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In demand response programs, users typically modify their energy consumption behavior in response to the grid. Distributed energy systems (DES) also need users' participation to ensure the efficient and stable operation of the system, especially under government-imposed carbon emission quotas. This study proposes a two-level collaborative demand-side management framework that allows users to participate in demand response in distributed energy systems, thereby ensuring that the systems' carbon emission remain within the quota while minimizing the impact on thermal comfort. Firstly, the framework realizes coordination between the supply and demand side. Changing energy use behavior not only reduces the amount of load but also enhances the system's efficiency. Secondly, different type of users can cooperatively adjust their air conditioners according to their load characteristics to achieve optimal overall thermal comfort. The effectiveness of the proposed method is demonstrated in a DES with four types of buildings, evaluated using two indoor thermal environment indexes. Under optimal guidance, the system efficiency is improved by 1.9%. Additionally, there is a 3.3% reduction in carbon emissions, along with a 13.2% improvement in overall indoor thermal comfort compared with unified temperature regulation. This study holds positive implications for users' participation in distributed energy systems to achieve energy saving and carbon reduction. • A two-level collaborative demand-side management framework for DESs is proposed. • Users can change the load to improve the system's efficiency through collaboration. • Multiple users can change the load cooperatively to improve overall thermal comfort. • The framework is verified in a DES with four types of buildings under two indexes. • The carbon quota can be achieved with higher efficiency and better thermal comfort. [ABSTRACT FROM AUTHOR]

The low-density residential building clusters exist widely in Chinese towns and rural areas, and have advantages to achieve zero emission with lower energy density and larger available space. However, the path for these areas to achieve zero emission is not clear yet and needs to be investigated. This study attempts to explore the approaches that the low-density residential communities achieve carbon neutrality considering local and external energy resources comprehensively. Regional zero-emission energy systems are designed and optimized to meet users' multiple energy demands. Five scenarios are established and compared based on the different combinations of energy resources. Results show that the regional self-sufficiency ratio can be 72.9%, and external energy supply is required even for the low-density areas. The PV installation area can be up to 100%, and the utilization of the local municipal waste can significantly increase the self-sufficiency ratio, about 24% of the power generation. The systems' economic performance is not attractive yet, with the minimum payback period about 8 years. If the carbon tax is adopted and the external fuels' price decreases, applications of the systems could be feasible. This paper would provide guidelines and suggestions to promote the zero-emission energy systems in the low-density areas. [ABSTRACT FROM AUTHOR]

• A comprehensive heat transfer model of the air permeable wall was developed. • Thermal insulation mainly lies in the exfiltration process across porous layer. • Sensitivity analysis was performed to identify the impact of design parameters. • The thickness of air permeable porous layer between 30 and 50 mm was recommended. The exhaust air insulation (EAI) wall is a novel type of air permeable wall that is characterized by a permeable porous layer. Such a wall design provides a solution to combine the building envelope with exhaust air heat recovery, and allows the exhaust air from a conditioned room to permeate through. The exfiltration process of the exhaust air across the porous layer can partly reduce the inward conductive heat flux through the wall. This makes the temperature at the innermost surface of the EAI wall close to the temperature of the indoor air, and leads to the reduction of cooling and heating loads through the wall. In this study, a comprehensive heat transfer model was developed to analyze the steady state thermal characteristics of the EAI wall. Forty different experiments were performed to verify the proposed model. A quantitative analysis was conducted on the differences when using the unsteady state model and proposed steady state model for the EAI wall with an outdoor thermal disturbance. A sensitivity analysis was carried out to investigate the impact of the design parameters on the thermal characteristics of the EAI wall. The results showed that using a porous material with relatively low thermal conductivity such as phenolic foam is beneficial to improve the heat recovery performance and thermal insulation of the EAI wall. The thermal insulation of the EAI wall is mainly due to the exfiltration process of exhaust air across the porous material. Considering the impact of the design parameters on the thermal characteristic, total thickness and pressure drop, a thickness of 30–50 mm is recommended for the porous material. At an exfiltration velocity of 0.003 m/s, the U-value of the EAI wall was lower than 0.1 W/(m2 K) for a porous material thickness of 30–50 mm. These results demonstrate that the EAI wall is applicable to both energy-efficient retrofitting of existing buildings and new buildings, and can potentially contribute to reduce the cooling and heating loads through the wall by the utilization of low-grade thermal energy in exhaust air. [ABSTRACT FROM AUTHOR]

Abstract Exhaust air insulation building envelope can recover and utilize the low-grade energy inherent in the exhaust air to prevent the heat transfer through the building envelope. The study investigates a triple glazed exhaust-air window (TGEW), which can switch its operation mode between the cooling and heating season. A two-dimensional numerical model was proposed to analyze the conjugated heat transfer in the TGEW. The experiment test of the TGEW was conducted and used to validate the proposed two-dimensional numerical model. The utilization efficiency of exhaust air within the TGEW was experimentally investigated under real outdoor weather condition. Numerical simulations were carried out to investigate the thermal performance improvement of the triple-glazed window by utilizing the exhaust air. Hourly and accumulated cooling/heating loads of the TGEW were calculated and compared with that of a conventional triple-glazed window (TGW). Results indicate that compared to the conventional TGW, the TGEW can reduce 25.3% and 50.1% of the annual accumulated cooling and heating loads. This demonstrates that the TGEW is applicable to the buildings installed with the fresh air supply system and can potentially contribute to decrease the cooling and heating loads through the window by utilizing the exhaust air. Highlights • Experimental test of a triple glazed exhaust-air window was conducted. • Two-dimensional numerical model of the exhaust-air window was verified. • The air temperature increment within the exhaust-air window was investigated. • The use of exhaust air can reduce the cooling and heating loads through the window. [ABSTRACT FROM AUTHOR]

District cooling systems are used in many areas, especially where the building density is high. However, its efficiency is still quite controversial compared with conventional individual cooling systems, especially in China. It is highly necessary to conduct a detailed study and give clear answers when a decision is made between the district cooling system and individual cooling system. Key factors that affect the decision need to be studied. This article therefore conducts a comprehensive performance assessment of district cooling systems by comparing with individual cooling systems. The comparative performance of both systems is analyzed when the combination of buildings with different functions varies. The optimal combinations for each system are obtained using genetic algorithms, and recommendations are summarized for better application of both systems. Impacts of the efficiency of chillers, the resistance of chilled water networks, and the cooling loads on the comparative performance are quantified considering uncertainties. Economic performance of both systems is analyzed, including the capital costs and operational costs. Suggestions are summarized for the future application of district cooling systems and individual cooling systems.ABSTRACT FROM PUBLISHERCopyright of Science & Technology for the Built Environment is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. [ABSTRACT FROM AUTHOR]

Uncertainty exists widely in the design of district cooling systems. Due to failures or improper maintenance of components or subsystems, the cooling systems may malfunction or work with reduced performance. In the conventional design method of district cooling systems, both aspects are often ignored or considered roughly. To ensure that district cooling systems achieve the expected performance as closely as possible, a robust optimization method is proposed in this paper. This approach relies on quantifying the uncertainty at the design stage and the reliability of the cooling system in operation. By taking the total annual cost (including the capital cost, operation cost and availability risk cost) as the objective, the robust optimal design of district cooling systems can be obtained. Uncertainties in weather, building design/construction and indoor conditions are considered and reliabilities of major equipment in the systems are dealt with as well. Individual cooling systems are often alternative to district cooling systems while uncertainty and reliability issues also exist at the design stage. The role of uncertainty and reliability in the design of district cooling systems and individual cooling systems are assessed and compared. Results show that both uncertainty and reliability have greater impacts on the design of individual cooling systems. [ABSTRACT FROM AUTHOR]

Uncertainties exist widely at the planning and design stages of district cooling systems, which have significant impacts on the design optimization. This paper therefore proposes a design method for district cooling systems by quantifying the uncertainties, which is so-called uncertainty-based design optimization method. Uncertainties in the outdoor weather, building design/construction and indoor conditions are considered. The application of the uncertainty-based design optimization method is examined in several aspects: the performance assessment, system sizing, configuration selection and technology integration. With the performance distribution at different risk levels, the design of district cooling systems can be determined by the stakeholders based on the compromise between quantified risk and benefit. Sensitivity analysis is conducted to identify influential variables with uncertainties for the cooling loads of district cooling systems. Results show that the uncertainties in the indoor condition are the most important and the uncertainties in building design/construction have the least impact. [ABSTRACT FROM AUTHOR]

District cooling system (DCS) has been widely used because of its low cost and high energy efficiency. Excessive studies have been done on DCSs, based on either actual projects or hypothesis. This paper presents a comprehensive review on the research and applications of DCSs. The characteristics and problems of DCS are introduced. The performance and progress of DCS integrated with sustainable energy technologies are summarized, including systems integrated with renewable energy systems, combined cooling, heating and power systems, and thermal storage systems. Efforts on the optimization of DCS are reviewed and categorized, including the efforts on district planning, DCS design, operation and control. An introduction on the existing typical DCS projects in China is presented. Challenges and opportunities for future application of DCS are discussed including the uncertainty issues at design stage, the control optimization and integration with smart gird. [ABSTRACT FROM AUTHOR]

Appropriate design provides the cooling system to achieve good performance with low energy consumption and cost. Conventional design method in heating, ventilation and air-conditioning (HVAC) field usually selects the cooling system based on certain cooling load and experiences. The performance of the selected cooling system may deviate from the expectations due to cooling load uncertainty. This paper proposes a novel design method to obtain the robust optimal cooling systems for buildings by quantifying the uncertainty in cooling load calculation and equipment reliability in operation comprehensively. By quantifying the cooling load uncertainty with Monte Carlo method and chiller reliability using Markov method, the robust optimal cooling system is obtained with minimum annual total cost. By applying the new method in the design of the cooling system for a building, its function and performance as well as potential benefits are demonstrated and evaluated. Results show that the proposed method can obtain the optimal cooling systems with low cost and high robustness and provides a promising means for designers to make their best design decisions based on quantitative assessment according to their priority. [ABSTRACT FROM AUTHOR]

Various uncertainties exist in cooling systems at the plan and design stage. The conventional design method usually selects the cooling system or configurations without considering uncertainties, which may be risky because the performance of the cooling system may deviate from the expected, together with increased cost and reduced benefit due to uncertainties and variations in actual working conditions. A new, simple, and effective method is proposed to optimize the design of cooling systems and get the robust optimal cooling system by considering uncertainties in the information used at the design stage. The mini-max regret theory is used to realize the method. Two important problems in the design of cooling systems are studied: chiller combinations and chilled water pump configurations. By considering the uncertainties in the cooling load, the robust optimal chiller combination can be obtained. By considering the uncertainties in the resistance of chilled water pipelines, the robust optimal chilled water pump configuration can be determined. [ABSTRACT FROM PUBLISHER]

Cooling load calculation is the basis for the design of building cooling systems. The current design methods are usually based on deterministic cooling loads, which are obtained by using design parameters or information. However, these parameters contain uncertainties and they will be different from that used in the design calculation when the cooling system is put in use. The actual cooling load profile will deviate from that predicted in design. By considering uncertainties of these parameters, the sizing and configuration of the cooling system can be improved. In this study, a design optimization method is proposed by considering uncertainties related to the cooling load calculation. Impacts caused by the uncertainties of nine factors are considered, including the outdoor weather conditions, internal heat sources and indoor set-points. The cooling load distribution is analyzed. The oversize problem is explained from the viewpoint of uncertainties. By presenting the probability distribution of the cooling load and the potential capital cost, the proposed method can determine the cooling system capacity with quantified confidence. Comparison between the cooling systems with different configurations is also conducted. With the distributions of their energy consumption, decision makers can select the optimal configuration based on quantified confidence. [ABSTRACT FROM AUTHOR]

A district cooling system supplies cooling to a group of buildings in a district. It has been widely used for its high energy and economic performance, especially in Asian and European countries. It is supposed that a district cooling system can achieve good performance when used in the subtropical area like Hong Kong, where the cooling is required throughout the year and the building density is very high. This study aims to quantitatively assess the performance of the district cooling system in a new development area in Hong Kong. By modeling the buildings and cooling systems of the new district based on the current plan, the performance of district cooling system is compared with the conventional cooling system, which refers to individual in-building cooling systems. Three cases with different chilled water systems are simulated and analyzed. Results show that the district cooling system is more efficient than the individual cooling system, with less energy consumption and operational cost. Energy consumption of main subsystems is compared and the energy saving potential of district cooling system is analyzed. Sensitivity study of district cooling system performance at partial load is conducted and results show that the district cooling system is more efficient under different load conditions during night time. [ABSTRACT FROM AUTHOR]

Ground source heat pump system attracts increasing attention worldwide in the past decades. It uses soil as the heat source/sink to supply heating and cooling to buildings. In the cooling dominated area, ground source heat pump system couples with the supplemental heat rejecter to avoid the unbalance underground, which is called the hybrid ground source heat pump system. The control strategy of the ground heat exchanger and cooling tower is very important to optimize the performance of the hybrid ground source heat pump systems. A new control strategy is proposed, which is to compare the cooling water temperature exiting the ground heat exchanger and cooling tower directly. Models based on artificial neural networks are built to realize the proposed control method. Four years’ performance of the hybrid ground source heat pump system controlled based on the new method is calculated and compared with another two frequently used methods. Results show that the new control method is more energy efficient and can make full use of the heat exchange advantage of outdoor air and the soil. [ABSTRACT FROM AUTHOR]

Accurate energy consumption prediction is the basis of predictive control for heating, ventilation and air conditioning (HVAC) systems. Data-driven models are widely used for energy consumption prediction. The prediction accuracy can be affected by data preprocessing or selection, which are not well studied yet. This paper attempts to study the impacts of different data processing methods and feature selection on the HVAC energy consumption prediction based on data-driven models. Long and short-term memory models are developed based on historical data to predict the day-ahead hourly energy consumption of HVAC systems. Two data smoothing methods, Gaussian kernel density estimation and Savitzky-Golay filter, are selected and compared. The impacts of feature selection, training set volumes and update frequency of models are analyzed and compared. To obtain general results of the above problems, three office buildings are selected. Results show that the smoothing methods can not ensure the improvement in accuracy by removing the exceptional data in the raw data which arise reasonably in practice. The inputs with raw 1-day historical energy consumption, the dry-bulb temperature and dew-point temperature in the next day, holiday type and day type is recommended to predict day-ahead HVAC energy consumption. It is recommended to use a larger training set if computing cost is acceptable. The model should be updated after being used for over 7 weeks. This study would guide the development of prediction models in practice. [ABSTRACT FROM AUTHOR]

Abstract: Hybrid ground source heat pump (HGSHP) system coupled with supplemental heat rejection equipment in parallel configuration is suitable for buildings where the cooling load is much higher than the heating load. Appropriate control is expected to improve its energy efficiency. A control strategy is proposed for cooling season as to compare the temperatures of the water exiting the ground heat exchanger (GHE) and the cooling tower (CT) directly. The logic is to choose the GHE or the CT to reject the condensing heat whenever the corresponding exit cooling water temperature is lower. During operation such a HGSHP system requires the knowledge of both the exit temperatures to take the shift control action. In many situations, however, only one of the two exit temperatures is measurable because only one is working at one moment. This paper develops artificial neural network (ANN) models for predicting the temperature of the water exiting the GHE. A numerical simulation package of a HGSHP system is adopted for training and testing the model. These models are also optimized regarding inputs, learning algorithms and neurons in the hidden layers. Results show that the ANN model can predict the GHE exit temperature with an absolute error less than 0.2°C. [Copyright &y& Elsevier]

[Display omitted] • A load allocation method is proposed to make full use of the recovered energy. • Flow rate or supply water temperature of thermal and electrical chiller is improved. • Absorption chillers use waste heat efficiently without being affected by heat pumps. • Primary energy efficiency and carbon emission reduction increased by 1.7% and 3.6%. Distributed energy systems fully utilize clean and renewable energy to satisfy the thermal and electrical loads of users. Absorption chillers are adopted to recover the waste heat from generators and are generally supplemented by electrical chillers or heat pumps to meet the insufficient thermal load. However, the load allocated to the absorption chillers can be affected by the heat pump/chiller owing to the chilled or hot water system distribution, leading to a lower energy utilization efficiency. In this study, a new load allocation method is proposed in which the water flow rate (F-method) or supply temperature (T-method) of chilled/hot water systems is adjusted according to the cooling production capability of absorption chillers. The proposed method was verified using a distributed energy system serving a campus. The results showed that the cooling utilization ratio of the absorption chillers could be maintained close to 1, and the absorption chiller could follow the system waste heat well. Consequently, the primary energy efficiency and cost savings could be increased by 1.74% and 1.55%, respectively, and carbon emissions from the cooling systems could be reduced by 4.21%. This study can thus help improve the application and performance of distributed energy systems. [ABSTRACT FROM AUTHOR]

Highlights • Various strategies have been proposed for short-term building energy predictions. • Three inference approaches have been exploited for multi-step ahead predictions. • Advanced techniques have been utilized for the development of recurrent models. • Model performance is evaluated based on prediction accuracy and computation loads. • The results can provide valuable insights for developing deep recurrent models. Abstract Accurate and reliable building energy predictions can bring significant benefits for energy conservations. With the development in smart buildings, massive amounts of building operational data are being collected and available for analysis. It is desired to develop big data-driven methods to fully realize the potential of building operational data in energy predictions. This paper investigates the usefulness of advanced recurrent neural network-based strategies for building energy predictions. Each strategy presents unique characteristics at two levels. At the high level, three inference approaches are used for generating short-term predictions, including the recursive approach, the direct approach and the multi-input and multi-output (MIMO) approach. At the low level, the state-of-the-art techniques are utilized for recurrent model development, such as the use of one-dimensional convolutional operations, bidirectional operations, and different types of recurrent units. The performance of different strategies has been assessed from different perspectives based on real building operational data. The research results help to bridge the knowledge gap between building professionals and advanced big data analytics. The insights obtained can be used as guidelines and references for developing advanced deep recurrent models for short-term building energy predictions. [ABSTRACT FROM AUTHOR]

The exhaust air insulation (EAI) wall provides a new solution to utilize the low-grade coolth energy of exhaust air in conditioned rooms for preventing the heat gain through the building envelope. Such a multi-functional building envelope takes advantage of the exfiltration process of the cool indoor exhaust air to block the inward conductive heat flux within building envelope in cooling season, and then cooling load is effectively decreased. Previous studies demonstrate the excellent thermal insulation performance of the EAI wall. However, current studies still lack a highly efficient compactional method for simulating the dynamic thermal performance of this wall. Moreover, thermal characteristics of the wall still have not been investigated in frequency domain, which would offer significant design guidance. To address these critical challenges, a frequency-domain finite-difference (FDFD) model of the EAI wall was developed in this study to analyze its transient heat transfer with high computational efficiency and no stability problem. An experimental platform was established to conduct the experimental analysis of the EAI wall and verify the proposed FDFD model. Moreover, the validated FDFD model was used to numerically evaluate the thermal characteristic of EAI wall in frequency-domain. The influences of some design parameters on the decrement factor and phase delay of the wall were also considered in numerical investigation. The result demonstrates that the frequencies of outdoor thermal disturbances exhibit a remarkable impact on the thermal characteristic of EAI wall. The decrement factor of the EAI wall can decrease to near-zero for all the frequencies of outdoor thermal disturbances, when airflow velocity reaches to 0.005 m/s or thickness of porous medium increases to 50 mm. This means that the EAI wall could effectively moderate the impact of outdoor thermal disturbances towards the indoor thermal environment under most scenarios of outdoor thermal disturbances. The outcomes of this study can provide a high-efficiency transient heat transfer model and some important design guidelines for this wall. [ABSTRACT FROM AUTHOR]

Distributed energy systems are becoming increasingly popular worldwide. The 100% renewable energy system can be an important energy supply alternative to reduce the carbon emissions and address energy shortage, especially for remote areas. However, the performance of 100% renewable energy system (RES) at community level needs further detailed analysis, which is affected by the climates, availability of renewable energy and local energy markets. This paper proposes a design optimization framework of 100% renewable energy systems for low-density communities and investigates the system performance. To investigate the integration and performance of 100% RES, thirty typical cities located in different regions of China were chosen considering different climates, geographical features, and renewable energy distributions. By taking the economic performance as the optimization objective, the optimal design for the 100% RES is obtained, and the energy and economic performance is analyzed. Results show that, under the current energy market conditions, the 100% RES is feasible for low-density communities in most regions of China. The payback periods of the systems in most cities are less than six years. When the cost of PV is reduced by half considering future technological developments, the payback period of a 100% RES can be reduced by 30%–60%. This paper would provide design suggestions and application recommendations in regard to promoting 100% RES in China. • Application of 100% renewable energy system at community level is studied. • 30 zones are selected considering climates, renewable energy sources and markets. • Solar energy and biomass can contribute to over 90% of the total energy supply. • Investment of 100% RES can be paid back in 6 years for most regions. • Payback periods can be reduced by 30%–60% when PV technology is further developed. [ABSTRACT FROM AUTHOR]

Roof receives heat directly from the solar radiation and outdoor air, and the heat transfer of the roof is often greater than that of any external wall. The building roof is usually overheated in summer, causing a great increase in the air conditioning load and negative effects on indoor thermal comfort. Thus improving the thermal insulation performance of the roof is essential for reducing air conditioning energy consumption and improving indoor thermal comfort. In this paper, an innovative pipe-embedded ventilation roof with outer-layer shape-stabilized PCM (named VRSP for short) was proposed. The heat gain is stored in the PCM to migrate excessive heat during the day and released through air ventilation at night. A three-dimensional transient-state heat transfer model of the VRSP system was built by CFD. The effects of phase transition temperature range of PCM, thickness of PCM layer and airflow rate in the ventilation duct on the thermal performance of the structure in five representative climate regions of China were evaluated. Results show that the optimum phase transition temperature ranges of PCM in severe cold region, cold region, hot summer and cold winter region, hot summer and warm winter region and mild region are 31–33 °C, 34–36 °C, 36–38 °C, 34–36 °C and 29–31 °C, respectively. The optimum thicknesses of the PCM layer are 25–30 mm, 25–30 mm, 30–35 mm, 25–30 mm and 20–25 mm, respectively. The suitable airflow rates are 1.5–1.9 m/s, 1.6–2.0 m/s, 2.1–2.5 m/s, 1.9–2.3 m/s and 1.4–1.8 m/s, respectively. The conclusion provides valuable guides for the application of VRSP under various climate conditions. • A pipe-embedded ventilation roof with shape-stabilized PCM is proposed. • Effects of physical properties of PCM and airflow rates are investigated. • The new system is optimized for its applications in different climate zones. • Considerable energy-saving effects are observed in Kunming, Harbin and Beijing. [ABSTRACT FROM AUTHOR]

Pipe-encapsulated PCM wall system with self-activated heat removal by nocturnal sky radiation cooler is a feasible means for building insulation and heat removal by using natural energy. In this paper, a system simulation platform including the simplified pipe-encapsulated PCM wall model, heat pipe heat-transfer model and nocturnal radiation model are established to investigate the thermal performance of the pipe-encapsulated PCM wall system with self-activated heat removal by a nocturnal sky radiation cooler. The temperature and heat flow of this system used in light-weight, medium-weight and heavy-weight walls under a dynamic boundary condition are respectively simulated on this platform. Results show that about 55.6%–82.8% of heat from the outdoor can be resisted by the pipe-encapsulated PCM wall, and 54.7%∼81.0% of that can be removed by the nocturnal radiation cooler at night. Comparing with the common wall, the proposed system can reduce by 32.4%∼55.5% of the accumulated heat entering into indoor environment. Good energy-saving potential can be achieved by this pipe-encapsulated PCM wall system. Besides, the result further reveals that the reduction of the accumulated internal surface heat transfer of this system used in medium-weight and heavy-weight walls is obvious larger than that of this system used in light-weight wall. • System platform of a pipe-encapsulated PCM wall system with heat removal. • Thermal performance of three walls (light, medium, heavy) with the PCM wall system. • 55.6%–82.8% of heat from the outdoor can be resisted by the PCM wall system. • Reduction of heat into the indoor is lager for the heavy wall with the PCM system. [ABSTRACT FROM AUTHOR]

Roof with outer-layer shape-stabilized phase change material (RSPCM) is a building construction that incorporates shape-stabilized phase change material (PCM) into the out layer of the roof. The decrement factor of the roof and the peak temperature of the inner surface can be greatly reduced by using the PCM in summer. CFD numerical simulation is used to investigate the thermal performance of RSPCM. The effects of the phase transition temperature, layer thickness and phase transition temperature radius of PCM are studied numerically. Results show that the suggested PCM thickness is 30 mm and the temperature radius should be as small as possible. The optimum phase transition temperatures are 31–33 °C, 34–36 °C, 36–38 °C, 34–36 °C, and 29–31 °C respectively in severe cold region, cold region, hot summer and cold winter region, hot summer and warm winter region and mild region. The decrement factors at the corresponding optimum phase transition temperature are about 0.030, which are lower than that of the roof without PCM by over 85%. The peak temperatures of the inner roof surface are all decreased by over 3.7 °C. These results can be used as a guideline for optimum design to improve the dynamic thermal performance of roof structure in summer. • Heat transfer model of roof with outer-layer shape-stabilized PCM is built by CFD. • Effects of phase transition temperature and radius, and PCM thickness are studied. • Decrement factor, time lag and latent heat utilization of this roof are analyzed. • PCM thickness of 30 mm is recommended. • Optimum phase transition temperature of PCM are obtained for five climate zones. [ABSTRACT FROM AUTHOR]

• Renewable energy assessment methods used in 12 GBRSs are analysed and compared. • Methods used in green neighbourhood rating system are also introduced. • Evaluation way, renewable energy types, building characteristics, etc. are analyzed. • The effects by using different methods in one building are analysed. • Suggestions are provided to improve the renewable energy assessment. Green buildings and neighborhoods can help mitigate impacts of buildings on the environment, society and economy. Many rating systems or tools have been developed worldwide to assess and certificate green buildings or green neighborhoods. Renewable energy plays an important role in achieving green buildings/neighborhoods or zero energy buildings/neighborhoods by reducing fuel consumption and pollution emissions. However, substantial differences exist in assessing or quantifying the renewable energy in green building/neighborhood rating systems. This paper therefore provides a comprehensive review on renewable energy assessment methods adopted in green building/neighborhood rating systems, which would be very helpful to understand and then improve the rating systems. These methods are analyzed and discussed regarding to the calculation way, involved renewable energy types, building characteristics and energy conversion. Then a case study is conducted to quantitatively illustrate the difference of typical renewable energy assessment. Suggestions are summarized to improve the assessment methods. This paper will help investors, users and policy makers understand the rating systems more thoroughly and promote the development of green buildings and green neighborhoods. [ABSTRACT FROM AUTHOR]

Distributed energy systems (DESs) are becoming increasingly popular because of their high-energy efficiency and low pollution emissions. Accurate performance evaluation of such systems is critical for processes at the early design stages. However, there are considerable uncertainties in terms of the parameters used for performance evaluation and design optimization, including component efficiencies, customer demands, and energy markets. These uncertainties can significantly influence the performance of DESs. Without consideration of these uncertainties, the performance of DESs can be overestimated or underestimated, which leads to inaccurate decision-making. Therefore, this paper presents a comprehensive evaluation of the performance of DESs by considering uncertainties in 12 parameters that relate to the electrical and thermal efficiencies of generators, efficiency of chillers and pumps, load density, energy markets, and so on. The energy and economic performance of DESs under each uncertainty are analyzed and compared with that of conventional energy systems. The suitable conditions for using DESs and other factors that can influence their performance are determined. The results of this study can serve as a guide for design optimization and policy development to promote the use of DESs in China. • Uncertainties affecting the performance of DESs compared with CES are investigated. • Impacts of 12 parameter uncertainties on the performance of DESs are quantified. • Four control methods are implemented and compared. • Suitable conditions, influential factors and suggestions to promote DESs are obtained. • The control method following the cooling demand is preferred. [ABSTRACT FROM AUTHOR]

Highlights • A novel quasi-3D simulation model was developed by introducing a shrinkage model. • The shrinkage model could predict the flow pattern accurately. • Non-wetting and mass transfer resistance in the air side hindered the performance. • Adopting nano-TiO 2 coating led to an increase of 15.2% absolute moisture removal. • Employment of curved dehumidifier enhanced the performance by 70%. Abstract The present study proposed a novel quasi-3D model for simultaneous simulation of heat and mass transfer process in a falling film dehumidifier with penetration mass transfer theory and CFD technology. Different from the existing 2D model, the new model took the shrinkage of falling film into consideration by introducing variable film wettability. Besides, an experimental system with a single channel falling film dehumidifier was designed and built up to validate the developed quasi-3D model. Results indicated that the shrinkage model could predict the flow pattern accurately, and the relative different between calculated and experimental wetting ratio was less than 4%. Combined with the shrinkage model, the CFD model was proved to be reliable to simulate the dehumidification process with the relative deviation of absolute moisture removal less than 10%. It was found that the non-wetting of falling film and mass transfer resistance in the air side hindered the dehumidification performance. Consequently, super-hydrophilic coating and curved plate were proposed to enlarge the wetting ratio and decrease the mass transfer resistance in the air side. By adopting the nano-TiO 2 coating, the wetting ratio of dehumidifier increased from 81% to 97.8%, which led to a relative improvement of 15.2% for absolute moisture removal. In addition, the employment of curved dehumidifier could enhance the dehumidification performance by 70%. [ABSTRACT FROM AUTHOR]

Ground heat exchanger takes the soil underground as heat source or sink to supply cooling or heating. It has been widely used in building heating and cooling systems due to high efficiency and environmental friendliness. This paper reviews the latest research on ground heat exchangers from several new perspectives and demonstrates their potentials in achieving zero energy buildings. Firstly, ground heat exchangers are classified into water-based and air-based ones based on the heat transfer medium. They can be used in a passive or active approach. Associated research and projects for each approach are introduced and analysed. Then the integration of ground heat exchangers with various cooling and heating technologies and related studies are reviewed. These technologies include solar thermal collectors, cooling towers, nocturnal radiative cooling technology, solar chimney, etc. Finally, a technical route for ground heat exchangers to help realize zero energy buildings is presented, which provides a promising solution to improve energy efficiency of buildings. [ABSTRACT FROM AUTHOR]

A concept of exhaust air insulation (EAI) is proposed for application in cooling dominated buildings. The EAI wall in basic form is composed mainly of an air-permeable porous material layer, a ventilated cavity, and an external protection structure. The excessive indoor air pressure or mechanical ventilation forces the exhaust air from the conditioned space to flow through the porous layer firstly, and eventually to ambient through the ventilated cavity. The outflowing exhaust air makes the temperature of the inner surface of the porous layer very close to that of the indoor air. And consequently, the heat gain through the building envelope wall can be dramatically reduced in the cooling season. In this paper, an unsteady-state heat transfer model is developed to predict the temperature distribution of the EAI wall. Experimental measurements are carried out for validating the heat transfer model. Numerical simulations are performed to simulate the transient heat transfer of the EAI wall in cooling season. The exfiltration heat recovery efficiency of the EAI wall is quantitatively investigated. Effects of the airflow velocity, the thickness of porous layer, and the thermal conductivity of porous material on the thermal performance of EAI wall are analyzed. Performances of a conventional brick wall and an external insulation wall are also calculated and compared with that of the EAI wall. Results show that the EAI wall can reduce 84.7% and 67% of the daily total heat gains in cooling season compared with the brick wall and the external insulation wall, respectively. Excellent thermal performance can be achieved by employing thicker porous layer or higher airflow velocity. At a velocity of 0.003 m/s with porous layer thickness of 50 mm, the heat flux entering indoor spare can be decreased to practically zero. [ABSTRACT FROM AUTHOR]

Distributed energy systems have been attracting increasing attention due to high efficiency and environmental friendliness. In subtropical and high density urban areas, district cooling system is regarded as an efficient alternative for cooling and dehumidification. Distributed energy systems integrated with district cooling systems (DES&DCSs) are supposed to be efficient energy supply options. However, the energy performance of such integrated systems is not sufficiently studied yet. To provide energy planning suggestions in these areas, this paper aims to investigate the energy performance of DES&DCSs under different control methods in detail. Annual hourly measurements of cooling and electricity loads of a campus are used. The energy performance of the DES&DCS is evaluated and compared with DCS and individual cooling systems which totally depend on the grid. The operation characteristics of the DES&DCS under four control strategies are analysed, as well as the impacts on the grid. Results show that the DES&DCS can be energy efficient in subtropical and high density areas. The energy saving is more than 10% and can be up to 19%. The control strategy following the cooling or electricity demand requiring more primary energy is recommended due to higher energy saving and more beneficial to the grid. [ABSTRACT FROM AUTHOR]

• Historical daily energy consumption data of 480 college dormitories are analyzed. • The energy consumption characteristics of dormitories in an entire year are investigated. • The impact factors including floor, orientation and occupant's gender are quantified. • The floor has the most significant impact on energy consumption among the three factors. • Two adaptive electricity pricing strategies are recommended to balance the bill difference. College buildings, especially college dormitories, have a high density of energy consumption. It is important to obtain the energy consumption characteristics and impact factors of college dormitories before implementing energy efficiency measures. However, few studies based on experimental data have been reported. This study attempts to analyze the energy consumption characteristics of college dormitories and determine the influential factors based on monitored data. Annual daily energy consumption data of 480 college dormitories with different orientations and floors were collected. The energy consumption characteristics and the impact of factors including the floor, orientation, and occupant's gender are investigated and quantified through the statistical methods and covariance analysis. The results show that the energy consumption varies significantly between different dormitories, and the floor location is the most influential factor. The annual energy consumption of the dormitories on the top floor is 10̃15% higher compared with those on the other floors due to higher cooling or heating load resulting from the roof. Then, two floor-oriented electricity pricing strategies are recommended to balance the different energy bills caused by different located floors of rooms. The electricity tariffs for rooms on the middle/top floors should be increased/decreased by 3.5%/10.3% in the proposed floor-based electricity tariff. This study would provide a basis for energy efficiency improvement and tariff optimization for college dormitories. [ABSTRACT FROM AUTHOR]

• Model uncertainty of water source heat pumps is investigated and quantified. • 13 commonly-used models of WSHPs are involved and validated using manufacture data. • Impact of model uncertainty on the energy consumption of WSHP system is significant. • Model uncertainty can result in very different conclusions and affect decision making. • Model uncertainty should be considered in design optimization and performance assessment. Water source heat pump systems are widely used for cooling and heating due to high efficiency. The energy source can be surface water or underground water. Accurate modeling of water source heat pump systems is the basis for performance prediction, design and control optimization. However, various heat pump models are available to predict the system performance and results obtained can be very different under different models due to the model uncertainty. Without considering these uncertainties, the performance of water source heat pump systems would be overestimated or underestimated and the decision making would be affected. This paper attempts to quantify the model uncertainty of water source heat pump and its impact on the system performance. Thirteen commonly-used models are selected and validated using the manufacture data. By importing these models into the water source heat pump system, the impact of heat pump model uncertainty on the system performance is quantified. It shows that the model uncertainty can result in a deviation of up to 30% in the annual energy consumption. The energy saving potential of water source heat pump systems can vary from -18.43% to 14.78% compared with the chillers & boiler in the hot summer and cold winter area. The priority of water source heat pump systems is also controversial. The difference in the annual average coefficient of performance of the system can be up to 1.22. It demonstrates that the model uncertainty of water source heat pumps affects the system performance significantly and should be taken into account in building energy prediction and design optimization. The models considering the correction of part load ratio are recommended. [ABSTRACT FROM AUTHOR]

• Energy and economic performance of TES using surplus energy for DES is investigated. • Impact of cooling and heating systems, climates and building mix is analyzed. • The maximum increase of the primary energy efficiency by TES is only 3.69%. • Economic performance of TES is limited with a payback period of always over 7 years. • Surplus energy is not fully used especially when the cooling/heating load is low continually. Distributed energy system becomes increasingly popular due to high efficiency and low pollution emissions. When it operates following the electricity load, thermal energy storage system can be used to accommodate surplus cooling and heating and improve the energy efficiency. This study investigates the energy and economic performance of thermal storage systems for surplus cooling and heating in distributed energy system, considering the impacts of climates, building combinations and cooling/heating supply systems. Results show that the thermal storage system can improve the primary energy efficiency and is more useful when residential buildings adopt centralized heating and decentralized cooling systems. By varying climates and building combinations, the thermal storage system can improve the primary energy efficiency by 0.28%–3.69%. The economic performance is not promising with a long payback period. The main reason is that the overall utilization rate of the surplus energy is low (less than 45%), especially when the cooling/heating load is low continually during spring and autumn. Additionally, the effect of static and dynamic thermal storage model is analyzed. Results show that the static model would over-estimate the performance of the thermal storage system significantly and the dynamic model is recommended. [ABSTRACT FROM AUTHOR]

The exhaust air insulation wall (EAIW), which is made from air-permeable porous materials, can be treated as a heat recovery building envelope. It can prevent the heat transferring through the wall by an exfiltration process of low-grade exhaust air. To analyze the transient heat transfer of the EAIW, a numerical model was established based on finite-difference approach, and the model was verified by comparing the measured data and simulated results. Moreover, numerical simulations were performed to identify the ability of the EAIW to buffer and eliminate the heat gain on a typical summer day. In addition, parametric studies were conducted to estimate the influences of each key parameter on the dynamic thermal behavior of the EAIW, such as the hourly temperature field, heat gain, decrement factor, and time lag. The results indicate that the exfiltration airflow can adjust the inside surface temperature of the wall extremely close to the indoor temperature during the entire day. The daily total heat gain of the EAIW can be approximately eliminated for an exfiltration rate of 0.005 m/s. The thickness and exfiltration rate of the porous materials play a dominant role in the prevention of heat conduction through the EAIW into the indoor space. • Exhaust air insulation wall (EAIW) is a heat recovery building envelope. • Exfiltration airflow prevents the heat conduction of wall towards indoor space. • EAIW can buffer and eliminate the influence of outdoor thermal disturbance. • Porous material thickness and exfiltration rate play the dominant role. [ABSTRACT FROM AUTHOR]