Study On Thermal And Hygrothermal Performance Of Light Wood-frame Timber Structures

The effective control of temperature and humidity in light wood-frame timber structures are not only important criterion for residential satisfaction,but also objective requirements for building physics.Indoor temperature and humidity are in a dynamic state during the building's construction and operation process.high humidity in the room will breed bacteria,produce mold,and cause health problems such as chest tightness and shortness of breath.Too low indoor moisture will cause wood shrinkage,warping,cracking,also lead to skin irritation and respiratory problems in occupants.In order to dynamically understand the thermal and hygrothermal performance of light wood-frame timber structures walls,the author analyzes the applicability of light wood-frame timber structures walls in hot summer and cold winter zone,predicts the future trend of heat and humidity change,and finds new breakthrough points in the initial stage of wall design.In this paper,light wood-frame timber structures'walls of A(cork of light wood-frame timber structures),B(preserved wood of light wood-frame timber structures),a wall(cork SPF),b wall(corkwood insulation cotton),c wall(preservative wood SPF)and d wall(preservation wood insulation cotton)are selected as test and research objects.With theoretical calculation as the research support,the following studies have been made on the thermal and hygrothermal performance of lightweight wooden building walls.First,the basic material properties(density,thickness),thermal properties parameters(thermal conductivity,specific heat capacity),moisture physical parameters(moisture storage content under different relative humidity,thermal conductivity related to temperature,heat conductivity related to water content)are tested.Then,the heat transfer coefficients of walls a,b,c and d are tested in two periods.At the same time,the indoor and outdoor temperature,humidity and moisture content of A?B are monitored from January to March;Finally,WUFI 6.0 is used to simulate the thermal and hygrothermal performance of four types of walls,and predict the wall temperature,humidity and water content change curves in one year from 2018 to 2019.Based on this analysis,the thermal performance,living comfort,coagulation and mold risk of A and B are analyzed.Meanwhile,the accuracy and credibility of the software simulation are confirmed.The main conclusions are as follows:(1)Among the tested building materials:cork and Jiadian insulation are high-efficiency thermal insulation materials;OSB and SPF are heat-insulating materials;anticorrosive wood hanging plate and waterproof vapor-permeable are thermal insulation materials.The isothermal moisture absorption capacity is as follows:Jiadian insulation cotton<cork<OSB<preservation wood<SPF;Water absorption capacity is as follows:OSB<cork<preservation wood<SPF<good insulation cotton;(2)The relative error of heat transfer coefficient in December 2017 is smaller compared to March 2018(Dec 2017,A:2.06%,B:7.08%;Mar 2018,A:3.51%,B:11.40%),which indicates that the test results of the most cold month are better.At the same time,the heat transfer coefficient of a,b walls and A are less than that of c,d walls and B,which indicates that the thermal performance of the former is superior to the latter.The measured heat transfer coefficient of A,B buildings and a,b,c,d are much smaller than those in hot summer and cold winter thermal zones(?1.0 W/(m~22K)),even reach the heat transfer coefficient of the severe cold zone(?0.4 W/(m~22K)).Therefore,A,B buildings and a,b,c,d walls are suitable for hot summer and cold winter zones.(3)Analyze the thermal stability,thermal inertia,heat storage coefficient and delay time based on the temperature,heat flow data and test curves of buildings A and B.The results show that:A building has stronger resistance to external fluctuations,better thermal stability and stronger heat storage capacity.The attenuation multiple of A building is less than that of B.The reason is that air temperature sensors are closer to the wall when testing,resulting in the test of the outside air temperature being affected by the wall temperature.(4)In the real-time monitoring of temperature,humidity and moisture content,the temperature and humidity adjustment performance of building A is better than that of building B.However,in terms of standard deviation,the standard deviation of indoor temperature and humidity of building B is less compared to building A,which indicates that the interior temperature and humidity of building B is more stable,also the moisture content of building B is much larger than that of building A.The moisture content of SPF in buildings of A and B shows a decreasing trend over time,and the rate of c wall decreases rapidly.The water content at the inside OSB of buildings A and B shows a decreasing trend over time.The moisture content of inside OSB inside in building A is larger than that in the building B,which indicates that the indoor temperature and humidity of A building fluctuates greatly.The experimental results confirm that the indoor temperature and humidity fluctuation of A building is larger than that of B building.(5)The average annual temperature and relative humidity in winter in A and B buildings are within the suitable humidity range.The temperature and humidity in summer are higher in other seasons,so it is necessary to install humid air conditioning to regulate indoor humidity.Within the four walls,the indoor temperature of the whole year is larger than the dew point temperature,and it is not easy to be condensed.The designed wall is suitable for the hot summer and cold climate zone in Nanjing.The actual water content of mould spore in surface of four walls are less than the critical moisture content,which indicates that in 2018-2019,there is a small possibility to germinate spore in surfaces of four walls,and it is not easy to produce mould.This research provides a new direction for the health design and future prediction of indoor environment in light wood-frame timber structures and other wood buildings,so as to accurately identify the heat and moisture coupling transfer risks in building components and wall structures.Meanwhile,effectively avoiding damage and maximizing the advantages of light wood-frame timber structures.This research aims to create a more comfortable and healthy housing environment for the residents,and to provide technical support for improving the application of thermodynamics,hygrothermal performance and air coupling transmission in light wood-frame timber structures in China,which has high guiding significances and engineering values for future studies.