Study On Air Infiltration Prediction Model For Residential Buildings With High Airtightness Envelope In Cold Area

The building air infiltration affects lots of building performance problems on different degrees,such as the building insulation,integrity of building materials,microbial growth in the building envelope,spread of air pollutants,indoor air quality,building energy consumption,and so on.The accurate and rapid prediction of air infiltration is the theory basic for the study on the couple relations among the building parameters,such as the building energy consumption,indoor air quality,need of fresh air and energy system design.With the rapid development of energy efficiency for residential buildings in China,the airtightness of the envelope of new built town residential buildings has been significantly improved which leads to the change in building air permeability characteristic.At present,there are several problems that reduce the prediction efficiency and accuracy of traditional long-term air infiltration prediction model,such as the large number of input parameters,the difficulty in obtaining air infiltration characteristic parameters,the disagree between the assumption of air flow path distribution and the physical truth in buildings with high airtightness,and the lack of air infiltration characteristic parameters of buildings with high airtightness.So,it is meaningful to conduct the study on the air infiltration prediction model for residential buildings with high airtightness envelope as it can provide theoretical basis for the analysis of the couple relations among the building parameters.Firstly,this study investigates the air infiltration characteristic of new built residential buildings(the energy efficiency rate is higher than 65%).Then,based on the test and analysis results,a standard air flow coefficient prediction model and a uniform distribution assumption of air leakage paths were promoted,respectively.Finally,an integral-type air infiltration prediction model and its quick solution method were promoted based on the above study.The main results are summarized,as follows:(1)Newly built regular residential buildings(Nine individual departments and then detached houses)and low energy residential buildings(three individual apartments and one detached house)in cold area of China were chosen to conduct the airtightness investigation.The test results show that the air change rate of the building envelope under the pressure difference of 50 Pa for the individual apartments changes from 1.14 h-1 to 2.44 h-1,and that for the detached houses changes from 0.84 h-1 to 1.89 h-1.The air infiltration volume under pressurization test mode is higher than that under depressurization test mode for most of the tested buildings.The air flow exponent of tested buildings changes from 0.516 to 0.729,and its variation range is small.(2)The typical air leakage paths in the tested buildings and the air infiltration of the main components of the low energy building were tested.The test results show that that there are many kinds of air leakage paths in the tested buildings which were randomly distributed all over the tested building envelope.It is also found that there are still a large percentage of tiny air leakage paths which were randomly distributed in the building envelope that were not identified in this test.The air infiltration volume proportion for the tested individual apartment and detached houses are 34.4%and 61.1%,respectively.With the improvement of building airtightness,the air infiltration and size of typical air leakage paths gradually decreased,and they were tend to be uniformly distributed.(3)Based on the test results,the Spearman coefficient was applied to find out the key influence factors on the standard air flow coefficient.Based on the analysis results,a multi-element linear regression method was applied to build the air flow coefficient prediction models for the individual apartments and detached houses,respectively.Then,statistical testing was done to these two models to increase their reliability.The built models are able to rapidly predict the air flow coefficient for the newly built residential buildings with reinforced concrete frame.(4)Based on the air infiltration characteristic of tested residential buildings,the refactoring hypothesis on the distribution of the air leakage paths in the building envelope was proposed,i.e.the air leakage paths are assumed to be uniformly and continuously distributed in the building facade except for the outer windows and doors,and the number of air leakage paths tends to be infinite.And the air permeability of all the air leakage paths is same under the same conditions.Compared with the concentrated distribution hypothesis of the air leakage paths,this refactoring hypothesis is closer to the actual situation in the residential buildings with high envelope airtightness.(5)The building envelope was classified into the permeable part(the facade except for the glass of the windows and doors)and the impermeable part(the glass of the outer windows and doors)according to the air permeability of components of the building envelope.The building was simplified into a polyhedron composed with a finite number of surfaces.The universal air infiltration prediction model was built by the definite integral method.(6)Then,the air infiltration prediction models for the envelope of single zone and multi-zone buildings were built based on the above study.The rapid solution methods to these two models were also given,i.e.the hierarchical method and the newton iteration method.A residential building with high envelope airtightness was chosen to verify the proposed model.The comparison results show that the proposed model in this study is in line with the tested results within the relative error of 10%.The new model can consider the influence of impermeable envelope on the air infiltration.Also,the refactoring hypothesis on the distribution of the air leakage paths can reduce the parameter number and the difficulty in obtaining the parameters of air leakage path.Based on the air infiltration characteristic of newly built residential buildings,a real time air infiltration prediction model for the residential buildings with high envelope airtightness was promoted.This model is capable for the rapid and accurate prediction of the whole year air infiltration of the newly built residential buildings,low energy and ultra-low energy buildings,and providing theory base for the performance coupling analysis of the above buildings.