Abstract: In this study, the decentralized ventilation (DV) performance of a small air ventilator to replace natural ventilation for use in urban areas is analyzed and compared to conventional centralized ventilation (CV) systems in European climates. Selected European weather conditions were used to determine acceptable conditions for the operation of fan-assisted ventilation systems and to analyze the decentralized ventilation system’s cooling and heating loads. Entire fan and pump loads of DV system are numerically calculated based on published data. Compared with a conventional centralized ventilation system, this system has shorter air transport distances and therefore entails lower pressure losses. In a decentralized system, fan speed and airflow rate are adjusted simply and effectively depending on indoor thermal conditions. A radiant panel with decentralized ventilation system (RPDV) is shown to have the lowest heating, ventilation, and air conditioning (HVAC) energy consumption because it not only minimizes supply and exhaust air pressure losses, but can also be operated as a fan-assisted natural ventilation system during periods when outdoor air can be used without additional thermal loads. Based on numerically calculated and measured data, this study newly adds fan and pump energy analysis of decentralized ventilation system compared to centralized ventilation systems. This study shows the fan and pump energy consumption with analysis of fan-assisted DV system considering outdoor weather condition in European climate.
Permalink: https://doi.org/10.1016/j.enbuild.2015.11.044

Abstract: Large-eddy simulations (LES) are carried out to investigate the shock induced transient flow through a planar nozzle mimicking a shock tube experimental setup at shock Mach number Ms=1.86. A fifth-order Weighted Essentially Non-oscillatory (WENO) scheme based 3D numerical flow solver equipped with an immersed boundary method and Wall-Adapting Local Eddy-viscosity (WALE) model is used for this purpose. A comparative study is presented to show the effect of different flow initializations namely, i) without flow fluctuation, ii) with white random noise and iii) with homogeneous isotropic turbulence superimposed on the flow-field. Results are in good agreement with the experimentally measured speeds of the primary shock wave and the following secondary shock wave. It is found that an improper initialization of the flow-field may lead to erroneous predictions of the flow characteristics, particularly the location of the separation point and the unsteady shock/boundary layer interaction. Substantial improvement in the prediction of the early-stage Mach reflection, complex shock/boundary layer interaction is observed with superimposed turbulent fluctuations as an initial flow-field. This is when a homogeneous incompressible isotropic turbulence superimposed on the shocked section is assigned as initial fluctuating field. An additional test case with the latter method, having an approximately four times higher mesh resolution, is used for detailed investigation of the unsteady flow fields, turbulent statistics and boundary layer separation. Results show considerable improvements in the prediction of the secondary shock and the flow separation location compared to the previous findings which dealt with lower mesh resolution. The turbulent flow structures are depicted using the mean flow-field which is spatially averaged over the span-wise homogeneous direction. Time-averaging on the fly turns out to be inadequate, since it leads to a spatial shift of the separation bubble. The reason for this is the use of past flow information only, due to the lack of future information. This in-turn invokes the need of phase-averaging to extract suitable physically statistics of the turbulent flow-field for further deeper analysis.
Permalink: https://doi.org/10.1016/j.ast.2016.03.006

Abstract: The aim of this study is to investigate experimentally and numerically the effect of the crosswind and wagon numbers to the aerodynamic characteristics as well as fuel consumption of the locomotive Alstom AD43C and some specified passenger wagons behind it. Turbulent, incompressible, and 3D airflow has been considered for numerical simulation. Simulations are carried out for yaw angles 0°, 15°, and 30° for different airflow velocities. A total of 16 pressure tabs were employed to measure the air pressure at various points on the 1:26 scaled model of the train in the experimental investigation. Comparison between the numerical and the experimental results verifies the numerical simulation method. The results show that the variation of the longitudinal force coefficient (LFC) and side force coefficient (SFC) in the middle wagons (except for the first two and last two wagons) is similar. The LFC and SFC of these wagons are 0.239 and 1.251, respectively, for the Reynolds number 1.587×10^5 (airflow velocity 30 m/s) and the yaw angle 30°. However, the Reynolds number effect is insignificant. The yaw angle effect on the train fuel consumption is more important. Moreover, the fuel consumption increases by approximately 25 % from the yaw angle 0° to 30° for ten wagons at the Reynolds number 1.587×10^5.
Permalink: https://doi.org/10.1007/s40997-016-0013-9

Abstract: In this paper, the natural convection heat transfer inside a square enclosure with partial heating has been studied in the unsteady and steady state. In order to implement the partial boundary condition, a part of the left wall was maintained at high temperature and the rest of it was considered to be insulated. The Rayleigh numbers were 10⁴, 10⁵ and 10⁶. The critical Rayleigh number which is defined as the transition of flow stream from pure conduction to natural convection was also investigated. The results indicated that in the unsteady state, with an increase in the heating region and decrease in the Rayleigh number, the time to reach the steady state of the solution decreases. Furthermore, heating from the middle of the left wall requires shorter time to reach the steady state. In the steady state, at Rayleigh numbers 10⁴ and 10⁶, heating from the middle part of the left wall results in higher Nusselt number for S/L < 0.6 compared to the heating from the bottom, while in the Rayleigh number 10⁶ this phenomenon occurs for S/L < 0.4. It was also observed that the increase in the Rayleigh number causes the flow pattern to be changed and the vortices to be multiple.
Permalink: https://doi.org/10.1615/InterJFluidMechRes.v43.i3.50

Abstract: In the present study, the lamination effect in a micro T-mixer with non-aligned inputs on the mixing index has been investigated numerically in four different cases. The multi-block lattice Boltzmann method has been implemented for the flow field simulation and the second order upwind finite difference scheme has been used to simulate mass transfer. Reynolds numbers includes in the range of 10 ≤ Re ≤ 70. The simulation results show that the lamination effect in the mixer inputs, despite of its simple design, causes the interface of two fluids to increase and also to make the vortex effect stronger in the confluence of two fluid streams that increases the mixing index considerably. Of four lamination cases included for the mixing input, the maximum mixing index is for the vertical and asymmetrical lamination at the Reynolds number of 70 that is equal 0.689 and the minimum mixing index is for the horizontal and asymmetrical lamination at the Reynolds number of 10 that is equal 0.198.
Permalink: https://doi.org/10.1007/s00231-015-1584-5

Abstract: Given the high impact that air leaks have on buildings’ energy expenses, most developed countries have set out norms which regulate their presence in homes. Chile will soon begin this process; however, the airtightness revision strategy in envelopes has not been resolved as of yet. This article presents a tool to Assess Airtightness in Design, EHeD. The software will allow predicting the performance of homes under the regulations which will be set out, aiding designers, builders or owners to make decisions when making changes to improve airtightness. EHeD has been validated through pressurization tests in diverse homes across the country, with results that are in line with expectations, thus validating its calculation model. The methodology considers three stages: determining the main factors that have an impact on the airtightness in Chilean homes, preparing an airtightness database for each component (wall, windows and doors) and preparing a calculation model that is integrated in an IT interface.
Permalink: https://doi.org/10.3390/su8101000

Abstract: The objective of the present study was to develop a solar shading control strategy for venetian blinds applied on office buildings in cold climates in order to achieve acceptable energy use and indoor environmental performance. A control strategy based on a combination of internal and external shading develop within the Norwegian R&D project “Fasader i glass som holder hva vi lover” (“Glazed facades keeping what we promise”, translation by author) was extended with factors related to glare, daylight sufficiency and view to the outside. The study used full-scale experiments in a test room in Aalborg, Denmark, to verify the performance of the control strategy, and the study was further expanded with annual simulations of the office room at different locations. Results of the annual performance illustrated that the proposed control strategy would lead to satisfying compromises between the energy and indoor environmental performance. Generally, the investigation exemplifies the importance of doing integrated evaluations of energy use and thermal and visual comfort when making decisions regarding solar shading control strategies.
Permalink: https://doi.org/10.1016/j.enbuild.2016.03.014

Abstract: The study investigates if antibiotic-resistance genes (ARGs) could be detected in floor dust in a Norwegian kindergarten using a polymerase chain reaction (PCR)-based approach. ARGs were found in samples from most of the rooms even though the kindergarten had only recently opened. This paper shows that a variety of ARGs quickly appear in kindergarten floor dust and that these can be efficiently detected by the approach described.
Permalink: https://doi.org/10.13140/RG.2.2.20693.01762

Abstract: The perceived indoor climate resulting from two ventilation control strategies was evaluated in a classroom of the first school built according to the Norwegian passive house standard. Both strategies consisted of varying the ventilation rate according to room demand, ie. Demand-Controlled Ventilation (DCV). The existing strategy consisted of varying the ventilation rate in order to maintain a constant carbon dioxide concentration of 800 ppm in the classroom (constant-CO₂ control). A new strategy was implemented which consisted of a combined CO₂ and temperature control, ie. to control towards a proportionally lower CO₂ concentration when the indoor temperature increases. The aim with this strategy was both to address overheating and the fact that perceived indoor air quality decreases when temperature rises. Indoor climate measurements, as well as questionnaires on the perceived indoor air quality and thermal comfort (completed by the pupils), were used to compare both strategies. An acceptable perceived indoor climate was reported for both strategies, with a slight improvement for the combined CO₂ and temperature control. The data from the questionnaires were then analyzed using a random effect linear regression model. The regression analysis revealed that the combined CO₂ and temperature control reduced the discomfort by variations of the indoor temperature significantly compared to the existing strategy (constant-CO₂ control). If correctly implemented, combined CO₂ and temperature DCV therefore appears to be a relevant solution for schools built to passive house standard.
Permalink: https://doi.org/10.1080/14733315.2016.11684094