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An Energy Performance Contracting (EPC) is a financing agreement offered by general contractors that enables cost savings from reduced energy consumption to building owners. To create such an offer, the contractor has to provide an energy consumption threshold and a measurement plan. This article aims to draw some recommendations to choose an appropriate approach to provide the information necessary to create the contract, regarding computation time budget, expected accuracy and type of information provided. To get these results, we couple thermal simulations to various uncertainty and sensitivity methods. We first compare screening and differential sensitivity to reduce the number of inputs of the statistical study. Then, we analyze various uncertainty analysis methods to set an appropriate energy consumption threshold, considering the input uncertainties and the study context (Quadratic combination, directional and importance sampling and reliability methods). Sensitivity analyses in various input spaces are then carried out to identify the most critical contributors to energy levels to create the measurement plan. Finally, two metamodeling approaches are tested to reduce the overall computational time: Kriging and sparse polynomial chaos. These methods are tested and compared on a 4000 m² office building in Nantes, France. The resulting recommendations can be applied to any building, depending on the model regularity, the number of uncertain parameters and the objective of the study. [ABSTRACT FROM AUTHOR]

Highlights: [•] Four gray box models are compared on their prediction ability. [•] Power and temperature prediction fitting exceed 84% in heating and cooling mode. [•] A novel R6C2 model presents the best results with a validated identification method. [•] A sensibility analysis allows to validate the R6C2 model architecture. [ABSTRACT FROM AUTHOR]

Abstract: Dwellings represent more than 40% of final energy consumption in France. They also present the highest potential of energy savings, while using technology already substantiated, without huge investments, in contrast to other sectors. Ventilation is one of the main sources of heating loss in buildings, so recovering heat from exhaust air could reduce significantly heating loads. In airtight and well insulated buildings, heat recovery ventilation (HRV) systems are often recommended to save heat energy. However, these savings should be balanced against the electrical power requirements of the fans. A HRV unit is modeled, using TRNSYS, and studied in order to characterize its annual performance when integrated into residential and commercial low energy buildings. The energy performance of HRV is compared to one of the standard ventilation systems. This comparison is based on the heating, cooling and ventilation primary energy consumption for different climatic zones. It is found that the adequacy of using HRV system depends on the building types, the heating loads and ventilation device characteristics. A sensitivity analysis by simulation is undertaken to investigate the influence of exchanger efficiency and specific fan power on the global energy performance of the HRV system. [Copyright &y& Elsevier]

Abstract: Natural ventilation can contribute to the reduction of the air conditioning demand and to the improvement of thermal comfort in buildings. In this paper, the flow field and the air change rate generated by a simple configuration of natural ventilation, namely single-sided ventilation, are examined experimentally. The experiments are realized in a full scale building exposed to outdoor conditions, using several measurement techniques. The main features of the flow generated by stack and wind effect are examined for different outdoor conditions (temperature difference, wind speed and direction). Finally, measured air change rates are compared to those calculated by existing correlations in order to analyze their applicability to the experimental configuration. Results show that the wind generates turbulence diffusion at the opening, counteracting the stack effect. Moreover, in the case of windward opening, there is an additional effect, namely the effect of mixing layer, which tends to increase the airflow rate. Existing correlations give reasonably good results in the case of windward opening, while in the case of leeward opening they overestimate the airflow rate. [Copyright &y& Elsevier]

Abstract: A desiccant wheel model has been developed in the aim to be adapted to building simulation tools. This model fulfils several criteria such as simplicity of parameterization, accuracy, possibility to characterize the equipment under all operation conditions and low computation time. The method of characteristics has been applied to the heat and mass transfer partial differential equations. This transformation provides new equations which are similar to those of a rotary heat exchanger. Then, the model is described by the Effectiveness-NTU method and it is identified from only one nominal rating point. The model has been compared to experimental and manufacturers’ data for a broad range of operating conditions. A good agreement has been found. [Copyright &y& Elsevier]

Abstract: A desiccant-wheel behavioural model has been developed. This model fulfils several criteria, such as simplicity of parameterization; accuracy; ability to characterize the equipment behaviour under all operation conditions; and short computation time. The method of characteristics has been applied to the heat-and-mass transfer partial-differential equations. This transformation provides equations which are similar to those of a rotary heat-exchanger. Then, the model is described by the effectiveness-NTU method and identified from only one nominal-rating point. The model predictions have been compared with experimental and manufacturers’ data for a broad range of operating conditions. Good agreement has been found. [Copyright &y& Elsevier]

A simplified model for indirect cooling towers behaviour is presented. The model is devoted to building simulation tools and fulfils several criteria such as simplicity of parameterisation, accuracy, possibility to model the equipment under various operation conditions and short computation time. On the basis of Merkel''s theory, the model is described by using the Effectiveness-NTU method. The model introduces only two parameters, air-side and water-side heat-transfer coefficients which can be identified from only two rating points, data easily available in manufacturers'' catalogues. Thus, the model allows one to estimate energy and water consumptions under different operating conditions such as variable wet-bulb temperatures or variable airflow rates. [Copyright &y& Elsevier]

Energy performance contracts (EPC) are types of agreements in which a service provider guarantees that customers' buildings will achieve a specified energy performance (i.e., minimum energy savings) to reduce the risk of their investment in energy efficiency improvements. EPC requires prediction of future energy consumption of the building, at the design stage, before construction or major retrofit. To this end, building energy simulations taking into account all the major energy-using components are performed. In particular, fans can contribute significantly to the total building consumption. The overall efficiency of fans is the combination of three factors: mechanical, motor, and variable frequency drive (VFD). Manufacturers usually provide fan mechanical efficiency curves for a broad operating range. In contrast, motor and VFD efficiencies are generally given at rating conditions only. To represent part-load conditions, correlations are typically used to estimate motor and VFD efficiency variations, to evaluate the overall electricity consumption. The first aim of this study is to evaluate existing correlations for motor and VFD efficiency as a function of load and speed, by comparison with manufacturer data, for a vendor that has shared its detailed test data. While VFD efficiency correlations from the literature provide reasonable accuracy against real data, motor correlations under predict actual motor efficiency at low loads. The second aim of the paper is to improve such correlations using Bayesian inference to fit the available data. [ABSTRACT FROM AUTHOR]

Highlights: [•] Six heating systems are compared in a low energy house for different climates. [•] MCHP and electric HPs are more efficient than gas or wood boilers and absorption HP. [•] The absorption HP would be the most efficient if small size products were developed. [•] The merit order of electric heat pumps drops with the current oversizing practice. [•] The intermittent heating has a limited interest in low energy houses. [ABSTRACT FROM AUTHOR]

Abstract: When a wind flow approaches a building, a recirculation zone is created on the leeward side of the building. This turbulent zone behind the building increases the air mixing at the leeward openings between entering and leaving air. As a consequence the effective temperature difference is reduced at the opening, counteracting the stack effect. Therefore, the air change rate is lower than that in absence of wind. Some empirical correlations have been set up to assess the airflow rate due to the combination of stack and wind effects. However these correlations do not take into account the reduction of airflow rate in leeward conditions. This paper aims to improve the existing correlations and in particular to confront the issue related to leeward openings. The study is based on CFD simulations and full scale experiments. A comparison of Warren''s correlation with CFD and experimental results shows that this correlation captures well the stack and wind effects in windward conditions but shows poor results in leeward conditions. Thus, a new correlation has been developed by using CFD simulations in leeward conditions. The new correlation is then compared with the full-scale experiments and concords well. [Copyright &y& Elsevier]

Battery-electric buses (BEBs) are a promising technology for replacing diesel buses and reducing their environmental burden. However, their charging process can take several hours, depending on the charging technique and strategy, making them susceptible to schedule disruptions. Furthermore, the selection of the charging strategy and battery size can increase the total capital investment and operational expenses of a BEB fleet, which is a major obstacle to its adoption. Therefore, to minimize the total cost of ownership (TCO) and prevent schedule disruptions, it is essential to establish a well-defined approach to determine an appropriate battery size and charging strategy for BEB fleets. This paper presents a method for reducing the TCO of BEB by determining the optimal battery size and charging strategy for each bus while satisfying operating constraints. The method involves a two-step optimization algorithm that uses Dynamic Programming and Genetic Algorithm. The study applies this approach to the bus fleet serving line 21 in Paris and generates the optimal battery sizing, charging strategy, and required charging infrastructure. The results indicate that 100 kWh batteries offer the best trade-off between capital and operational expenditure for the fleet deployment if used with 65–85 kW chargers at bus terminals. • Proposes a co-optimization method for e-bus battery size and charging strategy • Minimizes a comprehensive cost of deployment of electric bus fleet • Considers all different types of stationary charging infrastructure • Optimizes a comprehensive list of design and operation parameters [ABSTRACT FROM AUTHOR]

District Heating (DH) systems will play an important role in future sustainable energy systems. Existing networks can be optimized by lowering primary return temperatures in order to improve the use of geothermal resources. This can be done by installing triple-pipe systems. This paper defines the concept of triple-pipe configurations as it is understood in France. The objective of this paper is to demonstrate the relevance of those configurations for optimizing geothermal DH system efficiency. A dynamic thermal-hydraulic model was developed using the programming language Modelica. A generic case study is modeled considering the extension of an existing network. It is shown that triple-pipe configurations offer lower return temperatures and gas consumption, while increasing of the renewable energy share in the network energy mix. [ABSTRACT FROM AUTHOR]

• Issues related to the identifiability of RC models are highlighted. • The ISO 13790 RC model is relevant to meet the objectives of identifiability. • A Bayesian calibration method allowed identifying a problem of correlation between the parameters. • A re-parameterization of the model is successfully proposed to eliminate the convergence problems. This paper presents the construction of a RC building model with a good identifiability and a good predictive ability. The identifiability refers to the convergence of a calibration algorithm towards parameters that correspond to the physical properties of the building. This property allows accurate parameterization of the models and robust calibration. The calibrated RC models can be used for predictive control and the non-calibrated RC models are appropriate for urban energy simulation platforms for the analysis of flexibility and retrofit scenarios. From the state of the art, a modified RC model based on the standard ISO 13790 is proposed and then studied on a simplified mono-zone case study. A Bayesian calibration method has highlighted a problem of correlation between the parameters. A selection of parameters and the re-parameterization of the model have been successfully proposed to reach a good identifiability of the model. [ABSTRACT FROM AUTHOR]

With the deployment of battery electric buses (BEB) increasing worldwide, proper battery sizing becomes more critical for operators as it dictates bus driving range and costs. In this paper, we present a battery sizing framework based on comprehensive energy needs assessment for BEB. The bus operating conditions are first defined for different types of bus service (City, intercity, shuttle, regional, rapid-transit). Then, BEB energy consumption is evaluated using a comprehensive energy model developed by the authors. Finally, the required battery size is estimated for different types of charging infrastructure. Modeling results show that BEB energy consumption is sensitive to bus service type, ranging widely between 2 and 4.6 kWh/km, and that intercity buses require the largest battery size (320–680 kWh). A practical finding for operators from our Paris case study is that city bus batteries are unnecessarily oversized to accommodate a typically small fraction of trips in rare extreme cold weather conditions. • Study proposes a battery sizing framework for electric buses. • Evaluates energy consumption and battery sizing for different types of bus service. • Tool to estimate the required battery size and charging infrastructures. • Bus energy consumption and battery size are sensitive to its transit service type. • City bus Batteries oversized to accommodate small number of trips during the year. [ABSTRACT FROM AUTHOR]

In order to contribute to the decarbonization of heating consumption, France has set some objectives to develop District heating and/or cooling networks (DHCN). In this context, it is useful to identify the most appropriate district areas for implementing DHCN, and to assess their potential of development. After introducing the situation of DHCN in France, this paper presents a typology to assess the potential of development of those networks in France, based on an original method that involves the calculation of 3 variables: the linear heating/cooling density (LHD/LCD), the Proportion of Buildings anterior to 1990 and the share of energy consumption from the residential sector, to assess respectively the energy density, the supply temperatures and the energy mix between the different sectors of activities. LHD and LCD are calculated using a Delaunay triangulation and Kruskal's algorithm applied to buildings whose heating and cooling demands are calculated at a local scale. 18 different types of districts are defined for both DHN and DCN, among which 9 have a sufficient LHD/LCD. Then, the potential of development for DHN and DCN is calculated on the French territory. Thus, the DHN potential is assessed to 132 TWh/y while the DCN potential is assessed to 7.8 TWh/y. • Evolution of District Heating and/or Cooling Network (DHCN) in France. • A method to assess the linear density for potential networks. • A new typology of districts built from the point of view of the heating/cooling network integration. • An estimation of the potential of development for DHN and DCN in France. [ABSTRACT FROM AUTHOR]

Abstract: Nuclear steam generators are subject to clogging of their internal parts which causes safety issues. Diagnosis methodologies are needed to optimize maintenance operations. Clogging alters the dynamic behaviour of steam generators and particularly the response of the wide range level (WRL – a pressure measurement) to power transients. A numerical model of this phenomenon has previously been developed. Its input variables describe the spatial distribution of clogging and its output is a discretization of the WRL dynamic response. The objective of the present study is to characterize the information about the clogging state of a steam generator that can be inferred from the observation of its WRL response. A methodology based on several statistical techniques is implemented to answer that question. Principal component analysis reveals that clogging alters the WRL response mainly in two distinct ways. Accordingly, the output can be summarized into a vector of dimension 2. A sensitivity analysis is carried out to rank the input variables by magnitude of influence. It has shown that they can be divided into two groups corresponding to the two sides of the steam generator. Finally, sliced inverse regression is used to reduce the input dimension from 16 to 2. A sampling issue that arises when the input dimension is high is addressed. The simplification of the original problem yields a diagnosis methodology based on response surface techniques. [Copyright &y& Elsevier]

Abstract: To face winter electricity peaking issues the authors proposes an analysis of the potential of distributed gas technologies for demand side management. This impact has to be analysed at small scale before any large scale extrapolation. Bi-energy technologies (gas and electricity) are a path to transfer loads from one system to another. Indeed, the flexible gas infrastructure adapts to load while electricity demand variations cause risk of black-out. The impacts of two hybrid technologies are studied at transformer level with 1-min experimental load profiles of 40 dwellings equipped with micro Combined Heat and Power (μCHP) boilers over a year in France. An absolute peak load reduction by 17% at small scale is found. Different technology mixes are then simulated to assess the effect on local infrastructure. Finally a methodology for temperature dependence analysis of load is used to assess different potential benefits of gas technologies. [Copyright &y& Elsevier]

With the announced plans to ban diesel in major European cities from 2025, battery-powered electric buses (BEB) are attracting attention to replace diesel fleets, given their zero tailpipe emissions. However, their large-scale deployment faces several challenges, namely the limited driving range (DR) and the need for adequate charging infrastructure. The limited DR is due to the lower battery specific energy compared to oil-based fuels. Also, the use of electric auxiliaries, especially, air conditioning, reduces the DR further. The DR problem could be resolved either by increasing the battery capacity, which increases the bus cost or by rightsizing the battery alongside an adequate charging strategy to avoid schedule disruption. Therefore, this paper presents a comprehensive energy modeling of a BEB using Dymola, encompassing the different energy systems encountered in BEB. The proposed model serves as a platform to evaluate the bus energy needs during its service to properly size the battery. A powertrain model is presented to emulate the propulsion load. Then, a cabin model alongside a heating ventilating and air conditioning system are developed emulating the thermal load. Finally, auxiliaries necessary for the bus operation are modeled. The energy consumption of each system is assessed under several operating conditions. Image 1 • Study proposes a modeling methodology to assess battery electric buses energy consumption. • Assesses the impact of different driving and weather conditions and passengers load on the energy consumption. • Model serves as a platform to evaluate battery electric buses energy needs to properly size the battery. • Cabin thermal needs and auxiliaries reduce driving range by more than 50% under extreme weather and driving conditions. [ABSTRACT FROM AUTHOR]