In the present study,the insulation mechanism of building walls during the summer days and nights is investigated with a realistic approach to enhance their performance.A fiber layer,as a porous medium with air gaps,i...In the present study,the insulation mechanism of building walls during the summer days and nights is investigated with a realistic approach to enhance their performance.A fiber layer,as a porous medium with air gaps,is used along the wall layers to decrease the energy loss.Meanwhile,the radiation heat flux variation during five days in a row has been considered for each side of the building,and it is tried to reach the optimum values for geometrical factors and find suitable insulation for each side of the building.A lattice Boltzmann method(LBM) based code is developed to simulate the actual chain of the heat transfer which consists of radiation,conduction,forced and natural convection combination within wall layers including fiber porous insulation.The results indicate that for the current insulation model,the effect of natural convection on the heat transfer is not negligible and the existence of the porous layer has caused a positive impact on the heat loss reduction by decreasing the circulation speed.Also,by using the optimum location and thickness for the insulation layer,it is showed that each side of the building has different rates of energy loss during a day,and for the appropriate insulation,they need to be evaluated separately.展开更多
Water permeability is an important property of nonwoven geotextiles used in drainage field, and usually it is obtained by testing individual layer or multi-layered nonwoven geotextiles. However, the permeability coeff...Water permeability is an important property of nonwoven geotextiles used in drainage field, and usually it is obtained by testing individual layer or multi-layered nonwoven geotextiles. However, the permeability coefficient tested by using different layers would be different for the same nonwoven geotextile. In this paper, the relation between them is studied based on Darcy's law. The study shows that vertical permeability coefficients are theoretically invariable no matter how many layers are tested; but experimental results show that vertical permeability coefficients decrease with the increase of nonwoven geotextile layers number.展开更多
Traditional light bulbs （e.g., incandescent, fluorescent） use too much electricity, convert very little energy into light of sufficient quality and in their production use toxic contaminants. During the last few yea...Traditional light bulbs （e.g., incandescent, fluorescent） use too much electricity, convert very little energy into light of sufficient quality and in their production use toxic contaminants. During the last few years, a new type of light source, LED （light emitting diode） bulb, has gained increasing popularity and its costs are set to plunge even further. LED bulbs offer many advantages over traditional sources, and they can be used as a direct replacement to existing lighting. This paper will use a spreadsheet-based analysis with hourly solar data supplied by Ecotect to show that, the efficiency of LED installations can be increased when used in conjunction with photovoltaic modules, as the two generate （and use） DC （direct-current） electricity, thereby eliminating intermediate-level losses in the electronic circuitry. If a storage battery is included, the solar panels generate electricity during the times when the occupants are not necessarily using the lighting, but the stored electricity can be used to power the lighting when the energy is required. The latest results demonstrate that, a slight reduction in the required floor area to be lit allows the solar-battery-LED system to be implemented in small buildings using a storage battery size that is within the range of present commercial devices.展开更多
文摘In the present study,the insulation mechanism of building walls during the summer days and nights is investigated with a realistic approach to enhance their performance.A fiber layer,as a porous medium with air gaps,is used along the wall layers to decrease the energy loss.Meanwhile,the radiation heat flux variation during five days in a row has been considered for each side of the building,and it is tried to reach the optimum values for geometrical factors and find suitable insulation for each side of the building.A lattice Boltzmann method(LBM) based code is developed to simulate the actual chain of the heat transfer which consists of radiation,conduction,forced and natural convection combination within wall layers including fiber porous insulation.The results indicate that for the current insulation model,the effect of natural convection on the heat transfer is not negligible and the existence of the porous layer has caused a positive impact on the heat loss reduction by decreasing the circulation speed.Also,by using the optimum location and thickness for the insulation layer,it is showed that each side of the building has different rates of energy loss during a day,and for the appropriate insulation,they need to be evaluated separately.
文摘Water permeability is an important property of nonwoven geotextiles used in drainage field, and usually it is obtained by testing individual layer or multi-layered nonwoven geotextiles. However, the permeability coefficient tested by using different layers would be different for the same nonwoven geotextile. In this paper, the relation between them is studied based on Darcy's law. The study shows that vertical permeability coefficients are theoretically invariable no matter how many layers are tested; but experimental results show that vertical permeability coefficients decrease with the increase of nonwoven geotextile layers number.
文摘Traditional light bulbs （e.g., incandescent, fluorescent） use too much electricity, convert very little energy into light of sufficient quality and in their production use toxic contaminants. During the last few years, a new type of light source, LED （light emitting diode） bulb, has gained increasing popularity and its costs are set to plunge even further. LED bulbs offer many advantages over traditional sources, and they can be used as a direct replacement to existing lighting. This paper will use a spreadsheet-based analysis with hourly solar data supplied by Ecotect to show that, the efficiency of LED installations can be increased when used in conjunction with photovoltaic modules, as the two generate （and use） DC （direct-current） electricity, thereby eliminating intermediate-level losses in the electronic circuitry. If a storage battery is included, the solar panels generate electricity during the times when the occupants are not necessarily using the lighting, but the stored electricity can be used to power the lighting when the energy is required. The latest results demonstrate that, a slight reduction in the required floor area to be lit allows the solar-battery-LED system to be implemented in small buildings using a storage battery size that is within the range of present commercial devices.
