Research On The Thermal Characteristics Of Modern Wood Framed Construction Wall

The modern wood framed construction has drawn people's attention for its advantages such asgood heat insulation property, easy to build, good to health and comfortable to live in. Itdistinguishes the traditional wood flamed construction in China from architectural style,architectural methods, architectural materials and so on. The information about wood flamedconstruction design, material standardization as well as related technologies is scarce. So it isnecessary to systematically study the building technology for wood framed construction.As one of the most important parts of a construction, the outdoor wall plays a significant rolein heat insulation, heat preservation, sound insulation and energy saving. The wall takes up themaximum ratio in the exterior building envelope. Researches show that the heat loss from theoutdoor wall amounts to 30% of the whole heat loss in a construction. Heat transfer of theoutdoor wall is a sophisticated process, which has something to do with the thermal comfortand the energy saving of the whole construction. Researchers focus their research on how tolower the heat transfer coefficient of exterior wall, ie K value. Studying the thermalcharacteristics of the outdoor wall of the wood framed construction is significant not only forreasonably designing wall parameters and air-conditioner load but also for accuratelyevaluating the energy saving effects of the whole building. It will promote the development ofwood flamed construction in China and will provide fundamental reference for wall design andmaterial development of the wood flamed construction.This paper studies the thermal properties of modern wood framed construction wall.Guarding and calibration heat box method is applied to examine the steady thermalcharacteristics of wood framed construction wall. Different wood studs, wood studs distance,heat insulation materials and their influence on the thermal characteristics of wood framedconstruction wall are analyzed and discussed. The heat conductance value of different walls iscalculated. The finite difference method combined with Matlab, PDE tool and finite elementanalysis methods are utilized to study the unsteady thermal characteristics of wood framedconstruction wall. The temperature fields of wood flamed construction wall during applicationare analyzed. The architecture energy simulation software named Dest and onsite measurementare applied to evaluate the energy saving properties of wood framed construction. The mainresults are as follows.1. After being calibrated by standard sample, the Guarding and calibration heat box method isnot only suitable for the measurement and evaluation on the steady thermal characteristicsof concrete structured construction wall; it also fits for the measurement and evaluation on the steady thermal characteristics of wood framed construction wall.2. The modern wood framed construction wall has excellent heat insulation properties. Both2X4 and 2X6 structure wall has better thermal characteristics than common concretestructured construction including the exterior insulator wall and interior insulator wall.3. The steady thermal characteristics of wood framed construction wall are influenced bydifferent wood studs, wood studs distance and heat insulation materials. The detailedresults are:①When the wood studs distance and heat insulation materials are same, 2X6wall has better thermal characteristics than 2X4 wall.②The properties of heat insulationmaterials have significant impact on thermal characteristics of the wood framedconstruction wall. In this experiment, when the wall constitutes with the same type of woodstuds and wood studs distance, wall fixed with the extruded insulation board has the bestthermal characteristic, then is the wall with rockwool insulation board, the wall with thepolystyrene insulation board is marked third among the three above.③Wood studs alsohave significant impact on thermal characteristics of the wood framed construction wall.When the heat insulation material and type of wood studs are same, the thermalcharacteristics of wood framed construction wall increase with the wood studs distanceincreasing. So under the precondition of meeting the safety requirement, large wood studsdistance is preferred.4. Under the same exterior and interior environmental condition, the heat conductance valueof wood framed construction wall is obviously lower than concrete structured constructionwall including exterior insulator wall and interior insulator wall. The energy saving effectof wood framed construction wall is more obvious than concrete structured constructionwall.5. The finite difference method combined with Matlab and PDE tool can effectively assess theunsteady thennal characteristics of wood framed construction wall. Flourier transformationcan change the discrete data into continuous boundary condition, the parabolic partialdifferential equations is applied. The boundary condition of wall is the Neumann boundary.6. Under the same boundary conditions, the temperature field of wood framed constructionwall is similar with the one of concrete structured construction wall. The unsteady thermalcharacteristics of wood framed construction wall are better than concrete structuredconstruction wall. The detailed results are:①Compared with the concrete structuredconstruction wall, the wood framed construction wall has higher inner surface temperature.②Wood framed construction wall has better competence of counterbalancing the temperature surge.③Wood framed construction wall can not only better the heatcomfortability of the interior environment but also lower the energy consumption of thewhole construction.7. The finite element analysis method can accurately predict the temperature field of woodframed construction wall and can acquire the temperature in the wall. In the wood framedconstruction wall, the heat insulation materials and air cavity are the main parts to insulateheat transfer and counterbalance temperature surge. The temperature difference betweentwo sides of the heat insulator materials and air cavity is large. Wood studs serve as bothstructural load bearing and heat insulation.8. The architecture energy simulation software, Dest, can effectively analyze the energyconsumption of wood framed construction during utilization. Under the same condition:①wood framed construction has more days with natural temperature (16～29℃,withoutheating and cooling) than concrete structured construction. Wood framed construction hasbetter comfortability than concrete structured construction.②The heat load of woodframed construction is 25.5% lower than concrete structured construction and the coolingair-condition load of wood framed construction is 8.4% lower than concrete structuredconstruction.③The energy consumption of wood framed construction is 21.5% lowerthan concrete structured construction.9. From the onsite measurement, conclusions can be reached as follows:①Wood framedconstruction wall can effectively counterbalance the exterior environmental temperaturesurge. Both exterior and interior temperature changes periodically in 24 hours. The interiortemperature changes in a narrow range. The interior temperature peak lags behind theexterior temperature peak for about 2 to 3 hours.②The exterior relative humiditychanges periodically in 24 hours, while the interior relative humidity changes in a narrowrange and is hardly affected by the exterior ambient, the average relative humidity is about40%.③No condensation will occur on the inner surface of wood framed constructionwall. Condensation may occur in the wall at the layer of polystyrene and air cavity. Thepossible condensation value is 1.1221 g/(m~2h), which meet the requirement of GB50176-93.No condensation water is detected in the wood framed construction wall. All the wallmaterials are in dry state. No decay occurs. The heat insulation properties will not belowered caused by moisture.