Retrofit Design Research Articles

A New Diagram for Long-term Heat Exchanger Network Cleaning and Retrofit Planning

With the long-term operation of Heat Exchanger Networks (HENs), fouling is a frequent problem. This is related to decreasing long-term heat transfer performance. Fouling decrease the heat transfer coefficient and reduce the efficiency of heat exchange. Different fluid types have different characteristics in corrosiveness and contribute to different results for fouling. The current graphical tools cannot fully tackle the HEN cleaning and retrofit design in the long-term operation.This paper proposes a new graphical tool called Time vs Temperature Diagram (TTD) for HEN long-term management, taking fouling into consideration. It visualises the long-term temperatures change of each heat exchanger on hot and cold streams. The effect of heat exchanger cleaning can be shown visually in this diagram. This diagram can help to determine the cleaning and retrofit plan over a long period. An example is illustrated to show how to apply this diagram.

Retrofit design of an industrial natural gas liquids recovery process based on the pinch technology concept

Energy consumption is increasing very rapidly, especially in the high-energy consuming industries such as oil, gas, and Natural Gas Liquids refineries. Pinch analysis as a well-established and successful technique is used to improve the energy efficiency of the above-mentioned plants. However, the limitations on ΔTmin and those related to the technical and economic aspects result in the lack of capability by the pinch analysis in reducing the utility beyond a specific amount. Also, this analysis only uses the existing process streams and cannot identify and develop high potential streams reducing the external utility consumption. Opportunities for saving energy consumption would increase through the self-refrigeration methods, and they further decrease the utility consumption. Moreover, for minimizing the process changes, the Heat Exchanging Network should be optimized by pinch analysis and then, the opportunities for self-refrigeration of the process should also be challenged. Thus, the present study was conducted to consider the opportunities for reducing the energy consumption and the required utility in a real-life case study of a Natural Gas Liquids plant. Finally, the heat exchanging network redesigned by the grass root plant was revamped with side streaming from the demethanizer column by changing the ΔTmin to 3 °C resulting in the provision of an additional refrigeration stream for inlet feed instead of external utility. This scheme resulted in saving 3671 kW of refrigeration compressors shaft work and saving 6100 kW of the needed energy for the reboiler and condenser. As the result, 546 kW (53 %) of the plant's total energy consumption will be saved by the pinch and self-refrigeration scheme. The total savings in the purchased equipment costs and operating costs saving of the NGL plant are equal to 3,891,560 (USD) and 3,757,451 (USD/year), with 378 days' payback period.

Risk Management Design in Retrofitting Existing Administrative Buildings to Sustainable Buildings

There is an energy crisis around the world according and presented by many types of research and solutions shown up to reduce energy using and material towards the environment, this research present the energy crisis problem towards the building’s sector which using 40% of global energy in the world. Research objective: in the energy retrofitting solution of an energy crisis around the world into energy using in the office buildings by leading and supporting the management into the design risk and shell the light of energy crisis case The research theoretical method includes the research problem, aim, questions, the strategy of energy retrofitting, the definition of office buildings shell and core, the concept of energy retrofitting design, management of the energy projects, and the risk of energy retrofitting design. The practical method includes the case study in energy retrofitting programs around the world especially in developed countries, office buildings, and barries, and challenges of energy retrofitting in developing countries the results will lead to creating a structure for supporting the managers by knowledge from experts in developing countries like Egypt.

Integrated Optimization Framework for the Design and Scheduling of Batch Cooling Water Networks

Cooling water system (CWS) research traditionally focuses on the interactions between the cooling water network (CWN) and cooling tower performance, with a continuous background process. Very limited research has considered the integration of batch production and utility systems. This work presents a mathematical framework for the synthesis and optimization of a CWS consisting of multiple cooling towers operating with a batch background process. The CWN exhibits a series configuration, which is characterized by cooling water reuse. A batch CWS superstructure is developed which represents all different pairings between the cooling towers and the batch background network. It is worth mentioning that in previous research, the utilization of cooling water reuse opportunities was constrained by temperature only; however, due to the nature of batch processing, the utilization of cooling water reuse opportunities is subject to both temperature and time constraints. The benefits of this research for retrofit design is the increase in cooling tower availability. In the case of grassroots design, the capital expenditure for cooling tower capacity is reduced. The mathematical model is developed as a mixed-integer nonlinear programming (MINLP) problem within the GAMS platform. The MINLP is solved by making use of the BARON solver ensuring global optimality. Two illustrative examples are presented. Results indicate a 0.45% increase in the annual profit, a reduction of 42.1% in the total recirculating cooling water requirement, and a 25.3% increase in the average overall cooling tower effectiveness. Capital costs and plant area savings were introduced through a reduction in the number of cooling towers required from 3 to 2. The makeup water consumed was also reduced by 6.3%; this reduced the operational costs and plant water footprint. One of the drawbacks of the model presented is the computational time requirement. Future work will address this concern by implementing decomposition and investigating the use of alternative batch background scheduling formulations.

Experimental dynamic characterization of friction brace dampers and application to the seismic retrofit of RC buildings

Previous earthquakes have caused extensive damage to reinforced concrete (RC) structures with insufficient lateral force resistance or energy dissipation capacity. There is a need to retrofit vulnerable existing RC buildings, particularly those not originally designed for seismic effects or designed to an outdated seismic specification. This study investigates the use of friction dampers as displacement-dependent energy dissipation devices to retrofit RC moment frame structures. First, an experimental program was conducted to characterize the dynamic behavior of friction brace dampers with several different materials, finding that a sintered metal compound provided a stable friction coefficient of 0.4. A strength-based equivalent linearization design procedure was then developed based on the required friction slip force and considering the cracked state of the existing RC structure. A four-story RC school building was then designed using the proposed retrofit design method, validated using nonlinear response history analysis and compared to a previous retrofit scheme that employed buckling-restrained braces (BRBs) and a stiffness-based equivalent linearization design method. The analysis results suggest that the proposed retrofit design method and friction brace dampers are effective in reducing the maximum story drift.

Existing bridges on pile groups: In-situ measurement of stiffness

Retrofit of existing bridges founded on pile groups can be a challenging, costly, and time-consuming operation, especially when foundation interventions are required. The optimization of retrofit design, and hence of such complicated interventions, may be done by allowing controlled strongly nonlinear response of pile groups and associated energy dissipation mechanisms to develop during seismic loading. Taking advantage of such response may also offer improved seismic performance. Nevertheless, a prerequisite for the application of such rational design concepts is the realistic evaluation of actual stiffness and capacity of pile groups. The latter can be estimated based on in-situ soil testing (e.g. CPT) according to the current state of practice, while the former has been approached until now solely analytically and numerically. This paper proposes a first approach to a simplified stiffness estimation method based on in-situ measurements of lateral vibration response of existing bridges. Estimates of stiffness parameters are obtained with simplified equations of motion, using measurements of the lateral vibration response of a bridge pier and its foundation system to a controlled low-amplitude non-destructive dynamic loading. A numerical study is conducted to evaluate the efficiency of the proposed simplified method and to explore its applicability in real-scale projects.

Involving end users in retrofit of higher education buildings

Although the importance of end user participation during building improvement design is widely accepted, selecting the best approach for the engagement of users in design processes is a significant challenge. This paper assesses how qualitative end user engagement during retrofit planning can aid the design process of energy retrofits in higher education institutions. The application of this early stage approach to make design decisions is presented via a case study, carried out in the Faculty of Architecture Building at the Middle East Technical University, Ankara, Turkey. The proposed method uses semi-structured interviews with individual end users along with group interviews, to qualitatively assess priorities for a retrofit scheme of works. Utilising qualitative textual analysis software, specific elements to consider in the retrofit design process are defined, along with particular areas in need of focus, to best enhance user experience and energy efficiency gains. Using a case study approach, this research looks to showcase this method and highlight key elements of successful early design end user engagement, utilised to promote successful retrofit project completion. Findings highlight that retrofit project end users require engagement to aid articulation of requirements, along with the utilisation of engagement strategies to promote project buy in.

Process intensification in ternary distillation via comparative grassroots and retrofit designs: A case study of distilling an industrial multicomponent C6 alkane mixture in caprolactam processing

A systematic process intensification method via comparative grassroots and retrofit designs for distillation is proposed. Restricting to the ternary system, a case study of multicomponent C6 alkane separation in caprolactam processing is considered. The existing benchmark flowsheet of direct sequence (DS) features high economic cost but low thermodynamic efficiency. Through the investigation of the composition profile, two middle component remixing peaks and a large feed mismatch are diagnosed as the reasons of inefficiency. To achieve process intensification, potential candidates like side stream column (SSC) and dividing wall column (DWC) are enumerated and evaluated in the grassroots design step. Although DWC performs the best in thermodynamic efficiency, SSC is more preferred for retrofit as its structure is simple but has similar performance. To maximally reuse the existing equipment, two retrofit proposals of either indirect sequence (IS) or SSC are provided based on the grassroots design results. Among them, retrofitted SSC is recommended for long expected lifespan situation, while IS is more suitable for a short one. It is recommended that the proposed process intensification procedure can be extended to other similar processes or systems with more components, through enumerating and comparing the several best but similar grassroots designs with benchmark process.

Design of rubble mound slope protection for cellular cofferdam breakwater retrofitting

A rubble mound slope structure was designed to protect a decaying cellular steel sheet pile cofferdam breakwater which has been partially damaged. Reparation of this decaying cofferdam breakwater to its original form is considered uneconomic. Considering three basic design requirement, i.e. economic feasibility, environmental sustainability, and structural reliability and constructability, the rubble mound slope design has been proposed as a retrofit structure against 4.7m height of a 100yrs return period design wave. In this design, the existing vertical cofferdam stands originally at the harbour side, whereas the new additional rubble mound structure is attached to the cofferdam at the sea side creating together a new horizontal composite breakwater. The existing cofferdam supports the rubble mound structure at the harbour side, whereas the rubble mound structure provides protection against direct wave attack. This retrofit design of structure requires less 25% of materials volume and costs 30% cheaper than a full standalone rubble mound breakwater type. This less requirement of materials will consequently have positive impact on environment and natural resource conservation. The design of rubble mound slope that is directly attached to the existing breakwater will enable its easy construction by using vehicles that stand on the top of the existing breakwater. This article describes the design consideration including discussion on the structural reliability of the retrofitted breakwater.

Aerodynamic improved design and optimization for the rear stage of a High-load axial compressor

This paper proposes and discusses the aerodynamic retrofit design schemes for a multistage high pressure axial compressor. A high hub/tip ratio mixed-flow compressor is designed and analyzed to replace the rear stage of the axial compressor. In order to minimize the axial dimension and maximize the load capacity, three unconventional types of combined compressors equipped with the high hub/tip ratio mixed-flow compressor are explored. Further, the effects of blade number, splitter blades and dimensionless geometric parameters on the mixed-flow compressor performance are investigated by an improved loss model. A full-surface parameterization control method is introduced and adopted for blade optimizations of the mixed-flow impeller and the tandem stator. The results indicate that after aerodynamic improved design and optimization, the total pressure ratio is relatively improved by 3.71% and the adiabatic efficiency is improved by 0.95 percent point for the mixed-flow compressor at the near design point. Based on this, the retrofit schemes for the axial compressor are beneficial to improve the load capacity and reduce the axial dimension with a slight impact on efficiency and surge margin. These show the potential application prospects of high hub/tip ratio mixed-flow compressors.

Integrating human factors early in the design process using digital human modelling and surrogate modelling

Embedding ergonomics in the design process is often delayed as it requires building physical prototypes and human subject data collection. This causes retrofitting or expensive late design changes which increase overall cost and time-to-market. This paper presents a computational design methodology that employs Digital Human Modelling (DHM) research and the surrogate modelling technique to integrate ergonomics early in design. The goal of this methodology is to provide a proactive ergonomics assessment toolset that allows designers to identify the effects of design variables on human performance, computationally. In this research, a design space exploration study was conducted to evaluate the ergonomics of a concept aircraft cockpit model built based on a set of flight deck layout variables. Variability in the pilot's anthropometry was added through accommodating the extremities in population-based on computational human manikins. A genetic algorithm with the surrogate model was used to search the concept variants that meet ergonomics objectives. The results show that the proposed proactive ergonomics approach allows designers to explore the design space and evaluate trade-offs between the competing design objectives early in design. Our computational ergonomics approach, based on the cockpit packaging study, demonstrates the advantages of the DHM based surrogate modelling during product conceptualisation.

An extended multiple-strut model to estimate infill effects on multi-storey steel frames with different connection rigidities

The experiences of previous earthquakes highlight the necessity of modelling infills in the analysis of structures. In the 2017 Sarepol-e-Zahab earthquake, infills were the cause of most damages inflicted on structures. In this paper, a previously proposed multiple-strut model for infills in steel frames with rigid connections is further developed for non-rigid connections. A comprehensive sensitivity analysis is carried out on the single-storey, single-bay frames with pinned and semi-rigid connections. The parametric study includes the evaluation of the aspect ratio, friction coefficient, and infill-to-column relative stiffness in the models. The global and local effects of infills on multi-bay infilled frames are also explored. This study also presents an investigation of the application of the proposed model in multi-storey infilled frames. Finally, a method consisting of a few simple steps is proposed to optimally take into account the effects of infill panels in multi-storey frames. The accuracy of the model in predicting the base shear and the internal forces of the components of the frame shows that it is a reliable model in the retrofit and seismic design of the steel structures.

Force-based seismic design of steel haunch retrofit for RC frames

The paper presents a simplified force-based seismic design procedure for the preliminary design of steel haunch retrofitting for the seismic upgrade of deficient RC frames. The procedure involved constructing a site-specific seismic design spectrum for the site, which is transformed into seismic base shear coefficient demand, using an applicable response modification factor, that defines base shear force for seismic analysis of the structure. Recent experimental campaign; involving shake table testing of ten (10), and quasi-static cyclic testing of two (02), 1:3 reduced scale RC frame models, carried out for the seismic performance assessment of both deficient and retrofitted structures has provided the basis to calculate retrofit-specific response modification factor Rretrofitted. The haunch retrofitting technique enhanced the structural stiffness, strength, and ductility, hence, increased the structural response modification factor, which is mainly dependent on the applied retrofit scheme. An additional retrofit effectiveness factor (ΩR) is proposed for the deficient structure's response modification factor Rdeficient, representing the retrofit effectiveness (ΩR=Rretrofitted /Rdeficient), to calculate components' moment and shear demands for the retrofitted structure. The experimental campaign revealed that regardless of the deficient structures' characteristics, the ΩR factor remains fairly the unchanged, which is encouraging to generalize the design procedure. Haunch configuration is finalized that avoid brittle hinging of beam-column joints and ensure ductile beam yielding. Example case study for the seismic retrofit designs of RC frames are presented, which were validated through equivalent lateral load analysis using elastic model and response history analysis of finite-element based inelastic model, showing reasonable performance of the proposed design procedure. The proposed design has the advantage to provide a seismic zone-specific design solution, and also, to suggest if any additional measure is required to enhance the strength/deformability of beams and columns.

A drift capacity prediction model for retrofitted reinforced concrete columns

Seismic assessment of reinforced concrete (RC) buildings heavily relies on the deformation capacity predictions of members. Similarly, the prediction of the deformation capacity of retrofitted RC columns has the utmost importance for seismic retrofit design. In this paper, a new unified drift model is proposed in order to estimate the rotation capacity of RC columns retrofitted with concrete jacketing, steel jacketing and fibre-reinforced polymer (FRP) wrapping. In order to generate the model, an extensive database was compiled consisting of 269 columns composed of 39 concrete-jacketed, 91 steel-jacketed and 139 FRP-wrapped RC columns failing in flexure mode. In the proposed drift model, the key model parameters are the confinement stress ratio, the axial load ratio and the lap splice length. The accuracy and scatter of the estimations with regard to the previous models were studied. For all of the column retrofitting options, the proposed unified model was observed to have rotation predictions better than the previous models in terms of the mean of the predicted to experimental rotation capacity ratios and with a reduced standard deviation.

Displacement-based determination of BRBs in retrofitting an RC frame building

An RC frame school building was designed with lower fortification requirements than required. It collapsed in the 2008 Ms8.0 Wenchuan earthquake. This study evaluated the building’s deficiency and practiced a retrofit design based on traditional demand-capacity method but with a displacement-based (DB) procedure, in which target capacities were obtained from the equivalent single-degree-of-freedom (ESDOF) systems defined by target mode shapes of the MDOF system, and shear demands were assessed using an R- μ- T relationship to match different capacity levels. To make the DB procedure code-conforming, the retrofitting elements (BRBs) were simplified as bi-linear elements, with the two-phase parameters corresponding to the code’s two-stage requirements. Shear distribution to the MDOF building was also determined by displacement shapes. BRBs’ stiffness demands and sizes were from the difference of the required and available shear resistances. The effectiveness of the method was validated by time history analyses. Different earthquake level simulations showed that, the method realized the design goals but did not lead to over-retrofitting; the BRBs took most of the shear demand but would not induce other unexpected failures. So the method was suitable for retrofitting similar structures.

Evaluating the impact of thermostat control strategies on the energy flexibility of residential buildings for space heating

Buildings can be operated in an energy-flexible manner while respecting occupant thermal comfort. This energy flexibility of building operations, both in time and quantity, can be harnessed by the electrical grid for load balancing. In the context of smart grid and intelligent buildings, the concept of energy flexibility in buildings broadens the existing demand management thinking from the top-down one-way control to two-way communications. This paper, extending studies on thermostat controls of heating and air conditioning systems for demand response, evaluates the impact of different control schemes on the energy flexibility of residential buildings. Two control strategies, Model Predictive Control (MPC) and Rule-Based Control (RBC), are investigated for a space heating system using co-simulation studies. Four indicators are introduced and adapted from the literature to assess the control performances of the strategies. Simulation results show that different flexibility indicators favour different control strategies in this case study. For demand response events of four hours, the MPC strategy presents two to three times of flexible energy than that of RBC. MPC also delivers 20% more of maximum power reduction during the events against RBC. The RBC strategy, on the other hand, is twice of MPC for flexible energy efficiency. This evaluation work can be beneficial to guide the control system design of new buildings or control retrofits of existing buildings that consider better grid-building interactions for the future.

Engineering Design of a Full Scale Membrane Post-Combustion CO2 Capture System Retrofit for Duke Energy’s East Bend Station

This paper provides details of a recently completed U.S. Department of Energy funded study for a membrane-based, post-combustion CO2 capture (PCC) system retrofit to an existing U.S. coal power plant. The Electric Power Research Institute Inc. teamed with a technology supplier and engineering consultants to develop an initial engineering design and cost estimate for a membrane-based, PCC system for Duke Energy’s existing East Bend Station (EBS). A comprehensive overview of the proposed plant design will be presented, including the estimated costs associated with retrofitting the existing EBS coal-fired power plant with MTR’s second-generation Polaris™ membrane technology for CO2 removal from flue gas.

Facility Energy Management Application of HBIM for Historical Low-Carbon Communities: Design, Modelling and Operation Control of Geothermal Energy Retrofit in a Real Italian Case Study

The highest challenge of energy efficiency of building stock is achieving improved performance in existing buildings and, especially, in heritage buildings which per se are characterized by massive limitations against the implementation of the most sophisticated solutions for energy saving. In Italy, historical buildings represent more than 30% of the building stock and the vast majority require energy retrofit, while ensuring the preservation of the heritage value and acceptable comfort conditions. In this context, historical buildings must be retrofitted and re-functioned by introducing innovative technologies aimed at reducing energy consumption and improving human comfort, health, and safety. To this aim, this study implements the Historic Building Information Modeling (HBIM) approach for the integrated modeling, monitoring, management, and maintenance of a novel geothermal system involving horizontal ground source heat exchangers (GHEXs) coupled to an adsorption heat pump for the energy refurbishment of historical buildings. In detail, a rural building part of a medieval complex in Perugia, Central Italy, is considered as a pilot case study. The analysis stresses the potential of the Facility Management (FM) applications of HBIM to provide a tool for the human-centric operational management control of the building energy performance and indoor comfort when combined with the building monitoring and supervision system. Therefore, this integrated HBIM approach may drive the path towards the user-centric re-functioning of heritage buildings.

Dynamic Energy Modelling as an Alternative Approach for Reducing Performance Gaps in Retrofitted Schools in Denmark

When considering that over 80% of buildings in Denmark were built before the 1980′s, a holistic energy retrofitting of the existing building stock is a major milestone to attain the energy and environmental targets of the country. In this work, a case study of three public schools is considered for post-retrofit process evaluation. The three schools were heavily retrofitted by September 2018 with energy conservation and improvement measures that were implemented targeting both the building envelope and various energy systems. A technical evaluation of the energy retrofit process in the schools was carried out, when considering one year of operation after the completion of the retrofitting work. Actual data from the heating and electricity meters in the schools were collected and compared with the pre-retrofit design numbers which rely majorly on static tabulated numbers for savings evaluation. It was shown that the retrofit design numbers largely overestimate the attained savings, where the average performance gap between the expected and real numbers for the three schools is around 61% and 136% for annual heating and electricity savings, respectively. On the other hand, an alternative approach was proposed where calibrated dynamic energy performance models, which were developed for the three schools in EnergyPlus, were used to simulate the impact of implementing the retrofit measures. It was shown that implementing this approach could predict much better the impacts of the retrofit process with an average gap of around 17% for heating savings and 21% for electricity savings. Based on the post-retrofit process evaluation in the three schools, it was concluded that using dynamic model simulations has the potential of lowering the performance gap between the promised and real savings when compared to static tabulated approaches, although the savings are still generally over-estimated in both approaches.

Industrial Energy Retrofit Planning Using Automated Retrofit Targeting

There is increasing pressure for industrial sites to minimise energy consumption. A long-term energy reduction strategy plays a critical role in realising energy savings. A key exchange mechanism of energy for sites is the heat exchanger network, which can be revamped and retrofitted to lift process energy efficiency. Retrofit analysis of heat exchanger networks commonly looks for a modified design that could provide significant energy savings for a comparatively modest investment but rarely does the analysis consider how retrofit projects can be sequenced as part of an energy retrofit plan while staying with capital investment constraints. The challenge in developing a long-term plan is the identification of projects and their ideal order out of the numerous possible combinations. This paper aims at developing an energy retrofit planning tool by performing a multi-stage retrofit analysis based on the automated retrofit targeting algorithm used to search for retrofit designs. The key output of the energy retrofit planning analysis is several sets of retrofit plans that can be further analysed for case-specific practicality (e.g., space, distance, and fluid compatibility) and developed into an energy retrofit plan, forming a part of a company’s overall energy strategy. The method is demonstrated using two industrial case studies with complex features and room for multiple sets of retrofit modifications. For the petrochemical complex case study, the study concludes that a 4-stage retrofit plan could be undertaken under a strategic investment plan that in total requires 11 modifications to the system, which generates 1.47 million EUR in annual profit with a payback of 1.75 years.