Through the establishment of a mathematical model of underground aquifer which couples water flow with heat transfer,the temperature of pumping well was simulated and analyzed with different aquifer thickness,with temperature variation curve,the design spacing of groundwater heat pump pumping-injection wells was discussed.The simulation results show that,the effect of heat transfixion can be weakened with the increase of aquifer thickness by keeping the spacing of pumping-injection wells;With the same aquifer thickness,the spacing of pumping-injection wells may change within a certain range,but the heat transfixion degree does not change much.With the increase of aquifer thickness,the design spacing of pumping wells decreases.
For solar absorption cooling systems, it is difficult to generate lower chilled water for dehumidifying and cooling, as well as facing intermittency problems. In this work, the novel SACV system for indoor temper-ature and humidity control is proposed, which integrates the SSAR subsystem, the VCR subsystem, and the VMD subsystem. The VMD subsystem and the VCR subsystem solve the dehumidification difficulty and all-weather heating and cooling problems, respectively. This work also proposes a method for deter-mining the collector area that avoids frequent start-ups and shutdowns of the VCR subsystem. Besides, a thermodynamic model of the SACV system is established and validated, and a systematical performance analysis of the SACV system is carried out. For the SACV system, the sensitivity of the parameters to the MCOP is also discussed. Results indicate that the outdoor air temperature, the latent heat load ratio, and the solar radiation intensity are the key parameters for designing the SACV system; further, the evapora-tion temperature and the permeate side pressure are the key parameters for the SACV system optimiza-tion. The SACV system is more suitable for high-humidity environments. Moreover, during the cooling season, the SACV system of a commercial building can realize a power saving rate of 39.82% compared to the conventional VCR system. The proposed SACV system of a commercial building can reduce 19653.59 kg/year carbon emission compared to the conventional VCR system in Nanjing. The carbon reduction rate of the SACV system in the selected cities is rather similar, about 36.78%-39.79%.(c) 2023 Elsevier B.V. All rights reserved.
High photovoltaic (PV) module temperature leads to the degradation of electrical efficiency, and passive PV thermal management systems, such as phase change materials (PCMs) and heat pipes (HPs), have been widely adopted to address this challenge. Due to the low thermal conductivity of PCM and the limited heat exchange capacity in the HP condensation section, this paper proposes a novel configuration for a PV thermal management system utilizing a phase change material/heat pipe coupled module (PV-PCM/HP). The experimental results showed that the performance of the coupled PCM/HP system was superior to that of the single system. A numerical model was developed to simulate and analyze the temperature variation and coupled heat transfer characteristics of the PV-PCM/HP system. The main components of heat transfer gradually change from PCM (PCM-dominated) to HP (HP-dominated), and PCM even plays a negative role during the solidification stage, which means that the coupled thermal management depends on HP only. Four design parameters (the number of HPs, PCM thermal conductivity, PCM phase change temperature, and PCM thickness) of the PV-PCM/HP system are discussed to investigate the effects on the performance of the PV-PCM/HP thermal management system. This shows that the increase in the number of heat pipes and PCM thickness can effectively improve the performance, but they should be determined according to technical and economic analysis. When the PCM thermal conductivity is >2.7 W/(m.K), it has little effect on thermal management performance under the conditions described in this paper. The value of the PCM phase change temperature should be determined according to actual weather conditions, and the purpose is to make the PCM melting period coincide with the period of higher solar radiation and lower phase change temperatures.
空气源热泵"监测外管温变化及运行时间"的化霜判断方法,利用了结霜现象对热泵系统运行参数的时空累积影响效应,需要累积到一定结霜量时才能准确识别,无法实时判断当前换热器的结霜情况.基于此痛点问题,提出一种结霜量预测技术,通过分析结霜过程相关原理,利用神经网络和空气源热泵系统特性,搭建结霜量预测模型,从而对结霜量进行准确识别.试验结果表明,搭建的结霜量预测模型能够实时计算室外换热器的结霜量,且与实际结霜量相比误差在15%以内,对探索更精细更灵敏更智能的化霜判断方式具有参考意义.
In this work, the concept of hot gas direct defrosting（HGDD） of air-source heat pump is proposed at first, which does not need to add a hot gas bypass branch and the refrigerant flow direction during defrosting is the same as that of heating cycle.In the next, the flow rate demand of HGDD was analyzed, the flow rate curve of the electronic expansion valve was improved, and a biconical electronic expansion valve was designed to meet the flow rate demand during heating and hot gas direct defrosting.Finally, the heat loss of R32 refrigerant in the expansion valve under different expansion valve pulses during the hot gas direct defrosting process was simulated using CFD technology, and the results showed that there existed an optimal expansion valve opening to produce the largest defrosting heat at expansion valve outlet.
