Solar assisted air conditioning of buildings – an overview

Goal of this contribution is to draw a picture about some general issues for using solar thermal energy for air conditioning of buildings. The following topics are covered:

• –A basic analysis of the thermodynamic limits for the use of heat cooling in combination with solar thermal energy is drawn; thereby fundamental insights about control needs for solar thermal driven cooling are obtained.
• –A short overview about the state-of-the-art of available technologies, such as closed thermal driven cooling cycles (e.g., absorption, adsorption) and open cooling cycles (e.g., desiccant employing either solid or liquid sorbents) is given and needs and perspectives for future developments are described.
• –The state-of-the-art of application of solar assisted air-conditioning in Europe is given and some example installations are presented.
• –An overview about new developments of open and closed heat driven cooling cycles for application in combination with solar thermal collectors is given and some of these new systems are outlined more in detail.

     

Magnetic field influence on double-diffusive natural convection in a square cavity – A numerical study

In this paper double diffusive natural convection in a square cavity in the presence of external magnetic field has been studied numerically by Galerkin’s weighted residual finite element method using velocity-vorticity formulation. Simulation results are reported for 0?相似文献   

Droplet evaporation in a turbulent high-pressure freestream – A numerical study

This paper presents a 3D numerical model for predicting the evaporation of a droplet exposed to a turbulent, high-pressure and high-temperature gaseous nitrogen freestream. The governing complete set of time-dependent conservation equations of mass, momentum, energy, and species concentration for both gas- and liquid-phase are solved numerically. The turbulence term in the conservation equations of the gas-phase is modeled by using the shear-stress transport (SST) closure model. In addition, variable thermophysical properties, unsteadiness of the gas and liquid phases, radiation, non-ideal gas behavior, and solubility of gas into the droplet are all accounted for in the numerical model. A wide range of freestream conditions is explored. The present numerical predictions revealed that the freestream turbulence intensity still has an effect on the droplet vaporization even at significantly high-pressure and high-temperature conditions, although this effect weakens with an increase in both ambient pressure and temperature. More importantly, new correlations are proposed to account for the effects of freestream ambient conditions on the droplet vaporization process.     

Short contact time catalytic partial oxidation of biogas – A comprehensive study on CO2 and N2 dilution

The short contact time catalytic partial oxidation of methane diluted with nitrogen and/or carbon dioxide to act as a surrogate for biogas conversion was carried out. Experiments were carried out under varying operating conditions to determine the possible use of the products in pyrolysis.Carbon dioxide has a larger effect on the product selectivities and back face temperature of the catalyst compared to nitrogen for equal dilutions. Carbon dioxide is consumed in the reactor whereas nitrogen is not. Since carbon dioxide likely takes part in endothermic reactions, the temperature of the catalyst is lower as is the conversion of methane and selectivity to carbon monoxide and hydrogen.The product stream is at an appropriate composition and temperature for subsequent use in a pyrolysis reactor. The presence of hydrogen and carbon monoxide will result in the removal of oxygen from bio-oils that are produced in the pyrolysis reactor.     

Impact of unplanned power flows in interconnected transmission systems – Case study of Central Eastern European region

The unplanned power flows at the interconnections of the Central Eastern Europe and Central Western Europe electricity markets are assessed. The assessment is accomplished using optimal power flow simulations of the linked transmission systems of Germany, Poland, the Czech Republic, Austria and Switzerland. The unplanned flows are modeled using a multivariate model that is a function of time series of wind- and solar-generated electricity, power demand and commercial power flows. It is shown that for the case of Poland there is a 25% higher loading on sections of transmission grid in Poland due to the unplanned flows. The unplanned power flows are largely a consequence of the wind-generated electricity in northern Germany that must be routed to southern Germany through the grid in Central Eastern Europe region due to an inadequate grid capacity along the north–south German corridor. It is shown without the planned 2020 developments of the grid, Poland's grid will be very susceptible to congestion and destabilization.     

Solar industrial process heating in Australia – Past and current status

Thirty years ago in Australia, there was a significant research, development and demonstration programme in solar industrial process heating (SIPH). This activity was led principally by the Commonwealth Science and Industrial Research Organisation, the country’s main scientific research body. Other state government bodies also funded demonstration projects. Today, there is very little SIPH activity at any level in Australia. The contrast with the progress in other renewable energy technologies like wind and solar photovoltaic systems is striking. While the implementation of these technologies has progressed, SIPH has gone backwards. If Australia is to decarbonise its economy at the rate required, a massive deployment of solar thermal technology in those industries which use large quantities of low temperature hot water is also required. Recent developments nationally and internationally may rekindle new applications of solar thermal energy use by industry. This paper reviews the past achievements in SIPH in Australia and describes the lessons learned in order to better prepare for any new wave of SIPH activity.     

Agricultural biogas plants – A systematic analysis of strengths,weaknesses, opportunities and threats

In this paper, we discuss the prospects of agricultural biogas plants. We conducted an integrated SWOT–AHP analysis for such plants in Austria in order to identify strengths, weaknesses, opportunities and threats (SWOT factors), and to weight the factors identified based on expert judgments, calculated according to the Analytic Hierarchy Process (AHP) method. The results show that financial aspects are dominant in three of the four SWOT categories. Technological aspects and issues regarding utilization seem to play a relatively minor role. Factors that are not directly under the control of plant operators are currently perceived as crucial for the success of agricultural biogas plants. We conclude that such plants will only succeed in contributing to sustainable energy supply goals when economic and political conditions are favorable over the long term.     

A hybrid power plant (Solar–Wind–Hydrogen) model based in artificial intelligence for a remote-housing application in Mexico

World fossil fuel reserve is expected to be exhausted in coming few decades. Therefore, the decentralization of energy production requires the design and integration of different energy sources and conversion technologies to meet the power demand for single remote housing applications in a sustainable way under various weather conditions. This work focuses on the integration of photovoltaic (PV) system, micro-wind turbine (WT), Polymeric Exchange Membrane Fuel Cell (PEM-FC) stack and PEM water electrolyzer (PEM-WE), for a sustained power generation system (2.5 kW). The main contribution of this work is the hybridization of alternate energy sources with the hydrogen conversion systems using mid-term and short-term storage models based in artificial intelligence techniques built from experimental data (measurements obtained from the site of interest), this models allow to obtain better accuracy in performance prediction (PV_MSE = 8.4%, PEM-FC_MSE = 2.4%, PEM-WE_MSE = 1.96%, GSR_MSE = 7.9%, WT_MSE = 14%) with a practical design and dynamic under intelligent control strategies to build an autonomous system.     

Optimal utilisation of small-scale embedded generators in a developing country – A case study in Malaysia

Building integrated photovoltaic (BIPV) systems are likely to become a dominant type of small-scale embedded generator (SSEG) on public low voltage (LV) distribution network in Malaysia due to the enormous amount of initiatives and efforts taken by the government to promote the use of BIPV. The growth of BIPV systems on LV distribution networks has the potential to alter the direction of power flow across the distribution networks, hence imposing several serious technical issues relating to power quality, distribution system efficiency and possible equipment overloading. Therefore, the utility companies need to study the following technical issues: (i) voltage regulation, (ii) voltage rise, (iii) voltage unbalance, (iv) network power losses, and (v) cable and transformer thermal limits. This paper describes research carried out to investigate and quantify the impacts of BIPV on LV networks with particular reference to developing countries striving to increase the utilisation of renewable energy. This paper presents and discusses the impacts of BIPV systems on two types of LV distribution network: a commercial LV distribution network and a residential LV distribution network in the state of Selangor, Malaysia. The results of these studies are compared with those from European networks to identify how the differences in the electrical network characteristics influence the allowable penetration of small-scale embedded generators.     

Design and evaluation of passive concentrator and reflector systems for bifacial solar panel on a highly cloudy region – A case study in Malaysia

Photovoltaic (PV) systems are the most promising renewable energy source in Malaysia because it is a tropical country receiving a huge amount of solar irradiation every year. However, Malaysia is surrounded by South China Sea and Malacca Straits. The vapour from the sea water with the blow of seasonal winds causes a large amount of clouds passing over the country, hence creating the variation in the direct and diffused sunlight throughout a day. The performance of the concentrators and reflectors for bifacial solar cells under the variation of direct and diffused sunlight has not been studied thoroughly. Therefore, several concentrators and reflectors have been designed, constructed and placed under a specially designed bifacial solar panel. The setup of each concentrator and reflector is as follows; scattering particles (scatterers) sprinkled across the plane mirror under the solar panel, an array of adjustable small plane mirrors placed underneath the solar panel, and long triangular prisms in between solar cells with a plane mirror underneath. Another solar panel is constructed and placed on top of the plane mirror as a reference. Each setup of the concentrators or reflectors is evaluated by measuring the power output of the tested and the reference panels together throughout a day under the sun. Empirical approaches are developed to compensate for uncontrollable factors including solar cell manufacturing mismatch and unequal degradation between the tested and the reference solar panels. A few potentially working static concentrator and reflector systems are identified based on the experimental results. An assessment is carried out to show the economic viability of the proposed setups with respect to that of the mono-crystalline solar cells.     

Low stoichiometry operation of a proton exchange membrane fuel cell employing the interdigitated flow field – A modeling study

A multiphase fuel cell model based on computational fluid dynamics is used to investigate the possibility of operating a proton exchange membrane fuel cell at low stoichiometric flow ratios (ξ < 1.5) employing the interdigitated flow field design and using completely dry inlet gases. A case study of two different operating temperatures and two different operating pressures is presented. In all cases the cathode side stoichiometric flow ratio was varied from ξ_c = 1.5 to 1.2, and the anode side varied to as low as ξ_a = 1.05. It is found that operating at ambient pressure leads to a generally dryer cell, and the only possibility to prevent membrane dry-out is to operate at or below 70 °C. The cell is generally better humidified at an elevated pressure, and here it is found that the cathode channels will become flooded when the operating temperature is too low, e.g. 70 °C, while membrane hydration levels of λ = 7–10 can be achieved at 80 °C. Operation at stoichiometric flow ratios as low as ξ = 1.2 at the cathode side and ξ = 1.05 at the anode side appear feasible. If this can be verified, it would allow open-ended anode operation without recirculation or flow shifting, thus significantly reducing system complexity and cost.     

The value of flexible fuel mixing in hydrogen-fueled gas turbines – A techno-economic study

In electricity systems mainly supplied with variable renewable electricity (VRE), the variable generation must be balanced. Hydrogen as an energy carrier, combined with storage, has the ability to shift electricity generation in time and thereby support the electricity system. The aim of this work is to analyze the competitiveness of hydrogen-fueled gas turbines, including both open and combined cycles, with flexible fuel mixing of hydrogen and biomethane in zero-carbon emissions electricity systems. The work applies a techno-economic optimization model to future European electricity systems with high shares of VRE.The results show that the most competitive gas turbine option is a combined cycle configuration that is capable of handling up to 100% hydrogen, fed with various mixtures of hydrogen and biomethane. The results also indicate that the endogenously calculated hydrogen cost rarely exceeds 5 €/kg_H2 when used in gas turbines, and that a hydrogen cost of 3–4 €/kg_H2 is, for most of the scenarios investigated, competitive. Furthermore, the results show that hydrogen gas turbines are more competitive in wind-based energy systems, as compared to solar-based systems, in that the fluctuations of the electricity generation in the former are fewer, more irregular and of longer duration. Thus, it is the characteristics of an energy system, and not necessarily the cost of hydrogen, that determine the competitiveness of hydrogen gas turbines.     

Undergraduate studies in energy education – A comparative study of Greek and British courses

Undergraduate energy education in Greece is compared with relevant accredited courses of the United Kingdom, with the aim to transfer good practices applied in the latter for the development and improvement of the Greek courses. Despite the encouraging prospects for energy engineering courses, the situation in Greece seems declining, with only one course being offered in this period. The (unique) Greek course seems to share the same basis with the majority of the British accredited courses, but also a few peculiarities that could be amended for the improvement of the course.     

Pretreatment as the crucial step for biogas reforming over Ni–Co bimetallic catalyst – A mechanistic study of CO2 pretreatment

H₂ and CO₂ pretreatment over the Ni–Co/La₂O₃–Al₂O₃ catalyst has been shown to lead to significant increase in catalytic performance. A mechanistic study was investigated by a series of catalytic activity measurements. Ni was found to be the main metal that interacted with CO₂. Meanwhile, H₂ reduction is an indispensable step of the pretreatment route and CO₂ cannot be replaced by O₂. FT-IR spectroscopy investigations were used to confirm that carboxyl was created during the CO₂ pretreatment of the Ni–Al₂O₃ catalyst. The result proved that bicarbonate of Ni was formed during the CO₂ pretreatment. During CO₂-reforming of methane, the bicarbonate of Ni could decompose into CO and provide oxygen species. The oxygen species will react with accumulated carbon on Ni crystallites to produce CO and in turn protect the active sites. Thus, the performance of the catalyst was significantly improved.     

Solar lanterns or solar home lighting systems – Community preferences in East Timor

Access to electrification in rural areas of East Timor is extremely limited with as few as 5% of rural households connected to electricity. The government of East Timor intends to increase rural access to electricity significantly in the coming decade. The introduction of small PV systems is envisaged for many households in the most remote areas. Several agencies have piloted the introduction of small solar home systems (SHS) and solar lanterns. In the Railaco sub-district of East Timor, some 1000 households have experience of using either SHS and/or solar lanterns and are in a unique position to indicate a preference regarding these forms of PV lighting technology. This paper reports on a survey of 76 households in Railaco investigating experience with PV lighting systems. Results of the survey indicate a strong preference by users for SHS rather than lanterns. The preference for SHS arose from a range of factors including: a perception of better light quality; ability to illuminate the whole house; reduced risk of damage to the PV equipment; and longer duration of nightly operation. The research indicates that where a single PV lighting system is provided, users are likely to prefer SHS to solar lanterns.     

Pricing and affordability of renewable energy in China – A case study of Shandong Province

The global warming and climate change have put enormous pressure on both governments and industries to re-think their attitudes and behaviours towards sustainability issues. The past decades have witnessed a number of renewable energy developments across the world. Even though these developments are not issue-free, it is generally recognized that the benefits outweigh disadvantages. However, there is an increasing level of concern on the high initial cost associated with the renewable energies, which was claimed as one of critical barriers to the promotion of its further developments. A case study approach is adopted in this study to investigate the pricing and affordability issues associated with the renewable energy in China. The policy framework and related statistics are critically reviewed in order to discuss these issues from different stakeholders’ perspective in Shandong province, China. It is concluded that the affordability remains a critical issue despite numerous efforts have been made by the Chinese Government and Shandong Provincial Government on renewable power pricing. This study offers a useful reference to pricing and affordability of renewable energy.     

Using three chemical looping reactors in ammonia production process – A novel plant configuration for a green production

Production of three pure streams of H₂, N₂ and CO₂ makes the chemical looping reactors as an attractive intermediate technology to provide the feedstock of ammonia synthesis loop. As a goal of paper, for the first time, a novel and green plant configuration using three chemical looping reactors is proposed for ammonia production in which needed hydrogen and nitrogen are produced by means of a process simpler than the conventional technologies. Due to the reduction in plant units and also 30% increase in production ratio and simultaneously production of economically valuable by-products of H₂, N₂ and CO₂, significant potential for investment cost reduction along with CO₂ capture and storage can be anticipated. Moreover, the proposed plant for ammonia production is very flexible in terms of adjusting the desired main products.     

Optimization of multiple heaters in a vented enclosure – A combined numerical and experimental study

This paper discusses the results of an experimental and numerical study of fluid flow and heat transfer in an enclosure where multiple heaters are arranged in a staggered fashion. Experiments were carried out for Reynolds numbers, in the range 1800 ≤ Re ≤ 4500 and Grashof numbers in the range 2.5 × 10⁴ ≤ Gr ≤ 3 × 10⁵. Numerical simulations were carried out for two dimensional, steady, incompressible turbulent flow and the results of the numerical study are compared with the experimental results. The temperature distribution gives an insight into the power management among the heaters, so that the “coolest” heater can be loaded most to maximize the total heat dissipation, for a prescribed temperature excess, for all the heaters. Two methods are used to achieve the target temperature for all heaters, namely (i) trial and error method and (ii) the response surface method. The latter method was adopted, to simultaneously maximize the heat input and minimize the temperature deviation from the target temperature, by employing a composite objective function. The numerically obtained optimal solution was finally verified by carrying out experiments. The method of response surface was found to be effective in optimizing the total heat transfer for a given target temperature.     

A solution to renewable hydrogen economy for fuel cell buses – A case study for Zhangjiakou in North China

Fuel cell vehicles fueled with renewable hydrogen is recognized as a life-cycle carbon-free option for the transport sector, however, the profitability of the H₂ pathway becomes a key issue for the FCV commercialization. By analyzing the actual data from the Zhangjiakou fuel cell transit bus project, this research reveals it is economically feasible to commercialize FCV in areas with abundant renewable resources. Low electricity for water electrolysis, localization of H₂ supply, and curtailed end price of H₂ refueling effectively reduce the hydrogen production, delivery and refueling cost, and render a chance for the profitability of refueling stations. After the fulfillment of the intense deployment of both vehicles and hydrogen stations for the 2022 Winter Olympics, the H₂ pathway starts to make a profit thereafter. The practices in the Zhangjiakou FCB project offer a solution to the hydrogen economy, which helps to break the chicken-egg dilemma of vehicles and hydrogen infrastructure.     

Carbon capture and storage potential in coal-fired plant in Malaysia—A review

Secure, reliable and affordable energy supplies are necessary for sustainable economic growth, but increases in associated carbon dioxide (CO₂) emissions, and the associated risk of climate change are a cause of major concern. Experts have projected that the CO₂ emissions related to the energy sector will increase 130% by 2050 in the absence of new policies or supply constraints as a result of increased fossil fuel usage. To address this issue will require an energy technology revolution involving greater energy efficiency, increased renewable energies and nuclear power, and the near-decarbonisation of fossil fuel-based power generation. Nonetheless, fossil fuel usage is expected to continue to dominate global energy supply. The only technology available to mitigate greenhouse gas (GHG) emissions from large-scale fossil fuel usage is carbon capture and storage (CCS), an essential part of the portfolio of technologies that is needed to achieve deep global emission reductions. However, CCS technology faces numerous issues and challenges before it can be successfully deployed. With Malaysia has recently pledged a 40% carbon reduction by 2020 in the Copenhagen 2009 Climate Summit, CCS technology is seen as a viable option in order to achieve its target. Thus, this paper studies the potential and feasibility of coal-fired power plant with CCS technology in Malaysia which includes the choices of coal plants and types of capture technologies possible for implementation.