查看更多>>摘要：With the breakthroughs in generative artificial intelligence(GAI)models,the vast computational demands are placing an unprecedented burden on the data center(DC)energy supply.The cooling system is the second major energy consumer in the DC,maintaining the safe and efficient operation of computing equipment.However,time-varying temperature gradients and power distribution pose a considerable challenge for efficient cooling management in DCs.For this problem,this work proposes a multi-objective cooling control optimization(MCCO)method to minimize cooling energy consumption while maximizing the rack cooling index(RCI)to ensure energy efficiency and security of hybrid-cooled DCs.The proposed method relies on high-fidelity models that characterize the dynamic thermal evolution and cooling power.Therefore,a novel network model(TCN-BiGRU-Attention)combining temporal convolutional network(TCN),bidirectional gated recurrent unit(BiGRU),and attention mechanism is designed to capture the features of multivariate time-series to predict temperature changes in thermal environments and cooling loops.Moreover,considering the complex heat transfer and operational characteristics of hybrid cooling systems,a machine learning(ML)-based power model is constructed to evaluate the holistic cooling power.Subsequently,the NSGA-Ⅱ algorithm formulates the optimal cooling decision based on the predicted thermal distribution and cooling power,realizing the trade-off between energy consumption and cooling effectiveness.The results of numerical experiments using Marconi 100 data traces suggest that the proposed MCCO significantly reduces cooling energy consumption in summer and winter while maintaining the RCI above 95％.
查看更多>>摘要：Compared with traditional convection air conditioning,the radiant cooling(RC)system has higher energy-saving potential and better comfort.At present,the particle swarm optimization(PSO)algorithm is one of the most advanced methods to optimize the design of indoor radiant terminals.However,this method requires to discretize the design domain in advance.If the geometric division is rough,the accuracy of the optimized results will be too low.To improve the accuracy of the calculation results,the geometric division needs to be refined,but it will greatly increase the calculation load.For each new geometric model,users need to determine a reasonable geometric division every time,which is very time consuming.To solve that problem,this investigation proposed a parameterized level set method(PLSM)to inversely design the area,shape,and locations of the radiant terminal.It not only does not need to discretize the design domain in advance,but also can realize the continuous topological change of the radiant terminal region.The results show that the PLSM can realize the continuous topological transformation of geometric shapes,and the final result of the average absolute value of PMV(|PMV|avg)around the occupants achieved 0.066.To enhance the practical application of the optimized results,K-means cluster analysis is used to regularize the shape of the radiation terminal region.The corresponding average|PMV|around the occupants is 0.102,which is also within an acceptable range.All in all,PLSM can be used to inversely design the RC systems,which provides an effective design method for realizing accurate control of the indoor environment using the RC systems.
查看更多>>摘要：Due to the challenges of adjustment after installation and the elevated failure rate associated with the use of electric valves,which contributes to increased weight among other issues,single-hole restrictors(SHRs)are commonly employed within the ventilation system of the manned space station.These restrictors are pre-configured with parameters to ensure that the airflow at the termination of the ventilation system meets the designated requirements.However,given their inability to be modified post-installation,a preliminary optimization design process becomes imperative.Past solutions relying solely on experience are insufficient in precise and optimal outcomes.While computational fluid dynamics(CFD)simulations offer accurate results,they encounter difficulties in modeling larger systems and are time-intensive due to multiple iterative simulations.Hence,an optimizing design method through quicker Flowmaster simulations is proposed in this study.Utilizing the Functional Mock-up Interface(FMI)protocol,the ventilation system model established in Flowmaster could be exported as FMU files and fine-tuned within Python using a genetic algorithm(GA),swiftly achieving a well-balanced ventilation system design by adjusting the parameters of the SHRs.The findings from CFD calculations can corroborate the simulations conducted in Flowmaster.The vents'unbalanced factor and the pressure drops of the system are used as optimization objectives.After optimization,the system unbalanced factor and total pressure drop were 5.51％and 5.99 Pa,respectively,both of which are better than the results obtained using CFD through empirical and trial-and-error methods,and the computation time was reduced by 99.16％.
查看更多>>摘要：To ensure a comfortable building environment necessitates accurate measurement and control of air volume within duct systems to meet predetermined requirements for each area.Traditional eccentric torque dampers'measurement accuracy may be compromised by adjacent effects from local components,resulting in significant measurement errors.To solve this problem,the study combines CFD numerical simulation and full-scale experimental validation to derive a formula for controlling air volume within the dampers under operational condition.Based on the formula,a novel torque damper is developed,capable of effectively controlling and accurately measuring air volume in duct systems.By linking the two blades,the damper resists the adjacent effects of local components(elbow,variable diameter,tee)on air volume measurements without the need for additional devices,ensuring a measurement error within±5.5％.Additionally,the novel dampers have lower resistance compared to traditional dampers.This paper provides a reference for accurately measuring and effectively controlling air volume,while also maximizing the potential benefits of multi-leaf dampers.
查看更多>>摘要：As deep borehole heat exchangers(DBHEs)extract heat from geothermal energy with depth of 2-3 kilometers,the circulation water pressure drop is larger than that of shallow-depth borehole heat exchangers,influenced by the water flow rates.This paper conducted field tests and simulation analysis to study the heat transfer performance and water circulation resistance of DBHE in coupled,where the natural circulation characteristic has been discovered and analyzed quantitatively.Results show that the water temperature and density variation along DBHE forms the driving force of natural circulation.For mechanical flow rate of 6.0 kg/s and inlet water temperature of 20.0 ℃,the natural circulation flow rate reaches about 2.2 kg/s with transient heat extraction power of 78.5 kW,without energy consumption of water pumps.And the larger inlet water temperature,smaller mechanical water flow rate,higher inner tube thermal conductivity coefficient and larger depth of DBHE all contribute to the larger natural circulation water flow rate.In addition,the natural circulation could effectively decrease the comprehensive water pressure drops of DBHE,which is about 47.3％smaller than the calculated value of traditional models.Thus the natural circulation characteristic has significant influence on the heat transfer performance of DBHE,and also on the energy performance of whole heat pump systems.
Petr ZelenskýVladimír ZmrhalMartin BartákMiroslav Kučera...
2233-2247页
查看更多>>摘要：Insufficient fresh air supply due to the increased air tightness of building envelopes after building renovations and window upgrades is a major concern of HVAC engineering today.The paper demonstrates the application of CFD simulations in the development of a compact decentralised ventilation unit with integrated heat recovery system for local ventilation of rooms,targeting this common issue.The device houses an innovative cyclically rotating recuperative heat exchanger,allowing effective condensate removal and de-icing in winter for its independent operation throughout the year.The paper introduces the ventilation unit,describes preparation of its numerical models,and conducts CFD simulation using Ansys Fluent software.The initial design of the device was improved following the findings of the numerical analysis,and the proposed adjustments were tested through follow-up CFD simulations,confirming that the desired outcomes were achieved.A separate CFD analysis was performed to assess the use of different air supply elements at the air outlet to the room,recommending the use of adjustable nozzles.A prototype ventilation unit was manufactured and the volume flow rate under different operating conditions was measured to be compared with the simulation results.The outcome of the research is a new type of compact local ventilation unit.An increase in device energy efficiency was achieved,with the aid of simulations,while maintaining its compact size.In addition to presenting the potential of using variant CFD analysis in the development of new HVAC equipment,the paper also indicates the drawbacks of using the Multiple Reference Frame(MRF)method to approximate the rotation of radial fan impellers in CFD simulations.
查看更多>>摘要：Bioaerosol filtration is crucial for improving indoor air quality and reducing cross-infection risk.It is necessary to conduct a comprehensive study on the bioaerosol filtration performance of air filters under different influencing factors.Firstly,this study proposed a standardized test scheme for the comprehensive evaluation of bioaerosol filtration performance.Additionally,the high-efficiency particulate air(H13)and medium-efficiency particulate air(F8)filters were evaluated in depth using Serratia marcescens bioaerosol,considering the face velocity,relative humidity(RH),and operating time.This study also investigated the impact of removing static electricity on the bioaerosol filtration efficiency(BFE)of F-filter materials.The pressure drop(ΔP)value of H13-filter and the BFE of F8-filter were significantly affected by face velocity and RH.When the face velocity increased from 5 to 20 cm/s,the H13-filter maintained a BFE above 99％,while ΔP increased by 303 Pa.During a 90 min test,the maximum change in the BFE of the H13-filter was 0.80％and ΔP increased by 26 Pa.Conversely,the BFE of the F8-filter decreased by up to 12.21％,while ΔP increased by only 3 Pa.Higher RH resulted in more pronounced changes in BFE.After removing the static electricity from the F8-filter material,the BFE decreased significantly,with a maximum reduction of 25％.The results may provide valuable insights into the application of conventional filters in bioaerosol filtration and serve as a guide for the enhancement and optimization of filter design.
Chaojie XingZhengtao AiCheuk Ming MakHai Ming Wong...
2263-2280页
查看更多>>摘要：The high-volume evacuation(HVE)is commonly employed as a primary source control measure for removing splatter emitted from mouth during dental treatments,but there is still a lack of comprehensive understanding of its efficiency.Based on our previous experiments on the emission characteristics during dental treatments,this study employed computational fluid dynamics(CFD)simulations to investigate the impact of emission parameters(droplet size,emission velocity,emission angle),HVE usage methods(distance between HVE and the droplet release source),and HVE suction flow rates on its removal efficiency.The effect of HVE on fallow time(FT)was also examined.Cumulative removal efficiency that accurately reflected the HVE effect was proposed as an evaluation index.It was found that emission velocity and distance between HVE and the source were key factors determining cumulative removal efficiency.When the distance was 4 cm,the cumulative removal efficiencies for low-velocity(0.8 m/s),medium-velocity(3.4 m/s),and high-velocity droplets(6.0 m/s)were approximately 97.9％,73.6％,and 58.0％,respectively.For high-velocity droplets at 6.0 m/s,decreasing the distance from 4 cm to 2 cm and 1 cm increased the cumulative removal efficiency from 58.0％to 76.7％and 100％.This study was expected to enhance the understanding of HVE performance and provide information on its usage method.It also indicated the need for developing advanced control measures that could have high efficiency in removing both low-velocity and high-velocity droplets.
查看更多>>摘要：Accurate turbulence modeling is essential for simulation studies of urban physics.In this study,the comprehensive atmospheric boundary layer(ABL)model involving a variable model coefficient and an additional turbulent dissipation source term was implemented using the open-source software OpenFOAM.Combined with consistent inlet wind profiles and rough wall functions of different turbulence variables based on the aerodynamic roughness,the model maintained the horizontal homogeneity well.Then,a hybrid approach was introduced to consider buildings immersed in ABL flows,enabling automatic transformation of the turbulence model between the region around the buildings and the free flow region away from any building.Finally,the effects of applying different model forms to the airflow field around buildings were evaluated in detail through three-dimensional building cases representing six urban prototypes based on three wind tunnel databases.Our findings indicated that all modified k-ε models perform well in reproducing the flow data of the CEDVAL and Architectural Institute of Japan(AIJ)experiments consisting of a single building,an array of buildings,and an isolated high-rise building.However,the modified k-ε model with an additional correction term performed poorly in the database of Niigata Institute of Technology and the case of complex terrain and urban building configurations,because the correction term inhibited the generation of turbulent kinetic energy.In addition,from the comparison between the experimental data of all cases,the model with the original formulation of the coefficient performed the best in terms of prediction accuracy.The root mean square errors of the normalized velocity were 0.1250,0.0879,0.1145,0.1350,and 0.1492 in different cases,which proved the reliability of this turbulence model.
查看更多>>摘要：Range hoods are commonly used in residential kitchens to capture pollutants generated during cooking.Direct capture represents the true capture performance of the range hood as a local exhaust device.A better metric for evaluating range hood capture performance is direct capture efficiency(DCE),defined as the ratio of pollutant directly captured by the hood to the total pollutant emission from the source.This paper clarifies the dynamic functioning mechanism of direct capture and reflux capture,analyzes the dynamic characteristics of exhaust concentration,and deduces a simple method for DCE determination based on dynamic temporal separation,where DCE is the ratio of the peak concentration of direct capture(C1)to the peak concentration of total capture(C2).Experimental and simulation studies on dynamic exhaust concentration were conducted under different ventilation conditions,and the results were in good agreement.Then,the determination methods of C1 and C2,including the experimental methods,were further studied to calculate the DCE.The measured and simulated results for DCE based on dynamic temporal separation showed good consistency,with a deviation of less than 2.0％.Finally,the two spatial separation methods for determining DCE(mass flux ratio and virtual purification)proposed and verified in our previous study showed good agreement with the dynamic temporal separation method based on C1/C2 proposed here,with a maximum deviation of 2.0％.The determination method of DCE based on dynamic time separation,particularly the experimental method,is of great significance for evaluating the real capture performance of range hoods.
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