Savings-to-investment Ratio Research Articles

Enhancing energy efficiency of chemical absorption-based CO2 capture process with advanced waste-heat recovery modules at a high capture rate

A commercial-ready amine-based CO2 capture process (CCP) restricts its potential for industrial deployment at a high capture rate to achieve a net-zero carbon target due to its energy-intensive nature. This study aims to enhance the energy efficiency of a monoethanolamine (MEA)-based CCP, operating at a 95% capture rate, by developing advanced process modules that utilize low-grade waste heat. To establish a foundation for designing cascade modules that can recover energy from all available waste heat, the waste heat characteristics were analyzed, and the feasibility of four single modules was explored to recover the latent heat in a stripped gas. Subsequently, this study comparatively investigated the equivalent electrical works of the two designed cascade modules combined with lean vapor compression (LVC). A techno-analysis indicated that cascade modules provided outstanding energy-saving performance ranging from 12.27% to 24.55%, with an average improvement of 50% over single modules. Although the cascade modules combined with LVC showed similar energy-saving performances, higher robustness for equivalence factor (EF) and more energy-savings were discovered in the electricity generation and direct heat supply strategies, respectively. Economic analysis indicated that advanced process modules were economically feasible, with a savings-to-investment ratio (SIR) exceeding 1. The SIR and payback period (PBP) depended on EF and electricity prices. Significantly, the cascade module for direct heat supply emerged as the most appropriate in terms of both economic viability and energy-saving efficiency in amine-based CCPs, particularly at a higher EF.

Novel design of concentrating photovoltaic thermal collector – A comparative analysis with existing configurations

The aim of this paper is to propose a novel concentrating photovoltaic thermal (CPVT) collector based on parabolic trough concentrator with a semi-cylindrical receiver, and provide a comprehensive comparative analysis of the proposed configuration with the main existing CPVT collectors. To this end, a thermal model of the considered solar collectors is developed to investigate the impact of the receiver’s design on the collector’s performance in terms of their thermal, electrical, primary energy and exergy efficiencies. A residential building, located in the Moroccan city of Ouarzazate, characterized by its hot semi-arid climate, is considered as a case study to investigate the integration of solar collectors in air-conditioning application. A performance, economic and environmental analyses of CPVT driven cooling system are conducted by means of key indicators such as, solar coefficient of performance (SCOP), discounted payback period (DPP), levelized cost of cooling (LCOC), savings-to-investment ratio (SIR) and saved greenhouse gases (GHG) emissions.The results revealed that the proposed CPVT collector exhibited the highest primary energy efficiency with a value of 0.798. The performance outcomes of the solar cooling systems proved that a SCOP of 0.488 was achieved by the proposed CPVT collector followed by those based on the triangular, tubular and rectangular receivers with a value of 0.436, 0.406 and 0.367 respectively. Furthermore, from an economic perspective, the novel CPVT configuration has been proven to be the most cost-effective one with a LCOC, DPP and SIR of 0.129 $/kWh, 12.3 years and 1.488, respectively. Moreover, this configuration was found to be the most eco-friendly one with the lowest greenhouse gases emissions. This study could contribute to the promotion of the sustainable CPVT technology and is expected to be a guideline to select the most suitable configuration of CPVT collectors for solar cooling purposes.

Impact of cooling tower technology on performance and cost-effectiveness of CSP plants

Cooling towers are indispensable components for heat rejection in concentrated solar power (CSP) plants. However, the overall performance of CSP plants relies heavily on the choice of cooling tower technology. This paper aims at assessing the impact of cooling tower technology on CSP plant from performance, economic, and environmental perspectives. To achieve this goal, seven CSP projects worldwide with distinct features were selected, and multiple simulations on System Advisor Model software were performed to evaluate the annual energy production, capacity factor, and levelized cost of electricity (LCOE). Moreover, the impact assessment was performed in terms of key metrics, such as discounted payback period (DPP), savings-to-investment ratio (SIR), greenhouse gases (GHG) emissions, water-saving, and total costs savings (TCS) including energy, carbon and water costs savings.The results showed that the wet cooling technology achieved the highest performance findings followed by hybrid and dry cooling technologies. The environmental analysis revealed that the wet cooling technology could avoid roughly 7.02% and 2.93% of GHG emissions compared to dry and hybrid cooling ones, respectively; however, it was found that dry and hybrid cooling technologies could be more profitable in arid regions with water scarcity, since they could save on average 93.30% and 69.83% of water, respectively, compared to the wet technology. Furthermore, the economic results showed that wet and hybrid cooling towers exhibit the best cost-effectiveness over dry cooling one as the LCOE was found to be $0.231/0.244 per kWh, and the DPP ranged between 13.41 and 23.46/14.95 and 34.75 years by integrating wet/hybrid technologies in CSP plants. Overall, wet and hybrid cooling technologies yield better TCS and SIR outcomes over dry cooling one. However, with respect to energy conservation, water savings, and GHG emissions savings, hybrid cooling tower could be considered as an optimal technology. This paper is expected to be a guideline for selecting the most cost-effective and eco-friendly cooling technology for future CSP plants, based on key criteria.

EVALUATION OF ENERGY-EFFICIENCY IN LIGHTING SYSTEMS FOR PUBLIC BUILDINGS

Adoption of energy efficiency and conservation techniques in public buildings in Nigeria is significantly low due to the ignorance of its potential benefits. Consequently, this study presents the prospects of energy saving using different methods in a public building at a Nigerian University. A proposed remodelled students’ residential hostel at the University of Lagos, Nigeria was chosen as a pilot study. This research utilized three energy efficient lighting technology alternatives namely; intelligent controlled Incandescent lamp (ICIL), compact fluorescent lamp (CFL), and intelligent controlled CFL (ICCFL) and compared with a base case of conventional incandescent lighting configuration. Energy consumption, at the proposed hostel is analysed and modelled. The effectiveness of each lighting technology alternative and base case in terms of cost is estimated using economic indices such as the net present value (NPV), savings to investment ratio (SIR) and the discounted payback period (DPP). Results show that the CFL lighting technology give 39% cost benefit as compared to ICCFL which gives 11% overall cost benefit. From the study, it is established that adoption of energy efficient lighting techniques save a significant amount of energy, operational cost, electricity bills and consequently reduce emission.

A case study to improve the winter thermal comfort of an existing bus station

The thermal comfort retrofitting of existing transport stations is an opportunity to increase the interest in the use of public transportation while improving the performance of the building, and consequently reduce the energy consumption and greenhouse gas emissions. The aim of this study is to implement an innovative methodology to evaluate and improve the thermal comfort of an existing semi-outdoor bus station in the winter season through the application of retrofit solutions. Some research was recently published concerning the evaluation of the thermal environment in semi-outdoor spaces showing that thermal comfort is achievable. The thermal environment of the station was evaluated through an experimental campaign involving the measurement of physical parameters and the application of questionnaires to the passengers. The results of the questionnaires indicate a colder sensation in the morning period and a lower percentage of dissatisfied people when compared to the application of the thermal comfort models. However, the preference of the passengers for a warmer environment was also identified. A realistic thermal comfort target, adapted to this semi-outdoor space, could, therefore, be defined. An innovative integrated methodology articulated in a BIM2BEM approach was applied in this work. The methodology included the joint application of Building Information Modeling and Building Energy Modeling, allowing the simulation of different retrofitting alternatives. The decision-making process was completed with an economic analysis of the alternatives, using the Savings-to-Investment Ratio (SIR) as an indicator. In order to improve the passengers’ thermal comfort, the option to create an enclosed heated waiting area was technically supported by the results of the study.

Technical and economic feasibility of solar flat-plate collector thermal energy systems for small and medium manufacturers

Manufacturing industries require process heating for a wide variety of operations, such as drying, cooking, washing, and sterilizing. Studies of industrial energy consumption have shown that more than 50% of industrial heating demand is in the low (<60 °C), medium (60–150 °C), and medium-high (<250 °C) temperature ranges. A significant fraction of this low temperature thermal energy could be generated by commercially available solar flat-plate collector thermal energy systems, which would reduce the use of fossil fuels, energy cost volatility, and carbon emissions. However, manufacturing industries have not been able to take advantage of solar flat-plate collector systems for two main reasons: First, information is not readily available about when and what flat-plate collector system sizes can be economically applied and, second, manufacturers often do not have appropriate personnel or analysis tools to make decisions about installation of solar flat-plate collector systems. The goal of this research is to provide design decision support to small- and medium-sized manufacturers in conducting feasibility analysis for the application of solar flat-plate collector systems in their operations. The ϕ‾,f-chart method and modified ϕ‾,f-chart design method are used to predict the amount of energy collected by solar flat-plate collectors. A simplified model is proposed to assess the cost of solar flat-plate collector energy systems. To demonstrate the presented feasibility analysis methodology, a decision support software application is developed. What-if scenarios are presented for several geographic locations of varying climates. A sensitivity analysis of savings-to-investment ratio (SIR) was performed by changing selected input parameters by ±30% from the base case. It was found that SIR is sensitive to natural gas price, followed by collector area dependent cost, discount rate, cost of the auxiliary gas heater, and cost of the preheating system.

Multi-approach evaluations of a cascade-Organic Rankine Cycle (C-ORC) system driven by diesel engine waste heat: Part B-techno-economic evaluations

A novel transcritical cascade-Organic Rankine Cycle (C-ORC) system was proposed for recovering multi-grade waste heat from a typical heavy-duty diesel engine. The C-ORC comprises a high temperature ORC loop (HT-Loop) and a low temperature ORC loop (LT-Loop) for recovering waste heat from engine exhaust gas (EG), exhaust gas recirculation (EGR), jacket water (JW) and charge air (CA) in a cascaded pattern. The basic thermodynamic evaluation on energy and exergy aspects were covered in the companion piece-‘Part A-thermodynamic evaluations’, indicating that the proposed C-ORC possesses great heat-recovery capacities and efficiency-promotion potentials. The techno-economic evaluations in Part B of this paper will further explore the performance of the C-ORC system based on costs and benefits in order to reveal its practical benefits.Four techno-economic indexes are mainly focused on: component-to-system cost ratio (CSCR), electricity production cost (EPC), depreciated payback period (DPP) and savings-to-investment ratio (SIR). Under rated engine conditions, working fluids were initially compared to find the most economical fluids for the HT-Loop and the LT-Loop respectively. Results indicated that toluene and R143a still make the perfect match for the C-ORC with the lowest EPC (0.27Dollar/kWh), DPP (7.8years) and the highest SIR (1.6). As to component-to-system cost ratio (CSCR), the cost of expanders and heat exchangers together account for more than 3/4 of the total system cost, and the expander of the LT-Loop is the most costly single component. The C-ORC’s techno-economic performance was further evaluated based on engine’s practical operating conditions. Results showed that, under available conditions, the CSCR of expanders is within 25.9–48.0%, and it gradually increases as engine’s speed and torque increase; the CSCRs of heat exchangers and pumps are within 31.1–54.8% and 17.7–22.5% respectively. The EPC, DPP and SIR are within 0.27–0.48Dollar/kWh, 8.5–20.5years and 0.85–1.6 respectively, and according to their similar variations, an increase in engine speed will evidently benefit three indexes. In addition, the increasing torque will also improve the indexes to some extent.Summarily, the techno-economic evaluations in Part B of this paper further reveal the C-ORC’s merits and drawbacks, and in order to improve its full performance, provide directions for optimizations for higher system capacities and commercial potentials.

A parametric study on the feasibility of solar chimney power plants in North Cyprus conditions

The present work investigates the feasibility of installing a solar chimney power plant (SCPP) under North Cyprus (NC) conditions. The method utilized for the simulations of electricity production was compared and verified by the experimental recordings of the prototype in Manzanares, Spain, before carrying out performance predictions for different plant sizes, collector diameters and chimney heights. The annual electricity production of a 30MW hypothetical SCPP system is estimated to be 94.5GWh, which can cater for annual electricity needs of over 22,128 residences without any CO2, NOx and SOx emissions. For an installation cost of €145 million, it was estimated that the savings-to-investment ratio (SIR) would be 1.14, indicating a marginal economic feasibility. It is important to find ways of reducing the installation cost in order to strengthen the economic viability of the system. Considering that, at present, fuel oil no. 6 is being used in NC to produce electricity; the SCPP would cause avoidance of 24,840tonnes of CO2 delivered into the atmosphere annually, if it replaced an equivalently-sized conventional power unit. To identify the most feasible cost option for the installation of the SCPP, a parametric cost analysis is carried out by varying the parameters such as; capital investment costs, carbon dioxide emission trading system price, chimney height, collector diameter and SCPP plant capacity. In all cases, the effect of these parameters on the economic feasibility indicators, such as SIR, net present value (NPV) and internal rate of return (IRR) were calculated. The results showed that SCPP investment cost, capacity of the plant and chimney height are critical in assessing the project viability.

Strategies of investment in the management of urban bridges: a life-cycle approach illustrated for Paris

As demonstrated in past research, decisions regarding maintenance and rehabilitation strategies for a portfolio of bridges should be based on the analysis of both costs and benefits over their life cycle. Such decisions involve the priority and timing of expenditure. This is particularly important in the current era that is characterised by limited funding for infrastructure preservation in most countries. This article presents a probabilistic life-cycle-based investment framework to develop decisions for bridge maintenance and rehabilitation. The framework ranks different projects by priority, using the savings-to-investment ratio (SIR) as a measure of cost-effectiveness. The SIR computation includes the initial investment; annual operation, maintenance and repair/rehabilitation costs; and failure costs. These future costs are linked to probable events, such as natural hazards, vehicle and boat crashes, and user time delay. Since life-cycle analysis is sensitive to the analysis period, this article introduces the concept of infinite lifetime or perpetuity. A case study involving 37 bridges across the Seine River in the City of Paris is used to illustrate the framework application. The application considers pile protections and avoidance of traffic disturbance, and it is especially interesting because the examined bridges have a wide variation with regard to their dates of construction, material type and dimensions. Results of the study prove that this approach enables the decision maker to select the most cost-effective project, and to convey it to the public by incorporating social and political issues that represent practical considerations. In addition, the results seem to be relatively insensitive to the analysis period and the discount rate.

A feasibility integrated approach in the promotion of solar house design

SUMMARY In many countries, although solar energy is plentiful, due to technical and economic issues, micro-scale solar energy technologies have not properly found their places in the market. The present work demonstrates the convenience of employing economic feasibility assessments together with engineering analyses before applying solar strategies during the design stages, in order to convince house owners that these solar technologies can be economically viable. In a case study, this approach is tested for a real house project developed in North Cyprus (NC) in which solar energy applications for electricity generation, hot water preparation, space heating and passive cooling are investigated. It is reported that grid-connected photovoltaic (PV) systems would be economically feasible with savings-to-investment ratio (SIR) values of 2.9 to 3.4. A thermal performance analysis is carried out for a thermal storage wall (TSW) together with a direct solar gain (DSG) window in the living room. It is discovered that the temperature range of the living room was within 18–22 °C throughout the majority of winter days. This application is also proved to be economically feasible with an SIR of 1.3, compared to installing an 18,000 Btu/h heat pump. It is determined that both locally produced solar water heaters and imported solar water heaters (ISWHs) are economically viable compared to using a 3-kW storage-type electric water heater. Their SIR values are estimated to be 7.5 and 3.7, respectively. A solar-assisted stack-effect ventilation (SEV) system is verified to have techno-economic feasibility and is also useful in concealing the unattractive cold and hot water storage tanks on the roof. The prospective house owner decides to invest 3840 EUR in installing a grid-connected PV system of 1 kWp, an ISWH, a DSG window, building a TSW for space heating and a SEV system with an overall SIR value of 3.2. This procedure can be developed into a government policy where all these assessments are made mandatory to increase the awareness of the home builders before they make their decisions about the final designs of their houses. The present work demonstrates the convenience of employing economic feasibility assessments together with engineering analyses before applying solar strategies during the design stages, in order to convince house owners that these solar technologies can be economically viable. In a case study, this approach is tested for a real house project developed in NC in which solar energy applications for electricity generation, hot water preparation, space heating and passive cooling are investigated. Copyright © 2013 John Wiley & Sons, Ltd.