Proceedings of the 55th International Convention of Society of Wood Science and Technology August 27-31, 2012 - Beijing, CHINA The Hygrothermal Performance of Wood Frame Wall System in Suzhou Lake Tai Climate Zone Xiaohuan WANG Assistant Research Fellow, Beijing Forestry Machinery Research Institute of State Forestry Administration, China Benhua FEI Research Fellow, International Bamboo and Rattan Network Center, China Jun NI President, Suzhou Crownhomes co., Ltd., China Abstract Long-term on-site assessment of hygrothermal performance is necessary for developing energy-efficient and durable wood frame wall system. In this paper the hygrothermal performance of cavity insulation wall was examined from temperature, relative humidity, air pressure in cladding ventilation and wood material surface temperature throughout the year in Suzhou Lake Tai of hot summer & cold winter climate zone. The results clearly demonstrated the effect of the cavity insulation, cladding cavity ventilation, air and vapor barrier. Thermal performance was proved very well because of the wall cavity insulation. Cladding ventilation including openings was effective at lowering relative humidity of insulated wall cavities. Condensation and mold growth were not found inside the wall during the whole testing period. Wood frame wall system exhibited very good hygrothermal performance to be widely used in hot summer & cold winter climate zone in central China. Key words: hygrothermal performance, wood frame wall, insulation, vapor retarder PaperAP1-2 1 of 8 Proceedings of the 55th International Convention of Society of Wood Science and Technology August 27-31, 2012 - Beijing, CHINA Introduction Long-term on-site assessment of hygrothermal performance is necessary for developing energy-efficient and durable wood frame wall system. Dynamic changes of temperature, relative humidity and moisture content can reveal the function of each material in multilayer wall. Heat and moisture transfer through wall was measured under the different materials and climatic conditions[1-4]. These studies revealed the factors that affect the wall hygrothermal performance, such as ventilation, airtightness, insulation, infiltration and vapor diffusion. Experiments and simulation results have helped to improve hygrothermal performance of the exterior wall system, and professional guidance or recommendations were provided [5-7]. China is divided into five climate zones for having a vast terrain territory. Suzhou is identified as a hot summer & cold winter climate zone, which is a north subtropical monsoon climate of hot summer, cold and dry winter, wet and humidity. Complicated environment conditions increase the difficulty of building wall design to maintain energy saving and durability. The increasingly wood frame houses were built in hot summer & cold winter climate region. However, hygrothermal performance of wood frame wall system is still unknown under this climatic condition. This study is developing and implementing an on-site systems engineering approach to monitor long-term changes in the hygrothemal responses of wall system. The medial and lateral wall, ventilation cavity and insulated wall cavity conditions were monitored for air temperature, relative humidity, air pressure in cladding ventilation and wood material surface temperature in Suzhou Lake Tai of the hot summer & cold winter zone climate. The results will be used to support the future design standards regarding exterior wall requirements Tested building and Wall configuration Suzhou Crownhomes co., Ltd established a low-carbon demonstration wood house at park by the side of Suzhou Lake Tai (see figure 1). The building is a post and beam construction consisted of glulam. The wall thickness was 125mm filled in the main frame structure. Configuration and materials of multilayer wall illustrated in figure 2. Thermal insulation was by inserting the premium loose-fill fiberglass insulation into the cavity between studs in the exterior wall, which was then covered on interior panel with gypsum board and the exterior panel with OSB sheathing. The continuous polyethylene films were used as interior vapor retarders placed on the interior surface of cavity insulation. PaperAP1-2 2 of 8 Proceedings of the 55th International Convention of Society of Wood Science and Technology August 27-31, 2012 - Beijing, CHINA Figure 1 Demonstration test house Figure 2 Configuration of multilayer wall Instrumentation and sensor locations One frame in the south exterior wall was chosen to be tested according to the field conditions of the house. Air temperature and relative humidity were monitored by JWSK-6ACC05 sensor with accuracy of 0.1. Surface temperature was measured using type T thermocouples, calibrated to 0.1K. Ventilated cavity pressure was measured by JQYB atmospheric pressure transmitter with accuracy of 0.1kPa. Sensors were connected to the data collection equipment, which continuously monitor the hygrothermal performance of the test wall. Data were recorded and stored in computer every minute, and could be extracted every 30 min or every hour flexibly to analyze by operating software. The monitor process began in June 2010, and the testing has been done continuously 2 years. The sensor locations are illustrated in figure 3. Sensors of air temperature and relative humidity (RHT1~ RHT10) were distributed in each layer from the medial to lateral wall. These were installed 300mm from the top and bottom of the test wall respectively. Sensors of air pressure (P1 and P2) were placed in cladding ventilation cavity, which locations were same as RHT4 and RHT9. Sensors of surface temperature (T1~T6) of stud and OSB were located in cavity insulation. T1 and T5 were located in the center of top and bottom wood plate, T2 and T4 were located in exterior sheathing board, 300mm from the top and bottom wood plate respectively. T3 and T6 were located in stud and the exterior sheathing board respectively, centered vertically between the top and bottom plates. PaperAP1-2 3 of 8 Proceedings of the 55th International Convention of Society of Wood Science and Technology August 27-31, 2012 - Beijing, CHINA Figure 3 Schematic drawing of sensor locations in the test wall Results and discussion The trend was basically identical between RHT1~RHT5 and RHT6~RHT10 described in [7]. Figure 4 and figure 5 only present air temperature and relative humidity changes of RHT1~ RHT5 in the last one year in addition to the August data failed in this paper. Air temperature of the medial wall varies were less during the period of April to October than the period of November to May. Air temperatures of the medial wall were closer to air temperatures of the interface between the gypsum board and insulation layer. Air temperature changes trend of the interface between the insulation layer and OSB sheathing board was closer to air temperature of the lateral wall, which confirmed that effective function of the insulation layer. January was the indoor coldest month from the changes of the whole year. Although air temperature of the lateral wall was near to -3.0℃, air temperature of the medial wall could maintain 11℃. The peak of each interface air temperature clearly showed the hysteresis behavior from the medial to lateral of the test wall. PaperAP1-2 4 of 8 Proceedings of the 55th International Convention of Society of Wood Science and Technology August 27-31, 2012 - Beijing, CHINA 40 35 Temperature / ℃ 30 25 20 15 10 5 0 -5 6/24/11 7/9/11 9/16/11 10/18/11 11/12/11 12/12/11 1/12/12 2/12/12 3/12/12 4/12/12 5/12/12 Date(Month/Day/Year) the medial wall Figure 4 gypsum/insulation insulation/OSB air space ventilation cavity the lateral wall Changes of interface air temperatures for the whole year Relative humidity changes over time clearly suggested the opposite state compared with temperature. Relative humidity range of the lateral wall was from 30% to 99%, but relative humidity range of the medial wall was lower, more steady and proper to live. Relative humidity of the medial of wall was always little lower and nearer to relative humidity of interface between the gypsum board and insulation layer. Relative humidity changes trend of the interface between the insulation layer and OSB sheathing have been shown the same as those of the lateral wall, which were different with relative humidity of the gypsum board cavity-side obviously. It was shown that the vapor retarder of polyethylene film really prevented the vapor into the indoor through wall cavity. Relative humidity of the interface between the insulation layer and OSB sheathing was stable comparatively, and lower than relative humidity of inside the cladding cavity. Apparently, the waterproof and moisture permeable building paper was very indeed effective in condition of the high relative humidity of outdoor. But relative humidity of the OSB cavity-side was lowest when relative humidity of each the medial and lateral wall was high in summer, especially in July. The moisture was restrained from indoor into wall cavity by vapor retarder of polyethylene film. The temperature of ventilated cavity up to 36.7℃ in July, when the highest relative humidity was 83.9%. However, the time was not so long under this high temperature and relative humidity state. There was not mold growth according to reference [8]. Both the stucco and air space ventilation cavity resistance to moisture was obviously effective since data showed relative humidity inside the cladding cavity before reached the maximum was always lower than relative humidity of the lateral wall, and the peak of relative humidity inside the cladding cavity clearly showed the hysteresis behavior. PaperAP1-2 5 of 8 Proceedings of the 55th International Convention of Society of Wood Science and Technology August 27-31, 2012 - Beijing, CHINA 100 Relative humidity /% 90 80 70 60 50 40 30 6/24/11 7/9/11 9/16/11 10/18/11 11/12/11 12/12/11 1/12/12 2/12/12 3/12/12 4/12/12 5/12/12 Date(Month/Day/Year) the medial wall Figure 5 gypsum/insulation insulation/OSB air space ventilation cavity the lateral wall Changes of interface relative humidity for the whole year Temperature and relative humidity data measured at the coldest day of outdoor monthly from October to March of next year were chosen to analyze for illustrating the state of heat and moisture transfer through the multilayer wall. Temperature and relative humidity gradients through the test wall profile were obvious in Figure 6. Temperatures were reduced from medial to lateral wall, and the trends of relative humidity were opposite. Temperature difference was the largest between gypsum board and OSB sheathing in the process of heat transfer from medial to lateral wall. The largest temperature difference has reached 8.2℃ happened in December. The insulation kept the indoor warm. Temperature difference between ventilated cavity and lateral wall was about 4℃. There was a certain heat barrier because of air space. Figure 7 showed the surface temperature of SPF frame dimension lumber and OSB sheathing. The surface temperatures of OSB sheathing (T2, T4 and T6) developed continuously along with the changes of the lateral wall temperatures. The surface temperatures of wood frame (T1, T3 and T5) developed smaller than those of OSB sheathing. All surface temperatures were above 0℃. So the risk of water condensation in the wall could be eliminated in winter. Relative humidity gradients were largest between ventilated cavity and lateral wall. The maximum difference was 34% happened in December. In winter relative humidity maximum gradient was 14.6% from the interface between the gypsum board and insulation layer to the interface between the insulation layer and OSB sheathing. So the vapor retarder of polyethylene film was perfect. But at the same time relative humidity of medial wall didn’t attain to 40%. Therefore, the indoor environment was felt little dry. PaperAP1-2 6 of 8 Proceedings of the 55th International Convention of Society of Wood Science and Technology August 27-31, 2012 - Beijing, CHINA 90 25 80 70 Relative humidity /% Temperature / ℃ 20 15 10 5 0 60 50 40 30 20 10 -5 0 0 15 124.5 85 94.5 0 15 10/25/11 1/23/12 Figure 6 124.5 85 94.5 Distance/mm Distance/mm 12/17/11 3/12/12 11/21/11 2/3/12 10/25/11 1/23/12 11/21/11 2/3/12 12/17/11 3/12/12 Temperature and relative humidity gradients through the test wall profile 45 40 Temperature / ℃ 35 30 25 20 15 10 5 0 -5 10/18/11 11/12/11 12/12/11 1/12/12 2/12/12 3/12/12 4/12/12 5/12/12 Date(Month/Day/Year) T1 T2 Figure 7 T3 T4 T5 T6 the lateral wall Surface temperature of wood materials of SPF and OSB Figure 8 showed the air pressure of the top and bottom in cladding ventilation cavity. The top air pressure P1 was always less than the bottom air pressure P2. The average difference of air pressure was 0.12kPa. This indicated airflow entering low on the wall and exiting at the top through ventilation holes in metal strips. Winter air pressure was higher than other seasons’ from the whole year data. Air Pressure /kPa 104 103 102 P1 P2 101 100 10/18/11 11/12/11 12/12/11 1/12/12 2/12/12 3/12/12 4/12/12 Date(Month/Day/Year) Figure 8 Air pressure in cladding ventilation cavity The result analysis of two years data seems that the application of wood frame wall PaperAP1-2 7 of 8 Proceedings of the 55th International Convention of Society of Wood Science and Technology August 27-31, 2012 - Beijing, CHINA system in demonstration test house is very successful in Suzhou Lake Tai climate zone. Thermal performance of this system was good and no mold growth and water condensation occurred inside the wall during the testing period. Most time of temperature and relative humidity indoor were perfect or acceptable in addition to January night. The increasing humidity should be needed to protect the dry glulam against split in winter. Conclusions Long-term on-site assessment of hygrothermal performance was presented in this paper. The results indicated that water vapor control strategy performed well at reducing summertime mold growth and wintertime condensation in testing wall assemblies in Suzhou Lake Tai of hot summer & cold winter climate zone. Vapor retarder, waterproof & moisture permeable building paper and cladding ventilation cavity could increase the moisture tolerance and reduce risks related moisture for multilayer wall. Thermal performance was on perfect level because of cavity wall insulation from the whole testing period. Therefore, the same configuration design as testing exterior wall can be widely used in China hot summer & cold winter climate zone. Acknowledgements This research has been supported by the forestry industry research special funds for public welfare projects, State Forestry Administration of China, contract No. 201204701 and leading talent project in Suzhou Wuzhong District, contract No. WC201107. References 1. Gatland S.,Karagiozis A. (2007). The hygrothermal performance of wood-framed wall systems using a relative humidity-dependent vapor retarder in the Pacific Northwest. Thermal Performance of the Exterior Envelopes of Whole Buildings X International Conference, December 2-7. 2. Jan Toman, Alena Vimmrová, Robert Černý. (2009). Long-term on-site assessment of hygrothermal performance of interior thermal insulation system without water vapour barrier. Energy and Buildings, 41(1): 51-55. 3. Maref, W., Tariku, F. & B. Di Lenardo. (2008). NRC-IRC develops evaluation protocol for innovative vapour barrier, Construction Innovation, 13, (2): 6. 4. Robert Tichy, Chuck Murray. (2007). Developing innovative wall systems that improve hygrothermal performance of residential buildings. Washington State University, March. 5. Glass, Samuel V., TenWolde, Anton. (2007). Review of in-service moisture and temperature conditions in wood-frame buildings. General Technical Report FPL-GTR-174. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 6. Karagiozis A, Desjarlais A. (2007). Developing innovative wall systems that improve hygrothermal performance of residential buildings, Oak Ridge National Laboratory, May. 7. Tariku F.,Maref W., Di Lenardo B., Gatland, S. (2009). Hygrothermal performance of RH-dependent vapour retarder in Canadian coastal climate. 12th Canadian Conference of Building Science and Technology, Montreal, QC, May 6-8. 8. Xiaohuan Wang. (2011). Research on thermal performace of wood frame wall, Beijing: Chinese PaperAP1-2 8 of 8 Proceedings of the 55th International Convention of Society of Wood Science and Technology August 27-31, 2012 - Beijing, CHINA Academy of Forestry. 9. Jian Li. (2009). Wood science research, Beijing: Science Press, pp30. PaperAP1-2 9 of 8