Demand Flexibility of Residential Buildings:Definitions,Flexible Loads,and Quantification Methods

This paper reviews recent research on the demand flexibility of residential buildings in regard to definitions,flexible loads,and quantification methods.A systematic distinction of the terminology is made,including the demand flexibility,operation flexibility,and energy flexibility of buildings.A comprehensive definition of building demand flexibility is proposed based on an analysis of the existing definitions.Moreover,the flexibility capabilities and operation characteristics of the main residential flexible loads are summarized and compared.Models and evaluation indicators to quantify the flexibility of these flexible loads are reviewed and summarized.Current research gaps and challenges are identified and analyzed as well.The results indicate that previous studies have focused on the flexibility of central air conditioning,electric water heaters,wet appliances,refrigerators,and lighting,where the proportion of studies focusing on each of these subjects is 36.7%,25.7%,14.7%,9.2%,and 8.3%,respectively.These flexible loads are different in running modes,usage frequencies,seasons,and capabilities for shedding,shifting,and modulation,while their response characteristics are not yet clear.Furthermore,recommendations are given for the application of white-,black-,and grey-box models for modeling flexible loads in different situations.Numerous static flexibility evaluation indicators that are based on the aspects of power,temporality,energy,efficiency,economics,and the environment have been proposed in previous publications,but a consensus and standardized evaluation framework is lacking.This review can help readers better understand building demand flexibility and learn about the characteristics of different residential flexible loads,while also providing suggestions for future research on the modeling techniques and evaluation metrics of residential building demand flexibility.

Comfort assessment and energy performance analysis of a novel adjustable semi-transparent photovoltaic window under different rule-based controls

Self-powered photovoltaic windows,which integrate photovoltaic with electrochromic devices,have attracted widespread attention of scholars since they can generate electricity in situ and reduce building energy consumption by modulating the transmitted solar radiation.However,previous studies mainly focused on the material development and performance characterization,lack of comfort assessment and energy saving potential of its application to buildings.To address this issue,an adjustable semi-transparent photovoltaic(ATPV)window which integrates CdTe-based photovoltaic and WO3-based electrochromic,was taken as the research object,and a novel rule-based control strategy taking the beam solar radiation luminous efficacy(CtrlEff)as decision variable was proposed for the first time.The ATPV window model was established in WINDOW software based on the measured data,and then it was exported to integrated with a medium office building model in EnergyPlus for performance evaluation including the visual comfort,thermal comfort,net energy consumption,and net-zero energy ratio.The results of a case study in Changsha(E 112°,N 28°)indicated that the ATPV window under the CtrlEff strategy can effectively reduce the southward and westward intolerable glare by 86.9%and 94.9%,respectively,and increase the thermal comfort hours by 5%and 2%,compared to the Low-E window.Furthermore,the net-zero energy consumption can be decreased by 58.7%,65.7%,64.1%,and 53.8%for south,west,east,and north orientations,and the corresponding net-zero energy ratios are 65.1%,54.6%,62.7%,and 61.6%,respectively.The findings of this study provide new strategies for the control and optimization of the adjustable window.

Secondary solar heat gain modelling of spectral-selective glazing based on dynamic solar radiation spectrum

The secondary solar heat gain,defined as the heat flows from glazing to indoor environment through longwave radiation and convection,grows with the increasing of glazing absorption.With the rapid development and application of spectrally selective glazing,the secondary solar heat gain becomes the main way of glazing heat transfer and biggest proportion,and indicates it should not be simplified calculated conventionally.Therefore,a dynamic secondary solar heat gain model is developed with electrochromic glazing system in this study,taking into account with three key aspects,namely,optical model,heat transfer model,and outdoor radiation spectrum.Compared with the traditional K-Sc model,this new model is verified by on-site experimental measurements with dynamic outdoor spectrum and temperature.The verification results show that the root mean square errors of the interior and exterior glass surface temperature are 3.25°C and 3.33°C,respectively,and the relative error is less than 10.37%.The root mean square error of the secondary heat gain is 13.15 W/m2,and the dynamic maximum relative error is only 13.2%.The simulated and measured results have a good agreement.In addition,the new model is further extended to reveal the variation characteristics of secondary solar heat gain under different application conditions(including orientations,locations,EC film thicknesses and weather conditions).In summary,based on the outdoor spectrum and window spectral characteristics,the new model can accurately calculate the increasing secondary solar heat gain in real time,caused by spectrally selective windows,and will provide a computational basis for the evaluation and development of spectrally selective glazing materials.

Multi-objective optimal dispatch of household flexible loads based on their real-life operating characteristics and energy-related occupant behavior

A model-based optimal dispatch framework was proposed to optimize operation of residential flexible loads considering their real-life operating characteristics,energy-related occupant behavior,and the benefits of different stakeholders.A pilot test was conducted for a typical household.According to the monitored appliance-level data,operating characteristics of flexible loads were identified and the models of these flexible loads were developed using multiple linear regression and K-means clustering methods.Moreover,a data-mining approach was developed to extract the occupant energy usage behavior of various flexible loads from the monitored data.Occupant behavior of appliance usage,such as daily turn-on times,turn-on moment,duration of each operation,preference of temperature setting,and flexibility window,were determined by the developed data-mining approach.Based on the established flexible load models and the identified occupant energy usage behavior,a many-objective nonlinear optimal dispatch model was developed aiming at minimizing daily electricity costs,occupants’dissatisfaction,CO_(2) emissions,and the average ramping index of household power profiles.The model was solved with the assistance of the NSGA-III and TOPSIS methods.Results indicate that the proposed framework can effectively optimize the operation of household flexible loads.Compared with the benchmark,the daily electricity costs,CO_(2) emissions,and average ramping index of household power profiles of the optimal plan were reduced by 7.3%,6.5%,and 14.4%,respectively,under the TOU tariff,while those were decreased by 9.5%,8.8%,and 23.8%,respectively,under the dynamic price tariff.The outputs of this work can offer guidance for the day-ahead optimal scheduling of household flexible loads in practice.

DeST 3.0:A new-generation building performance simulation platform

Buildings contribute to almost 30%of total energy consumption worldwide.Developing building energy modeling programs is of great significance for lifecycle building performance assessment and optimization.Advances in novel building technologies,the requirements of high-performance computation,and the demands for multi-objective models have brought new challenges for building energy modeling software and platforms.To meet the increasing simulation demands,DeST 3.0,a new-generation building performance simulation platform,was developed and released.The structure of DeST 3.0 incorporates four simulation engines,including building analysis and simulation(BAS)engine,HVAC system engine,combined plant simulation(CPS)engine,and energy system(ES)engine,connected by air loop and water loop balancing iterations.DeST 3.0 offers numerous new simulation features,such as advanced simulation modules for building envelopes,occupant behavior and energy systems,cross-platform and compatible simulation kernel,FMI/FMU-based co-simulation functionalities,and high-performance parallel simulation architecture.DeST 3.0 has been thoroughly evaluated and validated using code verification,inter-program comparison,and case-study calibration.DeST 3.0 has been applied in various aspects throughout the building lifecycle,supporting building design,operation,retrofit analysis,code appliance,technology adaptability evaluation as well as research and education.The new generation building simulation platform DeST 3.0 provides an efficient tool and comprehensive simulation platform for lifecycle building performance analysis and optimization.

Study on the impact of window shades’physical characteristics and opening modes on air conditioning energy consumption in China

This paper focused on the impact of window shades’physical characteristics and opening modes on annual air conditioning energy consumption of residential buildings in China.Three building models with different window layouts were proposed initially,and then validated by the dimensionless indicator annual energy performance(AEP)to determine the final building model adopted in this study.Harbin,Beijing,Guangzhou,Changsha and Kunming were selected to represent five different climate zones in China.The shading model has taken six physical characteristics of window shades,viz.outer emissivity,inner emissivity,solar transmittance,solar reflectance,thermal infrared transmittance,conductivity and two opening modes,viz.up&down mode as well as left&right mode,into consideration.Besides,the window shades operation schedule was summarized through 949 valid questionnaires.The annual air conditioning energy consumption was calculated via EnergyPlus software,and then the impact of the above different opening modes and parameters on energy use were investigated.The analysis results indicated that the top&bottom opening mode is better than the left&right mode when used in Harbin,and the effect of two different modes in air conditioning energy consumption in Kunming is similar.But in the other three cities,the left and right mode is preferred.Besides,the analysis results of the impact of different physical characteristics on air conditioning energy use in different climate zones could help improve the energy performance of window shades.