Cooling load and supply air parameters are the essential inputs of energy performance evaluation of the air condition system. Non-uniform air distribution (NUAD) benefits energy-efficient provision of comfortable and healthy indoor environment, but leads to increased complexities in the estimations of cooling load and supply air parameters. The non-uniformity-to- uniformity surrogation methodology enables the fully mixed air model to accurately estimate the cooling load and supply air parameters of NUAD, which is technologically convenient and computationally efficient. This study contributes to enriching the non- uniformity-to-uniformity surrogation methodology, which proposes a direct non-uniformity-to-uniformity surrogation by quantifying the ratios of NUAD to UAD regarding the cooling load as well as the supply air temperature/supply airflow rate for the constant-air- volume system/variable-air-volume system. The ratios to UAD are derived as the functions of the outside surface temperature of exterior wall, reference room air temperature and supply airflow rate/supply air temperature of UAD using data-driven modelling (Gaussian process regression). The proposed method is tested on an energy efficient NUAD, i.e., stratum ventilation. Compared with the conventional method which ignores the non-uniformity of stratum ventilation, the proposed method improves the estimation accuracy of the cooling load and supply air parameters by at least 89.1%.
The battery model is the basis for battery state estimation, and its accuracy will directly affect the accuracy of the estimate. In the field of rail transit, combined with the actual operating conditions of the train to properly allocate the battery capacity, it is also necessary to establish an accurate battery model. At present, the commonly used battery model less considers the influence of temperature on the model parameters. Because of the extreme low temperature conditions during the actual running of the train, this paper uses lithium iron phosphate battery as the research object, based on the second-order equivalent circuit model of the battery. At the same time, considering the influence of low temperature on the available capacity of the battery, open circuit voltage, ohmic internal resistance and polarization parameters, a battery model suitable for room temperature below is proposed.
The objective of this paper is to study and make a comparison between an original boosted-system with one Booster (B-MED) and an optimized system with two boosters (2B-MED) of a combined trans-critical CO2 refrigeration and boosted multi effect desalination system. The two systems are analyzed and compared thermodynamically. The optimized system with two boosters produces around 361.72 m3/day of fresh water, on the other hand the original system with only one booster module produces around 290.3 m3/day of fresh water, which means that the optimized system with two boosters increased the fresh water production rate by 24.6 % in comparison with that of one booster module. In addition, the heat transfer rate of the gascooler to the environment in the original system is equal to 1059 kw while it is equal to 472.5 kw in the optimized one, which means that the optimized system (2B-MED) improves the refrigeration system by decreasing the heat transfer rate of the gas-cooler by 55.38 %. This leads to the reduction of the heat transfer area (HTA) of the gas cooler and all that will lead to the decrease of the total annual cost (TAC) of the refrigeration system. So that, the optimized system with two boosters is thermodynamically better than the original one.
The grids are facing the critical issue concerning the power imbalance. Demand response (DR) program are increasingly promoted to encourage the end-users to change their load profiles under a specified pricing policy or request of the grid. For buildings, the supply-based fast demand response strategy has been demonstrated that it can quickly response to the urgent request from smart grid and can reduce the load demand within very short interval. However, flow sensors are required for each air conditioning terminal equipment. In view of the high cost of flow sensors and the large number of airconditioning terminal equipment, there are few cases of installing flow sensors for air-conditioning terminal equipment in existing large public buildings. Therefore, it hinders the application of this method in practical projects. This study aims at developing an improved fast demand response strategy of building HVAC system with low cost measurement sensors for smart grid applications. The virtual flow meter was modelled to estimate the water flow rate of each AHU based on theair side measurements. Meanwhile, a modified selfadjustment chilled water distribution method was developed to realize the balanced distribution of cooling capacity in different indoor zones, which does not require additional work to offline identify the key parameters prior to application.
An appropriate battery model is crucial for accurate state of charge (SOC) estimation of lithium-ion batteries. A complex battery model can improve the accuracy, however, it leads to high computational cost. In this paper, the second-order resistor-capacitor (RC) model is selected due to its superiority in good balance between accuracy and complexity. Different factors, including RC parameters of battery model, relationship between open circuit voltage (OCV) and SOC, and measurement noise are investigated to extract the ones that significantly affect the accuracy of SOC estimation based on Kalman filters. The results revealed that in comparison with the resistors, the polarization capacitors have no obvious influence on the SOC estimation. In addition, the voltage measurement noise has greater influence on the SOC estimation compared with the current measurement noise. These results can be potentially used to guide us in deciding which parameters should be separately identified online and offline so as to achieve a proper balance between model accuracy and complexity.
In our previous work, a novel isobaric adiabatic compressed air energy storage (IA-CAES) system has been proposed on the base of volatile fluid, while large amount of waste heat should be employed to offer the energy required in the evaporation, which may restrict its applications. In this work, a novel adiabatic compressed air energy storage (A-CAES) system is proposed which is also based on the volatile fluid while without using waste heat. Carbon dioxide (CO2) is selected as the volatile fluid. The stead-state mathematical model and thermodynamic laws are employed to evaluate proposed system. The calculation results show that our proposed A-CAES system has the same round trip efficiency (RTE) with conventional one, while more than 30% additional cooling energy can be obtained and the total exergy efficiency (TEE) improves more than 2%. For a given total power generation (4 MWh), the total volume of air storage unit in proposed A-CAES is only accounts for 60.97% of that in conventional A-CAES.
Green building can effectively reduce building energy consumption and pollutant emissions. China has spent great efforts on developing green commercial buildings(GCBs). In this paper, we use the ANP-SWOT method to evaluate the development of GCBs in China. First, the SWOT matrix (Strengths, Weaknesses, Opportunities and Threats) was used to analyze the influence factors of the GCBs industry and to formulate alternative strategies. Then, the Analytical Network Process (ANP) methodology was utilized to establish a network structure and to calculate the weights of factors, sub-factors and strategies. Finally, based on strategies ranking, we drew the policy implications. The results showed that the insufficient economic incentives and inadequate attention are main factors curbing the development of China’s GCBs and strengthening preferential policies and improving evaluation system are two more effective strategies of GCBs development in China.
A novel systematic analysis framework based on modeling and simulation is provided for optimization of the methanation process using novel high-temperature tolerant catalysts. In this framework, the reactor is described by kinetic equation and energy balance. 3 schemes for methanation processes and 2 types of feedstock are investigated. In addition, different reaction temperature is considered for different schemes and different feedstock. Furthermore, the solution method is proposed for simulation and optimization the different process schemes. To compare the performance of different schemes, economic analysis including methane profit, steam profit, and compressing work consumption is investigated. Comprehensive considering different profit, the total profit for different schemes is provided and the optimal scheme is obtained.
The air of high humidity and high sea spray aerosol (SSA) on islands or coastal area always leads to the serious equipment corrosion and affects the living comfort of residents. Conventionally, the airconditioning system can only provide the cooling dry air, and the SSA reduction process is always separated and consumes precious electricity power as well as expendable materials. To simplified the procedure and reduce the energy consumption, this paper proposed a novel hybrid air‐conditioning system combined with sea spray aerosol removal. Based on the characteristics of liquid‐desiccant dehumidification and phase transitions of the ternary solution system, the combined system can be driven by the waste heat source of 90 oC. The proposed system was simulated by the thermodynamic equilibrium model. The results showed that the humidity ratio of the supply air can reach 6.83 g/kg(dry air), with a temperature of 21.14°C. Compared with the conventional cooling dehumidification system utilizing vapor compression refrigeration driven by power, the power saving ratio (PSR) and the equivalent power generation efficiency (ηeq) of the proposed system can reach 92.16% and 8.74%, respectively. Besides, the crystallization experiment is conducted to verify the feasibility of the NaCl separation process. This study provides a new hybrid air‐conditioning system to simultaneously remove moisture and sea spray aerosol by using low‐temperature waste heat.