Evaluation of Thermal Environment in Wooden Space Heated by Floor Heating System

Transcription

1 Evaluation of Thermal Environment in Wooden Space Heated by Floor Heating System Yoon-Seong Chang, Chang-Deuk Eom, Jun-Ho Park, Graduate Research Assistants, Department of Forest Sciences, Seoul National University, Seoul, KOREA Hwanmyeong Yeo+ Associate professor, Department of Forest Sciences, Research Institute for Agriculture and Life Science, College of Agriculture & Life Science, Seoul National University Seoul, KOREA Abstract Appropriate evaluation on thermal insulation of structural member and valid control on cooling/heating energy are important for improving building's energy efficiency. In winter seasons, the Korean household heating manner is floor heating. The radiation heating system is not only adequate to climates and geographic condition of Korea, but also has advantages to provide emotional comfort with the warm feeling of the floor. Based on living conditions in Korea, scale-models of the wooden space were manufactured. The ceiling was insulated with Styrofoam and the 4 sided walls were made of plywood. Tile floor was heated by heating film. Using thermal sensors, indoor vertical temperature distributions according to the floor heating were measured and surface temperature on wood wall measured by infrared thermography. Also, thermal insulation property of wooden wall was evaluated to get database for improving energy efficiency of wooden building. It is expected that data collected in the tests carried out with different compositions of floor and wall materials could be referenced for evaluating thermal environment in actual various houses. Key word: heat transfer, wooden space, IR(infrared) thermography, heat loss Paper WS-94 1 of 7

2 Introduction Degree of energy dependence on foreign countries in Korea reaches about 97%, and 30% of total domestic energy consumption is consumed in buildings. In addition, the amount of waste heat discarded from the buildings reaches about 40%. Because of this, it is urgently required to save the building heating energy whenever facing to the era of high oil price. Several efforts to solve this have been tried in building fields. Leading countries have been putting a certification system for improving energy efficiency and environmentality of buildings. LEED(Leadership in Energy and Environmental Design) by U.S., BREEAM(Building Research Establishment Environmental Assessment Method) by U.K., CASBEE(Comprehensive Assessment System for Building Environmental Efficiency) by Japan and Green star by Australia are dealing with this issues in building area. In Korea, from the beginning of 21th century, GBCC(Green Building Certification Criteria) has been being in effect. In winter seasons, the Korean household heating manner is floor heating. It is not only adequate to climates and geographic condition of Korea, but also has advantages to give little difference of temperature between upper and lower part in wooden space and provide emotional comfort with the warm feeling of the floor. In this study, thermal insulation performance of wooden wall with IR thermography was evaluated according to KS(Korea Standard) F 2829 with Temperature Difference Ratio(TDR) and thermal environments in wooden space. Materials & Method: Small scale-model house Based on these living conditions in Korea, scale models of the wooden space heated by floor heating system was manufactured. The model was manufactured in size of 500(width) ⅹ 500(length) ⅹ 450(height) mm. The ceiling was insulated with Styrofoam, the 4 sided walls were made of plywood, and the floor was heated with heating film and was covered with tiles. Using thermocouples, indoor vertical temperatures of the wooden space were measured. One sensor (o) was placed under the heating film, five sensors (1,2,3,4,5) were vertically placed in indoor space. Other three sensors (6,7,8) were placed on the inner and outer Paper WS-94 2 of 7

3 surfaces of wall and inside of wall. Figure 1 Thermal sensors in wooden space During heating model for 3 hours, the vertical temperature distribution was estimated. and compared ideal heating curve. Insulation performance of building In this study building insulation performance, heat transmission was evaluated, by infrared thermography (KS F 2829). And the results were compared to heat transmission calculated with component in wall. The concepts of TDR(Temperature Difference Ratio) Figure 2 Theoretical background of TDR q: heat flow rate(w) h: heat transfer coefficient(w/m K) K: heat transmission coefficient(w/m K) T i : inside temperature( ) T o : outside temperature( ) T is : inner surface temperature in wall( ) T os : outer surface temperature in wall( ) In steady state, heat flow rate by convection (q conv ) and heat flow rate by conduction (q cond ) is same at the surface of wall. TDR i is the ratio of the temperature difference between inside air and inside surface over the temperature difference between inside air and outside air. The less difference between T is and T i is the better insulation performance. As improving insulation performance, the value of TDR i will converge to 0. On the contrary, if the wall is not insulated well, the TDR i value will converge to 1. TDR o has same concept. Therefore, by equation of heat balance, the equation of TDR can be assigned as follows. Paper WS-94 3 of 7

4 TDR i : Inside Temperature Difference Ratio Ti Tis TDRi = T T i o (1) where: T i = inside temperature; T o = outside temperature (average temperature before 72hr); T is = inner surface temperature in wall. TDR o : Outside Temperature Difference Ratio To T TDRo = T T i os o (2) where: T i = inside temperature; T o = outside temperature; T os = outer surface temperature in wall. Heat transmission coefficient is defined as K TDRo. Outer surface temperature can be acquired by IR thermography. K TDRo can be defined by TDR o ⅹh o (convective heat transfer coefficient). Comparing heat transmission coefficient Heat transmission coefficient is the amount of heat passing through a unit projected area of materials(wall, floor, window etc.) per unit time. In this study, also, the heat transmission coefficient(=k) was calculated with thermal conductivity of materials consisting of the wall. Then it was compared with K TDRo. The K is defined by thermal conductivity of wall structure material over the thickness of wall, k/x (where x is thickness(10mm), k is thermal conductivity(0.12w/m K)). Results: Temperature profile in wooden space Figure 3 Vertical thermal distribution change in wooden space heated by floor heating Paper WS-94 4 of 7

5 Vertical thermal distribution change in the wooden space heated by 60 of heating film under tile was evaluated. Its heating curve is similar to vertical thermal distribution in real house heated by floor heating system. Also, it has similar pattern to the ideal heating curve. (Reference: Figure 4 Vertical temperature distribution for heating system Results: IR thermography for heat transmission During heating at 60, surface thermal image the envelopes of wooden model were captured by IR camera. According to KS F 2829, the insulation performance of the wooden model was evaluated with Temperature Difference Ratio(TDR). Figure 5 IR image of wooden building Paper WS-94 5 of 7

6 Table 1 Temperature conditions and thermal transmission in wooden wall Wall Materials Wood(plywood) T o Outdoor Temp.( ) T os Outdoor surface Temp.( ) T i Indoor Temp.( ) Thermal transmission (W/ m2 K) K K TDRo Heat loss was discovered at connected part between upper wall and ceiling. As being compared to K calculated by a material property of the wall, K TDRo was so lower because the warm inside air escaped through the gap. Conclusions The pattern of vertical thermal distribution change in wooden space is similar to the ideal heating curve. In some parts of wall, thermal transmissions determined by TDR(K TDR ) were lower than thermal transmissions(k) determined by thermal conductivity of wall materials. Infrared thermography testing proved to be used as a method detecting the sites of energy loss so that contribute to efficient air conditioning without damaging the structures. It is expected that data collected in further tests with different compositions of floor and wall materials can be referenced in comparing with actual houses. Acknowledgement This work was supported by "the Korea Research Foundation Grant funded by the Korean Government (MOEHRD)." (KRF-2007-F00021). References BH Choi, GS Choi, et al Insulation Performance Evaluation of Apartment Housing Using Infra-red Camera. Proceedings of International Journal of Air-Conditioning and Refrigeration. P CD Eom, JH Park, KB Kim, JJ Lee and H Yeo.: Thermography Analysis for detecting defects in lumber. Proceedings of IAWPS p J. P. Holman, Heat Transfer. Singapore. McGraw-Hill. Paper WS-94 6 of 7

7 KS F 2829: Thermal performance of buildings. H Wiggenhauser Active IR-applications in civil engineering. Infrared Physics & Technology. 43: Paper WS-94 7 of 7