Yongjun Sun

City University of Hong Kong | CityU · Department of Civil and Architectural Engineering

U-type medium-deep borehole heat exchanger (U-MDBHE) is a sustainable building heating technology. Current studies assess the long-term thermal performance of U-MDBHE using typical meteorological year weather data. The conclusions indicate a discernible deterioration in the thermal performance of U-MDBHE attributed to heat extraction attenuation. T...

The medium-deep borehole heat exchanger (MDBHE) coupled heat pump (HP) is a promising building heating solution for carbon reduction. Existing studies claim that the MDBHE-HP suffers a bottleneck challenge of long-term heating performance degradation because of the heating extraction attenuation of the MDBHE, which largely hinders the practical app...

Today’s plug-in electric vehicle (PEV) technology is one of the important ways to address the dependence of fossil energy and greenhouse gas emissions. With the explosive growth of the number of PEVs worldwide, surging PEVs charging has offered new opportunities and challenges for large amounts of existing buildings where more and more charging inf...

Short-term building cooling load prediction plays an import role in the building energy management. The concept of similar day approach is receiving special attention as an emerging alternative instance selection method for dataset with the purpose of accuracy improvement of machine learning algorithms in cooling load prediction. However, the perfo...

Central air-conditioning systems play a significant role in the demand response (DR) strategies of buildings due to their high energy consumption and flexible energy use. Previous simulation-based studies have shown that the use of phase change materials (PCM) in building envelopes can substantially increase cold storage capacity, which is a key me...

Developing solar-powered electric bus networks in high-density cities can greatly mitigate their increasing energy and environmental challenges such as carbon emission, street-level air pollution, and renewable penetration to the power grid. However, such solar-powered electric bus networks face a charging control issue that is caused by the severe...

Deployment planning of distributed rooftop photovoltaic (PV) systems remains a critical challenge for high-density cities, due to complex shading effects and diversified rooftop availabilities. Furthermore, such planning for large-scale systems could be extremely complex due to high dimensionality caused by the enormous number of buildings. To tack...

Using rooftop solar photovoltaics (PV) and batteries together to power electric buses is considered a novel and feasible approach to reducing carbon emissions and tackling street-level air pollution in high-density cities like Hong Kong. However, associated optimal deployment is highly challenging due to the involved high-dimensional system plannin...

The use of electric vehicles (EVs) has been on the rise during the past decade, and the number is expected to rapidly increase in the future. At aggregated level, the large EV charging loads, if not well regulated, will cause great stress on the existing grid infrastructures. On the other hand, considered as a resource-efficient and cost-effective...

Coatings applied on buildings are expected to perform well in both thermal and aesthetic aspects. Single-particle coatings can only perform satisfactorily in one of the two aspects, while mixed-particle coatings utilizing particles with complementary properties show substantial potentials to achieve desirable performance in both aspects. For accura...

The increasing applications of net-zero energy buildings (NZEBs) will lead to more frequent and larger energy interactions with the connected power grid, thereby being able to result in severe grid overvoltage risks. Control optimization has been proven effective to reduce such risks. Existing controls have oversimplified the overvoltage quantifica...

Accurate rooftop solar energy potential characterization is critically important for promoting the wide penetration of renewable energy in high-density cities. However, it has been a long-standing challenge due to the complex building shading effects and diversified rooftop availabilities. To overcome the challenge, this study proposed a novel 3D-g...

With large latent heat and nearly constant phase change temperature, phase change material (PCM) is an ideal energy storage material, but it suffers from severe leakage problems in applications. With large specific surface area, low cost, and easy availability, minerals have been widely used to encapsulate PCM to address its leakage issue. Meanwhil...

Phase change materials (PCMs) have the capabilities of thermal energy storage and temperature regulation. However, the application of PCMs in asphalt pavements is still limited due to the severe leakage and low thermal performance problem. In this research work, the phase change asphalt mixture (PCAM) with Polyethylene glycol/hydrophobic fumed sili...

Net-zero energy buildings (NZEBs) are considered as a promising method to mitigating the energy problems. Due to the intermittent characteristics of renewable energy (e.g., solar energy), NZEBs need to frequently exchange energy with the grid, which imposes severe negative impacts on the grid especially the overvoltage risk. Both planning and desig...

At present, the thermal properties (melting point, thermal conductivity, etc.) of common phase change materials (PCMs) cannot be accurately modulated, which limits their application in larger fields. Pseudo ionic liquid phase change materials (PILPCMs) have presented great potential due to its tunable thermal property and high physicochemical stabi...

Data-driven methods have gained increasing popularity due to their high-convenience and high-accuracy in practice. Considering the wide discrepancies in data availability across different buildings, transfer learning can be applied to improve the feasibility and robustness of data-driven solutions for individual buildings. In principle, the perform...

Solar energy radiation during the midday could causes the internal temperature of building rising, thus resulting in a significant source of power consumption to run air conditioner devices for thermal comfort environment. A growing interest developed in phase change materials (PCMs) applied in building envelope owing to the prevailing energy chall...

Utilizing renewable energy to meet the energy demand, net-zero energy building (NZEB) is considered a promising solution to the worsening energy and environmental problems. Due to the intermittent and unstable characteristics of renewable energy (e.g. solar energy), NZEB needs to frequently exchange energy with the power grid. Such frequent energy...

Phase change material (PCM) based thermal storage technology can help mitigate the increasing energy problems caused by the rapid economic developments and population growth. However, the extremely low thermal conductivity of PCM has substantially impeded their wide applications in practice. Therefore, this study has developed a novel palmitic acid...

With independent temperature and humidity control, desiccant air-conditioning (DAC) systems have multi-aspect advantages (e.g., high-efficiency moisture control, no ozone-depleting coolants use and easy renewable integration etc.) compared with conventional vapor-compression cooling systems, thereby attracting increasingly more research attention....

The increasing penetration of solar energy into buildings can mitigate the great challenges of energy shortage and global warming, while the inherent intermittence of solar energy could endanger power grids. This study investigated the energy flexibility of a net-zero energy (NZE) house using a solar-assisted air conditioning system with integrated...

The fault detection and diagnosis (FDD) of air handling units (AHUs) serves as a major task in building operation management and energy savings. Data-driven classification methods have gained increasing popularities considering their flexibilities and effectiveness in practice. One essential challenge in developing accurate and reliable FDD classif...

Proper energy storage system design is important for performance improvements in solar power shared building communities. Existing studies have developed various design methods for sizing the distributed batteries and shared batteries. For sizing the distributed batteries, most of the design methods are based on single building energy mismatch, but...

Thermoelectric generators (TEGs) with improved conversion efficiency are in great need for low-grade heat recovery. Existing studies primarily optimize the dimensionless figure of merit (ZT) of thermoelectric (TE) materials to improve TEG efficiency. However, TE material with a high ZT cannot guarantee that associated TEG has an optimal performance...

Utilizing renewable energy to meet the energy demand, net-zero energy building (NZEB) is considered a promising solution to the worsening energy and environmental problems. Due to the intermittent and unstable characteristics of renewable energy (e.g. solar energy), NZEB needs to frequently exchange energy with the power grid. Such frequent energy...

This study presents a new strategy using cluster analysis, multivariate adaptive regression splines and conditional inference trees to benchmark and evaluate building electricity usage. Different from the existing studies, cluster analysis was first used to group buildings based on their annual electricity usage patterns in order to improve the acc...

Existing studies have demonstrated that coating is highly effective in improving building energy efficiency. In practice, coating design requires performance considerations in both thermal and aesthetic aspects. For a single type of particle, such performance requirement is conflicting and difficult to fulfill. For instance, the commonly used TiO2...

Application of latent heat thermal energy storage unit is regarded as an effective method to improve the coefficient of performance of hot water heat pump systems (HWHPS). With consideration of energy efficiency and domestic hot water usage, phase change materials with a melting temperature range of 45–48 °C are suitable for practical applications....

A proper system design is crucial for a net-zero energy building (NZEB) to achieve the desired performance during its lifecycle. Most conventional design methods utilize TMY (typical meteorological year) data or multi-year historical data for NZEB system sizing. Due to the climate change, future weather data may differ considerably from these utili...

The wide availability of massive building operational data has motivated the development of advanced data-driven methods for building energy predictions. Existing data-driven prediction methods are typically customized for individual buildings and their performance are highly influenced by the training data amount and quality. In practice, building...

As buildings account for a substantial amount of energy worldwide, many developers encourage self-sustained net-zero energy buildings (NZEBs) to minimize buildings’ energy consumption and negative impacts on the environment. In contrast to regular buildings, NZEBs have interactive and complex energy systems that require synthetical evaluation of th...

Liquid desiccant cooling (LDC) has attracted increasing attention as an alternative to conventional vapour compression systems, to address the challenges of increasing electricity consumption and carbon emissions, and ozone depletion. The major advantages of LDC systems are that they can be driven by low-grade thermal energy such as solar energy an...

The crowded urban environment and busy traffic lead to heavy roadside pollutions in high-density cities, thereby causing health damages to city pedestrians. Electric vehicle (EV) is considered as a promising solution to such street-level air pollutions. Currently, in high-density cities, the number of public charging stations is limited, and they a...

Implementing thermal insulation on the building has been acknowledged as a highly effective way to achieve cost-effective energy conservation. For implementing thermal insulation, a key problem is the proper selection of wall insulation in terms of material types and optimum thicknesses because it is challenged to balance energy-saving effects and...

Presentation information: Poster presentation of "Optimum insulation thicknesses and energy conservation of building thermal insulation materials in hot-summer-cold-winter zone of China"; Conference information: 1st International Chinese Conference on Energy and Built Environment; 1st international Conference for Global Chinese Academia on Energy...

Active supply-demand interactions in a smart grid are essential for reducing grid power imbalance which is important for the security and efficiency of power supply. A key element to the success of such interactions is the proper pricing strategy. The latest game-theory based dynamic pricing methods require information exchanges not only between th...

Net-zero energy building (NZEB) is widely considered as a promising solution to the current energy problem. The existing NZEBs are designed using the historical weather data (e.g. typical meteorological year-TMY). Nevertheless, due to climate change, the actual weather data during a NZEB’s lifecycle may differ considerably from the historical weath...

Collaborations (e.g. renewable energy sharing) among nearly zero energy buildings can improve performances at cluster level. Demand response control is helpful to enable such collaborations. Existing studies have developed some dynamic pricing demand response control methods to reduce the nearly zero energy building cluster’ electricity bills and e...

The enrichment in building operation data has enabled the development of advanced data-driven methods for building energy predictions. Existing studies mainly focused on the utilization of supervised learning techniques for model development, while overlooking the significance of feature engineering. Feature engineering are helpful for reducing dat...

As the depletion of traditional fossil fuels and environmental pollution become a serious problem of human society, researchers are actively finding renewable green energy sources. Considered as a clean, efficient and renewable alternative, Hydrogen energy is considered the most promising energy source. However, the safe and efficient storage of hy...

Sizing the nZEB systems properly is crucial for nZEBs to achieve the desired performances. The energy demand prediction uncertainties and the components’ degradation are two major factors affecting the nZEB systems sizing. The energy demand prediction has been studied by many researchers, but the impacts of degradation are still neglected in most s...

Proper sizing of central air-conditioning (AC) systems is essential for high energy efficiency and desired levels of thermal comfort. However, due to the lack of accurate information at the design stage to predict the building peak cooling load and AC system performance, uncertainty exists in the sizing process. To directly deal with the uncertaint...

Net-zero energy building (NZEB) is widely considered as a promising solution to the current energy and environmental problems. The existing NZEBs are designed using the historical weather data (e.g. typical meteorological year-TMY). Nevertheless, due to climate change, the actual weather data during a NZEB’s lifecycle may differ considerably from t...

Collaborations among nZEBs (e.g. renewable energy sharing and battery sharing) can improve the nZEBs’ performance at the cluster level. To enable such collaborations, existing studies have developed many demand response control methods to control the operation of nZEB systems. Unfortunately, due to lack of consideration of demand prediction uncerta...

Among recent advances in electronic packaging technologies, electrically conductive adhesives (ECAs) attract most researchers’ attention, as they are environment-friendly and simple to apply. ECAs also have a lower operating temperature and volume resistivity compared with conventional electronic conductive adhesives. In ECAs, the conducting filler...

Due to inherent differences in building usage and system configuration, NZEBs frequently show different sufficiency of renewable energy at same moments, thereby providing chances of renewable-energy-sharing among NZEBs. Conventional controls are developed for NZEB performance improvements at single building level while potential collaborations (ren...

The development of information technologies has enabled real-time monitoring and controls over building operations. Massive amounts of building operational data are being collected and available for knowledge discovery. Advanced data analytics are urgently needed to fully realize the potentials of big building operational data in enhancing building...

Nearly zero energy buildings (nZEBs) are considered as a promising solution to mitigate the energy and environmental problems. A proper sizing of the nZEB systems (e.g. HVAC systems, PV panels, wind turbines and batteries) is essential for achieving the desirable level of thermal comfort, energy balance and grid dependence. Parameter uncertainty, c...

Cooling loss during transmission from cooling sources (chillers) to cooling end-users (conditioned zones) is prevalent in HVAC systems. At the HVAC design stage, incomplete understanding of the cooling loss may lead to improper sizing of HVAC systems, which in turn may result in additional energy consumption and economic cost (if oversized) or lead...

Real-time optimal control is widely adopted in central air-conditioning systems to improve the building energy management efficiency by adjusting system controllable variables according to system operating conditions. In time-driven optimal control, optimization actions are triggered periodically, which may not be efficient when the operating condi...

Near-zero energy buildings (nZEBs) are considered as an effective solution to mitigating CO2 emissions and reducing the energy usage in the building sector. A proper sizing of the nZEB systems (e.g. HVAC systems, energy supply systems, energy storage systems, etc.) is essential for achieving the desired annual energy balance, thermal comfort, and g...

With the increased complexity of air conditioning systems, the computational load and complexity of real-time optimization appear to be challenging for applications. To overcome the challenge, multiplexed optimization has been proposed in which multiple set-points are sequentially optimized and updated one by one. In such a way, it can achieve equi...

A deep understanding of household appliance standby energy use (SEU) and associated saving potentials in Chinese rural areas is vitally important due to the huge amounts of households and appliances. However, to date, few study has been conducted and very little is known about the SEU. Meanwhile, existing methods of estimating such saving potential...

Pipe-embedded concrete radiant floor system has gained much popularity due to its higher energy efficiency and better thermal comfort. Simplified yet accurate heat transfer models are essential for energy simulation of this system. This study presents the development and validation of a simplified RC-network model for the pipe-embedded concrete rad...

In residential buildings, occupant behavior and occupancy status have a significant impact on energy consumption variation. Although the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) recommends a uniform occupancy schedule for building energy assessment, occupant behavior patterns and schedules could be differe...

Purpose of review Heating, ventilation, and air-conditioning (HVAC) system control and building demand management play important roles in building energy efficiency and sustainability, and thus motivate numerous studies in recent decades. In this article, we provide a review of the developments in both HVAC control and demand management in recent 5...

Net Zero Energy Building (NZEB) has gained increasingly wide attentions over last few years and net zero energy starts to become a new design target of future buildings. This paper presents the first study on thermoelectric technology applications in NZEBs in which both thermoelectric cooling and thermoelectric generation are adopted. Substituting...

Real-time optimization (RTO) has been developed to improve the cost and/or energy efficiency of complex heating, ventilation and air-conditioning (HVAC) systems. In current literature, almost all of the developed real-time optimization methods belong to the type of time-driven optimization, in which the action of optimization is triggered by ?time?...

Net-zero energy buildings (NZEBs) are considered as an effective solution to current environmental and energy problems. To achieve expected performance, system sizes in a NZEB must be properly selected. Parameter uncertainties have been proved to have significant impacts on system sizing and need to be systematically considered. Due to complex unce...

The study proposes a new low-grade energy utilization system, i.e. a pipe-embedded wall integrated with ground source-coupled heat exchanger, and investigates its energy saving potentials in five typical climate regions of China. The cool/hot water produced by the ground source-coupled heat exchanger is supplied to the pipe-embedded wall to interce...

One main objective of demand response is to release grid pressures imposed by building peak demands through changing end-user electric usage in response to electricity price changes. Conventional demand response in heating, ventilation and air-conditioning (HVAC) systems is performed in an uncoordinated way which merely focuses on individual-buildi...

In large and complex HVAC systems, control optimization is always adopted to improve the operational efficiency since a small increase in the operational efficiency may lead to substantial energy savings. As the HVAC system becomes more and more complex, the real-time optimization of the system operation becomes a challenge due to the computational...

Uncertainties have significant impacts on system sizing in net zero energy building (NZEB) clusters and they have to be well considered. Through Monte Carlo simulation and statistical analysis, the impacts of three typical types of parameter uncertainties have been investigated in the study. Considering the uncertainty impacts, this study aims to c...

Net zero energy buildings (NZEBs) are promising to mitigate the increasing energy and environmental problems. For NZEBs, annual energy balance between renewable energy generation and building energy consumption is an essential and fundamental requirement. Conventional RES (renewable energy system) design methods for NZEBs have not systematically co...

Demand response controls, i.e. efforts from the demand side, are widely considered as a good alternative to supply side management for helping maintain grid balance. Conventional demand response controls of commercial buildings are conducted in an uncoordinated way and they focus on minimizing individual building level peak demand. But the overall...

Hollow blocks or bricks are widely used due to the good thermal insulation, lightweight, acoustic insulation, etc. This paper presents the development of a simplified heat transfer model of hollow block for simple and efficient heat flow calculation. This model is developed based on parameter identification in frequency domain by using finite eleme...

Chiller sequencing control is essential for a multiple-chiller plant that switches on and off chillers in terms of building instantaneous cooing load. It will not only directly affect the indoor thermal comfort but also building energy use. Various chiller sequencing control methods have been developed to assure the indoor thermal comfort while min...

Model-based optimal controls in HVAC systems involve uncertainties due to model uncertainties and measurement uncertainties. These uncertainties affect the accuracy and reliability of the outputs of optimal control strategies, and therefore affect the energy and environmental performance of buildings. This study proposes a method to enhance the rob...