Net energy analyses of eight technologies to provide domestic hot water heat

Net energy analyses have been carried out for eight trajectories which convert an energy source into heated domestic water. In addition, economic and metals consumed estimates have been made for three methods of producing heated domestic water. While some of the trajectories producing electrically heated water showed a slightly higher ratio of energy produced to energy consumed than a flat plate solar collector system, when all factors were considered (i.e. cost, quality of energy, and metals consumed), the flat plate solar collector system appears to be the system our energy policy should encourage for heating domestic water, even in the cloudy inter-Lakes area of the United States. Based on only net energy factors, it seems clear that the synthetic fuels program should not be encouraged as a means of providing a fuel source for heating domestic water.     

Net energy analysis of residential solar ponds

A net energy analysis (NEA) of three different residential solar pond scenarios is performed. A single home, a complex of twenty homes and a community system with district heating are considered. The designs considered, Rabl-Nielsen and Krass-LaViale, are studied for locations in Columbus, Ohio and in Northampton, Massachusetts. The analysis reveals that economies of scale and design considerations influence the net energy ratio (NER).     

Net energy analysis of space power satellites

A net energy analysis (NEA) of the Solar Power Satellite System is performed. Two options are compared using either silicon (Si) or gallium-aluminum-arsenide (Ga-Al-As) photovoltaic cells. The analysis is based on the DOE/NASA reference system. Maintenance and material energy costs are considered and are shown to be valid. Results show a net energy ratio (electrical output vs primary thermal input) of the order of 2–5 for the silicon cell option and 14–18 for the gallium-aluminum-arsenide option.     

Charcoal as an alternative energy carrier: Net energy and cost analyses

Principles for net energy analysis are reviewed and applied to a proposed system for charcoal production, district heating and electricity co-generation. Calculated net utilizable energy production (NUEP) is 49% for charcoal production, not counting waste products and rejected heat, and 78% for combined charcoal, heat, and electricity production, based on data for direct and indirect energy consumption in Norway. Comparisons with other widely used biomass energy systems, using NUEP and cost values, show that charcoal is a renewable energy carrier which is competitive on both an energetic and an economic basis.     

Exergy and energy analyses of absorption heat pumps

This paper presents a detailed thermodynamic analysis of absorption heat pumps and heat transformers. First and second law thermodynamic methods are both applied to calculate the respective energy efficiency (COP) and the energy efficiency (n) for the systems as well as the individual components. Using LiBr/H₂O as an example, two three-dimensional T-S-X diagrams for an absorption heat pump and a heat transformer are constructed by calculating the thermodynamic properties and the chemical potentials. From the calculated COP and n values, it is concluded that AHP for heating has better thermodynamic performance than both AHP for cooling and heat transformer.     

Net energy analyses for liquid-dominated and vapor-dominated hydrothermal energy-resource developments

The current status of the disciplines of energy analysis and net energy analysis is briefly reviewed. Various methodological approaches to the evaluation of energy flows in society are described and assessed.

Detailed evaluations of the energy requirements for construction and operation of 100-Mw_e flashedsteam, binary-cycle and total-flow power plant designs for utilization of liquid-dominated hydrothermal reservoirs indicate that the meaningful net energy ratios range from about seven to eleven. Utilization of dry cooling towers in place of evaporative cooling systems may be required in many locations and may reduce the specified net energy ratios by approximately 15%. Indirect energy requirements associated with the supply of external resource inputs necessary for the construction and operation of these electrical-energy generating stations account for approximately 85% of total energy requirements, with the balance being allocated to the direct consumption of fuels.

A similar analysis of the energy requirements for the construction and operation of a 100-Mw_e power plant utilizing a vapor-dominated hydrothermal reservoir leads to net energy ratios for vapor-dominated hydrothermal electrical-power generation stations as high as nineteen. In this case, direct fuel consumption accounts for approximately 24% of the total energy requirements.

The major indirect energy requirements are associated with power plant construction for liquid-dominated developments, while production well drilling contributes most heavily to these requirements of vapor-dominated resource utilization. Direct consumption of fuel is predominately concentrated in production well drilling for both classes of hydrothermal facilities.     

Comparative analyses of seven technologies to facilitate the integration of fluctuating renewable energy sources

An analysis of seven different technologies is presented. The technologies integrate fluctuating renewable energy sources (RES) such as wind power production into the electricity supply, and the Danish energy system is used as a case. Comprehensive hour-by-hour energy system analyses are conducted of a complete system meeting electricity, heat and transport demands, and including RES, power plants, and combined heat and power production (CHP) for district heating and transport technologies. In conclusion, the most fuel-efficient and least-cost technologies are identified through energy system and feasibility analyses. Large-scale heat pumps prove to be especially promising as they efficiently reduce the production of excess electricity. Flexible electricity demand and electric boilers are low-cost solutions, but their improvement of fuel efficiency is rather limited. Battery electric vehicles constitute the most promising transport integration technology compared with hydrogen fuel cell vehicles (HFCVs). The costs of integrating RES with electrolysers for HFCVs, CHP and micro fuel cell CHP are reduced significantly with more than 50% of RES.     

Modern residential energy inequalities in Indonesia: spatial and income analyses

ABSTRACT

This study put forward the inequality issues in modern residential energy consumption from both income and spatial viewpoints, with special regard to the Indonesian case. Energy inequality was viewed from the perspective of energy justice in both distribution and recognition. This study employed qualitative analysis with Theil’s, Gini, and mixed-Gini index methods. The energy usage inequalities have declined, both overall and by the dimensions of spatial and income levels, except in urban areas. However, this paper found that some groups were susceptible to fall into energy-poor, especially residents in rural areas, remote areas, and eastern Indonesia. Besides improving a more stable electricity grid, the government should continue the energy-saving solar lighting (LTSHE) program and promote small-scale decentralized technologies. LPG distribution should be improved. A program such as the cheap clean stove needs to be developed to reach those without access to clean cooking fuel.     

Solar seasonal thermal energy storage for space heating in residential buildings: Optimization and comparison with an air-source heat pump

ABSTRACT

This study evaluates the techno-economics of replacing an air-source heat pump (ASHP) system with a solar seasonal thermal energy storage (STES) system for space heating in Hangzhou, China. Three heating systems, solar STES, ASHP, and ASHP with short-term storage of solar energy, are developed using TRNSYS for a house with 240 m² of floor area. The ratio of tank volume to collector area (RVA) of the STES is optimized for the lowest equivalent annual cost over a lifespan of 20 y. The determined optimal RVA is 0.33 m³/m², although it depends on the system and electricity prices. The optimized STES reduces the electricity demand to 1,269 kWh (74% reduction). Despite the superior energy performance, the economic benefit is only possible with large STES systems, which enjoy low tank prices due to scale effects. The results suggest that policy support is needed for STES, where district scaling is not an option.     

Economic optimization and sensitivity analysis of energy requirements in residential space heating

An analytical model which relates performance with costs of additional insulation has been developed and the optimum set of insulation values for the various surfaces of a new building has been determined in a generalized form. On this basis the determinants of the specific energy requirements, corresponding to an optimal level of insulation are identified. The sensitivity of the energy needs to variations in the building structure or design, in the economic conditions, and in the climate characteristics, is also investigated.     

Net energy analysis of district solar heating with seasonal heat storage

A net energy analysis of district solar heating using seasonal heat storage has been performed. The use of seasonal heat storage is of great importance in northern latitudes when the solar contribution is to be increased. Different system alternatives were considered. Net energy ratios for the most favourable options were found to be between 3 and 5.     

On the potential trade-offs between energy supply and end-use technologies for residential heating

In Sweden, where district heating accounts for a significant share of residential heating, it has been argued that improvements in end-use energy efficiency may be counter-productive since such measures reduce the potential of energy efficient combined heat and power production. In this paper we model how the potential trade-offs between energy supply and end-use technologies depend on climate policy and energy prices. The model optimizes a combination of energy efficiency measures, technologies and fuels for heat supply and district heating extensions over a 50 year period. We ask under what circumstances improved end-use efficiency may be cost-effective in buildings connected to district heating? The answer hinges on the available technologies for electricity production. In a scenario with no alternatives to basic condensing electricity production, high CO₂ prices result in very high electricity prices, high profitability of combined heat and power production, and little incentive to reduce heat demand in buildings with district heating. In contrast, in a scenario where electricity production alternatives with low CO₂ emissions are available, the electricity price will level out at high CO₂ prices. This gives heat prices that increase with the CO₂ price and make end-use efficiency cost-effective also in buildings with district heating.     

Net energy: Results for small-scale hydroelectric power and summary of existing analyses

The net energy ratios of most small-scale (≤ 25 MWe) hydroelectric demonstration projects are in the range of 10 to 12:1. This ratio compares quite favorably with ratios for thirteen other electric technologies. Of the eight nonelectric technologies summarized, natural gas systems yield the most net energy and systems producing alcohol from crops yield the least.     

Detailed parametric analyses of heat transfer in CPC solar energy collectors

A detailed parametric analysis of heat transfer in compound parabolic concentrating solar energy collectors has been performed, using a unified model for their optical and thermophysical behaviour. The effects of angular inclination and collector acceptance angles on free convection within the cavity are presented. The circumferential variation of local Nusselt number about the absorber is determined. A convective heat transfer correlation is obtained for the average Nusselt number with respect to Grashof number that takes into account acceptance angle and angular inclination. The developed correlation is extended to truncated compound parabolic concentrators.     

钢铁流程能耗分析及节能技术的研究进展

综合阐述钢铁流程系统能耗模型的发展,能耗计算与影响因素分析以及节能技术的研究进展,基于钢铁流程基本的物质流、能量流网络模型,提出"解析-集成-协同"的能耗分析思路。同时,指出热力学分析方法与优化目标在流程节能方面的关键性作用,以及在余能余热回收与利用方面的主要应用,并基于此从节能技术发展的角度对减少流程能耗进行了深入探讨。     

Numerical simulations and analyses of temperature control loop heat pipe for space CCD camera

As one of the key units of space CCD camera,the temperature range and stability of CCD components affect the image's indexes.Reasonable thermal design and robust thermal control devices are needed.One kind of temperature control loop heat pipe(TCLHP) is designed,which highly meets the thermal control requirements of CCD components.In order to study the dynamic behaviors of heat and mass transfer of TCLHP,particularly in the orbital flight case,a transient numerical model is developed by using the well-established empirical correlations for flow models within three dimensional thermal modeling.The temperature control principle and details of mathematical model are presented.The model is used to study operating state,flow and heat characteristics based upon the analyses of variations of temperature,pressure and quality under different operating modes and external heat flux variations.The results indicate that TCLHP can satisfy the thermal control requirements of CCD components well,and always ensure good temperature stability and uniformity.By comparison between flight data and simulated results,it is found that the model is to be accurate to within 1℃.The model can be better used for predicting and understanding the transient performance of TCLHP.     

Analysis of residential energy use

The structure, inputs, validation and operation of a residential energy use model are examined with the intention of providing an analytical tool for evaluation of energy conservation option for effects on energy use and related costs.     

Optimisation of a Swedish district heating system with reduced heat demand due to energy efficiency measures in residential buildings

The development towards more energy efficient buildings, as well as the expansion of district heating (DH) networks, is generally considered to reduce environmental impact. But the combined effect of these two progressions is more controversial. A reduced heat demand (HD) due to higher energy efficiency in buildings might hamper co-production of electricity and DH. In Sweden, co-produced electricity is normally considered to displace electricity from less efficient European condensing power plants. In this study, a potential HD reduction due to energy efficiency measures in the existing building stock in the Swedish city Linköping is calculated. The impact of HD reduction on heat and electricity production in the Linköping DH system is investigated by using the energy system optimisation model MODEST. Energy efficiency measures in buildings reduce seasonal HD variations. Model results show that HD reductions primarily decrease heat-only production. The electricity-to-heat output ratio for the system is increased for HD reductions up to 30%. Local and global CO₂ emissions are reduced. If co-produced electricity replaces electricity from coal-fired condensing power plants, a 20% HD reduction is optimal for decreasing global CO₂ emissions in the analysed DH system.     

Fuel cells and energy networks of electricity,heat, and hydrogen in residential areas

Fuel cells for domestic purposes have been recently launched in the commercial markets of Japan. They comprise fuel cell stacks, fuel processors that generate hydrogen from natural gas, heat recovery equipment, and hot-water tanks. These systems do not require additional infrastructure and can influence consumer acceptance, however, there are limitations in terms of efficiency and flexibility.