Search

• A bottom-up intra-hour proactive scheduling for household peak avoiding. • Physic-based modeling and simulation of thermal appliances. • MPC controller formulation with soft constraints and flat tariffs. • Minimization of high-power appliances' concurrent operations considering user comfort. • Key factors and computational complexity analyzed. Residential-level peak shaving is beneficial for the supply–demand balance of buildings with a limited power capacity of renewable energy sources like building-integrated photovoltaics. Thermostatically controlled loads (TCLs) are recognized as flexible resources for peak shaving. In practice, most thermal appliances are controlled by local on–off controllers without any communication and coordination. Multiple appliances may operate simultaneously and produce load peaks. Existing studies assume the existence of an electricity market and time-varying tariffs, which are not always available. This paper developed a model predictive control (MPC) based bottom-up proactive method to leverage the thermal inertia of residential thermal appliances for avoiding household peak load without relying on time-varying tariffs. First, we used a physics-based modeling approach to model the thermal dynamics of several residential thermal devices. Then, we designed a centralized MPC controller to minimize the appliance concurrent operations considering occupant comfort zones and appliance rate powers. Consequently, the house peak load is reduced by minimizing concurrent operations. Simulations over homogenous and heterogenous appliance set validated that the MPC-based proactive scheduling method can effectively reduce household peak load without compromising user comfort too much. Finally, we discussed the impact of control interval, appliance rated powers, and penalty factors on peak avoiding and the computational feasibility of the MPC controller. We concluded that the MPC-based proactive scheduling is feasible and effective for a limited number of thermal appliances with short horizons (i.e., six-step). Replacing a mixed-integer nonlinear program solver with a mixed-integer quadratic program solver could significantly reduce the computational burden. However, the application of the MPC controller to multiple households at the system level is still impractical. Further research efforts are emphasized, like mining and forecasting occupant demand and appliance usage patterns in households and designing scalable control strategies for system-level peak shaving. [ABSTRACT FROM AUTHOR]

Driven by advances in smart grid technologies, building prosumers have closer interaction in sharing energy and information towards net-zero energy communities with energy flexibility and smart readiness. Many studies have focused on transactive energy systems, whereas limited attention was paid to coordinated prosumer management involving electric and electro-thermal energy storages. In this paper, a hierarchical energy management system was developed for a commercial neighbourhood, where distributed prosumers can share their generation and batteries, and manage cooling loads and thermal storages, in subtropical Hong Kong. Several operational scenarios were formulated considering building-level and neighbourhood-level controls, to explore the synergies through peer-to-peer (P2P) sharing and demand flexibility. Techno-economic-environmental impacts were analysed comprehensively from the perspectives of the network, the utility, and each participant. Results show that by integrating the demand-side flexibility, the P2P system could use electricity more effectively and economically. The formulated P2P operation strategy utilising neighbourhood-level control minimised the operational cost by 24.6% and net equivalent CO 2 emission by 7.1%, compared to the traditional peer-to-grid operation. The profit for each participant can be allocated by regulating the compensating price in the dynamic internal trading. The study provides prosumers energy-flexible and grid-friendly operation to facilitate the sustainability of the smart grid. • Hierarchical energy management for active prosumers with hybrid energy storages. • Performance comparison under individual and coordinated demand-side controls. • Enhancing local self-sufficiency by 22.8% via the power and information sharing. • Analysis of the participants' cost savings with a dynamic internal trading model. • Guidelines for system planners and operators to promote low-carbon communities. [ABSTRACT FROM AUTHOR]

Independent cascade hybrid heat pump (ICHHP) can bridge the large temperature gap between low-grade air sources and high-temperature industrial demands. However, the working fluids used in previous studies are just considered sufficient as long as they perform their functional role. They may not always be the most suitable choices in different situations, and the maximum efficiency of ICHHP has not been achieved. Ionic liquids (ILs) as alternative absorbents have shown the potential to enhance ICHHP performance with their unique ability to tailor thermal properties by freely combining anions and cations. However, the scarcity of IL thermodynamic properties data, underscored by limited vapor-liquid equilibrium experiments, has impeded the full exploitation of this inherent advantage. Obviously, the lack of dedicated research on screening optimal working fluids limits ICHHP performance. To address the identified limitations, the optimal fluid is recommended in this paper by comprehensively evaluating the performance among 100 fluid combinations under different working conditions. The results indicate that R161 is the best choice for the compression subloop. For the absorption subloop, the performance improvement is more sensitive to the anionic species, with the order of influence generally being [OAC]− > [Br]− > [OMS]− > [TFA]−. Specifically, H 2 O/[EMIM][OAC]—R161 stands out, with maximum improvements in coefficient of performance (COP) and exergy coefficient of performance of 9.4% and 5.6%, respectively, compared to other candidates. Furthermore, it doubles the COP relative to the reference fluid H 2 O/LiBr—R134a. Consequently, H 2 O/[EMIM][OAC]—R161 is the superior working fluid, significantly advancing industrial heating efficiency for ICHHP in large temperature lift conditions. • The performance of cascade heat pump can be further improved after optimizing fluid. • R161 in compression subloop has 233.9% higher COP than other low-GWP refrigerants. • H 2 O/[EMIM][OAC] in absorption subloop yields 19.1% higher COP than other H 2 O/ILs. • COP of optimal combination H 2 O/[EMIM][OAC]—R161 is 106.3% higher than the reference. [ABSTRACT FROM AUTHOR]

A novel low-temperature radiant structure (LTRS) has been developed to create local thermal environment and thermal comfort. This design incorporates an air layer that separates the air-contact surface from the radiant cooling surface, which enables low-temperature radiant cooling, increases cooling capacity and reduces condensation risk. The study addresses the concern of whether the LTRS with low-temperature radiant cooling would degrade thermal comfort. Heat transfer models of the LTRS were developed, and agreed well with the experimental results with difference within ±0.3 °C. Four cases with radiant surface temperatures of 27.9, 15, 10 and 5 °C were investigated, and in all cases a consistent operative temperature was maintained. This study evaluated various parameters, including the air temperature and velocity distributions, mean radiant temperature, operative temperature, and thermal comfort indices. Results indicated that the application of the LTRS increased the supply air temperature by 1.6 °C, suggesting significant energy-saving potential ranging in 28.4 %–52.7 % compared to traditional all-air cooling systems. Moreover, both general and local thermal comfort under the regulation of the LTRS satisfied the criteria in the ASHRAE Standard 55. These findings demonstrate that the novel LTRS has the capability of improving energy efficiency while maintaining satisfactory levels of thermal comfort. This study provides valuable insights and serves as a reference for promoting the use of personalized radiant cooling systems and enhancing building energy efficiency. [ABSTRACT FROM AUTHOR]

Aiming at reducing the heating and cooling loads for built environments, the thermal resistance and capacitance (R C) model has widely been acknowledged as an effective method for predicting the heat flux through building walls by simplifying wall structures and their properties into R and C allocations. This paper demonstrates an inverse optimization method based on particle swarm optimization (PSO) for determining the optimal R C allocation that minimizes the heat flux through building walls. A thermal R C model with three resistances and two capacitances was used as an example to search for the optimal building R C allocation in the hot summer and warm winter zone of China. The inverse optimization could be efficiently accomplished in 2.5 h with an ordinary computer, approximately 0.12% of the time consumed by using the exhaustive search method. The optimized R C allocation was composed of three resistances of 0.43, 0.18 and 0.39 and two capacitances of 0.50 and 0.50. Compared to the three typical thermal insulation (e.g., internal, external, and internal/external), the optimal R C allocation could reduce the heat flux into/from buildings by 17.3%–44.3%. The proposed inverse PSO method shows an effective and efficient capacity in searching for the optimal R C allocation of thermal R C models. • An inverse PSO method for the optimal RC allocation is proposed. • Optimization shows fewer steps and less time cost. • An optimal RC allocation is obtained. • Heat flux is reduced by 17.3%, 34.9% and 44.3% than three traditional RC allocations. • The effect mechanism of RC allocation on heat flux is explored. [ABSTRACT FROM AUTHOR]

Radiant cooling in buildings, as an energy-saving and comfort cooling method, is very promising in creating a green and healthy indoor thermal environment in buildings. However, radiant panels are prone to dew condensation and have low cooling capacity; thus, their application in hot and humid regions is limited. Covering the surface of the radiant cooling panel with a high transmittance low conductivity material (HTLCM), and, separating the air contact surface and the radiating surface, to form a new decoupled radiant cooling technology is an effective way to address the deficient radiant cooling capacity and easy condensation. Radiation heat exchange occurs between the radiant cooling surface and the indoor heat source surface through the HTLCM, while the indoor humid air undergoes convective heat exchange with the higher temperature HTLCM surface. The optical, and thermal properties of the material determine the cooling capacity and condensation resistance (thermal performance) of the radiant cooling air conditioning. This review provides a summary of the research advances in HTLCM-assisted radiant cooling air conditioning (RCAC) in recent years. First, the classification and optical and thermal properties of the currently used HTLCMs for radiant cooling are presented. Second, the heat transfer mechanism of RCAC with HTLCM is introduced. Finally, the research advances in the application of HTLCM-assisted radiant cooling are summarized, and the challenges and future development in this field are provided. The practical engineering application of HTLCM-assisted radiant cooling units in hot and humid regions is highlighted. • Material, mechanism, application of HTLCM-assisted radiant cooling are discussed. • Structural design, thermal performance, and cooling effective of RCAC are presented. • HTLCM improves condensation resistance, cooling capacity, temperature range of RCAC. • An updated review and discussion of HTLCM-assisted RCAC is provided. [ABSTRACT FROM AUTHOR]

Indoor air humidity has a significant impact on indoor air quality, building energy consumption, and equipment performance. Excessively low or high humidity is not good for living and working. Hygroscopic materials can be used to moderate the indoor air humidity level. This paper presents a simplified dynamic moisture transfer model of building wall layer of hygroscopic material, and the parameter identification of the simplified model with genetic algorithm by comparing the frequency characteristics of the simplified model with the theoretic frequency characteristics. The proposed simplified model was validated against the published experimental measurements on the system level. The results show that the predicted moisture flux by the simplified model agrees well with the experimental test. The simplified model was also validated on room level by a common exercise in IEA 41 project. The results show that the simplified model has a good agreement with the analytical solution, within ±2.2% in the case CE1A. In the realistic case CE1B, the model prediction matches the results of these detailed models provided in public literature. The proposed simplified dynamic moisture transfer model can be used in building indoor humidity environment and energy consumption simulation with good accuracy and efficiency. • Developing a simplified dynamic moisture transfer model of building wall layer of hygroscopic material. • Model parameters are identified in the frequency domain by the basic material properties. • Validated against the published experiment measurements as well as by a published benchmark exercise. • Much more accurate than the EMPD model and more efficient than the CFD model. • Can be easily integrated into conventional simulation software, such as Simulink or TRNSYS etc. [ABSTRACT FROM AUTHOR]

Abstract Aerogel insulating panels (AIPs) exhibit extensive prospects for application in aerospace, industry and buildings as excellent energy-saving thermal insulators owing to their ultra-low thermal conductivity. This work aims to numerically and experimentally investigate the thermal performance of AIPs in building energy efficiency. The AIPs were prepared and used as an insulation layer in an insulating cell. Three insulating cells with three different insulating materials as the insulation layer were prepared to measure and comparatively analyse their thermal performances. A resistance-capacitance thermal network model to predict the thermal performance of the insulating cells was developed and validated with the experimental data. The thermal indices of cells, i.e. the time lag, decrement factor and daily heat loss, were explored under periodic disturbances of exterior air temperature. Furthermore, the thermal performance of AIPs for exterior walls was predicted by adopting the typical wall structure in the hot summer and warm winter zone of China. The results showed that the AIP wall has decreases of ∼20% and ∼40% in the fluctuation amplitude of the internal temperature and heat flow, respectively, compared with the traditional insulating walls. Highlights • A method to indicate thermal performance of AIP for energy efficiency is proposed. • Three insulating cells with EPS, GF and AIP are prepared and compared. • AIP cell shows twice time lag, 40% less decrement factor and 35% less daily heat loss. • AIP wall has ∼20% and ∼40% decreases in amplitudes of temperature and heat flow. [ABSTRACT FROM AUTHOR]

Traditional energy planning methods are mostly related to newly-built area. However, in most already-built regions, the existing district energy systems (DESs) need to be ameliorated due to insufficient capacity and low efficiency. This paper investigates the methodology of expansion planning, which can offer planners a viable way to expand existing DESs. The term “expansion” aims to increase the supply capacity of the energy forms, e.g., steam, hot water and electricity, which cannot be accessed from national or urban energy supply network, and meanwhile increase energy utilization efficiency and cut CO 2 emission. Three parts of the methodology, including problem analysis in current DESs, demand side analysis and the existing DES expansion, are introduced in this paper. New concepts of load structure and evaluation system of the whole district are proposed in this methodology. A case analysis of Ningbo Hi-Tech District, China is conducted to shed light on the application of this method. [ABSTRACT FROM AUTHOR]

As most urban residents spend an average 90% of their time in buildings, it is crucial for building residents to monitor and maintain a comfortable indoor environment and air quality. Controlling the indoor carbon dioxide (CO2) concentration level is the major objective of mechanical ventilation systems to ensure healthy indoor air quality (IAQ). Current methods utilize proportional–integral–derivative (PID) controllers and multi-zone equations to operate ventilation systems in large spaces based on ASHRAE Standard 62. However, this approach suggests to determine the fresh air supply rate primarily based on CO2 level without considering occupancy. This often results in insufficient fresh air or energy waste in unnecessary mechanical operations in unoccupied building zones. Therefore, this study proposes a ventilation strategy based on occupancy profiles that captured by a Wi-Fi probe enabled occupancy sensing system. Based on the detected occupancy profiles, the proposed ventilation strategy and other two conventional strategies were compared in a two-day experiment conducted a multi-zone space. The comparison results in the experiment show that the proposed approach could maintain a CO2 concertation level lower than 1000 ppm for 94% (weekday) and 80% (weekend day) of day time for all zones. At the same time, the proposed strategy saved about 44.26% (weekday) and 55.5% (weekend day) of ventilation energy consumption when compared to the fixed rate ventilation strategy and saved about 23.6% (weekday) and 46.1% (weekend day) of ventilation energy consumption when compared to the multi-zone equation strategy. [ABSTRACT FROM AUTHOR]

Data centres (DCs) are energy-intensive facilities that convert most of their energy use into waste heat. Given the rapidly increasing energy and environmental impacts of DCs, and the need to optimize regional energy structures, there is an increasing effort to recover DC waste heat for district heating (DH) systems. However, previous research mainly focused on exploring the possibilities and proposing technical solutions for capturing DC waste heat for DH systems. They rarely investigated solutions on optimal control of the DH system after recovering DC waste heat, particularly for a DC waste heat-based heat prosumer with thermal energy storage (TES). Therefore, this study applied a model predictive control (MPC) scheme for a university heat prosumer with DC waste heat and water tank TES by simulation. In the framework, the objective function minimized the overall energy cost considering the dynamic heating and electricity prices simultaneously, and the incorporated model described system dynamics including DC waste heat recovery units, TES, and campus DH system. The MPC framework was demonstrated to be more effective than a traditional rule-based control approach in terms of 1) providing more stable chilled water for the DC cooling system and 2) cutting monthly energy costs by up to 3.2%. • MPC for a data centre waste heat-based heat prosumer is developed. • Dynamic heating and electricity prices are considered simultaneously. • Implementation of MPC at a district level is tested. • MPC provides more stable chilled temperatures for data centre cooling system. • Cut monthly energy costs by up to 3.2%. [ABSTRACT FROM AUTHOR]

Radiant cooling is an energy-efficient space cooling technology in built environments to achieve high thermal comfort. However, there are technical bottlenecks of condensation risk and insufficient cooling capacity in hot and humid climates. The use of double-skin infrared-transparent membranes (DIMs) to separate the radiant cooling surface from the air-contact surface can improve the cooling capacity while preventing condensation. Current research focuses on theoretical analysis and reduced scale experiments, and the lack of measured operational and performance data creates a key limitation on DIMs use. Therefore, the verification of radiant cooling system with DIMs in a full-scale experimental space and its radiant cooling performance need to be further studied. In this study, two full-scale radiant cooling chambers (one with DIMs and one without DIMs) were constructed. The effect of DIMs on radiant cooling performance was studied by monitoring surface temperature, condensation risk and cooling capacity. The results indicated that the air-contact surface temperature in radiant cooling with DIMs was always maintained above the dew point temperature for condensation-free safety at a low water supply temperature of 8 °C. In contrast, the conventional radiant cooling without DIMs had severe condensation. Moreover, the cooling capacity of radiant cooling panel with DIMs was 105.5 W/m2 at water supply temperature of 8 °C, 24.4 % improved compared to radiant cooling panel without DIMs at water supply temperature of 14 °C. This study provides prototype experimental verification for new technology with DIMs to improve radiant cooling performance and provides experimental data as a reference for related theoretical and model studies. [ABSTRACT FROM AUTHOR]

In buildings, there are two yet conflicting optimization goals: 1) minimize energy use and energy cost and 2) maximize thermal comfort. Model predictive control (MPC) is an ideal control strategy to deal with the above conflicting optimization goals. However, one challenge hindering the implementation of the MPC in buildings is the weather forecast uncertainty. This study aimed to improve the performance of the MPC under weather forecast uncertainty by introducing an error model. The error model used a straightforward approach based on easily measurable and accessible data to improve the quality of weather forecast data. The proposed method was tested by simulation on a university building located in Norway, while the detailed information and measured data from this real building were used to develop and validate the building model used in this study. Results showed that the MPC with the error model was able to achieve almost the full theoretical potential of the MPC in terms of the energy cost and thermal comfort, with 3.4% of weekly energy cost saving and 73% of indoor temperature violation numbers reduction compared to a conventional rule-based controller. In contrast, due to the existence of weather forecast error and a lack of error addressing mechanism, the MPC without error model did not perform well and gave the energy cost saving of only 0.7% and the indoor temperature violation numbers even increased by 20%. Meanwhile, the results indicated the introduction of the error model always benefited the MPC performance even under the condition of the low error of weather forecast. This study may facilitate the real application of the MPC in buildings. [ABSTRACT FROM AUTHOR]

[Display omitted] • Distributed real-time optimal control was developed for typical HVAC systems. • Physical meaning in decomposition was enhanced in the proposed scheme. • Computation load was significantly distributed from BEMS to local computation unit. • Global convergence of the distributed optimal control was investigated. • Distributed and centralized optimal control led to similar energy performance. Real-time optimal control (RtOpt) is an efficient tool to improve the energy efficiency of heating, ventilating and air-conditioning (HVAC) systems. RtOpt is always centralized and solved entirely in building energy management systems (BEMSs). However, centralized optimization is not be an efficient solution because real-time operation data in local loops need to be sent to the central computation unit in BEMS for optimization. This paper, therefore, proposes a distributed RtOpt scheme for typical centralized HVAC systems, which uses a dual decomposition mechanism to break the centralized problem into one mater problem and several sub-problems that can be solved in parallel and independently. The mater problem is converted to a simple mean value calculation using a projected sub-gradient method, thus distributing the computation load from the central computation unit into local computation units. Unlike available decomposition schemes in literature, the proposed method considered the functionality and spatial distribution of the major components of HVAC systems, which could enhance the physical meaning and facilitate the application of the decomposition scheme. The proposed distributed RtOpt scheme was tested in case studies, with numerical analysis being used to demonstrate its potential benefits. [ABSTRACT FROM AUTHOR]

• Nonuniformity factors of thermal resistance and capacitance are proposed. • The transmission load is reduced by ∼35% after optimizing nonuniformity factors. • Optimal nonuniformity factors of resistance/capacitance are 0.8 and 0.6 respectively. To increase the energy efficiency of buildings and lower carbon emissions, heat losses through exterior walls could be considerably decreased by using high-performance thermal insulation materials with superlow thermal conductivities or superhigh heat capacities. A superinsulating layer would result in a highly nonuniform distribution of thermal resistance and capacitance within the exterior wall. An interesting problem concerns how to engineer the nonuniform thermal distribution for given total resistances and capacitances to improve energy efficiency. This paper proposes using a thermal nonuniformity factor to quantitatively characterize the nonuniform distribution of thermal resistance and capacitance in an exterior wall built with superthermal aerogel insulating panels and given total resistance and capacitance values. Various thermal nonuniformity factors for several insulation modes were investigated by calculating the relevant transmission loads through the walls. The effect of the thermal nonuniformity factor on the wall transmission load was explored to improve the energy efficiency of a building. The results indicated that the wall heat flux could be greatly decreased by engineering walls with a high nonuniformity factor. For instance, engineering a wall in a sandwich mode with thermal nonuniformity factor of 0.97 could decrease the wall heat flux by ∼35% compared to a uniform wall. These findings on engineering walls based on thermal nonuniformity factors to decrease the wall heat flux could be a useful reference for superinsulated buildings and for further improving thermal insulating performance and building energy efficiency. [ABSTRACT FROM AUTHOR]

• Exploring the thermal performance of phase change asphalt mixture. • Equal volume replacement of mineral filler and fine aggregate with CPCMs. • Exploring the mechanical strength of phase change asphalt mixture. 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 silica composite phase change material (PEG/HFS) and Polyethylene glycol/SiO 2 composite phase change material (PEG/SiO 2) replacing mineral filler and fine aggregate was prepared and tested. The leakage experiment illustrated that the PEG/HFS with PEG content of 45% (wt) and PEG/SiO 2 with PEG content of 70% (wt) had good thermal exudation stability. The results of XRD and FTIR showed that the preparation process of composite phase change materials (CPCMs) was a pure physical mixing process without chemical reactions. In addition, based on the results of the indoor radiation test, Marshall test, and rutting test, we found that when mineral filler and fine aggregate were replaced by 25% of the same volume of CPCMs, the PCAM exhibited a better cooling effect and relatively small decrease in mechanical strength. Therefore, the PCAM developed in this research has great potential for improving the thermal performance of asphalt steel bridge deck. [ABSTRACT FROM AUTHOR]

[Display omitted] Energy efficiency in residential buildings can be improved considerably by optimizing the allocation of thermal resistance (R) and capacitance (C) of external walls. However, it is difficult to identify which RC allocation yields the minimum heat loss or heat gain for a given climate region, due to a lack of understanding of how regional climate affects optimal RC allocation. In this study, we determine the effect of the climate characteristics on the development of optimal RC allocation by combining the RC network model and the particle swarm optimization algorithm, taking five representative climates in different Chinese cities as examples. The energy efficiency potential and the ratio of heating to cooling load are introduced to comparatively analyse the energy savings after optimization for the five cities. The results indicate that the energy efficiency potential of residential buildings in Harbin is the largest, ranging from 6.2% to almost 20.6% for different total building capacitance. In Harbin, Beijing and Kunming, the energy efficiency potential is larger than those in Guangzhou and Shanghai, which is attributed to the larger heating to cooling load ratio of the former than that of the latter. An approximately linear relationship between the energy efficiency potential and the ratio of heating to cooling load is also built to fast predict the maximum energy savings for any given climate regions. This study could serve as useful references for the optimal design of thermal resistance and capacitance in different climate regions to save energy of residential buildings. [ABSTRACT FROM AUTHOR]

The thermal properties of the heat storage medium integrated with the heat pump (HP) should be suitable for the desired application in terms of providing thermal comfort for the end–users and matching the operation condition of the HP. In this study, a novel melting point modified composite phase–change material (CPCM) was developed for air–source HP. We concluded that sodium acetate trihydrate (SAT) modified with 10 wt% acetamide, 4 wt% nucleator, and 4 wt% thickener, which yielded the desired melting point (47.8 °C) and high latent heat (219.8 kJ/kg) presented better thermal reliability than the other component groups. The coefficient of performance of HP with novel CPCM was significantly enhanced compared to that of SAT CPCM, in which the maximum difference was 13.2%. Moreover, the average temperature of the discharging water drained from the novel CPCM unit was 4 °C higher than that of the control group. The overall efficiency of the heating system containing novel CPCM shows an increasing trend with a higher flow rate within a certain range. The system exhibits a payback period of about 5 years and a high bill saving of HK$6627.62 (US$861.59) over a 10-year analysis compared with conventional heaters. • Novel melting point modified SAT CPCMs for heat pump applications were proposed. • SAT–AC CPCM owns the melting point of 47.8 °C and the latent heat of 219.8 kJ/kg. • The overall efficiency of the system with novel SAT–AC CPCM was enhanced by 5.2%. • The average outlet temperature of novel–CPCM unit was 4 °C higher than SAT CPCM. [ABSTRACT FROM AUTHOR]

• An EG-based SAT-KCl-urea composite with improved thermal properties was prepared. • The thermal conductivity of the resulting novel CPCM was enhanced to 1.48 W/m·K. • The CPCM exhibited a desirable melting point of 47.5 °C and better shape stability. • The phase-change period of the novel CPCM was 30% less than that of SAT-KCl-urea. • The novel SAT-KCl-urea/EG CPCM showed great potential for latent energy storage. To create an energy–efficient heat pump latent heat thermal energy storage (HPLHTES) system, a novel sodium acetate trihydrate (SAT)–potassium chloride (KCl)–urea/expanded graphite (EG) composite phase–change material (CPCM) was developed in this study. EG was introduced into the base composite salt to prepare the novel CPCM, SAT–KCl–urea/EG. The thermal properties, crystalline phase, and morphology of the resulting CPCM were experimentally characterized. It was found that the SAT–KCl–urea/EG CPCM comprising 9 wt% EG was optimal for affording improved thermal–energy storage performance without compromising phase–change properties. The obtained CPCM exhibits an appropriate melting point of 47.5 °C and a high phase–change enthalpy of 200.3 kJ/kg. The thermal conductivity of the SAT–KCl–urea/EG CPCM was 1.48 W/m·K, approximately 5.3 times that of the SAT–KCl–urea composite salt (0.28 W/m·K). The required phase–change duration of the SAT–KCl–urea/EG CPCM was approximately 30% less than that of the SAT–KCl–urea composite salt. After 100 thermal–cycle tests, the SAT–KCl–urea/9 wt% EG CPCM retained a desirable phase–change temperature of 45.9 °C, high latent heat of 190.8 kJ/kg, and an acceptable supercooling degree of 1.56 °C. These thermal feature results showed that the SAT–KCl–urea/9 wt% EG CPCM exhibited great potential for use in the HPLHTES systems. [ABSTRACT FROM AUTHOR]

Heat storage phase change materials (PCM) has been widely used in various thermal energy systems, such as solar-heat pump. Harvesting solar energy requires low-cost and efficient PCM with proper melting points and high energy absorbing capacity. This paper proposed a novel Sodium acetate trihydrate (SAT) -Acetamide (AC) -micron/nano Aluminum nitride (AlN) composite phase change material (CPCM) with a melting point of 47.3 °C for solar-heat pump implementation. 10 wt% AC was selected as modifier to lower the melting point of SAT. The nano AlN or micron AlN was added to CPCM to suppress "supercooling" and improve its thermal conductivity. In order to determine the optimal ratio of mixture and examine the composite's thermal properties, DSC, SEM, XRD, FTIR and other characterization methods were implemented in this study. The results showed that 3 μm and 30 nm mixed AlN were the most effective nucleating agent and thermal conductivity filler. Also, the optimal composite with 5 wt% mixed AlN could reduce the "supercooling" degree to 0.27 °C and improve the thermal conductivity to 0.6484 W/m·K. After 100 heat absorbing and releasing cycles, the latent heat of CPCM maintained a respectable value of 226.8 kJ/kg. Unlabelled Image • A novel Sodium acetate trihydrate-Acetamide-micron/nano Aluminum nitride composite phase change material was prepared for solar-heat pump systems. • The combination of 5 wt% mixed micron/nano AlN and 4 wt% Na 2 HPO 4 ·12H 2 O reduced the "supercooling" degree to 0.27 °C. • Thermal conductivity of the novel composite material varied from 0.5621 to 0.6799 W/m·K depended on the mass ratio of mixed AlN. • The composite material still maintained a suitable phase change temperature of 47.3 °C and a high latent heat of 222.6 kJ/kg after 100 heat absorption and release cycles. [ABSTRACT FROM AUTHOR]

Ionogels have grabbed significant interest in various applications, from sensors and actuators to wearable electronics and energy storage devices. However, current ionogels suffer from low strength and poor ionic conductivity, limiting their performance in practical applications. Here, inspired by the mechanical reinforcement of natural biomacromolecules through noncovalent aggregates, a strategy is proposed to construct nanofibril-based ionogels through complex coacervation-induced assembly. Cellulose nanofibrils (CNFs) can bundle together with poly(ionic liquid) (PIL) to form a superstrong nanofibrous network, in which the ionic liquid (IL) can be retained to form ionogels with high liquid inclusion and ionic conductivity. The strength of the CNF-PIL-IL ionogels can be tuned by the IL content over a wide range of up to 78 MPa. The optical transparency, high strength, and hygroscopicity enabled them to be promising candidates in moist-electricity generation and applications such as energy harvesting windows and wearable power generators. In addition, the ionogels are degradable and the ionogel-based generators can be recycled through dehydration. Our strategy suggests perspectives for the fabrication of high-strength and multifunctional ionogels for sustainable applications.

The temperature distribution is always assumed to be homogeneous in a traditional single-input-single-output (SISO) air conditioning control strategy. However, the airflow inside is more complicated and unpredictable. This study proposes a zonal temperature control strategy with a thermal coupling effect integrated for air-conditioned large-scale open spaces. The target space was split into several subzones based on the minimum controllable air terminal units in the proposed method, and each zone can be controlled to its own set-point while considering the thermal coupling effect from its adjacent zones. A numerical method resorting to computational fluid dynamics was presented to obtain the heat transfer coefficients (HTCs) under different air supply scenarios. The relationship between heat transfer coefficient and zonal temperature difference was linearized. Thus, currently available zonal models in popular software can be used to simulate the dynamic response of temperatures in large-scale indoor open spaces. Case studies showed that the introduction of HTCs across the adjacent zones was capable of enhancing the precision of temperature control of large-scale open spaces. It could satisfy the temperature requirements of different zones, improve thermal comfort and at least 11% of energy saving can be achieved by comparing with the conventional control strategy., Electronic Supplementary Material Esm: The Appendix is available in the online version of this article at 10.1007/s12273-022-0942-8., (© Tsinghua University Press 2022.)

In this paper, we develop a mathematical model that aims (1) to predict the distribution of negative ions generated by an air ionizer installed in a ventilation duct and (2) to predict the efficiency with which it inactivates bacteria. The transportation equation for the negative ions was resolved combined with the bulk air velocity and the electric field. The bacteria distribution was solved numerically by integrating the susceptibility constant, which was acquired from the experiments. Two types of bacteria ( Serratia marcescens , Staphylococcus epidermidis ) were aerosolized and released into a 9-m ventilation duct system. Inactivation efficiencies were calculated for inlet velocities from 2 to 6.5 m/s and for various ion intensities. The efficiencies for S. marcescens and S. epidermidis were 31.53% (SD, 11.4%) and 12.17% (SD, 0.43%), respectively, with susceptibility constants of 8.67 × 10 -11 Colony-Forming Units (CFU)/ions and 2.72 × 10 -11  CFU/ions, respectively. The modeling results matched those of the experiments well. The pressure penalty at the maximum velocity (6.5 m/s) was only 9 Pa. The results show that the use of negative ions has great potential to enhance indoor air quality by reducing airborne microorganisms in ventilation systems., (© 2017 Elsevier Ltd. All rights reserved.)