Heat Transfer Characteristics And Ventilation Properties Of Double Windows

With the improvement of living standards and increase need of indoor comfortin rural areas of northeast China, the insulation performance of building envelope isgetting much better. Because of the good thermal insulation and airtightperformance of the double windows, they’re now widely used in northeast China.Double windows, though greatly reducing the heating load, lead to poor ventilationindoor. The poor indoor air quality in heating priod greatly affects the residents’health.The paper aims at the double windows. Firstly, the heat transfer characteristicsfor various double-windows, including double-glazed, triple-glazed and four-glazedwindows, have been theoretically studied. Also, four heat transfer influence factors（number of window pane, glazing arrangements, glass thickness and air chamberwidth） have been discussed respectively. Then, according to the Chinese65%energy efficiency standards in severe cold regions, the double window types whichsuitable for severe cold regions have been put forwarded, as well as somesuggestions for the design and installment of double windows.Then, a little improvement is made for the double window（single windowoutside+double insulating glass inside） to turn it into a ventilated window, leavingan air inlet bar on the lower part of outside window and an air outlet bar on theupper part of inside window. With the effect of temperature difference betweenindoor and outside and solar radiation, the fresh air circulates through the windowgap and preheating by the window pane under heat pressure. The preheated fresh airis introduced to the interior and dilutes the indoor pollutants.The CFD technology is used to study four factors, including solar radiationintensity, window height, air chamber width and inlet/outlet height, which affect theventilation rate and supply air temperature. The study shows that the temperaturedifference between inside and ouside and double windows’ structure are the maininfluence factors of ventilation rate. Solar radiation intensity has much influence onsupply air temperature other than ventilation rate. Then, the heat recovered per unittime is set as a goal for choosing the optimal double windows’ structure, which is 1.8m height,150mm air chamber width and30mm height inlet/outlet.Finally, CFD and theoretical analysis are used to analysis the effect ofventilated window respectively from two aspects: indoor thermal environment andindoor air quality. Because different pollutants produced in different time, the paperclassifies various pollutants and time prieod （daytime, night and fire-making time）for better studying the dilution curves of each pollutant.For indoor thermal environment studies, the ventilation rate obtained by thestimulation increases linearly with the temperature difference between indoor andoutside, while supply air temperature decreases linearly. Without the effect of soalrradiation, the temperature rise of supply air will be9.7¹3.1℃. As the supply airvelocity is small and high location of outlet, there’s no blow feeling in activity area.But the supply air temperature in January is low, there will be3℃drop whilefire-making period and6.6℃drop while night period. The supply air temperaturein March is higher and won’t affact indoor thermal comfort.For indoor air quality studies, the pollutants dilution effect of January is betterthan that of March, because of bigger temperature difference between indoor andoutdoor. In all pollutants exceed standard, NO_xhas the best dilution effect. NO_xcanbe reduced to a standard value in1.5²h ventilation time in January and3⁵hventilation time in March. For ventilation at night, CO₂can be reduced to a standardvalue in January but will lead to6.6℃drop in respiratory region; CO₂can’t bereduced to standard value in March but can be kept stable and only exceed0.2times,giving little cold for the people. In addition, owing to the serious pollution of PM2.5and SO₂outside, they can’t be diluted to thelimited value by ventilation but theconcertration can be reduced significantly.