Research On The Construction Of Solar Heat Collection/Insulation Energy-Saving Window And Its Thermal Characteristics In Building

At present,building energy consumption accounts for nearly 30%of the total social energy consumption,so the development and promotion of low-energy buildings has become the key to promote energy conservation and carbon reduction.After years of development,the thermal insulation effect of exterior walls and roofs has reached the limit.Exterior windows of buildings are key building components to realize indoor lighting,lighting,ventilation,landscape and other functions,as well as weak components of thermal insulation.It is difficult for existing energy-saving windows to take into account the dual performance of exterior windows as building heat gain and heat loss components.It is of urgent practical significance to develop a kind of energy-saving thermal insulation window to to improve indoor thermal environment and reduce building energy consumption.In this paper,we propose and construct a solar heat collection/insulation energy-saving window(SHC/IESW),which is an energy-saving component that can be adjusted to meet the different heat transfer requirements of building windows in different seasons and time periods.The SHC/IESW is formed by the installation of an adjustable thermal insulation curtain as a core component on one side of the transparent glass window,which can be classified as A,B,C and D(structure A,B,C and D):the air layer thickness of structure A and C is 8 cm and 11cm,respectively,the thickness of the thermal insulation curtain is 2 cm,and the thermal insulation device is installed on the outdoor side.The thickness of the thermal insulation curtain of structure B and D is 2 cm and 3 cm respectively,and the thickness of the air layer is 8 cm,which are installed in the indoor side.Turning on the thermal insulation device only at night in winter to reduce heat loss,and turning off the device at other times,which can simultaneously realize daytime heat collection and nighttime thermal insulation in winter,daytime shading and nighttime heat dissipation in summer.In Taiyuan meteorological conditions,parameters such as indoor temperature,internal and external surface temperature of glass in rooms with four structures SHC/IESW and transparent6mm glass window(OW)were experimentally monitored,and their respective thermal insulation,shading and heat collection effects were compared and analyzed;through experimental value combined with theoretical analysis,Nu number characteristic correlation formula of convective heat transfer was derived,the total heat transfer coefficients for each SHC/IESW were calculated and verified,the annual combined energy saving of SHC/IESW relative to ordinary hollow glass windows was obtained,temperature,flow rate,pressure,and energy changes in the SHC/IESW cavity were analyzed by numerical simulation and hydromechanics calculations to explore the mechanism of air flow and convective heat transfer in the cavity;the influence of SHC/IESW on indoor thermal environment and building energy consumption was determined by energy consumption and indoor thermal environment simulation,the installation conditions were optimized,the optimal critical window-wall ratio for a typical urban SHC/IESW installed in a south-facing building was obtained.The main results are as follows:(1)SHC/IESW has significant thermal insulation,shading and heat collection effects.Compared with OW room,the installation of A,B,C and D structures can increase the average indoor temperature at night in winter by 2.9%,7.6%,4.8%and 12%respectively.When the width of the cantilevered structure increases by 0.1 m,the average indoor temperature decreases by 0.12℃in summer day.The average daytime indoor temperature in SHC/IESW rooms in winter is 1-2℃higher than that in ordinary hollow glass windows.B and D structures are suitable for installation in the north of the building to maximize the thermal insulation effect;Structure A and C are suitable for installation in the south of the building to achieve thermal insulation,sun shading and heat collection effect.(2)The Nu number characteristic correlation of SHC/IESW cavities under different Reynolds numbers is derived.Then the heat transfer coefficient and load coefficient of A,B,C and D are 1.71 W/m~2·K,1.39 W/m~2·K,1.60 W/m~2·K,1.12 W/m~2·K and 0.551 k Wh/K,0.538k Wh/K,0.546 k Wh/K and 0.531 KWh/K,respectively.Compared with OW,the energy saving potential of the four structures is 13.8%,15.9%,14.5%and 16.9%,respectively.4 m~2 of SHC/IESW(A)was installed on the south side of the building,compared to conventional hollow glass windows,providing 309.929 k Wh of cumulative shading during the summer day and 113.697 k Wh of cumulative heat loss at night.In winter,the accumulated heat collection during daytime is 167.894 k Wh,the accumulated heat preservation at night is 262.839 k Wh,and the annual accumulated energy saving is 854.359 k Wh.(3)The thickness of the air layer and the width of the outlet have significant effects on the heat transfer intensity of the SHC/IESW cavity.When the outlet width is 10 mm,the thickness of air layer increases from 20 mm to 120 mm,and the wind speed of cavity section,outlet temperature,section temperature and thermal insulation curtain surface temperature decrease by 0.53 m/s,9.13℃,6.65℃and 8.66℃,respectively.When the air layer thickness is 80 mm,the outlet width increases from 5 mm to 150 mm,and the wind speed,outlet temperature,section temperature and insulation curtain surface temperature decrease by 1.71 m/s,1.68℃,1.1℃and 0.97℃,respectively.Air layer thickness and outlet width should be 100 mm.(4)Kinetic energy difference between cavities is the dominant factor of fluid movement in cavities and the main mechanism of SHC/IESW heat transfer.The larger the kinetic energy difference is,the larger the momentum difference is,and the larger the blocking force is.At the same time,the velocity reconfiguration intensity and local vortex effect are enhanced during the flow process,leading to the greater energy loss of the flow between the sections,the lower the activity of the cold air in the cavity,the less heat removed from the cavity thermal wall,and the better the SHC/IESW insulation effect.Increasing the thickness of the air layer and appropriately increasing the width of the outlet can increase the kinetic energy difference between the inlet and outlet sections of the cavity and improve the SHC/IESW insulation effect.(5)SHC/IESW installation has a significant impact on both the indoor thermal environment and building energy consumption.SHC/IESW has a more uniform temperature field and greater comfort than OW rooms.The room thermal efficiency increased with the decrease of HTC and the increase of ESS,and increased first and then decreased with the increase of WWR.When HTC was 1.12W/m~2·K,WWR was 0.53,and ESS was 75%,the highest thermal efficiency was 0.386 K/W.Compared with OW room,the annual heat load reduction rate of B and D room can reach 20%～30%.The annual cooling load drop rate of structure A and C varies with the orientation,and when the orientation is south,north,east and west,it is 14.8%,7.1%,8.2%and 10%,respectively.The width of the overhanging structure increases from 0.5m to 1.5m,and the cooling load reduction rate increases from 16.6%to 43.9%.The influence factors on the annual total load per unit gross floor area were window-wall ratio,SHC/IESW structure and SHC/IESW orientation,which were 67.50,3.28 and 0.11,respectively.For the south-facing SHC/IESW,typical cities Lhasa,Changchun,Taiyuan,Nanchang,Nanning and Kunming have optimal south-facing window-wall ratios of 0.61,0.46,0.53,0.55,0.58 and0.61,respectively,which exceed the local limits specified in the residential building energy efficiency design standards.(6)SHC/IESW has significant environmental and economic benefits per unit of floor area.Based on the material prices of Taiyuan city in 2020,taking OW as a reference,SHC/IESW can save up to 52.88 k Wh/(m~2·year)of energy consumption and 0.012 tons/(m~2·year)of coal consumption per year.The annual emissions of carbon dioxide,sulfur dioxide,soot and ash are reduced by 29.97 kg/m~2,0.038 kg/m~2,0.132 kg/m~2 and 2.406 kg/m~2,respectively.SHC/IESW can reduce building energy costs by 8.78 yuan/year·m~2 and save 27%compared to hollow glass windows.SHC/IESW has significant thermal insulation,shading,and heat collection and cooling effects,with a small overall heat transfer coefficient and significant energy saving potential.Through controlling the structural parameters and installation conditions,the heat transfer performance can be effectively adjusted,the indoor thermal environment can be improved,and the building energy consumption can be greatly reduced.When it is placed in the south of the building,the existing window-wall ratio limit can be broken,and it can be widely used in low energy consumption buildings,especially to promote the energy saving and consumption reduction of industrial and commercial buildings and rural dwellings.