Tilted Window Research Articles

Transmittance of transparent horizontal and tilted windows supporting large non-absorbing pendant droplets

This study establishes that the deviation of large pendant droplets from an ideal cap-shape due to gravity can have significant and complex impacts on the normal-hemispherical and directional-hemispherical transmittances of light through horizontal and tilted transparent windows. First, the shape of pendant droplets larger than the capillary length was predicted numerically by balancing gravitational and surface tension forces for various droplet volumes, contact angles, and window tilt angles. Then, light transfer through windows supporting such numerically generated droplets was simulated using the Monte Carlo ray-tracing method. The window transmittance for large droplets was found to be nearly independent of droplet spatial arrangement and size distribution for relatively narrow size distributions. Furthermore, the droplets could be assumed to be cap-shaped in predicting the normal-hemispherical transmittance for droplet volumes V< 10 µL and contact angles θc<θcr where θcr is the critical angle for total internal reflection at the droplet/air interface. However, for larger droplets and/or contact angles, assuming droplets to be cap-shaped caused the transmittance to be overestimated by as much as 37% for horizontal windows. This was due to gravity-induced deformation of the droplet shape resulting in increased reflection at the droplet/air interface. For tilted windows, the droplet deformation caused the normal-hemispherical transmittance to increase with increasing droplet volume and window tilt angle. For both horizontal and tilted windows, transmittance decreased linearly with increasing droplet surface area coverage. These results and numerical tools can be used to design energy efficient solar stills, greenhouses, and covered photobioreactors, for example.

Determination of a Methodology to Derive Correlations Between Window Opening Mass Flow Rate and Wind Conditions Based on CFD Results

This paper presents a methodology for the development of an empirical equation which can provide the air mass flow rate imposed by single-sided wind-driven ventilation of a room, as a function of external wind speed and direction, using the results from Computational Fluid Dynamics (CFD) simulations. The proposed methodology is useful for a wide spectrum of applications, in which no access to experimental data or conduction of several CFD runs is possible, deriving a simple expression of natural ventilation rate, which can be further used for energy analysis of complicated building geometries in 0-D models or in object-oriented software codes. The developed computational model simulates a building, which belongs to Rheinisch-Westfälische Technische Hochschule (RWTH, Aachen University, Aachen, Germany) and its surrounding environment. A tilted window represents the opening that allows the ventilation of the adjacent room with fresh air. The derived data from the CFD simulations for the air mass flow were fitted with a Gaussian function in order to achieve the development of an empirical equation. The numerical simulations have been conducted using the Ansys Fluent v15.0® software package. In this work, the k-w Shear Stress Transport (SST) model was implemented for the simulation of turbulence, while the Boussinesq approximation was used for the simulation of the buoyancy forces. The coefficient of determination R2 of the curve is in the range of 0.84–0.95, depending on the wind speed. This function can provide the mass flow rate through the open window of the investigated building and subsequently the ventilation rate of the adjacent room in air speed range from 2.5 m/s to 16 m/s without the necessity of further numerical simulations.

A novel coupling control with decision-maker and PID controller for minimizing heating energy consumption and ensuring indoor environmental quality

Due to climate change, global energy crisis, and high-quality life requirement for people, decreasing building energy consumption and enhancing indoor environment quality through control of heating, ventilation, and air conditioning systems tend to be increasingly important. Therefore, favorable control methods for heating and ventilation systems are urgently necessary. In this work, a new coupling control with decision-maker was proposed, developed, and investigated; meanwhile, several demand controlled ventilation strategies combined with heating control method was compared considering heating energy consumption, thermal comfort, and indoor air quality. In order to properly model the service systems, the air change rates and thermal time constants have been first measured in a reference office installed with commonly applied bottom-hinged tilted windows in our low-energy building supplied by geothermal district heating. Then, simulations have been carried out across two typical winter days in the reference office. The results illustrate that the proposed combination of suitable heating and demand controlled ventilation coupling control methods with decision-maker and proportional-integral-derivative (PID) controller could greatly reduce heating consumption in the reference room during the office time: around 52.4% (4.4 kW h energy saving) per day in winter in comparison to a commonly suggested method of intensive and brief airing. At the same time, it could ensure indoor CO2 concentration to keep within the pre-set ranges (Pettenkofer limit: 1000 ppm) as well as low variations of indoor temperature (standard deviation (SD): 0.1°C).

Study of infiltration through sliding windows with respect to closing mechanisms and their locations in a building during winter season

ABSTRACTInfiltration through windows accounts for a significant heat loss in buildings during winter, leading to the need to minimize uncontrolled air flow. Improvement of window air tightness is important for reducing heat loss by infiltration through windows. In this study, infiltration is measured for general sliding (GS), parallel sliding tilt (PST) and lift sliding (LS) windows according to ASTM E283, a standard for window infiltration measurement. Measured window infiltration data, pressure coefficients calculated with STAR-CCM+ and outdoor weather data of Seoul are used in CONTAM, a network based ventilation simulation program to estimate infiltration during winter season for three sliding window types and their locations in a building. The results show that infiltration is highest for east located general sliding type window, and lowest for west located parallel sliding tilt window. Monthly analysis shows that for an east located window, infiltration is highest during January and lowest during December.

Field investigations of stack ventilation in a residential building with multiple chimneys and tilted window in cold climate

Ventilation stacks are becoming increasingly common in the design of naturally ventilated buildings. They offer a method for achieving a fixed flow pattern irrespective of internal and external conditions. In this paper, the field measurements results are presented on the stack ventilation effect in a configuration with multi-chimneys which interact with tilted pivot windows. A residential two-family detached house was chosen to perform the measurement campaign. The house was located in a cold climate region in northern Poland. The measurements were performed in June during the time period of transient climate conditions between spring and summer. Local climate conditions, indoor climate conditions and air velocities in vent inlets and outlets were measured. In order to interpret measurement results, a modified model of a tilted pivot window with an axis at the bottom was proposed, based on a model used in single-sided ventilation investigations. The measured results confirmed the usefulness of the proposed approach. The loss coefficient (discharge coefficient) of 0.345 was lower than the loss coefficient of 0.60, usually assumed for small rectangular openings during natural ventilation. In the absence of wind when the stack effect acted only, the air changes per hour slightly exceeded the standard minimum value. The tilted window leeward wind significantly reduced the stack effect and ACH.

Effects of ventilation behaviour on indoor heat load based on test reference years.

Since 2003, most European countries established heat health warning systems to alert the population to heat load. Heat health warning systems are based on predicted meteorological conditions outdoors. But the majority of the European population spends a substantial amount of time indoors, and indoor thermal conditions can differ substantially from outdoor conditions. The German Meteorological Service (Deutscher Wetterdienst, DWD) extended the existing heat health warning system (HHWS) with a thermal building simulation model to consider heat load indoors. In this study, the thermal building simulation model is used to simulate a standardized building representing a modern nursing home, because elderly and sick people are most sensitive to heat stress. Different types of natural ventilation were simulated. Based on current and future test reference years, changes in the future heat load indoors were analyzed. Results show differences between the various ventilation options and the possibility to minimize the thermal heat stress during summer by using an appropriate ventilation method. Nighttime ventilation for indoor thermal comfort is most important. A fully opened window at nighttime and the 2-h ventilation in the morning and evening are more sufficient to avoid heat stress than a tilted window at nighttime and the 1-h ventilation in the morning and the evening. Especially the ventilation in the morning seems to be effective to keep the heat load indoors low. Comparing the results for the current and the future test reference years, an increase of heat stress on all ventilation types can be recognized.

Air change rates driven by the flow around and through a building storey with fully open or tilted windows: An experimental and numerical study

Abstract Air change rates (ACH) through open and tilted windows in rooms of residential buildings driven by atmospheric motions are investigated to evaluate natural ventilation concepts. Model experiments in wind tunnels, numerical flow simulations (CFD) and thermal building simulations are used. Pressure profiles are measured on the facade of a building model for selected wind directions and velocities. A separated sample storey and a sample single room in larger scales were used to measure air transport through window openings under the influence of the external pressure distribution. The ACH was obtained by velocity measurements in the window cross sections and by tracer gas measurements using the decay method. ACH from CFD computations of the wind tunnel environment agreed well with the experimental values. Therefore the numerical simulations were extended to real dimensions. The dependency of the ACH on the position in the external flow field and a scaling law for the ACH are presented. The wind-driven ACH obtained are much larger than the temperature-driven values prescribed in the Austrian standard O-NORM B 8110-3 on the prevention of high room temperatures during summer. A comparison of the impact of temperature-driven with wind-driven ACH, i.e. natural ventilation concepts, in thermal building simulations is presented.

Window ventilation efficiency in the case of buoyancy ventilation

This paper presents the results of a number of measurements that were carried out in order to quantify the ventilation efficiency of different types of windows under buoyancy ventilation. The tested window types were double vertical slide window, turn window, tilt window, awning window, horizontal pivot window and vertical pivot window. Each testing of these types comprised different opening rates, so that the performances could be compared across a wide range of window states. Performance criteria were the mass flow, the air change rate and the CO2 removal rate, each of them normalised to a temperature difference of 1K. The horizontal pivot window turned out to be the best performing type of window.

창의 기울기에 따른 건축물 에너지 소비량 예측

Most of domestic building generally don`t have fixed shading devices considering of appearance and aesthetic issues. In this study is suggested that tilt window simultaneously has a role of shading and blocking solar radiation. The tilt window thermal performance is investigated by relation ship between inclination and heating cooling road. As comparing vertical window with and of tilt window respectively, the heating load is increased by 3.6% and cooling load is reduced by 8.1% on tilt window and the heating load is increased by 5.3% and cooling load is reduced by 11.5% on tilt window. Especially, the total load of alternative tilt window is showed the reduction rate 2.6% and3.6% compared of vertical window. Therefore, the tilt window is possible to role of shading of solar radiation and reduction of heating and cooling load.

High power Er-Yb linear optical fibre amplifierfor CATV applicationswith gain tilt window over 11 nm and integrated dispersion pre-compensation

An Er-Yb fibre amplifier has been constructed with dispersion compensation and gain tilt correction. Gain tilt has been minimised within 0.2 dB/nm for the spectral width of 11 nm and input power range of 0–4 dBm. A noise figure of 5 dB and output power of 21 dBm has been obtained for this operating range. Tests using a 77 channel NTSC signal show its compatibility to CATV applications.

Microcomputer-aided measurement of air change rates

Air change rates are measured by a non-dispersive one-beam IR gas analyzer using the decay and constant-emission methods with nitrous oxide as tracer gas. Disturbing influences due to H 2O and CO 2 are low. The analyzer is coupled via a RS-232-C interface to a microcomputer, which is programmed to service the following functions: (1) calibration, (2) preparation and control of measurements, (3) recording, displaying and storing of data, (4) evaluation of results, and (5) error analysis. The implemented programs provide an instant access to results. The whole equipment is installed in compact form on a mobile rack. Measurements have been taken in a university laboratory to examine air change rates with (1) closed door and window, (2) open door only, and (3) tilted window only. Typical results are given and show where the decay method or the constant-emission method is more appropriate.