Prediction of turbulence control for arbitrary periodic spanwise wall movement

In order to generalize the well-known spanwise-oscillating-wall technique for drag reduction, non-sinusoidal oscillations of a solid wall are considered as a means to alter the skin-friction drag in a turbulent channel flow. A series of Direct Numerical Simulations is conducted to evaluate the control performance of nine different temporal waveforms, in addition to the usual sinusoid, systematically changing the wave amplitude and the period for each waveform. The turbulent average spanwise motion is found to coincide with the laminar Stokes solution that is constructed, for the generic waveform, through harmonic superposition. This allows us to define and compute, for each waveform, a new penetration depth of the Stokes layer which correlates with the amount of turbulent drag reduction, and eventually to predict both turbulent drag reduction and net energy saving rate for arbitrary waveforms. Among the waveforms considered, the maximum net energy saving rate is obtained by the sinusoidal wave at its optimal amplitude and period. However, the sinusoid is not the best waveform at every point in the parameter space. Our predictive tool offers simple guidelines to design waveforms that outperform the sinusoid for given (suboptimal) amplitude and period of oscillation. This is potentially interesting in view of applications, where physical limitations often preclude the actuator to reach its optimal operating conditions

Effects of Section Geometry on the Energy-saving Rate of PBCF and Model/full-scale Correlation - A CFD Study

The steady flows and hydrodynamic performances of a propeller without and with the Propeller Boss Cap Fins (PBCFs) are simulated by solving the Reynolds-averaged Navier-Stokes (RANS) equations using the software package STAR-CCM+. To determine a suitable grid setting, a grid convergence study is carried out first by changing the grid sizes separately in the sub-domains enclosing the propeller blades and the PBCFs. The CFD investigation into the energy-saving rate of the PBCFs with systematically varied section profiles at model-scale shows the PBCFs with modified ‘NACA M7’ section geometry performs better than the flat plate in energy-saving effect. Full-scale simulations are also carried out using typical PBCF geometries investigated at model scale, and the results are compared with model-scale ones to evaluate the Reynolds scale effects on the energy-saving rate. The hydrodynamic forces acting on the propeller blades, the PBCFs, and the boss cap are compared to explore the mechanism behind the scale effects on the PBCFs. The study indicates that the scale effect positively influences the energy-saving effect of all the PBCFs investigated, while the flat-plate PBCFs benefit more from the scale effect

Comparative study of commercial building energy-efficiency retrofit policies in four pilot cities in China

The energy efficiency of existing commercial buildings is more challenging to regulate and improve than the energy efficiency of new constructions. In 2011 and 2012, the Chinese Government selected four cities- Shanghai, Tianjin, Shenzhen, and Chongqing- to implement pilot commercial building energy efficiency retrofit program. Based on site surveys and expert interviews in these pilot cities, this research conducted a comparative analysis on incentive policies of local city level. The analysis results show that policy designs of existing commercial buildings should be further improved. The aspects that influence the implementation effect in the future, such as subsidy level, installments, and business model promotion, should be specified in the policy clauses. Referring to the technical solution and cost-benefit in Chongqing, we found that lighting system is the most common retrofit objects while envelope system is the least common one. And the subsidy incentive is greatest for educational buildings, followed by office buildings. In the end, we further discussed the problems and obstacles in commercial building retrofit market, and provided a series of recommendations

A three-stage optimization methodology for envelope design of passive house considering energy demand, thermal comfort and cost

Due to reducing the reliance of buildings on fossil fuels, Passive House (PH) is receiving more and more attention. It is important that integrated optimization of passive performance by considering energy demand, cost and thermal comfort. This paper proposed a set three-stage multi-objective optimization method that combines redundancy analysis (RDA), Gradient Boosted Decision Trees (GBDT) and Non-dominated sorting genetic algorithm (NSGA-II) for PH design. The method has strong engineering applicability, by reducing the model complexity and improving efficiency. Among then, the GBDT algorithm was first applied to the passive performance optimization of buildings, which is used to build meta-models of building performance. Compared with the commonly used meta-model, the proposed models demonstrate superior robustness with the standard deviation at 0.048. The optimization results show that the energy-saving rate is about 88.2% and the improvement of thermal comfort is about 37.8% as compared to the base-case building. The economic analysis, the payback period were used to integrate initial investment and operating costs, the minimum payback period and uncomfortable level of Pareto frontier solution are 0.48 years and 13.1%, respectively. This study provides the architects rich and valuable information about the effects of the parameters on the different building performance

Optimized Blind Control Method to Minimize Heating, Cooling and Lighting Energy

AbstractEnergy saving has become a hot issue all over the world. To minimize the energy use in buildings, the cooperative control coupled with heating, cooling, lighting and blind control system was proposed in this study. The blind condition is optimized to minimize the total energy of heating, cooling and lighting.In this study, the control behaviors and energy saving effect of the proposed system were evaluated by field measurement. The results show that the proposed control system reduces the cooling energy demand by about 40.8% and 19.6% of the lighting energy compared to the conventional control system with maintaining the same thermal comfort level. The total energy saving rate reached 29.7%

Study on Energy-Saving Performance of a Novel CO2 Heat Pump with Applications in Dairy Processes

In dairy processes, there are significant simultaneous heating and cooling demands. A novel type of transcritical CO2 heat pump system is proposed, and its features and benefits are introduced. Bassed on the technical characteristics, primary energy-savings, and operating cost aspects, the CO2 heat pump system is simulated and compared to current heating and cooling systems used in dairy plants. The results show that the highest primary energy-saving rate of the CO2 heat pump is 51.5%. For fluid milk and cheese manufacturing processes, the primary energy-saving is 36.2% and 45.1%, respectively. In addition, the operating cost savings of fluid milk and cheese production are evaluated based on the cost structures in the states of Wisconsin, California and New York

Evaluation of the impact of phase change humidity control material on energy performance of office buildings

Phase change humidity control material (PCHCM) is a new kind of composite made of high performance PCM microcapsules and diatomite. The PCHCM composite can moderate the hygrothermal variations by absorbing or releasing both heat and moisture and significantly reduce the peak/valley values of indoor temperature and relative humidity. In this paper, a novel model is developed to evaluate the energy performance of office buildings with PCHCM. The model is validated by a series of experiments, and then applied to investigate the effect of PCHCM on energy consumption in different typical climates worldwide (i.e. Beijing, Paris, Atlanta, and Guangzhou). Results show that high values of energy efficiencies can be obtained in the climates which characterized by a wide amplitude of temperature and humidity difference all day along (Paris and Atlanta). Noteworthy, the highest potential energy saving rate could be up to 19.57% for the office building in Paris

Performance losses of drag-reducing spanwise forcing at moderate values of the Reynolds number

A fundamental problem in the field of turbulent skin-friction drag reduction is to determine the performance of the available control techniques at high values of the Reynolds number $Re$. We consider active, predetermined strategies based on spanwise forcing (oscillating wall and streamwise-traveling waves applied to a plane channel flow), and explore via Direct Numerical Simulations (DNS) up to $Re_\tau=2100$ the rate at which their performance deteriorates as $Re$ is increased. To be able to carry out a comprehensive parameter study, we limit the computational cost of the simulations by adjusting the size of the computational domain in the homogeneous directions, compromising between faster computations and the increased need of time-averaging the fluctuating space-mean wall shear-stress. Our results, corroborated by a few full-scale DNS, suggest a scenario where drag reduction degrades with $Re$ at a rate that varies according to the parameters of the wall forcing. In agreement with already available information, keeping them at their low-$Re$ optimal value produces a relatively quick decrease of drag reduction. However, at higher $Re$ the optimal parameters shift towards other regions of the parameter space, and these regions turn out to be much less sensitive to $Re$. Once this shift is accounted for, drag reduction decreases with $Re$ at a markedly slower rate. If the slightly favorable trend of the energy required to create the forcing is considered, a chance emerges for positive net energy savings also at large values of the Reynolds number.Comment: Revised version: change of title, revised intro, small improvements to figures and tex

ANALISIS HEMAT ENERGI PADA SELUBUNG BANGUNAN BIRO LAYANAN PENGADAAN BARANG DAN JASA DINAS PUPR PROVINSI PAPUA DENGAN OTTV

Building performance is a necessity in the context of a sustainable built environment. The design of buildings that involve the study of building performance has been contained in Law Number 30 of 2007 concerning Energy and Government Regulation Number 70 of 2009 concerning Energy Conservation. The purpose of this energy-efficient building analysis is to determine the level of energy savings of the Papua Province Procurement Services Bureau building that uses a shading device as a control for excess solar radiation intensity by using the Overall Thermal Transmitte Value (OTTV) calculation using the energy saving rate parameter based on SNI 6389:2011, where the building is said to be energy efficient if the OTTV shows a figure of less than 45 W/m2. The results show the number 34.02 W/m2, which means the building can be said to be an energy-efficient building

Effect of geometric factors on the energy performance of high-rise office towers in Tianjin, China

To improve energy efficiency of office buildings in Tianjin, we select a prototypical high-rise office tower as an example and focus on the effect of geometric factors on building energy performance. These factors include the orientation, plane shape, floor area, plane shape factor (the ratio of the plane length to the plane width, only as regards to a rectangle-shaped plane), floor height, floor number and window-to-wall ratio. The simulation is performed in DesignBuilder, which integrates artificial lighting with instantaneous daylight during the energy simulation process. The geometric factors of the defined prototype are examined in both single-parameter and multi-parameter evaluations. As to the multi-parameter results, the energy saving rate can vary by up to 18.9%, and reducing the floor height is observed to be the most effective means of reducing annual total end-use energy consumption, followed by increasing the plane shape factor and reducing the floor area. The results can serve as a reference for passive design strategies related to geometric factors in the early design stage