Numerical parametric study of a new earth-air heat exchanger configuration designed for hot and arid climates

ABSTRACT

Thermal potential for cooling and heating can be achieved by new configuration of earth–air heat exchanger (EAHE). This paper presents a numerical investigation of thermal performance of a spiral-shaped configuration of EAHE intended for the summer cooling in hot and arid regions of Algeria. A commercial finite volume software (ANSYS FLUENT) has been used to carry out the transient three-dimensional simulations and the obtained results have been validated using the experimental and numerical data obtained from the literature. The agreement between our simulation results and those from literature is very satisfactory. A parametric analysis of the new geometry of (EAHE) has been performed to investigate the effect of pitch, depth, pipe length and of the flow velocity on the outlet air temperature and the EAHE’s mean efficiency as well as its coefficient of performance (COP). It has been shown that when the pitch space varies between 0.2 and 2 m the difference of outlet air temperature increases by 6 ^°C. When the air velocity increases from 2 to 5 m/s the mean efficiency decreases from 60 % to 33 % and the COP of the EAHE decreases from 2.84 to 0.46.     

Indicators for sustainable energy development: Brazil's case study

This article summarizes the results of the project on indicators for sustainable energy development (ISED) in Brazil. The project's aim was to present energy related economic, social and environmental data to policy makers in a coherent and consistent form, showing interlinkages, time‐series and cross‐sectoral analyses and assess energy policy. Two priority areas assessed by these indicators, regarding the country's energy supply and demand, helped in the identification of a number of energy policy options that focused on specific aspects of the country's energy sector. On the supply side, these options include the development and stimulation of renewable energy, such as small‐scale hydroelectric, wind, solar photovoltaic power and bagasse cogeneration; stimulation of programmes for ethanol use as automotive fuel and sugarcane bagasse cogeneration; and implementation of natural gas‐fired, combined heat and power (CHP) plants. On the demand side, policy options include: the full implementation of the law on efficiency standards for appliances; expansion of utility investment in end‐use energy efficiency; adoption of targets and protocols to reduce energy intensity in the industrial sector; improvement of passenger transport efficiency; and the creation of a fund to improve energy affordability for the poor.     

Indicators for sustainable energy development in Mexico

This article presents a summary of a study on the application to the Mexican energy sector of a core set of indicators for sustainable energy development (ISED), developed by the International Atomic Energy Agency (IAEA). The study focused on the elaboration of socio‐economic and environmental indicators related to energy production and use, and was aimed at assessing Mexico's existing energy policies and identifying strategies and possible policies that could bring about improvements in major priority areas: energy intensity, atmospheric emissions, energy import dependency and use of renewables. While positive trends have been observed in relation to energy intensity and atmospheric emissions, Mexico is becoming more dependent on imports of gasoline, natural gas and other high‐value secondary energy sources, while exporting significant amounts of primary fuels, such as crude oil. Also, no significant increase has been observed in the use of renewable sources of energy. Social, economic and environmental policies need to be formulated for the energy sector and related investments (public and private) reinforced so that all economic sectors have access to energy from cleaner and more diverse sources.     

Monitoring the sustainability of Russia's energy development

This article presents an assessment of Russia's energy sector, its current state and planned future direction. The analysis of Russia's energy trends is based on a set of indicators for sustainable energy development (ISED), developed under the leadership of the International Atomic Energy Agency (IAEA). The article discusses Russia's Energy Strategy to 2020, and outlines major developments and challenges of the country's energy system. Russia's energy priorities, captured in the Strategy to 2020, emphasize securing a stable and uninterrupted energy supply; reducing energy intensity and improving energy efficiency; developing the domestic energy resource base; reducing negative environmental impacts; and ensuring affordable energy for the poorer segments of the population. Energy needs and challenges are discussed in relation to the three aspects of sustainability as defined in Agenda 21: economic, social and environmental. Concerns are expressed regarding environmental repercussions of energy development, in particular since Russia's 1998 economic rebound. There are also concerns, despite the economic recovery, that anticipated increases in energy tariffs may exceed the affordability of poorer segments of the population.     

Energy indicators and sustainable development: The International Energy Agency approach

The International Energy Agency (IEA), together with the International Atomic Energy Agency (IAEA), UN‐DESA, Eurostat and the European Environmental Agency, has recently published a comprehensive joint‐agency overview of energy indicators for sustainable development. The IEA's contribution to this publication is based on the IEA energy indicator approach. This approach has been developed and used by the IEA over a number of years. The indicators advocated by the IEA are relatively disaggregated to allow for meaningful analysis of sustainability issues in the energy sector. Using a decomposition approach helps reveal the causal links between human/economic driving forces, energy use and emissions. This article presents examples of IEA's work with indicators and an overview of the methodology used, including an explanation of the link to sustainable development. It also provides an example of a simplified indicator analysis of India, to illustrate the importance of improved data systems in developing indicators that can provide meaningful policy analysis.     

Total recycling of CCA treated wood waste by low-temperature pyrolysis

A system to turn a potentially harmful stream of solid waste into a set of substreams with either commercial value or highly concentrated residual streams is presented. The waste which is considered is metal impregnated (in particular Chromated Copper Arsenate (CCA) treated) wood waste and timber, such as telephone poles, railway sleepers, timber from landscape and cooling towers, wooden silos, hop-poles, cable drums and wooden playground equipment. These waste streams sum up to several 100,000 tons of material per year currently to be dumped in every major country of the European Community (EC). Technologies need to be developed to reduce this CCA treated wood waste, such that all of the metals are contained in a marketable product stream, and the pyrolysis gases and/or pyrolysis liquid are used to their maximum potential with respect to energy recuperation. Pyrolysing the CCA treated wood waste may be a good solution to the growing disposal problem since low temperatures and no oxidising agents are used, which result in lower loss of metals compared to combustion. An experimental labscale pyrolysis system has been developed to study the influence of the pyrolysis temperature and the duration of the pyrolysis process on the release of metals and the mass reduction. The macrodistribution and microdistribution of the metals in the solid pyrolysis residue is studied using Inductively Coupled Plasma Mass Spectrometry (ICP–MS) and Scanning Electron Microscopy coupled with Energy Dispersive X-ray Analysis (SEM–EDXA). Furthermore, a complete mass balance is calculated over the pyrolysis system. Based on these results a semi-industrial pyrolysis system (pilot plant scale) has been developed consisting of three stages: grinding, packed bed pyrolysis and metal separation. Special types of equipment have been developed to carry out the three stages. A new grinding system has been developed, based on a crushing mechanism rather than a cutting mechanism. The crushed wood is introduced by means of a screw feeding system into a reaction column. In this pyrolysis reactor the wood is heated by subjecting it to a flow of hot gases. This causes an adiabatic pyrolysis, which results in volatilisation of the volatile compounds whereas the mineral compounds (containing the metals) remain entrapped in a coal-type residue which is very rich in carbon. The condensable compounds in the pyrolysis gas condense while leaving the reaction zone due to the inverse temperature gradient. The pyrolysis gas leaving the reactor is used as fuel for the hot gas generator. The charcoal which is extracted at the bottom of the reactor, is cooled, compressed, removed and stored, ready to feed the subsequent stage. A specially developed grinder is used to remove the metal particles from the charcoal and the separation between metal and charcoal particles is accomplished in a pneumatic centrifuge as a result of the difference in density. Using this system the ultimate waste is less than 3% of the initial wood mass. Results obtained with a semi-industrial scale prototype confirm the effectiveness of the process.     

Fuel substitution and efficient woodstoves: Are they the answers to the fuelwood supply problem in Northern Nigeria?

Fuelwood consumption in Northern Nigeria exceeds the sustainable production, and the deficit is currently met through long-distance transport from the southern part of the country at an artificially low cost Current household fuel consumption patterns and factors affecting stove choice are discussed. Little has been done to promote more efficient woodstoves in the region, but prospects for stove programs are only good where fuelwood is marketed and the policy environment is conducive. At subsidized official prices for kerosene, liquefied petroleum gas (LPG), and electricity, wood is more expensive on a net usable heat basis, but the high capital cost of stoves for these fuels prevents many households from switching. Moreover, these fuels are often only available at much higher parallel market prices, which result in wood being the less expensive choice. There is little prospect for substitution of coal, solar cookers, or biogas digesters.     

Economics of an ecotourism operation in Belize

The economic inputs and outputs for the Possum Point Biological Station in Belize during 1990–1992 are described to illustrate some aspects of an ecotourism operation. Eight hundred fifty-four people in 59 groups visited Possum Point during the study period to tour rain forests, estuaries, and coral reefs. The economic input to Possum Point from these groups increased from $74,552 in 1990 to $166,268 in 1992. Outputs were for license fees, capital improvements, goods and services, labor, fossil fuels, and development of a historic sugar mill site. An annual donation was also made to a scholarship fund for local Belizean students. The net cash balance of income and outputs changed from negative (−$6678) in 1990 to positive (+$4811) in 1992, suggesting development of the economic operation. Possum Point meets the economic criteria for ecotourism by feeding back some tourist monies for community and environmental support, particularly donations for the sugar mill site and the scholarship fund. Most of the outputs from Possum Point (about 80%) were retained in the local economy through employment and purchases, which have a positive influence on the local community. We conclude that ecotourism operations, such as Possum Point, offer important sustainable development opportunities for Belize.     

Energy economy of salmon aquaculture in the Baltic sea

Resource utilization in Atlantic salmon aquaculture in the Baltic Sea was investigated by means of an energy analysis. A comparison was made between cage farming and sea ranching enterprises each with yearly yields of 40 t of Atlantic salmon. A variety of sea ranching options were evaluated, including (a) conventional ranching, (b) ranching employing a delayed release to the sea of young smolts, (c) harvesting salmon both by offshore fishing fleets and as they return to coastal areas, and (d) when offshore fishing is banned, harvesting salmon only as they return to coastal areas where released. Inputs both from natural ecosystems (i.e., fish consumed by ranched salmon while in the sea and raw materials used for producing dry food pellets) and from the economy (i.e., fossil fuels and energy embodied in economic goods and services) were quantified in tonnes for food energy and as direct plus indirect energy cost (embodied energy). The fixed solar energy (estimated as primary production) and the direct and indirect auxiliary energy requirements per unit of fish output were expressed in similar units. Similar quantities of living resources in tonnes per unit of salmon biomass output are required whether the salmon are feeding in the sea or are caged farmed. Cage farming is about 10 times more dependent on auxiliary energies than sea ranching. Sea ranching applying delayed release of smolts is 35–45% more efficient in the use of auxiliary energies than conventional sea ranching and cage farming. Restriction of offshore fishing would make sea ranching 3 to 6.5 times more efficient than cage farming. The fixed solar energy input to Atlantic salmon aquaculture is 4 to 63 times larger than the inputs of auxiliary energy. Thus, cage farming and sea ranching are both heavily dependent on the productivity of natural ecosystems. It is concluded that sustainable development of the aquaculture industry must be founded on ecologically integrated technologies which utilize the free production in marine ecosystems without exhausting or damaging the marine environment.