Implementation of a building foundation heat transfer model in EnergyPlus

In this article, a two-dimensional transient ground-coupled numerical model for slab-on-grade foundation is developed and integrated into EnergyPlus. A verification analysis is first presented to ensure that the developed building foundation heat transfer module is properly implemented within EnergyPlus. Then, predictions from the developed model are compared with those obtained from a simplified building foundation model currently used in EnergyPlus. Finally, the impact of several foundation insulation configurations on the annual variation of both heating and cooling loads is investigated for a one-storey single-family ranch house. The results show that the developed foundation heat transfer module accounts more accurately for the effects of the ground thermal mass than the foundation model currently used in EnergyPlus. In particular, it was found that annual heating and cooling loads can be overestimated by over 20% for a typical residential building if ground-coupled heat transfer calculations are not fully integrated in EnergyPlus.     

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.     

EnergyPlus在日光温室热环境模拟中的应用验证与分析

为了寻求将现有商用能耗分析软件应用于日光温室热环境的设计、优化、建造和日常运营管理的方法,基于EnergyPlus软件,建立了日光温室模型,通过现场实验测试对所建立的模型进行了验证,并利用建立的模型对日光温室热环境进行了模拟分析。研究结果表明:提出的数值方法和建立的日光温室模型是正确可靠的,可以用于日光温室热环境的模拟分析;温室北墙夜间单位面积的供热量是东、西墙与地面总和的1.1~1.2倍,增强日光温室北墙体的蓄热和保温能力是提升日光温室调控自身热环境能力和水平最重要的途径。该研究结果可为日光温室的优化设计与热工性能分析提供参考。     

EnergyPlus model-based predictive control within design–build–operate energy information modelling infrastructure

This study proposes a design–build–operate energy information modelling (DBO-EIM) infrastructure to allow users to deploy the design-stage building energy model for model predictive control (MPC) system in the building operation. A newly constructed office building is studied as a test bed. An EnergyPlus model-based predictive control (EPMPC) system is designed and simulated in the Matlab/Simulink environment within the DBO-EIM infrastructure. EPMPC aims at minimizing heating, ventilation, and air conditioning energy consumption while maintaining occupant thermal comfort. Compared to the baseline rule-based control system, EPMPC demonstrates a 28.9% energy reduction in one-week simulation in the heating season and 2.7% energy reduction in one-week simulation in the cooling season. The comfort constraint is met during more than 90% of the simulated hours. The study demonstrates one significant contribution of the DBO-EIM infrastructure that a design-stage EnergyPlus model can be integrated in an MPC system and the preliminary simulation results are satisfactory.     

Building energy model reduction using model-cluster-reduce pipeline

This paper introduces a novel building energy model reduction pipeline called ‘model-cluster-reduce’. It is centred around using clustering techniques to identify archetypes and eliminate redundant zones. An experiment was conducted in this paper using a detailed EnergyPlus model generated from building information modelling directly. A total number of four reduced models were generated and compared against the original model, random select models and an expert model. The reduced models estimated annual energy simulation and parametric simulation results within 5% error margin, while reducing the overall simulation time by 95%. The proposed method – which is aimed at large models where inter-zone heat transfer is not significant – can be used to approximate parametric simulations or optimizations with greatly reduced runtime.     

EnergyPlus与DeST的对比验证研究

在相同的内外扰量和空调运行方式下,采用EnergyPlus和DeST软件对同一建筑进行逐时冷热负荷计算,结果存在差异.分析发现主要原因是两个软件的热模型存在差异,说明通过围护结构表面的传热计算方法和相邻房间的邻室传热模型对负荷计算结果有重要影响.     

Comparison study of a novel solid desiccant heat pump system with EnergyPlus

The variable refrigerant flow (VRF) air conditioning system usually needs to be operated with a ventilation system, since the VRF system cannot provide fresh air. The commonly used ventilation unit with the VRF system is the heat recovery ventilation (HRV) unit due to its merits of energy saving. In this study, a novel solid desiccant heat pump unit (DESICA) is introduced and mathematical model of DESICA is developed based on the dynamic building energy simulation software—EnergyPlus. The mathematical model is validated with experimental results. Based on the model, performance comparison study is conducted among the novel joint DESICA and VRF (DES&VRF) system, the conventional joint HRV and VRF (HRV&VRF) system, and the original VRF standalone with ventilation (VRFSA) system in an office building in Shanghai. Simulation results show that, HRV&VRF and VRFSA can handle the sensible load, though both of them cannot well deal with the latent load. On the contrary, DES&VRF system can keep both indoor temperature and humidity ratio at the target value, resulting in the best indoor thermal comfort than the other two systems. In addition, through the whole year, DES&VRF consumes 5% more energy than VRFSA and 20% less energy than HRV&VRF.     

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.     

办公建筑围护结构墙体传热性能分析

办公建筑的外围护结构型式影响能源消耗。针对外墙为干挂石材的办公建筑墙体进行热工性能分析,建立围护结构与墙体的传热数学模型,采用有限差分法进行仿真。通过监测墙体温度变化分析外围护结构传入到室内热量情况,判定办公建筑墙体围护结构的节能状况。通过采取三次样条插值环境温度函数作为有限差分法的数据,输入传热数学模型,模拟墙体的传热性能,得出如下结论:干挂石材外墙的办公建筑内墙表面温度在不同气候环境下波动不大,节能效果较好。     

Thermal design tool for outdoor spaces based on heat balance simulation using a 3D-CAD system

This paper focuses on the development of a thermal design tool for use in planning outdoor spaces by combining a heat balance simulation for urban surfaces, including buildings, the ground and greenery, with a 3D-CAD system that can be run on a personal computer. The newly developed tool is constructed by improving the previous simulation model, which uses the geographic information system (GIS) for the input data. The simulation algorithm is constructed so as to predict the surface temperature distribution of urban blocks while taking into account the actual design of the outdoor space using the 3D-CAD system. A method of multi-tracing simulation to calculate the sky view factor and radiative heat transfer is established. The optimal mesh size is examined for the tool so as to provide detailed spatial geometry within a suitable calculation time. The simulation model is integrated with an all-purpose 3D-CAD software, and the pre-processing method are constructed for practical use. The results obtained by applying this simulation tool to an area of detached houses reveals that the tool is able to evaluate the effects of building shape, materials, and tree shade on the surface temperature distribution, as well as the MRT and HIP, which are evaluation indices of the outdoor thermal environment.     

Research on the application of water-loop (tank) heat pump systems in catering buildings

The use of thermal energy in catering buildings is normally mishandled and causes significant waste of thermal energy. To increase the efficient use of energy and decrease the total amount of a catering building’s energy consumption, independent thermal systems should be integrated. If thermal systems are integrated, coupling utilization of thermal energy will be possible, and the primary energy input of a building will be utilized to a greater extent. To implement this concept, a water-loop (tank) heat pump system is necessary and its most important aspect is the design of the thermal storage tank (serving as the water-loop). In this paper, a typical catering building has been selected, and the building’s thermal service systems (processes) are studied in detail. The amount and state of the current thermal energy utilization within each service system is analyzed, and a specific integrated thermal system model is suggested. The research work conducted for this study is based on simulations, such as building thermal load simulations (DesignBuilder software), characteristic simulations of the water-loop heat pump system (TRNSYS software), optimal dimensions and thermal characteristic simulations of the thermal storage tank, etc. The energy consumption characteristic analysis and the technical and economic analysis of the entire building model are discussed, and the optimal scheme for process allocation and optimal operation mode are also presented in this paper. Based on the analytical results (including simulation of building thermal load, simulation of systematic energy consumption, performance analysis of the system, economical analysis, and exergy analysis), the advantages of the system model are demonstrated.     

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.     

Model-based predictive control of office window shades

In the automation of interior window shading devices, a control system that relies on a prediction of environmental conditions and a building's thermal response can provide savings to space-conditioning loads beyond what can be achieved using a reactive approach. The development of these control strategies can be difficult because of the uniqueness of each building. A simplified model-based predictive control (MPC) method for window shades is proposed. To this end, a control-oriented model representing the heat transfer problem in a perimeter office space was developed. The parameters of the model were estimated using the ensemble Kalman filter (EnKF). The energy-savings potential of the EnKF-based MPC approach for window shades was investigated using EnergyPlus simulations. This was accomplished by implementing the control-oriented model into the energy management system application of EnergyPlus. Simulations were conducted to assess the energy saving potential of using the EnKF-based MPC for roller blinds in a south-facing perimeter office space in Ottawa, Canada. The simulation-based results indicate the potential for about 35% reduction in electricity usage for space conditioning over manually operated interior roller blinds.     

Development of Artificial Neural Network based heat convection algorithm for thermal simulation of large rectangular cross-sectional area Earth-to-Air Heat Exchangers

An Earth-to-Air Heat Exchanger (ETAHE) is a low energy cooling and heating building component. It uses the ground's thermal storage to dampen ambient air temperature oscillations by delivering the air through a horizontally buried duct. To reduce airflow resistance, some hybrid ventilated buildings have recently adopted large cross-sectional area ducts. This paper describes the development of an Artificial Neural Network based Heat Convection (ANN-HC) algorithm to predict local average Nusselt Numbers along the duct surfaces. Furthermore, the ANN-HC algorithm is integrated with a transient three-dimensional heat transfer model based on finite element analysis of heat conduction in the ground domain surrounding the ETAHE to establish a new thermal modeling method for ETAHEs. A case study is presented to demonstrate the working principle of the new method. It is shown that the method can very well simulate the interactions between an ETAHE and its environment.     

土壤蓄热与土壤源热泵集成系统运行特性分析

为了提高对工业余热、废热和太阳能的利用,结合土壤蓄热技术与土壤源热泵技术的优点,本文提出了土壤蓄热与土壤源热泵集成系统及其地下管群换热器的布置方式。并在能量平衡的基础上建立了地下管群换热器蓄热、释热和停止运行的数学模型。通过数值模拟,分析了埋管间距对蓄热与释热运行特性的影响,为土壤蓄热与土壤源热泵集成系统的应用奠定了理论基础。     

Coupled heat transfer modes for calculation of cooling load through hollow concrete building walls

A CFD model was developed to study thermal performance of hollow cement wall constructions of buildings under hot summer conditions. The approach employed couples conjugate, laminar natural convective flow of a viscous fluid in hollow building blocks with long-wave radiation between the cavity sides. Realistic boundary conditions were employed at the outdoor and indoor surfaces of the wall. A state-of-art building energy simulation program, ESP-r, was used to determine the outdoor thermal environment that included solar radiation, equivalent temperature of the surroundings and convective heat transfer coefficient. The CFD problem is put into dimensionless formulation and solved numerically by means of the control-volume approach. The study yielded comprehensive, detailed quantitative estimates of temperature, stream function and heat flux throughout the wall domain. A detailed parametric study showed that using a wider cavity within a building block does not necessarily reduce heat flux through the block. Radiation heat transfer between cavity sides may account for a significant fraction of heat flux through the block and neglecting its effect can lead to errors that could be as large as 46%. The geometry of the hollow blocks was demonstrated to affect the heat flux by as much as 30%.     

Modeling of the hygrothermal absorption and desorption for underground building envelopes

The hygrothermal storage characteristics of an underground building envelope have discernible effects on the heat and humidity of the indoor environment. To predict the hygrothermal storage capacity, it is necessary to accurately calculate the transient heat and moisture flux through the envelope. This paper describes the development of a new hygrothermal model described with relative humidity and temperature based on the results of existing researches. The moisture model fully states actual moisture transfer process involving both vapor diffusion and liquid water migration in porous building envelopes. Verified using the results calculated by the mathematical model of Mendes et al., the new hygrothermal model can accurately predict the heat and moisture transfer of building envelopes. Hygrothermal absorption and desorption of three types of common underground building envelopes in Chengdu region in China are analyzed by using the new model. The results show that the hygrothermal absorption and desorption of underground building envelopes must be considered when the heat and moisture environment is controlled by HVAC. Taking account of these factors can reduce air-conditioning equipment capacity and save running energy.     

蓄冷系统水平冰盘管外结冰数值模拟及分析

蓄冰桶是直接式蓄冷系统主要部件之一，主要由水平管或螺旋式盘管构成。蓄冰过程中，管内外存在两个复杂的相变过程，即管内液同相变过程和管外液固相变过程。文中建立了直接蒸发式盘管结冰过程的动态数学模型，利用有限差分法对模型进行了数值求解，并对模拟结果进行了讨论分析。该模型可应用于预测管外结冰量随时间的变化关系，因此，可为直接蒸发盘管蓄冰系统的设计及运行优化提供理论依据。     

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.