Assessing scalability of a low-voltage distribution grid co-simulation through functional mock-up interface

State-of-the-art Modelica tools for modelling and simulating multi-physical systems have reached certain maturity among the building physics community. Hence, simulation is widely used for control, sizing and performance assessment of energy systems. However, serious efficiency issues arise for large-scale models. This article proposes a practical application of co-simulation methods on detailed district energy systems. The aim of this study is to assess performance and scalability of co-simulation through functional mock-up interfaces on a detailed and multi-physical district model. In particular, we propose a comparative analysis between classical simulation and co-simulation methods and a scalability analysis on a growing number of buildings. The models have been implemented using Modelica language and the OpenIDEAS library. A decomposition approach is taken for modelling the entire system, while stochasticity in the inputs is taken into account. Results are presented for various integration scenarios, including a classical integrated simulation for reference and co-simulations involving different master-algorithms within Dymola and DACCOSIM 2017. Scenarios are compared in terms of speed-up and accuracy of principal physical quantities representing key performance indicators such as indoor temperature, current and voltage at building's connection. The analysis shows that co-simulation can run up to 90 times faster than the integrated simulation for 24 buildings, while ensuring acceptable accuracy.     

Co-simulation between ESP-r and TRNSYS

The quest for innovative architectural designs and the development of novel and integrated energy conversion, storage, and distribution technologies presents a challenge for existing building performance simulation (BPS) tools. No single BPS tool offers sufficient capabilities and the flexibility to resolve all the possible design variants of interest. The development of a co-simulation between the ESP-r and TRNSYS simulation tools has been accomplished to address this need by enabling an integrated simulation approach that rigorously treats both building physics and energy systems. The design, verification, and demonstration of this new co-simulation environment are demonstrated in this paper.     

Integrated simulation through the source-code coupling of component models from a modular simulation environment into a comprehensive building performance simulation tool

No single building performance simulation program contains sufficient capabilities and flexibility to fully respond to the full complexity of modern building design and analysis. Consequently, considerable efforts and advances have been made to facilitate the integrated use of multiple simulation tools to provide more extensive modelling capabilities. The research reported in this article has made a contribution towards the goal of integrated simulation by focusing on the internal coupling of component models from a modular simulation environment into a comprehensive building performance simulation tool. A flexible and extensible facility has been designed and developed to enable the use of HVAC component models (TYPEs) from the TRNSYS simulation program within the ESP-r simulation platform. With this, the source code for any number of TRNSYS TYPEs can be compiled with the ESP-r source code to produce an integrated simulation tool that possesses greater capabilities than either simulation program alone.     

Coupling the multizone airflow and contaminant transport software CONTAM with EnergyPlus using co-simulation

Building modelers need simulation tools capable of simultaneously considering building energy use, airflow and indoor air quality (IAQ) to design and evaluate the ability of buildings and their systems to meet today’s demanding energy efficiency and IAQ performance requirements. CONTAM is a widely-used multizone building airflow and contaminant transport simulation tool that requires indoor temperatures as input values. EnergyPlus is a prominent whole-building energy simulation program capable of performing heat transfer calculations that require interzone and infiltration airflows as input values. On their own, each tool is limited in its ability to account for thermal processes upon which building airflow may be significantly dependent and vice versa. This paper describes the initial phase of coupling of CONTAM with EnergyPlus to capture the interdependencies between airflow and heat transfer using co-simulation that allows for sharing of data between independently executing simulation tools. The coupling is accomplished based on the Functional Mock-up Interface (FMI) for Co-simulation specification that provides for integration between independently developed tools. A three-zone combined heat transfer/airflow analytical BESTEST case was simulated to verify the co-simulation is functioning as expected, and an investigation of a two-zone, natural ventilation case designed to challenge the coupled thermal/airflow solution methods was performed.     

Sub-zonal computational fluid dynamics in an object-oriented modelling framework

Airflow modelling is of fundamental importance for evaluating ventilation performance and energy consumption in buildings, and various approaches to the problem—starting from purely empirical up to the CFD ones—have been proposed and evaluated in the past years. Moreover, since the ultimate goal is whole building modelling, airflow simulation needs coupling with Energy Simulation (ES), in order to assess the overall energy performance. Due to the substantial differences between the software employed for airflow and ES, co-simulation is very often felt as the only way to handle such a problem. For example, in recent years a lot of effort has been spent in to couple ES and CFD tools. This paper proposes an alternative, in the form of an approach for solving the Navier-Stokes equations in a general multi-domain modelling framework. Since co-simulation is not involved, the correctness of the numerical solution relies on a single solver, thus being really transparent to the analyst. This is a first step towards a whole building simulation tool embedded in a unique framework capable of performing energy analysis, computing airflows, and representing control systems.     

Urban and building multiscale co-simulation: case study implementations on two university campuses

The co-simulation of both urban and building-level models leverages the advantages of both platforms. It better accounts for the localized effects of surrounding buildings, geography and climate conditions while maintaining high-fidelity building systems representation. This paper describes the co-simulation process of the building and urban-scale models of two university campuses in Switzerland using EnergyPlus and CitySim. In the first case study, on-site measured performance data is compared to the co-simulation results. The second case study examines the results of the two engines. The results show that coupling of EnergyPlus with CitySim resulted in a ?15.5% and ?7.5% impact on cooling consumption and a +6.5% and +4.8% impact on heating use as compared to solo simulations.The co-simulation process was able to better model realistic conditions for heating, but not cooling in one case study. It was able to substantially reduce the discrepancies in prediction between the engines in the other study.     

An artificial intelligence-based method to efficiently bring CFD to building simulation

A computational procedure known as co-simulation has been proposed in the literature as a possibility to extend the capabilities and improve the accuracy of building performance simulation (BPS) tools. Basically, the strategy relies on the data exchanging between the BPS and a specialized software, where specific physical phenomena are simulated more accurately thanks to a more complex model, where advanced physics are taken into account. Among many possibilities where this technique can be employed, one could mention airflow, three-dimensional heat transfer or detailed HVAC systems simulation, which are commonly simplified in BPS tools. When considering complex models available in specialized software, the main issue of the co-simulation technique is the considerable computational effort demanded. This paper proposes a new methodology for time-consuming simulations with the purpose of challenging this particular issue. For a specific physical phenomenon, the approach consists of designing a new model, called prediction model, capable to provide results, as close as possible to the ones provided by the complex model, with a lower computational run time. The synthesis of the prediction model is based on artificial intelligence, being the main novelty of the paper. Basically, the prediction model is built by means of a learning procedure, using the input and output data of co-simulation where the complex model is being used to simulate the physics. Then the synthesized prediction model replaces the complex model with the purpose of reducing significantly the computational burden with a small impact on the accuracy of the results. Technically speaking, the learning phase is performed using a machine learning technique, and the model investigated here is based on a recurrent neural network model and its features and performance are investigated on a case study, where a single-zone house with a triangular prism-shaped attic model is co-simulated with both CFX (CFD tool) and Domus (BPS tool) programs. Promising results lead to the conclusion that the proposed strategy enables to bring the accuracy of advanced physics to the building simulation field – using prediction models – with a much reduced computational cost. In addition, re-simulations might be run solely with the already designed prediction model, demanding computer run times even lower than the ones required by the lumped models available in the BPS tool.     

Integrated energy performance modeling for a retail store building

This paper presents an integrated energy performance modeling approach that considers heat and mass transfer through building envelope, HVAC (heating, ventilation, and air conditioning) and refrigeration systems of a retail store building with limited measured data. The internal heat gains/losses were estimated based on an Extended Kalman Filter. The simulation coupling strategy among room top units (RTUs), refrigeration display cases and zones is based on the ping-pong coupling strategy. The integrated model was validated against measured data from June to August, 2011. The results show that temperature prediction is within the ±1.5°C error band and the RTU electricity energy use prediction is within the ±10% error band. The difference between measured and simulated annual electricity consumption from the refrigeration system is 3%. Based on further analysis and diagnostics, deviations of model predictions from measured data were found to be partially due to the faults in the RTUs. Such deviation accounts for a 4% saving of the total building electrical energy consumption.     

Buildings.Occupants: a Modelica package for modelling occupant behaviour in buildings

Energy-related occupant behaviour is crucial to design and operation of energy and control systems in buildings. Occupant behaviours are often oversimplified as static schedules or settings in building performance simulation ignoring their stochastic nature. The continuous and dynamic interaction between occupants and building systems motivates their simultaneous simulation in an efficient manner. In the past, simultaneous simulation has relied on co-simulation approaches or customized source code changes to building simulation programmes. This paper presents Buildings. Occupants, an open-source package implemented in Modelica, for the simulation of occupant behaviours of lighting, windows, blinds, heating and air conditioning systems in office and residential buildings. Examples were presented to illustrate how the models in the Occupants package are capable to simulate stochastic occupant behaviours. The major contribution of this work is to introduce the equation-based modelling approach to simulate occupant behaviours in buildings and to develop an open-source Occupants package in the Modelica language.     

建立适应建筑节能的暖通空调设计机制

列举了我国设计机制不适应建筑节能需求的现象。提出了在规划设计中应用综合资源规划(IRP)方法、建立各专业参与的会商制度、将建筑模拟技术用于设计阶段的能耗权衡、建立全程优化调整机制,以及采用基于性能的设计合同等方法,以进一步提高我国暖通空调节能设计水平。     

Co-simulation of a HVAC system-integrated phase change material thermal storage unit

A co-simulation environment, consisting of a detailed mathematical model of a thermal energy storage unit which is incorporated with an EnergyPlus simulation model of a full building HVAC system, is described. The two models are integrated using the user-defined plant component feature in EnergyPlus and the Building Controls Virtual Test Bed (BCVTB) environment. The thermal energy storage unit, which consists of encapsulated phase change material in a series of flat plates and a heat transfer working fluid (water), is modelled using a transient one-dimensional forward finite difference method. The thermal storage model is executed within MATLAB and is verified against experimental data, showing a discharging heat transfer accuracy to within 2.5%. The building model, which incorporates a retrofitted ground source heat pump system within a thermally massive building, is simulated in the EnergyPlus environment. The co-simulation arrangement allows for in-depth analysis of the integrated system under dynamic operating conditions, which is currently not possible within the EnergyPlus environment. Moreover, the overall adopted approach, based on generic integration of a detailed mathematical model, using a third party generalised programming environment, into an established building simulation environment, serves as a successful exemplar for other researchers and practitioners working in the field.     

Coupling indoor airflow,HVAC, control and building envelope heat transfer in the Modelica Buildings library

This paper describes a coupled dynamic simulation of an indoor environment with heating, ventilation, and air conditioning (HVAC) systems, controls and building envelope heat transfer. The coupled simulation can be used for the design and control of ventilation systems with stratified air distributions. Those systems are commonly used to reduce building energy consumption while improving the indoor environment quality. The indoor environment was simulated using the fast fluid dynamics (FFD) simulation programme. The building fabric heat transfer, HVAC and control system were modelled using the Modelica Buildings library. After presenting the concept, the mathematical algorithm and the implementation of the coupled simulation were introduced. The coupled FFD–Modelica simulation was then evaluated using three examples of room ventilation with complex flow distributions with and without feedback control. Further research and development needs were also discussed.     

Implementation and verification of the IDEAS building energy simulation library

Building and district energy systems become increasingly complex, requiring accurate simulation and optimization of systems that combine building envelope, heating ventilation and air conditioning, electrical distribution grids and advanced controllers. Hence, it becomes more challenging for existing simulation tools to provide integrated solutions for these multi-physics problems. Moreover, common building simulation frameworks tightly integrate model equations and their solvers in the program code, which affects model transparency and hampers tool extensions. This is contrasted by equation-based tools such as Modelica, for which different solvers can be used. In this context, the Integrated District Energy Assessment by Simulation (IDEAS) library is developed. After a recent development shift towards more detailed, multi-zone models, this paper presents a comprehensive, well-documented, overview of the buildings part of IDEAS. This includes new computational aspects of the library, improved usability aspects, an updated intercomparison with BESTEST and a verification based on IEA EBC Annex 58.     

Semantics for assembling modular components in a scalable building performance simulation

This work investigates a scalable building performance simulation (BPS) based on a modular setup deploying the recently developed functional mock-up interface standard. A procedure for the realization of such an approach is presented and a prototypical implementation is described. One of the key obstacles of the modular simulation is identified to be the collocation of simulation modules, which is addressed using a knowledge-based method enabled through ontology. The procedure allows to automatically derive a simulation topology based on the information about the interfacing variables for varying levels of detail. Also information from other sources such as building information models is incorporated. The feasibility of the proposed method is demonstrated by deploying it in test cases of a single-zone and a multi-zone BPS as well as a zonal airflow simulation.     

Simulation and visualization of energy-related occupant behavior in office buildings

In current building performance simulation programs, occupant presence and interactions with building systems are over-simplified and less indicative of real world scenarios, contributing to the discrepancies between simulated and actual energy use in buildings. Simulation results are normally presented using various types of charts. However, using those charts, it is difficult to visualize and communicate the importance of occupants’ behavior to building energy performance. This study introduced a new approach to simulating and visualizing energy-related occupant behavior in office buildings. First, the Occupancy Simulator was used to simulate the occupant presence and movement and generate occupant schedules for each space as well as for each occupant. Then an occupant behavior functional mockup unit (obFMU) was used to model occupant behavior and analyze their impact on building energy use through co-simulation with EnergyPlus. Finally, an agent-based model built upon AnyLogic was applied to visualize the simulation results of the occupant movement and interactions with building systems, as well as the related energy performance. A case study using a small office building in Miami, FL was presented to demonstrate the process and application of the Occupancy Simulator, the obFMU and EnergyPlus, and the AnyLogic module in simulation and visualization of energy-related occupant behaviors in office buildings. The presented approach provides a new detailed and visual way for policy makers, architects, engineers and building operators to better understand occupant energy behavior and their impact on energy use in buildings, which can improve the design and operation of low energy buildings.     

Review of modelling approaches for passive ceiling cooling systems

Passive ceiling cooling systems can lead to reduced cooling requirements, less fan energy and downsized ductwork, compared to conventional all-air systems. Additionally, radiant cooling of occupants allows for improved comfort while allowing for higher operating temperature, improving chiller efficiency. This paper presents a comprehensive review of current modelling approaches for passive ceiling cooling systems in order to document the state of the art and identify current research gaps and modelling development needs. Modelling methods are separated in three main categories, based on the domain of interest: component or “passive ceiling cooler” models, “indoor environment” models and “integrated” models. Simplified, detailed and empirical models are presented for each category. Different modelling approaches may be appropriate for different purposes (design vs. control analysis, and system simulation vs. whole building performance). The study summarizes useful findings, modelling limitations and applications, and presents needs for further modelling and simulation research, including passive chilled beams.     

A framework to integrate object-oriented physical modelling with building information modelling for building thermal simulation

This paper presents a framework for integrating building information modelling (BIM) and object-oriented physical modelling-based building energy modelling (BEM) focusing on thermal simulation to support decision-making in the design process. The framework is made of a system interface between BIM and Modelica-based BEM and the visualization of simulation results for building designers. The interface consists of the following two major features: (1) pre-processing BIM models to add required thermal parameters into BIM and generate the building topology and (2) translating BIM to Modelica-based building energy modelling automatically and running the thermal simulation. The visualization component presents the simulation results in BIM for designers to understand the relationship between design decisions and the building performance. For the framework implementation, we have created a ModelicaBIM library and utilized the Modelica Buildings library developed by the Lawrence Berkeley National Laboratory. We conducted a case study to demonstrate and validate the framework simulation results.     

Development of HAM tool for building envelope analysis

Moisture-related building envelope failures have resulted in costly rehabilitation in various regions of North America. To advance building envelope design towards an engineering approach and reduce the occurrence of future failures, an advanced numerical tool was developed, in conjunction with an extensive full-scale experiment, to investigate hygrothermal performance of various wood-frame wall assemblies. Major features of the tool are multi-dimensional and transient coupling of heat and moisture transport; natural air convection integrated in hygrothermal simulation through Darcy–Boussinesq approximation; heat transfer by conduction and convection of sensible and latent heat; moisture transport by vapor diffusion, capillary suction and convection; material database of common building materials in North America; experimental settings or weather data as boundary conditions; and moisture added in the building envelope to simulate the wetting process. The numerical tool achieves good compliances to the benchmarking cases of the HAMSTAD project, and its predictions have shown good agreement with data from the full-scale wall experiment. The numerical tool employs the commercial finite-element software to solve the governing equations. This approach provides building science researchers the flexibility to modify, maintain and share their modeling work efficiently.     

Performance assessment of innovative seismic resilient steel knee braced frame

Buckling restrained knee braced truss moment frame (BRKBTMF) is a novel and innovative steel structural system that utilizes the advantages of long-span trusses and dedicated structural fuses for seismic applications. Steel trusses are very economical and effective in spanning large distance. However, conventional steel trusses are typically not suitable for seismic application, due to its lack of ductility and poor energy dissipation capacity. BRKBTMF utilizes buckling restrained braces (BRBs) as the designated structural fuses to dissipate the sudden surge of earthquake energy. This allows the BRKBTMF to economically and efficiently create large span structural systems for seismic applications. In this paper, a prototype BRKBTMF office building located in Berkeley, California, USA, was designed using performance-based plastic design procedure. The seismic performance of the prototype building was assessed using the state-of-the-art finite element software, OpenSees. Detailed BRB hysteresis and advanced element removal technique was implemented. The modeling approach allows the simulation for the force-deformation response of the BRB and the force redistribution within the system after the BRBs fracture. The developed finite element model was analyzed using incremental dynamic analysis approach to quantify the seismic performance of BRKBTMF. The results show BRKBTMF has excellent seismic performance with well controlled structural responses and resistance against collapse. In addition, life cycle repair cost of BRKBTMF was assessed using the next-generation performance-based earthquake engineering framework. The results confirm that BRKBTMF can effectively control the structural and non-structural component damages and minimize the repair costs of the structure under different ranges of earthquake shaking intensities. This studies conclude that BRKBTMF is a viable and effective seismic force resisting system.