Simplified model for a ventilated glass window under forced air flow conditions
TL;DR: In this paper, the authors presented a study on a ventilated window composed of two glass sheets separated by a spacing through which air is forced to flow, and the model is one dimensional and unsteady based upon global energy balance over the glass sheets and the flowing fluid.
Abstract: This paper presents a study on a ventilated window composed of two glass sheets separated by a spacing through which air is forced to flow. The proposed model is one dimensional and unsteady based upon global energy balance over the glass sheets and the flowing fluid. The external glass sheet of the cavity is subjected to variable heat flow due to the solar radiation as well as variable external ambient temperature. The exchange of radiation energy (infrared radiation) between the glass sheets is also included in the formulation. Effects of the spacing between the glass sheets, variation of the forced mass flow rate on the total heat gain and the shading coefficients are investigated. The results show that the effect of the increase of the mass flow rate is found to reduce the mean solar heat gain and the shading coefficients while the increase of the fluid entry temperature is found to deteriorate the window thermal performance.
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TL;DR: In this article, the integrative thermal performance of a water-flow absorbing window as compared to the conventional single and double-pane absorptive glazing was investigated in a health club environment.
Abstract: While window glazing will be more and more extensively used in modern architecture, the increase in space thermal load as a result will deteriorate the global environment, incurring problems of air pollution and climate change. By connecting the cavity of a double pane window to a water-flow circuit, absorbed solar heat at the window glasses can be readily removed by the water stream. The water passage in this way can effectively lower the glass pane temperature, reduce room heat gain and therefore, the air-conditioning electricity consumption. Thermal comfort can be enhanced. Furthermore, the water-flow window can function as a hot-water preheating device. This article reports the integrative thermal performance of a water-flow absorbing window as compared to the conventional single and double pane absorptive glazing. The results based on the operation in health club environment are very encouraging. This demonstrates its good application potential in domestic–commercial buildings with stable hot-water demands.
67 citations
TL;DR: In this article, a comprehensive three-dimensional CFD model is proposed to model the physics in supply air windows and the results indicate that good agreement can be obtained, between experiment and CFD, if the LDV seeding issues are resolved and a turbulence model that is capable of resolving anisotropic turbulence and transition is used.
Abstract: Computational Fluid Dynamics (CFD) has been used, with considerable success, in modelling the physics in supply air windows. In this research, a comprehensive three-dimensional CFD model is proposed. Under the conditions investigated, the temperature rise and heat gain ranged from 6 K to 24 K and 23.45 W/m2 to 96.34 W/m2, respectively. The temperature rise and heat gain were higher in the natural flow case than in the forced flow cases. The models were experimentally validated in terms of velocity field, flow field and temperature rise. The velocity field was measured using Laser Doppler Velocimetry (LDV) and the overall flow field was captured using smoke for flow visualisation. Qualitatively, the CFD predictions are in good agreement with experiment. Quantitatively, there is noticeable error between experiment and CFD. The average error between CFD and experiment is: 3.46 K for temperature values at the outlet, 35% for axial velocities in the cavity and 44% for turbulence intensity in the cavity. The results indicate that good agreement could be obtained, between experiment and CFD, if the LDV seeding issues are resolved and a turbulence model that is capable of resolving anisotropic turbulence and transition is used.
52 citations
TL;DR: In this article, the thermal performance of a natural airflow window was examined through the use of a dynamic model, developed based on the integrated energy balance and airflow networks, and the validity of the model was first tested by measured data obtained from a prototype installed at an environmental chamber.
Abstract: Airflow window is highly useful in conserving building energy, and lessens the comfort problems caused by glazing. In this study, the thermal performance of a natural airflow window was examined through the use of a dynamic model, developed based on the integrated energy balance and airflow networks. The validity of the model was first tested by measured data obtained from a prototype installed at an environmental chamber. The application in the subtropical and temperate climate zones were then examined with the typical weather data of Hong Kong and Beijing. The findings confirmed that the natural airflow window can achieve substantial energy saving in both cities, and the reversible window frame is only required for Beijing, a location with hot summer and cold winter. The space cooling load via fenestration in Hong Kong, a subtropical city, can be reduced to 60% of the commonly used single absorptive glazing. In Beijing, as an example of the temperate climate, this can be reduced to 75% of the commonly used double glazing configuration in the summer period, and the space heat gain can be improved by 46% in the winter period.
50 citations
TL;DR: Suspended particle device (SPD) switchable glazing has potential to control transmission of solar radiation in the visible range by changing its transparency from 55% to 5%.
Abstract: Suspended particle device (SPD) switchable glazing has potential to control transmission of solar radiation in the visible range by changing its transparency from 55% to 5%. Outdoor test cell characterisation of a SPD switchable glazing offered the dynamic solar heat gain coefficient (SHGC) which varied between 0.05 (when opaque) and 0.38 (when transparent). Reduction of maximum temperature rise of 11% and 15% was possible using SPD “transparent” and “opaque” state compared to same area double-glazing. Insulated test cell with water flow heat exchanger was employed to measure the cooling load reduction potential of SPD glazing while its transmission changed from “transparent” to “opaque” state. A cooling load reduction up to 6 kW h for a 0.343 m 3 volume test cell was possible by changing a 0.21 m × 0.28 m SPD glazing transparency from “transparent” to “opaque”. Average overall heat transfer coefficient of SPD glazing varied between 5.02 W/m 2 K and 5.2 W/m 2 K for two different states.
50 citations
Cites background from "Simplified model for a ventilated g..."
...In a water flow glazing, water acts as an antireflection coating that absorbs short wave radiation but does not reduce the transparency of the glazing [18,19]....
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TL;DR: An improved zonal approach with a dynamic optical model of the venetian blind and airflow network model is proposed to model the mechanical ventilated double skin facade (DSF) in hot summer and cold winter zone in China as mentioned in this paper.
Abstract: An improved zonal approach with a dynamic optical model of the venetian blind and airflow network model is proposed to model the mechanical ventilated double skin facade (DSF) in hot summer and cold winter zone in China. It is validated by the experiment in both cooling and heating season cases. The comparison results show that the simulated results fit well with the measured results. The effects of the ventilation rate and slat angle on the inner glass temperature and heat gains through the DSF are discussed. Both increase ventilation rate and slat angle can decrease the inner glass temperature and heat gains through the DSF, but the decrease range is greater by increasing the slat angle. Compared to the slat angle at 0°, heat gains can be reduced by 63% when the slat angle at 60°. The proposed method can not only meet the requirements of engineering application, but also spend less computational time in modeling DSF dynamically in hot summer and cold winter zone in China. It can be used to evaluate the thermal performance and simulate the annual energy consumption of DSF.
50 citations
References
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01 Jan 1981
TL;DR: In this article, the authors developed composite relations for the variation of the heat transfer coefficient along the plate surfaces, and the mathematical development and verification of such composite relations as well as the formulation and solution of the optimizing equations for the various boundary conditions of interest constitute the core of the presentation.
Abstract: While component dissipation patterns and system operating modes vary widely, many electronic packaging configurations can be modeled by symmetrically or asymmetrically isothermal or isoflux plates. The idealized configurations are amenable to analytic optimization based on maximizing total heat transfer per unit volume or unit primary area. To achieve this anlaytic optimization, however, it is necessary to develop composite relations for the variation of the heat transfer coefficient along the plate surfaces. The mathematical development and verification of such composite relations as well as the formulation and solution of the optimizing equations for the various boundary conditions of interest constitute the core of this presentation.
481 citations
TL;DR: In this paper, the authors developed composite relations for the variation of the heat transfer coefficient along the plate surfaces, and the mathematical development and verification of such composite relations as well as the formulation and solution of the optimizing equations for the various boundary conditions of interest constitute the core of the presentation.
Abstract: While component dissipation patterns and system operating modes vary widely, many electronic packaging configurations can be modeled by symmetrically or asymmetrically isothermal or isoflux plates. The idealized configurations are amenable to analytic optimization based on maximizing total heat transfer per unit volume or unit primary area. To achieve this anlaytic optimization, however, it is necessary to develop composite relations for the variation of the heat transfer coefficient along the plate surfaces. The mathematical development and verification of such composite relations as well as the formulation and solution of the optimizing equations for the various boundary conditions of interest constitute the core of this presentation.
462 citations
TL;DR: In this article, the authors present a review of heat-mirror deposition technology including chemical vapor deposition using hydrolysis and pyrolysis reactions, dc and rf sputtering using reactive, biased and nonreactive techniques, vapor deposition and ion plating.
Abstract: Heat-mirror coatings are important as transparent insulation for a host of applications, including building window glazings. They reduce thermal emittance of glass and polymeric substrates, thereby decreasing the effective radiative loss of a glazing or window assembly. Properties of coatings and substrates, as well as various window designs, are detailed. The paper reviews heat-mirror deposition technology including chemical vapor deposition using hydrolysis and pyrolysis reactions, dc and rf sputtering using reactive, biased and nonreactive techniques, vapor deposition and ion plating. The properties of single-layer films including coatings of In 2 O 3 :Sn, doped SnO 2 , Cd 2 SnO 4 , noble and transition metal films are enumerated. Multilayer films described include dielectric overcoated metals such as ZnS/metal/ZnS, Bi 2 O 3 /Au/Bi 2 O 3 and TiO 2 /Ag/TiO 2 . Electrical, solar and infrared radiative properties are tabulated. Much of the data presented is also useful for photovoltaic and collector applications. New and innovative materials systems are suggested.
291 citations
TL;DR: In this article, the results of a numerical and experimental study on thermally efficient windows were presented, which indicated large reduction in the infrared and ultraviolet radiations while maintaining good visibility.
Abstract: This paper presents the results of a numerical and experimental study on thermally efficient windows. Experimental investigation using spectrophotometry was realized on simple and composite glass samples filled with air or phase change material. The transmittance and reflectance tests indicated large reduction in the infrared and ultraviolet radiations while maintaining good visibility. The number of glass sheets, their thickness and the gap between them were also investigated. The numerical model is based upon one-dimensional formulation of the composite window. The program was optimized and the predicted results are presented and discussed.
128 citations
TL;DR: In this article, the authors present the last 10 years of development in sun protection by use of electrochromic devices, thermotropic gels and polymer dispersed liquid crystalline systems.
Abstract: The aim of this review is to present the last 10 years of development in sun protection by use of electrochromic devices, thermotropic gels and polymer dispersed liquid crystalline systems. Furthermore, the properties of new lyotropic liquid crystalline and thermotropic hydrogels are discussed. Thermochromic hydrogels, which change their colour by changes in the temperature, also are presented. The relationship between gel composition, optical behaviour and thermodynamic properties as investigated by differential scanning calorimetry (DSC) is also demonstrated.
81 citations