Conditions for the installation of a fresh air system in a house
Standardization of building energy efficiency has been carried out since the 1980s, and the building energy efficiency standard has increased from the initial energy saving rate of 30% to 50% and then to the current energy saving rate of 65%. At present, some local standards such as Beijing and Hebei have reached 75%.
In recent years, energy consumption of building energy efficiency standards have also started to implement. Residential air tightness as it is getting better and better with the increase of building energy efficiency standards, outside the window, air tightness level reaches the national standard GB/T 7106-2008 "building outside the window, wind resistance, airtight, watertight classification and testing method of magnitude 7, number of indoor ventilation is about 0.25 times/h, Closed doors and Windows cannot meet the requirements of indoor ventilation, so it is necessary to set up a fresh air system. When the outdoor is seriously polluted, natural ventilation will aggravate the pollution of indoor environment. Fresh air system can be set up to send fresh air into the room after purification treatment to ensure that people breathe in fresh air and ensure indoor air quality. There is no uniform standard for the definition of severe outdoor pollution. Referring to China's air quality Index technical standard, the number of days in which the average outdoor PM2.5 concentration is greater than 75 g/m3 is calculated according to the "good" low limit of 75 g/m3. If the number of days is not less than 20% of the whole year, the outdoor pollution is considered to be serious and the indoor air quality should be improved by setting fresh air system.
According to statistics, the number of days in which the average daily outdoor PM2.5 concentration was greater than 75 g/m3 in some cities of China from 2014 to 2016 and the proportion were shown in Table 2. In recent years, with the enhancement of air pollution control efforts in China, the overall atmospheric environment has improved. Therefore, the number of days and the proportion of the average daily concentration greater than 75 g/m3 per year in each city are also in constant change. The data of the last three years can be analyzed in the design. In addition, for the building layout and indoor layout of the residence, it is not easy to realize the natural ventilation rate, so fresh air system should also be set to ventilate the room.
