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• To improve data center performance, it must be efficiently cooled. • This paper undertakes a detailed examination of the most recent cooling optimization techniques. • Several methods are discussed like regular air conditioning, free cooling, and liquid cooling. • An assessment of overhead and underfloor air delivery technologies is presented. • The effects of baffles, variable airflow control, and server placement are investigated. In order to increase data centers' efficiency and performance, a proper cooling system should be applied. This article provides a comprehensive assessment which explores current cooling optimization technologies for data centers. Standard traditional technologies like air conditioning, free cooling, and liquid cooling are investigated. Their limitations as well as proposed improvements are thoroughly discussed. The article also delves into underfloor and overhead air supply technologies, presenting their advantages and drawbacks. The review introduces novel approaches at the rack level cooling, including baffles, variable airflow management, and optimal server placement. Key findings stress the efficacy of optimized airflow systems and innovative rack-level cooling, underlining their role in reducing energy consumption and enhancing overall performance. Notably, potential energy savings of up to 67.2 % compared to traditional methods are demonstrated. The adoption of advanced cooling technologies, such as direct and indirect natural cooling, liquid-cooling cold plates, submersion, heat pipe, and thermosiphon-based cooling, exhibits promising energy efficiency gains and reduced Power Usage Effectiveness (PUE) values. Research into content-specific efficiency enhancements, adaptable energy-saving tactics, and all-encompassing server power consumption models is necessary. To work toward future sustainable, energy-efficient data centers, researchers should investigate how CRACs and server fans interact, find ways to integrate thermal and power management, and how artificial intelligence can be used to cool servers in an eco-friendly way. [ABSTRACT FROM AUTHOR]

• FDD methods and process discussed in detail. • IoT and cloud technology for FDD is discussed. • Presents the detailed discussion on fault modeling. • Challenges and future prospects of FDD systems are discussed. This review study examines the latest research and developments in the fault detection and diagnostics of Heating Ventilation and Air Conditioning (HVAC) systems. This review describes the basics of Fault detection and diagnostics in the HVAC systems, and the methods developed for the FDD have been discussed in detail. Machine learning methods have become prevalent in the FDD. Supervised and unsupervised machine learning methods have been discussed. Data preprocessing and feature selection are the two essential steps of the FDD process using machine learning. Fault prognosis has also been discussed in brief. Further, fault modeling and its applications in the FDD have been covered. Various approaches have been used to model the different faults in HVAC systems. This paper reviews FDD systems based on four aspects, i.e., detection, diagnostics, prognostics, and modeling of faults. Then this review provides a comparative study of different FDD methods. Finally, the paper discusses future challenges for the more efficient FDD systems to reduce the energy consumption of the HVAC systems. [ABSTRACT FROM AUTHOR]

In their quest to enhance energy efficiency and carbon footprint management, many enterprises are turning their attention towards optimizing their facilities through amplified data monitoring and innovative control methods. In this context, this research highlights a practical solution in a commercial building located in the United States. It explains the creation, implementation, and costs of a universally applicable model predictive control (MPC) framework for the building's heating, ventilation, and air conditioning (HVAC) system. The paper elaborates on both the hardware and software used to accumulate pertinent data and the formulation of the MPC system. This approach leverages cloud-based microservices and can be seamlessly integrated into current building management systems. In this regard, this paper presents three innovative strategies: Proportional–integral (PI)+Preheating, MPC, and occupancy-based control. These scenarios were designed to improve energy efficiency and thermal comfort significantly by reducing temperature fluctuations and adhering more closely to the setpoint temperature. The implementation of these strategies resulted in substantial energy savings, with reductions in energy consumption of 12.83%, 19.21%, and 14.98%, respectively. • A novel cloud-based MPC scheme is proposed for controlling the educational building HVAC system. • Real-world case installation details are provided with a focus on cost and sensor information. • A comprehensive discussion on thermal modeling, occupants' comfort, and control performance. [ABSTRACT FROM AUTHOR]

With recent energy and environmental crises, the energy consumption prediction of air conditioning (AC) is essential. Notably, existing general prediction systems use the air temperature, real-time AC usage, time, occupancy, and AC historical energy consumption as inputs and employ feedforward neural networks. However, such systems face certain challenges. First, the input system may be difficult to reflect the real-time interaction among the building environment, occupants, and energy system; Second, the algorithms need to be upgraded to further improve accuracy, speed up convergence, and avoid overfitting. his paper introduces a novel parameter (group occupant behavior probability, GOBP) in the input system; and uses swarm intelligence algorithms with chaotic mapping and adaptive weight adjustment as optimization with LSTM and BP as the basic algorithms. The verification results obtained from five different buildings indicate the following: (1) The novel prediction system improved prediction performance with 20.08%–78.37 % of MAPE and 3.99%–53.28 % of CV-RMSE, however, it will increase 148.70s–1065.11s of calculation time. (2) For accuracy, using GOBP will improve the 0.30%–51.87 % and 0.18%–64.77 % by using swarm intelligence optimization algorithms. (3) This paper discusses the priority of selecting suitable inputs, algorithms, and optimization to combine a whole prediction system. • The definition of a simplified model using the group occupant behavior probability is proposed. • The chaotic mapping and adaptive weight adjustment are used for optimizing the swarm intelligent algorithms. • A reconstituted AC energy consumption prediction system is proposed with novel inputs and improved algorithms. • The reconstructed prediction system demonstrates improved prediction accuracy and data acquisition difficulty\. • The best combination of inputs and algorithms is discussed based on 60 groups of comparative experiments. [ABSTRACT FROM AUTHOR]

The thermal management system (TMS) in electric vehicles (EVs) is a comprehensive system that integrates an air conditioning system for the cabin, a temperature control system for the battery, and a cooling system for the motor. The currently used PI control strategy can only meet the basic TMS functions and cause high energy consumption. In this paper, we present a novel model predictive control (MPC) strategy for the TMS to optimize operational performance in real time. Different from the independent PI control for the individual components, MPC can predict future operation conditions and provide the optimal operating inputs in advance. A complete control-oriented model for MPC is developed, and the MPC strategy is designed to minimize the total power consumption of the TMS under the control-oriented model and constraints. The evaluation is carried out under several cases including the fixed ambient temperature, realistic ambient temperature, and different vehicle speeds. The results showed that the novel MPC strategy saved energy consumption by 5.9%–10.3% in these cases when compared to the PI strategy, demonstrating the effectiveness and feasibility of the proposed MPC control. • Proposed a model predictive control strategy for thermal management systems in EVs. • Developed a control-oriented model based on data-driven methods and physical principles. • Minimizes total power consumption while maintaining cabin and battery temperatures. • Results demonstrate the effectiveness of the MPC strategy under various conditions. [ABSTRACT FROM AUTHOR]

As the national digitization process accelerates, the number and energy consumption of data centers are increasing year by year. Want to reduce the PUE of the data center. It is correct to start from the perspective of optimizing the energy consumption of air conditioning system operation. In this paper, a predictive optimization control method that is different from previous real-time optimization control is proposed. Predict, optimize, control and adjust the operating parameters of the air conditioning water system in the data center. At the same time, it solves the energy saving problem of the air conditioning system and the lag problem of previous adjustments. Predictive optimization control has broad prospects in research on operation optimization of data center air conditioning water systems. • Reducing air conditioning water system energy consumption in data centers can lower PUE. • Predictive optimization can solve the lag problem of water systems. • After global prediction optimization, energy consumption was saved by 12.9%. [ABSTRACT FROM AUTHOR]

• The vertical temperature gradient were analyzed in offices. • An evaluation index for air-conditioning energy consumption was proposed. • The energy-efficiency advice on air-conditioning for offices is given. Installing curtains on windows prevents direct sunlight from entering the indoor working space. It also alters the direction of solar heat radiation and the spatial distribution characteristics of indoor heat gain. This paper analyzes the relationship between the change of heat gain in the working and non-working spaces of the room under the effect of curtains. Meanwhile, it proposes an index of The Useless Cooling Capacity Ratio (UCCR) of the room to analyze its useless cooling capacity. In the hot summer and cold winter region, this study employs experimental and simulation methods to investigate the influence of solar radiation intensity, curtain thermal characteristics, and other factors on the vertical temperature gradient and heat flux indoor during the summer. The results showed that installing curtains on the windows reduced the vertical temperature gradient of the working space and improved the thermal comfort. The vertical temperature gradients in the working and non-working zones under the experimental conditions were 0.24 °C/m and 0.66 °C/m for the room with curtains and 0.62 °C/m and 0.57 °C/m for the room without curtains, respectively. Curtains can regulate the spatial distribution of heat loads and UCCR in a room and make the room more energy efficient. The UCCR for rooms with and without curtains were 24 % and 18 %, respectively, with curtains adding 120 kJ of useless cooling capacity to the work area. [ABSTRACT FROM AUTHOR]

Air-cooled chillers are extensively employed to meet cooling demand in commercial and tertiary sectors. To enhance their performance during part-load operation, variable-speed drives have been integrated into compressors and condenser fans. In existing systems, condenser fans are either operated at a fixed speed or modulated to maintain a predetermined condensing pressure or temperature difference between the refrigerant and outdoor air. In the search for increased efficiency, it is worth investigating innovative control strategies aimed at minimizing energy consumption. A preliminary mapping of chiller performance at different fan speeds, loads, and operating conditions is required to achieve this goal. In this respect, this paper investigates the operation of air-cooled chillers equipped with variable-speed condenser fans, both in the case of constant- and variable-speed compressors. An ad hoc matrix test is adopted to cover appropriate ranges conditions, in terms of load and outdoor air temperatures. Performance maps are developed for a 50-kW c chiller using a 1-D simulator. As the main findings, it may be stated that (i) in the case of the variable-speed chiller, the energy efficiency ratio increases almost linearly with fan speed, resulting in an 8.8% increase when increasing the speed from the nominal to the maximum; (ii) in the case of constant-speed chillers, the system exhibits a different behavior with the cooling capacity and the energy efficiency ratio increasing with the fan speed between 380 and 980 rpm and then decreasing (slightly or sharply, at full and part load respectively) with fan speed between 980 and 1280 rpm, and a percentage increase of EER in the range 7.8–45% is observed. Also, the sensitivity of such results to the system design is investigated, analyzing a chiller equipped with a larger condenser that resulted in achieving minimum energy consumption at an optimal 980 rpm fan speed. Finally, for a constant-speed chiller serving an office building in the Mediterranean, the proposed fan control strategy could yield an electricity saving of up to 12.1% compared to the base case, confirming the potential for energy savings through optimized and system-tailored management of condenser fan speed. • The effect of variable-speed fans on the performance of air-cooled chillers is investigated. • Maps are developed for chillers with both variable-speed and constant-speed compressors. • Fan speed significantly influences the cooling capacity of constant-speed chillers. • In variable-speed chillers, it is advisable to always run the condenser fan at high speed. • The enhanced fan strategy enables 12.1% energy savings for a chiller in an office building. [ABSTRACT FROM AUTHOR]

In this paper, a 1 kW-class Solar-Ocean Thermal Energy Conversion integrated Air-Conditioning (S-OTEC/AC) experimental system, which can provide both electrical energy and cooling energy without any pollution, is constructed for the first time. Based on the experimental data, the system's overall performance was comprehensively evaluated in terms of energy, exergy, economy, and environment (4 E). Furthermore, the performance difference between the system using solar energy (i.e., S-OTEC/AC) and the system without solar energy (i.e., OTEC/AC) was compared. The experimental results revealed that the maximum thermal efficiency of the S-OTEC/AC system could reach 2.10%, which was 1.91 times higher than the OTEC/AC system. For the OTEC/AC and S-OTEC/AC systems, the maximum cold energy utilization efficiency was 4.12% and 10.09%, and the maximum isentropic efficiency was 18.81% and 76.84%, respectively. The minimum payback period for the S-OTEC/AC system was 13.90 years, which was much lower than the 18.40 years of the OTEC/AC system. Additionally, the maximum primary energy saving achieved by the OTEC/AC system was 0.53 kW, while the S-OTEC/AC system reached a higher value of 1.56 kW. From the results, the superiority of the S-OTEC/AC system over the OTEC/AC system was confirmed. This work not only provides data references for the actual operating characteristics of the S-OTEC integrated system, but also provides a new technical way for comprehensive utilization of ocean temperature difference energy. • 1 kW class S-OTEC/AC experimental system was built for the first time. • The first 4 E analysis was used to characterize S-OTEC/AC with experimental data. • The S-OTEC/AC system has a thermal efficiency of up to 2.10%. • The S-OTEC/AC system achieves a cooling energy utilization of 10.09%. • The S-OTEC/AC system is superior to the OTEC/AC system in all aspects. [ABSTRACT FROM AUTHOR]

• This paper presents an experiment on solar-powered air conditioning. • The study compares two scenarios: on-grid and off-grid, offering insights into their respective performances. • Evaluation metrics include solar fraction, energy consumption, and operational time fraction. • The solar-powered air conditioning system exhibits superior performance under higher demand and elevated temperatures. • The economic viability of the system is attractive, enhancing its appeal and potential for widespread adoption. Air conditioning is vital in maintaining indoor comfort and improving air quality, particularly in regions with high temperatures and humidity. However, the increasing demand for air conditioning has significant implications for energy consumption and the environment. Solar air conditioning can play a vital role in mitigating such impacts. This study presents an experimental setup that utilizes a solar photovoltaic system to power an air conditioning unit. The system is installed in a 36 m2-research lab at The University of Jordan, equipped with PV panels with a capacity of 2.67 kWp, a battery pack, a charge controller, an inverter charger, and an air conditioning unit. Two testing scenarios are conducted: an on-grid system connected to the electrical grid and an off-grid system operating independently. A clear sky day and a partially cloudy day were selected for each scenario in testing. The results were evaluated based on the solar fraction, energy consumption, and operational time fraction (OTF). The solar fraction was found to be higher during periods of higher demand and ambient temperature, and the average OTF was 70 % for all trials. In off-grid trials, the system had maintained operation solely on PV power during the studied load profile in the clear sky day. In contrast, limitations in charging power caused system shutdown in the partially cloudy trial. An economic analysis for the local payback period (PBP) was conducted based on the Hourly Analysis Program and PVsyst software simulation, which shows an attractive simple local PBP for on-grid and off-grid systems of 6.91 and 6.4 years, respectively. [ABSTRACT FROM AUTHOR]

Natural cooling energy and high-efficient radiant cooling techniques are essential to mitigate energy resources shortage crisis, breakthrough on traditional convective air-conditioning systems in isolation between indoor and outdoor environment with high indoor air quality. In this paper, a polyethylene aerogel (PEA) and phase change material (PCM) integrated novel Trombe wall was proposed, involving natural cooling energy harvesting, cooling energy storage, indoor ventilation and radiant cooling. A two-dimensional unsteady numerical model based on surface-to surface (S2S) radiation model and effective specific heat capacity method was developed in the commercial software Ansys Fluent to evaluate the cooling performance and dynamic heat-transfer mechanism of the novel Trombe wall. Subsequently, climate-responsive operation strategies on ventilation modes were proposed to maximize natural cooling energy utilization and fresh air supply. Parametrical and comparative studies were conducted on optimal structural design and robust operation. Our results showed that, with the novel design and advanced operation strategies, passive cooling capacity of 0.64 kWh/m2·day can be provided, together with fresh air supply of 2705.2 kg/day (1.4 m2 Trombe wall), corresponding to air change rate per hour (ACH) of 1.15. In terms of active cooling system, the integration of PEA and PCM can effectively prevent moisture condensation and shift peak cooling load. Hence, radiant cooling capacity of 0.99 kWh/m2·day and radiant cooling ratio of 47 % can be achieved by the novel Trombe wall, with electricity consumption only at valley period. Moreover, economic saving of 55.0 CNY/day and decarbonization potential of 23.8 kg CO 2,e /day can be achieved when the novel Trombe wall is integrated into a typical office building in subtropical climate Guangzhou. This study provides a novel structural design and optimal operation strategies on a Trombe wall, together with guidelines on techno-economic-environmental performance improvement, promoting effective natural cooling energy utilization and energy-flexible/efficient radiant cooling for decarbonization of buildings in cooling-dominant regions. • A novel Trombe wall for natural cooling energy harvesting and radiant cooling. • An unsteady numerical model for thermodynamic analysis. • Passive cooling capacity of 0.64 kWh/m2.day and fresh air supply of 2705.2 kg/day. • Radiant cooling capacity of 0.99 kWh/m2·day and radiant cooling ratio of 47 %. • Daily CO 2 reduction of 23.8 kg and economic saving of 55.0 CNY in a typical office building. [ABSTRACT FROM AUTHOR]

[Display omitted] • The LCA methods and findings of 41 papers on air-conditioning systems are examined. • Retrieved studies presented discrepancies in the LCA goals and scope definition. • The global warming potential (GWP) was the most evaluated indicator across papers. • Grid-connected electrical heat pumps generally had a higher life cycle GWP. • Improvements related to AC energy sources and other life cycle aspects are proposed. Air conditioning (AC) has become the fastest-growing energy end-use in buildings worldwide, and its adoption is expected to increase further due to various socioeconomic factors and climate change. Despite this, the decarbonization of space cooling is progressing slowly; hence, the emissions burden at each stage should be examined in detail. Given this context, it is crucial to assess the environmental performance of AC systems by considering a comprehensive approach like the Life Cycle Assessment (LCA). While several studies have already targeted the LCA of AC systems, a clear overview of those studies' methodologies, assumptions, and results is still lacking. Therefore, this systematic review examined the methods and key findings of 41 peer-reviewed articles. Although the results revealed discrepancies among the goals and scope, impact assessment methods, and indicators, most articles predominantly focused on the global warming potential (GWP) impact, and its reported quantification was further analyzed. It was observed that grid-connected vapor-compression heat pumps/chillers (conventional systems) presented higher GWP impacts than other AC systems powered by renewables, which in contrast, exhibited higher impacts in some toxicity and resource depletion-related indicators. However, the share of GWP showed different distributions, as the pre-operation emissions of solar-powered AC systems (either PV or thermal) were higher than those of conventional systems, mainly driven by reduced energy consumption usage. This review concludes with some recommendations for each stage of the life cycle. Since the operation phase generally showed the highest impact, more efforts should be devoted to accelerating the transition to a 100% clean electricity power system at a national scale. In contrast, the need to power AC systems with on-site renewables should be carefully assessed based on the context. [ABSTRACT FROM AUTHOR]

• A two-layer framework is proposed for building HVAC and associated multi-energy consumption optimization. • 100% renewable complementarities are proposed for building multi-energy supplies. • A R-C thermodynamic network is formulated to model the building HVAC. • AC slow charging and DC fast charging types of EVs are considered and managed via a novel real-time supply–demand pricing. Building heating, ventilation, and air conditioning (HVAC) and associated energy consumption make up the more and more important part of the world, whose reduction provides a cost-effective path to the "dual carbon" goal. This paper proposes a two-layer management of HVAC-based multi-energy buildings under proactive demand response of fast/slow-charging electric vehicles (EVs). In this paper, the building HVAC is mathematically formulated via a R-C thermodynamic model, which coordinates with multi-energy converters and storages to form a 100% renewable building. The building management is a challenging optimization problem due to its severe constraints and strong spatio-temporal couplings. In the first layer, a day-ahead multi-energy dispatch is formulated to economically optimize the electrical, heat, gas energy carriers. In the second layer, alternating current (AC) slow charging and direct current (DC) fast charging types of EVs are considered and managed via a novel real-time supply–demand pricing mechanism. After acquiring the economical dispatch references in the first layer, the second layer implements a model predictive control (MPC)-based real-time scheduling to handle the multi-energy supply–demand fluctuations. The original two-layer optimization is further handled via mixed-integer linear program (MILP) reformulation for high-efficient solving. Comparisons have shown the advantageous performances of the proposed two-layer optimization over economics and practicability. Simulations results show that the overall system operating cost can be reduced by at most 3.01% with a higher operational flexibility in building management. [ABSTRACT FROM AUTHOR]

Highlights • EnergyPlus is capable of accurately estimating the heat transfer in parked vehicles. • Spectrally selective glazing can cause an average temperature difference inside the cabin as high as 12.5 °C. • Solar-reflective opaque coating in combination with ChLC glazing can reduce the cabin air temperature up to 23.8 °C. Abstract Parked vehicles have the tendency to overheat quickly. This can lead to a negative impact on the thermal comfort of the driver and its passengers, as well as intensive use of air conditioning systems, and thus fuel consumption of the vehicle or, in the case of electric mobility, a reduced cruising range. In the search for effective measures to mitigate this effect, important guidance can be provided by the field of sustainable building design. On the one hand, inspiration can come from design strategies in terms of shapes and advanced cover materials, but this paper advocates that this can also pertain to the simulation-based design support tools that are used by building engineers. This paper first presents the results of a thermal soak test, and then uses this data to demonstrate the suitability of the building performance simulation tool EnergyPlus for predicting the thermal behavior of parked vehicles. This fit-for-purpose validated model is used to evaluate the performance of three overheating mitigation measures for two car models in two climates. The results show that spectrally selective glazing can reduce the cabin air temperature by 12.5 °C and when combined with solar reflective opaque surfaces, the reduction of cabin air temperature can reach 23.8 °C. Increased use of building performance simulation in the automotive domain can help to further optimize the overheating reduction potential of cars. [ABSTRACT FROM AUTHOR]

Highlights • One-stop archive for developments in solid desiccant coated heat exchangers (DCHEs). • Comprehensive study on the selection of desiccants and binders. • Thorough analysis on the effect of operating parameters on dynamic performance. • Detailed review of advances in mathematical modeling of DCHEs. • Discussion on the potential system-level applications of DCHEs. Abstract Rapid urbanization and higher thermal comfort requirements have sharply increased buildings' energy demands. In tropical countries, for achieving energy efficient air-conditioning, desiccant dehumidifiers, which decouple sensible and latent load, are essential. While fixed-bed and rotary wheel desiccant dehumidifiers suffer from reduced adsorption capacity and lowered heat transfer efficiencies, desiccant coated heat exchanger (DCHE) system is a promising technology that can improve the energy efficiency of the standard vapor-compression air conditioners. Moreover, DCHEs also have prospective benefits in heat pump, adsorption chiller, and atmospheric water harvesting applications. In this paper, the advantages of DCHEs over other dehumidifiers are established, and a comprehensive review of various desiccant materials and binders used in DCHEs is carried out. The possibilities of using advanced materials to achieve superior energy efficiencies are also underlined. Different methods of coating the desiccant on heat exchangers are described, and quantitative parameters required to analyze the performance of the system are presented. Operating parameters affecting the dehumidification and thermal performance are identified, and the effect of their variation on the dynamic behavior of DCHEs is elaborately studied. The significance of using mathematical models as design tools is recognized, and the underlying assumptions, applicability, and limitations of the models for simulating the complex heat and mass transfer phenomenon are highlighted. The possibility of integrating an additional heat transfer equipment such as sensible heat exchangers, heat recovery devices, solar evacuated tube collectors, cooling towers, and evaporative coolers with DCHE is also presented. Finally, the potential system-level applications of DCHEs as heat pumps, adsorption chillers, water harvesters, and standalone air-conditioners are assessed. This review paper provides an update on recent developments in desiccant dehumidification and is intended to be a "one-stop" archive of known practical solutions that DCHEs can offer. [ABSTRACT FROM AUTHOR]

Traditional air conditioning may be inappropriate for electric vehicles due to its moving parts noise besides using chlorofluorocarbons that harm the environment. In addition, it consumes a significant portion of the stored energy in batteries, reducing the vehicle's driving range. So, in this paper, a novel design of thermo-electric cooling (TEC) system coupled with a photovoltaic (PV) panel replacing the vehicle roof is studied. This system consists of a sandwich of PV panel outside the vehicle and TEC inside with a heat sink system integrated between them. The air temperature variation in the cabin during the daytime is predicted by solving a complete mathematical transient thermal model of the whole system before and after mounting the cooling system. The air streams through the vehicle moving are exploited to improve the TEC and PV system performance. The system performance is investigated for different cases during the day with and without including the PV output power and for the vehicle parks inside or outside. The results indicate that, for each scenario, the number of used TEC modules influences the system performance where the best number varies between 128 and 98. Coupling the PV panel with the TEC system reduces the daily required energy from batteries by about 19%. Running the TEC system during parking from 8 to 10 am decreases the cabin air temperature from 47.5 to 34°C while the input power declines by about 45%, which reduces the interior temperature to 25°C in 10 min (transition time). The contribution of the PV panel based on the studied conditions can increase the range of the vehicle by 10.4 km/day and about 160kWh/year energy saving. The reduction in the input power during transition time reaches 27.8% when the vehicle speed increases from 30 to 60 km/h, while this ratio declines to 10.8% as the vehicle speed rises from 60 to 90 km/h. During vehicle moving, powering the TEC system by the PV panel only can prevent the cabin temperature from rising over 40°C, whereas during parking, there is an optimum fan air velocity that gives the maximum reduction of the cabin temperature. • A novel design of a thermo-electric air conditioning system for electric vehicles is studied. • Contribution of the PV panel reaches 19% of the daily energy consumption in some scenarios. • PV panel increases the range of the vehicle by 10.4 km and can save 160kWh/year. • The best number of TEC modules is about 128 for scenarios 1 and 2 and 98 for the others • Power the TEC by PV power in parking reduces the vehicle temperature less than ambient. [ABSTRACT FROM AUTHOR]

This paper describes a method for residential water use modeling predicated on metered energy data. Actual measured hot water volumes for major indoor consumption are used to verify and adjust the outputs in gallons of hot water consumption based on climate variables, water heater technical features, and set-point and intake temperatures. Three independent datasets for residential energy (RECS 2009), water heater efficiency (Air-conditioning, Heating and Refrigeration Institute-AHRI), and end-use domestic water (Residential End Uses of Water, Version 2-REU II) are applied to identify specific demographic, built environment and geographic factors that relate patterns of energy demand to water consumption. The proposed model acts within the broader Integrated Urban Metabolism Analysis Tool (IUMAT), a system-based analytical framework for evaluating the environmental performance of the built environment. The method described in this paper offers an alternative approach to residential water consumption modeling by implementing volume of hot water consumption as a proxy for indoor water use. It provides utilities with the potential to parse and prioritize energy and water conservation measures. [ABSTRACT FROM AUTHOR]

• A comprehensive parametric study of roller shades and cellular shades. • Identify key parameters affecting window attachment's energy performance through simulation results. • Sensitivity analysis of different parameters. • A new index for a unified assessment of different window attachments. This paper investigated the energy performance of window attachments and analyzed the impact of window attachments' parameters on air conditioning energy consumption of residential buildings in a cooling-dominated city (Houston) and a heating-dominated city (Minneapolis). Roller and cellular shades were selected as research objects in this study. Nine parameters related to window attachment energy performance were chosen as the probable important influence factors for the parametric study. Three values, high, medium and low levels, were set for each parameter, resulting in a total of 9520 (roller) and 9072 (cellular) combinations respectively. The optical and thermal properties of each combination were calculated with Berkeley Lab WINDOW program before coupling with an EnergyPlus typical residential building model. Based on simulation results, an annual energy performance (AEP) index was proposed to rate the energy saving potential of window attachments. Key parameters which have significant impacts on air conditioning energy consumption were determined through the parameter sensitivity analysis. The research results indicated that solar transmittance and solar reflectance are the most influential factors to the energy performance of window attachments among the nine selected parameters. The current cellular shade could achieve the AEP h and AEP c of 0.19 and 0.12. Among all combinations, the best AEP h and AEP c of cellular shades are 0.68 and 0.89, respectively. Besides, as for roller shades, the current level of AEP h and AEP c are 0.14 and 0.09, and the optimal AEP h and AEP c are 0.43 and 0.79. [ABSTRACT FROM AUTHOR]

In this paper, PSO-OMRC model is proposed for heating ventilation and air conditioning (HVAC) system. The PSO-OMRC predicts SPT in HVAC for energy saving and thermal comfort of persons in room. PSO-OMRC used data collected from temperature, humidity, PIR, and thermal camera sensors in HVAC installed rooms for SPT prediction. In existing HVAC systems, SPT is constant and consumes more energy. Moreover, SPT prediction using traditional machine learning algorithms considers various parameters such as room temperature, humidity and person count in room. Existing algorithms considers the above parameters for energy saving in HVAC and thermal comfort for persons, whereas other parameters such as room walls and ceiling temperature, human body temperature need to be considered for SPT prediction and for energy saving in HVAC. The PSO-OMRC model predicts the SPT based on number of occupants and microclimatic conditions such as environment temperature, humidity, room wall temperature and ceiling temperature. From experimental results, the utilization of the thermal image occupant model provides significant energy savings in the PSO-OMRC model. In nano coated room, PSO-OMRC model is evaluated with the implementation of a thermal image occupant model to improve energy savings, resulting in approximately 25.2% of energy savings while maintaining the level of thermal comfort. • Microclimatic and occupant data-based setpoint temperature prediction in HVAC. • Gaussian Process Regression algorithm is used to predict setpoint temperature. • The proposed PSO-OMRC model provides thermal comfort for occupants. • Nano coated room has considerable energy savings with PSO-OMRC model in HVAC. [ABSTRACT FROM AUTHOR]

• Propose a novel machine learning-based model predictive control (MLB-MPC) framework with predictive inputs of cooling load and outdoor wet-bulb temperature. • Obtain the optimal match of prediction models and optimization algorithms for improving the performance of the MLB-MPC. • Investigate the impact of disturbances on the performance of global optimization. • Achieve an energy-saving ratio of 7.1% for the air-conditioning system when compared with the measured operation data. The dynamic optimization of key setpoints (e.g., supply water temperatures of chillers and cooling towers, or indoor temperature and humidity) can track the efficient performance point of the air-conditioning system (ACS), thus obtaining a great energy-saving effect. The model predictive control is an effective way to precisely adjust these setpoints. However, most of the existing studies focused on simple linear strategies, e.g., experience-based, rule-based, or component-based, which results in unsatisfactory energy efficiency. Aiming at this, the paper proposed a novel machine learning-based model predictive control (MLB-MPC) framework with predictive inputs of disturbances. The framework first employed the grid search and cross-validation to optimize the total energy consumption prediction models (TECPMs), which were built by data-driven models (e.g., multiple linear regression, artificial neural network, support vector regression (SVR), and random forest). And then the optimization performances of each TECPM to the controlled variables were obtained by using different optimization algorithms (e.g., genetic algorithm, particle swarm optimization (PSO), and simulated annealing). Finally, the optimal match of TECPMs and optimization algorithms was achieved by trade-off among prediction accuracies, optimization accuracies, and optimization time. The case studies demonstrated that the optimal match for the MLB-MPC is SVR and PSO as they had the highest prediction accuracy (mean absolute percentage error of 2.5%) and shortest optimization time (41 ms/per) and optimization accuracies with little difference. After adopting the optimal match, the MLB-MPC with predictive disturbing inputs achieved a great energy-saving ratio of 7.1% for the ACS, which was only less than the MLB-MPC with ideal disturbing inputs by 0.4%. This indicated that exact predictions of disturbances (e.g., cooling load and outdoor wet-bulb temperature) are important for the MLB-MPC. The proposed MLB-MPC framework would provide a method for improving the energy efficiency of ACSs. [ABSTRACT FROM AUTHOR]

This paper presents new metrics to measure the effect of thermal mass on the energy required to heat and cool buildings. Previous studies have been flawed as they have not considered the interaction between intermittent occupancy and thermal mass, which has a significant impact on overall energy use. However, existing parameters do not adequately capture these effects, so the new metrics developed in this paper are used to analyse the impact of thermal mass in hot climates with active cooling, and cold climates with active heating. The results agree with existing literature that high thermal mass structures are likely to be effective in hot climates; however, in cold climates the drawbacks of high thermal mass likely outweigh the advantages, and high thermal mass can cause an increase in energy use. This finding has implications for the design of buildings in cold climates, and contradicts the commonly-held assumption that high thermal mass is correlated with low energy use. The new metrics (transient energy ratio and effective U -value) provide a generalisable method to quantify these effects. They are further used here to analyse the dynamic performance of heavily insulated buildings and show that high thermal mass often leads to higher energy use in cold climates. [ABSTRACT FROM AUTHOR]

There has been an increasing concern on thermal comfort in sleeping environments and its associated energy use in the past few years. To improve the thermal environment and to reduce energy use of air conditioning in bedrooms, applications of task/ambient air conditioning (TAC) systems were proposed and studied previously. It’s indicated that the TAC system can be well integrated with a bed. Due to the variation of the envelope heat gain in a bedroom during night, it is necessary to study the thermal environment inside a bedroom and the energy use of a TAC system for the bedroom at varying envelope thermal loads. Therefore, this paper reports on a numerical study on a TAC system applied to a bedroom with different envelope heat gains. The influences of envelope heat gain on energy consumption of the TAC system and the indoor thermal comfort were studied in this paper. The research results show that at supply air flow rate ( Q s ) of 50 l/s, energy consumption was increased from 47.78 W to 213.11 W, and the PMV value was increased from −1.69 to −1.29 with the increase in envelope heat gain from 3.11 W to 155.6 W. To make PMV equal to zero under different envelope heat gains, linear regression models between supply air parameters and PMV were built and solved. The obtained values form curves where PMV = 0 and give a guide for operation of the TAC system. It was found that the calculation of energy consumption on these curves depends only on envelope heat gain. [ABSTRACT FROM AUTHOR]

This paper presents an energy-saving controller for automotive air-conditioning/refrigeration (A/C-R) systems. With their extensive application in homes, industry, and vehicles, A/C-R systems are consuming considerable amounts of energy. The proposed controller consists of two different time-scale layers. The outer or the slow time-scale layer called a set-point optimizer is used to find the set points related to energy efficiency by using the steady state model; whereas, the inner or the fast time-scale layer is used to track the obtained set points. In the inner loop, thanks to its robustness, a sliding mode controller (SMC) is utilized to track the set point of the cargo temperature. The currently used on/off controller is presented and employed as a basis for comparison to the proposed controller. More importantly, the real experimental results under several disturbed scenarios are analysed to demonstrate how the proposed controller can improve performance while reducing the energy consumption by 9% comparing with the on/off controller. The controller is suitable for any type of A/C-R system even though it is applied to an automotive A/C-R system in this paper. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel approach to control CO 2 and H 2 O composition in an enclosed environment. • A cyclic CO 2 adsorption process and dehumidication units are considered. • The mathematical model shows superior performance of the proposed system. • Carbon footprint of the system is discussed with scale-up study. • Influence of parametric uncertainties in the model is discussed. Rapid growth in global energy consumption has raised concern on the environmental impacts such as ozone layer depletion and climate change. Enclosed space, such as commercial buildings, accounts for about 40% of global energy consumption and the demand is constantly increasing due to increasing population, urbanization, and economic development. The energy demands in the building sector calls for strategic measures to develop energy efficient technologies. This paper presents a strategy to decrease energy demands inside buildings by proposing a ventilation system which regulates the enclosed air quality resulting in reduced air conditioning. The system consists of multiple adsorption beds with zeolite 13X monoliths for CO 2 removal, and silica gel for humidity control, inside the enclosed space. The air conditioning system results in decrease in energy requirement and improvement in economics by 55% as compared with conventional ventilation system. The model is scaled up to the size comparable with total office inventory of New York City, and the reduction in carbon emissions by introducing the air composition control system for New York City is equivalent to replacing 57 million incandescent light bulbs by LEDs. This paper concludes that the air conditioning system proposed in this study results in the improvement in performance as compared to a conventional ventilation system and could reduce energy consumption inside commercial buildings. [ABSTRACT FROM AUTHOR]

The American Society for Heating, Refrigeration, and Air Conditioning Engineers (ASHARE) prescribes fixed ventilation rates for the operation of heating, ventilation, and air conditioning (HVAC) systems, which is sub-optimal in terms of controlling indoor air pollutants and energy consumption. This paper relies on a physics-based model of a residential house to predict the concentrations of indoor pollutants such as ozone, formaldehyde (HCHO), and particulate matter (PM) as function of time, outdoor conditions, and indoor emissions. The model captures real-world scenarios such as pollutants entering the house from ambient air through an air handling unit (AHU) and pollutants emitted in the house. A dynamic optimization problem is then formulated and solved to calculate the optimal ventilation rate at each time instant, that minimizes the total energy consumption, while maintaining the indoor pollutant concentrations below or as close as possible to their respective acceptable thresholds. For the considered example day, operation under optimized conditions reduces the peak pollutant concentration by 31%, time of exposure to undesirable concentrations by 48%, and energy consumption of the AHU by 17.7%. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A consolidated advanced adsorbent is studied. • N-butane has the highest relative potential exergy for power generation. • This novel system is multi-function in providing air conditioning/refrigeration/heat pump heat-power generation. • The total exergy efficiency can be improved from 0.15 to 0.31. Abstract The shortage of fossil fuel, greenhouse gases emission, air pollution and global warming have attracted more and more researchers' attention on the adsorption technology, which utilizes low temperature thermal heat of solar thermal energy and waste heat. Moreover, the usage of natural materials as refrigerant such as water and methanol adds to its advantage. However, the low coefficient of performance and specific cooling power limits its further application. This paper proposes a novel combined adsorption system, which can provide the functions of air conditioning/refrigeration/heat pump heating and ammonia/organic expanding power generation. In addition, the consolidated advanced adsorbent is used in this system, the effect of which is investigated. The author also analyzed the most suitable organic for organic Rankine cycle in this system. The results reveal that the organic of N-Butane has the highest potential exergy and the most appropriate work pressure. The cooling exergy efficiency in the working modes of air conditioning, refrigeration and heat pump heating are about 0.18, 0.13 and 0.24, respectively. The simulation results indicate that, compared to the system with only cooling effect, the total exergy efficiency of the combined system can be improved from 0.15 to 0.31, because of the additional expanding power generation effect. [ABSTRACT FROM AUTHOR]

Abstract Liquefied natural gas (LNG) is widely used in many countries around the world primarily as a mode of transport for natural gas. However, massive amount of energy (around 830 kJ/kg of LNG) is wasted during the regasification process in the LNG regasification terminals. Therefore, the technologies to utilize the LNG cold energy have received significant attention over recent decades. In this paper, we review various studies on the current LNG cold energy utilization systems, including power generation, air separation, desalination, cryogenic carbon dioxide capture, and NGL recovery. Utilizing LNG cold energy on such systems can improve the energetic and exergetic efficiencies significantly. Furthermore, several potential applications to utilize LNG cold energy in the future are proposed and discussed to broaden the perspectives of the researchers in the community. Among these potential applications, recovering LNG cold energy on cold chain for food transportation, data center cooling and hydrate based desalination are very promising. Finally, the limitations and challenges to be addressed for LNG cold energy utilization are discussed in detail. Graphical abstract Image 10764500 Highlights • Abundant amount of cold energy can be recovered during LNG regasification. • A comprehensive review on the state-of-the-art LNG cold energy utilization systems is provided. • LNG cold energy can be utilized for power generation, air separation, air conditioning and desalination. • Technologies to utilize LNG cold energy are analyzed and compared. [ABSTRACT FROM AUTHOR]

Highlights • HVAC system, the objective function, limit conditions in the matrix or vector form. • A universal set of constant parameters, decision variables and limiting conditions. • System analysis and matrix calculation in the optimization of the HVAC system. • A global form of the objective function that captures all HVAC subsystems. Abstract The new complex selection strategy of low energy ventilating or air conditioning system (HVAC system) from a holistic perspective is presented in the paper. The strategy carries out the solution of the whole optimization problem that consists of the HVAC system model, optimization model and optimization procedure. The practical function is the starting point of the optimization problem, whereas the energy optimal variant of the HVAC system is the final stage. Universal sets of constant parameters, decision variables and limiting conditions of the HVAC system were formulated for the mathematical description of the problem. In optimization procedure, the sets of all variants and permissible variants of the HVAC system were defined based on the system analysis with the use of matrix calculation. The objective function was determined by the use of the simulation model of the HVAC system where the algorithms of energy optimal control is determined by dynamic optimization. [ABSTRACT FROM AUTHOR]

Abstract This paper presents a mathematical model to enable a more in-depth understanding of the combined heat and mass transfer processes of a counter-flow indirect evaporative cooler operating in semi-arid regions. A series of simulation was conducted to compare the performances between a single-purge and four-purge configurations. Furthermore, the effect of several parameters on the performance of the single-purge configuration was investigated under the baseline condition. The developed model was validated against experimental data from literature to within 2% discrepancy. Key results revealed that the single-purge configuration produced higher cooling capacity (around 20% higher), as well as higher dew-point effectiveness under the same operating conditions. A parametric study was also made on the single-purge configuration. The results revealed that lower product air temperature and higher dew-point effectiveness were achieved with longer channel length and larger purge ratio. However, the maximum cooling capacity approached its maximum with longer channel length and 35% purge ratio. [ABSTRACT FROM AUTHOR]

Abstract In tropical climates, the energy consumed by ventilation and air conditioning can exceed 50% of the total consumption of a building. Demand for cooling is rising steadily, driven mainly by growing incomes in developing economies, and is expected to also increase with climate change. Tropical, coastal areas with narrow continental shelves are good sites for the implementation of Seawater Air Conditioning (SWAC), a renewable and low CO 2 emission cooling process. This paper presents the existing SWAC projects around the world and gives details on the technology. Data on ocean temperature profiles, ocean bathymetry and world surface temperature are processed with the intent of estimating the world potential of SWAC. The results present the required distance from coast to reach seawater with a temperature of 5 °C or less. This is combined with the potential demand for air conditioning, taking into account surface air temperature and a set SWAC design for cooling from 30 to 20 °C. The pipeline length, seawater depth and capacity factor are then used to estimate the costs of SWAC projects around the world. It is concluded that the locations with the highest potential for SWAC are intertropical islands and some continental locations. Highlights • This renewable source is ideal for tropical coastal areas with narrow continental shelves. • The energy in a m3/s of SWAC can be equivalent to 49 ha of solar PV or 42 MW of wind turbines. • A novel SWAC potential model is developed to identify the most promising sites worldwide. • Capacity factor, pipeline length, depth extraction and cost estimates are presented in detail. • The cheapest SWAC project costs $0.0185/KWh t and is located in Nauru, Pacific Ocean. [ABSTRACT FROM AUTHOR]

Highlights • A novel hybrid desiccant cooling system with a condenser is studied. • Thermal balancing technique is applied for zero and single extraction systems. • A mathematical model of the proposed system using enthalpy pinch method is explained. • The coefficient of performance is improved by 85% using the single extraction. • The investigated hybrid system also produces fresh water as a by-product. Abstract This paper focuses on thermodynamic balancing of the regeneration process in a hybrid liquid desiccant cooling/desalination system. The thermal balancing technique is investigated by adding a single extraction between the system regenerator and condenser. This technique is considered as a potential method to reduce energy consumption and increase the hybrid system performance, dramatically. The mathematical procedure to model the proposed system using enthalpy pinch is outlined to study the effect of extraction on the hybrid system performance. The hybrid system, with a single extraction and without extraction (zero extraction), is analyzed in terms of the normalized entropy generation, local enthalpy losses, the coefficient of performance, and proper extraction location. The results show that at enthalpy pinch of 20 kJ per kg of dry air, single extraction system performance is 85.7% better than zero extraction. In addition, the single extraction produces 103.2 kg of fresh water per hour as a by-product compared to 94.2 kg per hour for the zero extraction system. [ABSTRACT FROM AUTHOR]

This paper proposes the design, construction, and test of a prototype R141b ejector refrigeration system. It was used as an air conditioner for a hot climate country (Thailand). The prototype machine was designed to work as a water chiller to provide thermal comfort condition for the tested room with the cooling capacity up to 4500 W. It was driven by hot water with temperatures of 90–98 °C. The condenser was cooled by water, which was provided by a cooling tower, with temperatures of 28–32 °C. CFD simulation was also employed to design the ejector. The tested results indicated that the prototype R141b ejector refrigerator working as an air conditioner was satisfactory in operating conditions consistent with a hot climate (Thailand's environment). The temperature of the air conditioned space was around 23 to 25 °C with the cooling load of 4500 W. The coefficient of performance (COP) was between 0.42 and 0.47. [ABSTRACT FROM AUTHOR]

The paper presents numerical analysis of heat recovery exchanger, which operates as an indirect evaporative air cooler in summer conditions and as a typical heat recovery unit during winter season. The numerical simulation is performed with the original mathematical model which is able to simulate the operation during summer and winter season. The model was validated against existing experimental data (operation as indirect evaporative air cooler) and against experimental data collected by authors at Wroclaw University of Technology (operation as heat recovery exchanger). Obtained results allowed for analysis of heat and mass transfer process occurring in considered exchanger during round-year operation. The characteristic heat and mass transfer zones for evaporative air cooler and heat recovery exchanger were established. Results also allowed for analysis of most important problems connected with achieving highest efficiency of the exchanger and achieving safe operating conditions during winter season (preventing the exchanger from freezing). Safe operating conditions (parameters of the ambient air in winter which would guarantee that no frost would be formed on the plates) were established. The analysis of the effectiveness of the novel exchanger with selected factors (i.e. obtained cooling capacity, thermal efficiency and relative effectiveness) was also presented in the paper. [ABSTRACT FROM AUTHOR]

Under the influence of building load stochasticity and thermal inertia of central air conditioning system, the lag of control strategy makes it difficult for the cooling source system to meet the cooling demand of users in real time, which affects the operational energy efficiency ratio of the cooling source system. In this regard, this paper proposes a chiller dynamic optimization method based on Markov chain model predictive control algorithm, which studies the optimization of parallel operation characteristics of multiple chillers on the basis of correcting the occurrence of small probability events and avoiding frequent chiller starts and stops, reveals the prediction law of hourly load distribution of the future air conditioning system, explores the balance point between the prediction time of building load and the calculation time of chiller control strategy, provides a theoretical basis and reference for determining the time limit of the optimal calculation and the output of the optimal control strategy. The study provides a theoretical basis and reference for determining the time limit of the optimal calculation and the output of the optimal control strategy. It is found that the optimal control strategy not only has good optimization effect, but also the confidence is significantly increased by 56.7%. • Markov chain predictions of building loads are time-bound. • Consider the impact of the randomness of the load time distribution. • The model takes into account the occurrence of small probability events. [ABSTRACT FROM AUTHOR]

This paper summarises the results of a study to identify and quantify the potential impact of measures and policies to reduce the energy consumption of air conditioning in European countries over a 10-year period. The market penetration of air conditioning in Europe has increased steadily over several decades. On a “business as usual” basis, its energy consumption would increase by over 50% by 2020. Measures to restrict this increase are therefore important, but the savings potential straddles several overlapping areas which are subject to different constraints including those imposed by the replacement rates of systems and products, and the refurbishment rates of existing buildings. This work reported in this paper is based on the use of information from a variety of sources in a highly disaggregated model to assess the “realisable” savings over a 10-year period, taking into account relevant constraints. The paper summarises results at a European level, focussing on those cases that generate the greatest realisable savings. Savings are possible in three areas: improved equipment and system efficiency, reduced cooling loads, and more effective operation. The cases that offer the largest savings provide the basis for recommendations for policy measures, often using existing policy instruments. In addition, areas where further work is needed are identified. More detailed results and information about the study and additional recommendations can be found at http://www.bre.co.uk/searchresults.jsp?category=5&q=energy+management [1] . [ABSTRACT FROM AUTHOR]

Heat pumps for space heating and cooling are a mature and highly efficient technology that can take advantage of renewable energies. They can also provide energy savings by load shifting when they operate together with thermal energy storage (TES). This paper presents a literature review of TES systems using phase change materials (PCM) potentially applicable to domestic heat pumps used in residential and administrative buildings. The paper describes the systems proposed by the different authors and presents the main conclusions of the studies. The TES systems presented are not only used as energy storage to shift the load demand but also for other applications such as heat recovery or defrosting in air-conditioners. The PCM have the suitable melting temperature to work together with standard heat pumps in each application. Moreover, some systems where the heat pump is coupled to latent heat thermal energy storage (LHTES) units and other energy sources or where the TES system is incorporated in a radiant floor or air distribution system have also been included. [ABSTRACT FROM AUTHOR]

In this paper, the waste heat of exhaust gases and jacket cooling water in marine diesel engines are analyzed to operate the absorption refrigeration unit (ARU). Thermo-economic and environmental analysis of the absorption refrigeration cycle operated with the two heat sources that use lithium bromide as an absorbent is carried out. The analysis is performed using Engineering Equation Solver (EES) software package where the thermodynamic properties of the steam and the LiBr-water mixtures are provided. The used EES code is verified by published experimental data. As a case study, high speed passenger vessel operating in the Red Sea area has been investigated. The results show that a considerable specific economic benefit could be achieved from ARU jacket cooling water operated over that gained from main engine exhaust gases. Environmentally, applying ARU machine during cruise will reduce the annual fuel consumption for the diesel generators by 156 ton with a reduction percentage of 23%. This will reduce the exhaust gas emissions by 6.3% from the applied main engine emissions. In addition, this will result in reducing NO x , SO x , and CO 2 emissions with cost-effectiveness of 4.99 $/kg, 13.18 $/kg, and 0.08 $/kg, respectively. [ABSTRACT FROM AUTHOR]

This paper presents an autonomous hierarchical control method for a direct expansion air conditioning system. The control objective is to maintain both thermal comfort and indoor air quality at required levels while reducing energy consumption and cost. This control method consists of two layers. The upper layer is an open loop controller that allows obtaining tradeoff steady states by optimizing the energy cost of the direct expansion air conditioning system and the value of predicted mean vote under the time-of-use price structure of electricity. On the other hand, the lower layer designs a model predictive controller, which is in charge of tracking the tradeoff steady states calculated by the upper layer. Control performance of the proposed control method is compared to a conventional control strategy. The results show that the proposed control strategy reduces the energy consumption and energy cost of the direct expansion air conditioning system by 31.38% and 33.85%, respectively, while maintaining both the thermal comfort and indoor air quality within acceptable ranges, which validate the proposed methodology in terms of both comfort and energy efficiency. [ABSTRACT FROM AUTHOR]

The electric vehicles (EVs) are drawing much attention worldwide due to low fuel consumption and local pollution. However, the range of EVs is still not parallel to that of internal combustion engine vehicles. Moreover, the EV's range suffers a significant decrease in cold and hot climate due to the climate control load of the air conditioning system. These two combined making the range extension strategies a hot spot in EV research. In this paper, the review on EV range extension strategies is provided. First, the climate control load reduction strategies are reviewed. The characters of heating load in cold climate and the reduction methods are introduced. Second, the review on heat pump heating is conducted based on the different structures of heat pump systems. The combination of load reduction and heat pump heating seems to be a promising way in solving the range reduction problems. [ABSTRACT FROM AUTHOR]

Nowadays, the main two issues of heating ventilation and air conditioning (HVAC) are refrigerant alternative and system efficiency improvement. As a safe and environmental protective refrigerant, CO 2 has drawn a lot of attention these years. The improvement on its transcritical cycle efficiency has always been the study hotspot. On the basis of the traditional cycle system, this paper adds the internal heat exchangers (IHE) and pressure control devices into the system and optimizes the CO 2 transcritical system with the dual throttling device. Engineering equation solver is used to build each module in the system as an object-oriented model. The effects of the IHE and bypass valve on system performance are investigated. The performance and configuration of four CO 2 transcritical refrigeration cycles are analyzed and compared. Numerical studies also propose the formula expressing the relationship of the optimum high pressure, the gas-cooler CO 2 outlet temperature and the evaporation temperature under specific operating conditions. In addition, the modified system can significantly improve the performance of the system under the operating conditions below the optimum high pressure. This research has played an effective guiding and facilitating role for CO 2 transcritical refrigeration system development, optimization and improvement. [ABSTRACT FROM AUTHOR]

Under the double pressure of energy shortage and environmental pollution, ice thermal storage air-conditioning and photovoltaic air-conditioning has been applied in refrigeration field. In order to improve application scope and reduce investment operation cost, the ice thermal storage adopted to store solar energy in ice thermal storage air-conditioning driven by distributed photovoltaic energy system was proposed in this paper. Two operation models had been tested by experiment. Research results revealed all of the solar energy accepted by PV array had been stored with ice or cold water. Moreover, the experimental results analysis showed that it is feasible to use ice thermal storage instead of battery bank to store solar energy in the field of distributed photovoltaic refrigeration. In operation mode 1, the average system energy utilization efficiency was 0.525 and the average refrigeration efficiencies η ¯ r and η ¯ r s were 0.7292 and 0.0690, respectively. When system operated in mode 2, the average system energy utilization efficiency was 0.3377 and the refrigerator performances parameters η ¯ r and η ¯ r s were 4.49 and 0.3875, which were 6.16 times and 5.62 times of the average η ¯ r and η ¯ r s under working model 1. [ABSTRACT FROM AUTHOR]

Vapor compression systems in hot climates tend to operate at higher pressure ratios, leading to increased discharge temperatures, higher irreversibilities during compression, lower specific enthalpies differences across the evaporator, and possibly a reduction in the compressor life due to the breakdown of the oil. To counter these effects, the use of economized, vapor injection compressors is proposed for vapor compression systems in high temperature climates. Such compressors are commercially available however an accurate method for mapping single-port injection compressors is unclear. This paper establishes compressor maps for a single-speed R-407C scroll compressor with two-phase injection and vapor-injected compression. A dimensionless-PI correlation for mapping the injection ratio, refrigerant discharge temperature, compressor power consumption, overall isentropic and volumetric efficiencies, and the heat loss ratio for these compressor maps and a variable speed R-410A compressor with vapor injection is presented. The mapping results are compared to the AHRI 10-coefficient polynomial and another proposed correlation. [ABSTRACT FROM AUTHOR]

Configuring the number and size of chillers in a multiple-chiller plant properly is an efficient way to improve the plant energy efficiency. At the design stage, the optimal configuration can be achieved through matching the capacity to load as closely as possible across the full-load profile. However, in spite of the fact that current literature offers practical recommendations, a systematic method to optimize the configuration of multiple-chiller plants is lacking. Due to the lack of accurate information at the design stage and only limited knowledge of the eventual realization it is hard to predict the building’s cooling load. Moreover, there is no operational data to predict the system performance. Both explain the existence of uncertainty in the HVAC plant design process. This paper, therefore, proposes a strategy to optimize the configuration of multiple-chiller plants, which takes account of the load side uncertainty as well as the COP uncertainty and selects the optimal configuration through a life-cycle analysis. Both the load side uncertainty and the COP uncertainty are quantified using statistical distributions. To facilitate applications, the distributions of the cooling load profile of different types of buildings under different weather conditions are investigated and are classified into four categories, and the optimal configuration schemes under each type of cooling load distribution are analyzed and summarized in a tabulated form. [ABSTRACT FROM AUTHOR]

The increased demand of energy in domestic applications necessitates the development of innovative engineering solutions in building heating, ventilating, and air conditioning (HVAC) systems. As the largest energy intensive sector is domestic buildings, more focus is currently directed to reduce air conditioning energy consumption. Double-pipe heat exchangers are considered one of the practical solutions in today’s HVAC industry. Nevertheless, a few studies focus on using double-pipe heat exchangers in air conditioning applications. This paper experimentally investigates the usage of double-pipe condenser and evaporator in an air conditioning system serving a 45 m 3 balanced calorimeter of 2.24 kW heat load. Deionized water (DIW) was used as the secondary heat transfer working fluid for both the evaporator and condenser units, and R-22 was used as the AC system refrigerant. Experimental results of the double-pipe heat evaporator/condenser setup showed a promising reduction in the compressor work and an increase in the system coefficient of performance (COP). The collected data showed that the system efficiency depends more on the evaporator DIW flowrate than on the condenser DIW flowrate. By increasing the DIW flowrate in the evaporator, the compressor work was shown to decrease, while the COP was shown to increase. In comparison with a standard rated air conditioning unit, using a double-pipe evaporator and condenser units with the maximum DIW flowrates resulted in a decrease of about 53% in the compressor work and a similar percentage of increase in the system COP. [ABSTRACT FROM AUTHOR]

The purpose of air-conditioning systems is to provide a suitable indoor environment with respect to temperature, humidity and fresh air. Liquid desiccant dehumidification constitutes an effective method for extracting moisture from humid air with less energy consumption. Current studies mainly focus on dehumidification system under certain heat and mass transfer ability (number of mass transfer units NTU m ). This paper will investigate NTU m of counter-flow packing tower and its influence on system performance. An experiment including a counter-flow packing tower was conducted. When the height of tower was 0.7 m, the volumetric mass transfer coefficient was between 1–4 kg/(m 3 ·s) and NTU m presented a range between 0.9–1.4, when air flow rate changes from 1 kg/(m 2 s) to 2.5 kg/(m 2 s). When the height changed to 2.1 m, the NTU m of the tower presented a variation from 3.3 to 4.3. Furthermore, a simulation model is developed, which is validated by experimental data and past research results. The influence of NTU m on total circulation flow path is mainly caused by heat and cold offset and an NTU m value approximately of 4 constitutes a suitable value of increasing heat and mass transfer ability. Comparing three typical flow paths, when NTU m is lower than 3.5, inter-stage circulation presents improved performance in system COP. When NTU m is large, total circulation is efficient. The system COP cross points of flow paths are caused by heat and cold offset and concentration difference of the solution circulation between the dehumidifier and the regenerator, which can be quantified by loss coefficient ε and χ respectively. The heat and mass transfer ability of the system should be considered in the designing process of flow path configuration to obtain an efficient performance for different range of NTU m . [ABSTRACT FROM AUTHOR]

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 equivalently-good energy performance but with exponentially reduced computational load if compared with those traditional methods that optimize all set-points simultaneously. In fact, the time instant for each set-point optimization and the set-point optimization sequence have impacts on the overall performance of the multiplexed optimization. Considering such impacts, this paper proposes a new multiplexed optimization method for enhanced performance. In the proposed method, optimization is activated as the system energy efficiency is low. The set-point optimization sequence is selected according to their impacts on the system energy performance. The one with the most energy saving potential will be firstly optimized. The case study results demonstrate the improved performance of the proposed method in terms of energy, computation load and system stability when compared with the conventional multiplexed optimization. The proposed method can be applied in complex air conditioning systems for energy saving, computation load reduction and system stability improvement. [ABSTRACT FROM AUTHOR]

The liquid desiccant air-conditioning system (LDAS) is a novel air-conditioner with good energy saving potential. Regenerator is the key component of the liquid desiccant air-conditioning system, which is the main energy-consumed part. Electrodialysis regenerator is a new liquid desiccant regeneration method which can meet the dehumidification requirements even when the environment air is hot and wet. In this paper, in order to reduce the waste of electrode solution and the operational cost of normal electrodialysis regenerator, a novel multi-function liquid desiccant regeneration system was developed and investigated. Moreover, an experimental system was constructed to achieve the accurate current efficiency of the new system. The results show that in order to improve the current efficiency of the multi-function desiccant regeneration system, the operational current and the concentration difference between solutions in regenerate chambers and dilute chambers should be both decreased. The ideal performance coefficient of liquid desiccant air-conditioning system can exceed 7 when the conductivity of liquid desiccant is higher than 300 mS/cm. In the practical application of the multi-function liquid desiccant regeneration system, the operational current will be designed to fulfill the hydrogen and halogen gas production of the system. [ABSTRACT FROM AUTHOR]

The main purpose of this research is to suggest a virtual water flowmeter applicable in hydraulic systems with low-cost sensors. Practical procedures for realizing virtual water flowmeters for constant flow pumps (i.e., Cases 1 and 2) and variable flow pumps (i.e., Cases 3 and 4) are proposed in this paper. In Case 1, for measuring the water flow rate through a constant flow pump, the pump head was measured and the water flow rate was estimated using the pump characteristic curve obtained from the manufacturer or by deriving an empirical model based on the field measurement data. In Case 2, the water flow rate through a valve with a constant flow pump was estimated by measuring the pressure head between the valve and the valve opening position. The valve characteristic curve can be obtained by deriving an empirical model based on the initial field test results. The water flow rate through the variable flow pump was calculated, using the pump affinity laws and an empirical model, by measuring the frequency (i.e., Case 3) or input power (i.e., Case 4). The initial setup and test procedures for virtual flowmeters are also proposed in this research for practical use in the field. To verify the proposed procedures, experiments were conducted using constant and variable flow pumps in a pilot system. It was found that the virtual water flowmeters showed 2.9% to 6.7% of root mean square error from Case 1 to Case 4, compared with an ultrasonic water flowmeter, through long-term experimental verification. [ABSTRACT FROM AUTHOR]

It is expected that energy saving may be attained by connecting heat source equipment and air conditioning equipment in multiple buildings with piping network and operating heat source equipment flexibly in consideration of heat demands required by air conditioning equipment. In this paper, an optimization method is proposed to operate such heat supply systems with piping network rationally. Mass flow rates and temperatures of water are adopted as basic variables to express heat flow rates as well as pressure and heat losses in piping segments. The discreteness for the selection of piping segments for water flow are also taken into account. To avoid treating the nonlinearity directly, mass flow rates are discretized, and the optimization problem is finally formulated as a mixed-integer linear programming one, and its suboptimal solution is derived efficiently by a two-stage approach. A case study is conducted for a heat supply system for space cooling and heating of an exhibition center with multiple buildings. Through the study, the validity and effectiveness of the proposed optimization method is shown in terms of solution optimality and computation time. In addition, it is shown how the primary energy consumption can be reduced using piping network. [ABSTRACT FROM AUTHOR]

R32/R1234ze(E) mixtures are potentially low-GWP alternative refrigerants for air conditioning and heat pumps while the rare pure refrigerants can totally meet the requirements of new international protocols on environmental conservation, thermodynamic performance, and safety. The system performance under different concentrations is important for selection of working concentration for the new R32/R1234ze(E) refrigeration or heat pump. In this paper, the thermodynamic model of an ASHP with R32/R1234ze(E) mixtures is built and used to investigate the influence of the refrigerant composition on the performance of the system. The results show that when the mass fraction of R1234ze(E) changes from 0% to 100%, the heating capacity of the ASHP decreases by 67.2%, while the COP continuously increases by 70.3%, which means the changing tendency of system COP is quite different from previous research under fixed evaporating and condensing temperature. Adjusting the refrigerant concentration will be a good system modulation method for ASHPs with R32/R1234ze(E) to meet both the heating capacity and energy efficiency requirements. Furthermore, temperature matching degree is an important factor that affects the energy efficiency of ASHPs with non-azeotropes, which can guide the circuitry optimization of evaporator and condenser in ASHPs with non-azeotropes. [ABSTRACT FROM AUTHOR]