio in the double-pipe heat exchanger 1 is increased from 55% to 95%, the collector's heat collecting capacity, power generation efficiency, and system coefficient of performance (COP) increase by 8.99%, 1.22%, and 6.4%, respectively. Moreover, the increase in solar irradiance can promote more refrigerant flow into the double-pipe heat exchanger 1 and improve heat pump COP more than the effect of increased ambient temperature. The research results can provide an effective reference for further optimization of solar heat pump systems and full utilization of renewable energy. [ABSTRACT FROM AUTHOR]

The growing demand for new and eco-friendly energy resources has raised the need of sustainable sources or renewable energy for use in present era. A vapor absorption refrigeration system (VARS or VAS) is a closed loop refrigeration system which requires low heat for its functioning and, it is therefore, considered an eco-friendly solution. Since, generator is the main component of VAS which can significantly influence the efficacy of overall system, the current paper involves modeling and thermal analysis of generator using Computational Fluid Dynamics (CFD). The objective of this study is to optimize the heat transfer by changing baffle spacing of generator heat exchanger, running on a single effect LiBr/water absorption cycle. For this purpose, hot water driven generator of 1ton capacity is taken. The simulation results of CFD were validated by comparing them with theoretical results. The overall design estimation and design technique that follows Birmingham Wire Gauge (BWG) and Tubular Exchangers Manufacturers Association (TEMA) standard are considered in this study. It was found from the analysis that the design model with smallest baffle spacing has the highest heat transfer coefficient. On reducing the baffle spacing from 137mm to 101mm, an increment of 48% in overall heat transfer coefficient was observed. Likewise, an increase in velocity by 36% and drop in static pressure by 27% were seen. Similar trend was observed in the theoretical results. [ABSTRACT FROM AUTHOR]

Ground heat exchanger takes the soil underground as heat source or sink to supply cooling or heating. It has been widely used in building heating and cooling systems due to high efficiency and environmental friendliness. This paper reviews the latest research on ground heat exchangers from several new perspectives and demonstrates their potentials in achieving zero energy buildings. Firstly, ground heat exchangers are classified into water-based and air-based ones based on the heat transfer medium. They can be used in a passive or active approach. Associated research and projects for each approach are introduced and analysed. Then the integration of ground heat exchangers with various cooling and heating technologies and related studies are reviewed. These technologies include solar thermal collectors, cooling towers, nocturnal radiative cooling technology, solar chimney, etc. Finally, a technical route for ground heat exchangers to help realize zero energy buildings is presented, which provides a promising solution to improve energy efficiency of buildings. [ABSTRACT FROM AUTHOR]

In this paper we offer energy metric for evaluating the need for transformational technology in the context of resources management for sustainability. This metric measures the margin for improvement between the actual energy used and the theoretical minimum needed for the same task, irrespective of the technology considered. We first define the parameter space of sustainability metrics. Furthermore, we argue that, for any energy related sustainability study, the rate of change of the related process energy use (hence, ultimately at the lowest hierarchical level) has to be considered for a given task, not only for a given technology. Finally, we identify the margin between actual energy resources use and theoretical minimum. The paper offers, as an example, a study (at the process level) of a state-of-the-art manufacturing technology, broadly used in many applications, e.g., manufacturing of compact heat exchangers for the automotive industry. The margin between the theoretical minimum and the actual energy resources use for bonding an aluminium assembly by brazing is established. It is confirmed that the minimum theoretical energy resources needed, associated with a manufactured product, may be a number of orders of magnitude smaller than the actual energy resources used, irrespective of the technology implemented. [ABSTRACT FROM AUTHOR]

This paper presents detailed energy and exergy analysis and comparison of low-grade solar heat source powered superheated and saturated organic Rankine cycle (ORC) using zeotropic mixture butane/R1234ze. The required expression to evaluate the power output, first law efficiency exergetic efficiency, exergy destruction, and required heat exchangers area are coded in Matlab 2015a interfaced with REFPROP 9.0. Moreover, saturated and superheated ORCs are further optimized by genetic algorithm by selecting exergetic efficiency and product of overall heat transfer coefficient and heat exchanger area. It is observed that superheated ORC exhibits better net power output, first law and exergetic efficiency, lower exergy destruction and poorer economy than saturated ORC. Further, the performance of saturated ORC is increased by 34.02% and that of superheated ORC by 17.06% by the multiobjective genetic algorithm. [ABSTRACT FROM AUTHOR]

Abstract: The main results of a theoretical work on the use of a low temperature heat source for power generation through a carbon dioxide transcritical power cycle are reported in this paper. The procedure for analyzing the behaviour of the proposed cycle consisted in modifying the input pressure to the turbine from 66 bar, maintained constant each evaluated temperature (60 °C, 90 °C, 120 °C and 150 °C) until the net work was approximately zero. As a result, the maximum exergy efficiency was 50%, while the energy efficiencies obtained were 9.8%, 7.3%, 4.9% and 2.4% and the net specific work was 18.2 kJ/kg, 12.8 kJ/kg, 7.8 kJ/kg and 3.5 kJ/kg, respectively. Furthermore, the effect of the addition of an internal heat exchanger, which obviously supposed an increase in the efficiency, was analyzed. The analysis of the proposed system shows the viability of implementing this type of process as an energy alternative and/or strengthener of non-conventional energy sources in non-provided zones, or for increasing the energy efficiency in the industry. [Copyright &y& Elsevier]

As one of the environmentally friendly technologies, heat pumps have been widely utilized in residential and commercial buildings all over the world. The use of renewable energy sources and environmentally friendly refrigerants are two major challenges associated with heat pumps applications. Due to the advantages of cascade heat pumps over single-stage heat pumps and the higher energy demand met by cascade heat pumps, investigation of the effects of geographic conditions (weather and soil conditions) as well as the simultaneous use of two refrigerants for high and low temperature cycles on performance of cascade heat pumps would provide critical information for practical applications. This paper compares the performance of air source and ground source cascade heat pumps using refrigerants by low global warming potential and zero ozone depletion potential in top 10 coldest cities of Russia. The effects of variations in temperature of evaporator and cascade heat exchanger on optimal operational conditions are investigated based on energy, exergy, economic and environmental analysis using Pareto front curve. Optimization results show that there is an optimal point for evaporator temperature and cascade heat exchanger temperature where the maximum COP, maximum exergy efficiency and minimum total cost rate for ASHP and GSHP systems are obtained. It is found that at low air temperature, since the underground temperature is higher than ambient air, the efficiency of GSHP system is better than efficiency of ASHP system. The maximum COP of 2.357 and 2.44 are respectively obtained for ASHP and GSHP systems in Saint Petersburg. In addition, Yakutsk city has the maximum exergy efficiency of 40.7% and 43.2% and maximum total cost rate of 14714 $ year−1 and 13693 $ year−1 for ASHP and GSHP systems, respectively. Finally, it is concluded that Saint Petersburg is the best city to employ ASHP system while GSHP system is suggested for Khabarovsk city. • Performance of ASHP and GSHP is compared in 10 coldest cities of Russia, thermoeconomically. • Maximum COP of 2.357 and 2.44 are respectively obtained for ASHP and GSHP in Saint Petersburg. • Maximum exergy efficiency of 40.7% and 43.2% are achieved for ASHP and GSHP in Yakutsk, respectively. • Yakutsk also has the maximum total cost rate of 14714 $ year−1 and 13693 $ year−1 for ASHP and GSHP. • Saint Petersburg and Khabarovsk are the best cities to employ ASHP and GSHP. [ABSTRACT FROM AUTHOR]

In the present paper a quasi-steady state mathematical model is developed to predict the outlet air temperature and monthly heating and cooling potentials of an earth-air heat exchanger. Monthly values of heating and cooling potentials are estimated by rigorous experimentation throughout the year for composite climate of New Delhi. The uncertainty values are calculated for each month; for December the value is 4.9%. It is observed that there is an 8.9 and a 5.9°C temperature rise and fall during winter and summer due to the earth-air heat exchanger buried at a depth of 1.5m underground. The correlation coefficient, root mean square of percentage deviation, reduced chi-square and mean bias error have been computed for each month. The values are 1, 3.0%, 0.8 and -0.63 for December. Statistical analysis shows that there is fair agreement between theoretical results and experimental observations for each month. Monthly values of heating and cooling potentials have also been predicted for other climatic conditions in India namely Jodhpur, Chennai, Mumbai and Kolkata. [ABSTRACT FROM AUTHOR]

Based on a traditional integrated solar combined cycle system, a novel integrated solar combined cycle (ISCC) system is proposed, which preferentially integrates the solar energy driven lithium bromide absorption refrigeration system that is used to cool the gas turbine inlet air in this paper. Both the Aspen Plus and EBSILON softwares are used to build the models of the overall system. Both the thermodynamic performance and economic performance of the new system are compared with those of the traditional ISCC system without the inlet air cooling process. The new system can regulate the proportions of solar energy integrated in the refrigerator and the heat recovery steam generator (HRSG) based on the daily meteorological data, and the benefits of the solar energy integrated with the absorption refrigeration are greater than with the HRSG. The results of both the typical day performance and annual performance of different systems show that the new system has higher daily and annual system thermal efficiencies (52.90% and 57.00%, respectively), higher daily and annual solar photoelectric efficiencies (31.10% and 22.31%, respectively), and higher daily and annual solar photoelectric exergy efficiencies (33.30% and 23.87%, respectively) than the traditional ISCC system. The solar energy levelized cost of electricity of the new ISCC system is 0.181 $/kW·h, which is 0.061 $/kW·h lower than that of the traditional ISCC system. [ABSTRACT FROM AUTHOR]

The share of cooling is rising in the energy balance of buildings. The reason is for increasing occupants' comfort needs, which is accentuated by the fact that the number and the amplitude of heat waves are increasing. The comfortable and healthy indoor environment should to be realized with the minimum amount of energy and fossil fuels. In order to meet this goal, designers should know the effect of different parameters on the buildings' energy consumption. The energy need for cooling is mainly influenced by the glazed ratio and orientation of the facades, the quality of glazing and shading. In this paper the heat load analysis was done by assuming different types of summer days and surface cooling, depending on the glazing ratio, shading factor and solar factor of glazing. It was proven that, for a certain parameter, the sensitivity of the heat load depends on the orientation and chosen summer day. If the glazing area is doubled, the heat load increases with about 30%. Decreasing the glazed area to 50%, the heat load decreases with about 10%. The heat load decreases with about 3% if the g factor is lowered with 25% or the shading factor is reduced with 60%. [ABSTRACT FROM AUTHOR]