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This paper presents the thermal performance evaluation of a dynamic insulation technology applied to the building envelope of a timber framework house. The concept of dynamic insulation technologies is to draw outside air in through insulation materials in a wall to recover conduction heat loss from inside the building. The authors applied dynamic insulation technology to the walls and ceiling of a timber framework house to allow outside air to pass through permeable insulation materials within the walls and ceiling. The experiment was conducted at a building in Sapporo, Hokkaido to evaluate the thermal performance of a building envelope with dynamic insulation technology in a real environment. The results showed that the dynamic insulation technology can significantly reduce heat loss through the building envelope. Keywords: Dynamic Insulation; Thermal Performance 1. Introduction paper presents the results of the thermal performance Considering the current global environmental evaluation. problems and demands for net zero energy buildings/ houses (Chung, 2013), various energy saving methods 2. Experimental Building should be developed. In this study, the authors applied 2.1 Details of the Experimental Building a dynamic insulation (DI) technology to a timber The experimental building was constructed in framework house to reduce the energy consumption Sapporo, Hokkaido using the timber framework and to improve the indoor air quality. The concept of method. The experimental building comprised a single DI technologies is to draw outside air inward through room with dimensions of 1820 mm width × 2730 mm insulation materials to recover conduction heat loss length × 2200 mm height. Fig.1. shows the floor plan from inside the building. Research on DI technologies and cross section plan of the experimental building. has been conducted for heavyweight structures such Wood fiber insulation (thermal conductivity of 0.038 as masonry walls (Baily, 1987; Qiu, 2007; Gan, 2000; W/mK) was installed in the ceiling, walls, and floor. Imbabi 2013). However, few studies have applied The building included a window of triple-glazed low-E DI technologies to a timber framework house. The glass with Ar gas (u-value of 0.75 W/m K) and door of authors conducted an experiment by simply applying double-glazed low-e glass (U-value of 1.23 W/m K). A DI envelopes to a timber framework house in a cold sirocco fan acted as an exhaust ventilation system. region. Compared to a conventional timber framework house, which prevents interstitial condensation with an airtight sheet, DI technology has the advantage of both improving the thermal performance and preventing interstitial condensation without an airtight sheet by (Note) introducing dry air in the building envelope . This *Contact Author: Kyosuke Hiyama, Associate Professor, Yamaguchi University, 2-16-1 Tokiwadai, Ube-shi, Yamaguchi 755-8611, Japan Tel: +81-836-85-9711 Fig.1. Floor Plan and Cross Section Plan of the Experimental E-mail: firstname.lastname@example.org Building ( Received October 8, 2013 ; accepted November 12, 2014 ) Journal of Asian Architecture and Building Engineering/January 2015/218 213 Table 1. Specifications of the Experimental Building The sirocco fan had an inverter and damper to control the air flow rate and pressure difference Specification between the inside and outside of the room. The Roof Galvanized iron + asphalt roofing + 9.0 mm structural plywood specifications of the experimental building are given in Ceiling Siding + 250 mm wood fiber insulation Table 1. With DI, the ventilation inlet was sealed, and + moisture-proof airtight layer the outside air flowed inward through the ventilation + 9.5 mm plasterboard holes in the walls. Without DI, the ventilation holes Wall Siding + 140 mm wood fiber insulation were sealed; therefore, the outside air flowed inward + moisture-proof airtight layer through the ventilation inlet. The area of the opening + 9.5 mm plasterboard was adjusted to be equal to the total area of the Floor Siding + 150 mm wood fiber insulation ventilation holes in the case with DI. + moisture-proof airtight layer 2.2 Concept of the DI Technology Applied to an + 24 mm structural plywood Experimental Building Door Double-glazed low-E glass U = 1.23 [W/m K] The working principle of DI technologies is to draw Window Triple-glazed low-E glass U = 0.75 [W/m K] outside air into the building envelope through porous materials to recover conductive heat loss. In this study, the authors applied a DI technology to the walls and ceiling of the experimental building. A ventilating layer was provided by siding materials outside the walls, and ventilation holes were opened within the walls from the inside to allow outside air to pass through the permeable insulation materials of the walls into the room. The outside air recovered conduction heat loss from inside the building when it passed through the walls. Fig.1. shows the areas with DI in red. Fig.2. shows a cross section of the DI-applied wall and outside air inflow route. Table 2. presents the details of Fig.2. Cross Section of the Wall and Outside Air Inflow Route the ventilation holes in the walls. The ratio of the area of ventilation holes to the total area of the DI-applied Table 2. Details of the Ventilation Holes walls was approximately 0.03%. Diameter [mm] Number 2.3 Air Tightness Performance East Wall 2.5 242 The air tightness test was conducted in the West Wall 2.5 242 experimental building. To maximize the effect of DI South Wall 2.5 121 technology, a high level of air tightness is required Ceiling 2.5 288 in areas other than the DI-applied areas to pass a sufficient volume of outside air through the DI-applied walls. The equivalent leakage area was calculated by measuring the air flow rate and pressure difference between the inside and outside of the room. Fig.3. shows the air leakage graph. When no openings are established, the ventilation inlet and ventilation holes are sealed, and the equivalent leakage area is small. The equivalent leakage area of 0.26 indicates that the experimental building had a high level of air tightness. To calibrate the equivalent leakage area of the different cases, the air tightness test was performed for each case. For the case with DI, the authors measured the equivalent leakage area including the ventilation holes. For the case without DI, the ventilation holes were sealed, and the opening area of the ventilation inlet was adjusted to ensure the equivalent leakage area was equal to that of the case with DI. The results are shown Fig.3. Air Leakage Graph in Table 3. 2.4 P–Q Characteristics of the Sirocco Fan fan and the air flow rate. The output of the sirocco The air flow rate during the experiment was fan inverter was set to 48.8 Hz in all cases. The air calculated by using the P–Q characteristics of a flow rate during the experiment was calculated by the sirocco fan; these were obtained by measuring the regression line of the P–Q characteristics. Fig.4. shows differential pressure of the front and rear of the sirocco the graph of the P–Q characteristics of the sirocco fan. 214 JAABE vol.14 no.1 January 2015 Aya Yaegashi Table 3. Equivalent Leakage Area 3. Results 3.1 Experimental Condition Equivalent Leakage An experiment was conducted to evaluate the Case Regression Line Area thermal performance on November 6–12, 2012. The 2 2 [cm /m ] thermal performance of the experimental building No 0.26 was evaluated according to the coefficient of heat ����� = ���0.11� ����� Opening 0.93 loss from the entire building envelope; the results Without 2.94 ����� = ���6.�3� ����� with and without DI were compared. This is because DI 1.98 evaluating the thermal performance of each wall was With DI 2.63 ����� = ����.0�� ����� 1.76 difficult because the air flow rate of each wall could be different. With DI, the ventilation holes in the walls and ceiling were used as an air supply inlet, whereas ������ the ventilation inlet was used as the air supply inlet in �� = � �� � � the case without DI. The experiment was conducted without DI on November 8–10 and with DI on � � � = �� � � �� � �� ��� November 10–12. The inverter output of the sirocco fan was set to the identical frequency of 48.8 Hz in each case to equalize the electric consumption from the sirocco fan. The pressure difference between the inside and outside of the room was set to 20 Pa, and the air flow rate was set to 28 m /h. These values were determined by assuming that the DI technology was applied to one side of a room with 2.7 m width, 3.6 m length and 2.2 m height at 0.5 ACH. In this case, the ventilation rate is approximately 10.7 m /h (2.7 m x 3.6 m x 2.2 m x 0.5 Fig.4. P–Q Characteristics of the Sirocco Fan ACH). Supposing that one wall in the room with 2.7 m width and 2.2 m height was used for the DI wall, the Table 4. Experimental Conditions Air Flow velocity at the wall was 1.8 m/h (10.7 m /h ÷ (2.7 m x. Air Pressure Rate Indoor Load 2.2 m)). When the velocity was applied to the DI wall Case Supply Difference (Measured Condition in the experiment (area: 13.8 m ), the required air flow Inlet Value) 3 2 rate was 24.8 m /h (1.8 m/h x 13.8 m ). An air flow Radiant heater Without Ventilation 28 m /h rate of 28 m /h was set to ensure that the air flow was 400 W 20 Pa DI inlet (28.6 m /h) Electric fans more than required. The pressure difference between 40 W the inside and outside of the room was set to 20 Pa to Flourescent light reduce the influence of fluctuations in wind velocity. Ventilation 28 m /h 35 W With DI 20 Pa A radiant heater provided heat constantly to the room holes (27.3 m /h) Sirocco fan Equivalent at an output of 400 W, and two electric fans stirred the Leakage 5 W Case Regression Line air in the room. A fluorescent light was on throughout Area 2 2 the experiment. Table 4. shows the experimental presented in the next section. [cm /m ] No conditions. Note that the pressure differences in this 3.2.2 Thermal Performance 0.26 ����� = ���0.11� ����� Opening 0.93 table indicate those between the outdoors and indoors. To evaluate the thermal performance of the building Without This difference is distinct from the sirocco fan pressure envelope, the authors introduced the following formula 2.94 ����� = ���6.�3� ����� DI 1.98 in Fig.4. to simply calculate Q′,[W], which is the heat loss from 2.63 With DI ����� = ����.0�� ����� 3.2 Results of Thermal Performance the building envelope divided by the environmental 1.76 3.2.1 Thermal Image temperature difference. A thermal image of the case with DI was taken at ������ the south wall of the experimental building at 19:40, �� = 3 h after sunset. Fig.5. shows the thermal image and � �� � � picture of the experimental building taken from the � � � = �� � � �� � �� ��� south. The right side of the south wall, shown in red in the picture, is the DI-applied wall. In a comparison of the right and left sides of the south wall, the outer where H [W] is the internal heat generation, L [W] surface temperature of the former was lower than that is the heat load because of ventilation, V [m /s] is of the latter. This image qualitatively shows the effect the air flow rate, P [Pa] is the kinetic pressure in the of the DI system; the system decreases the temperature exhaust air, θ and θ [ C] are the indoor and outdoor i o of the outdoor wall surface. This reduction originates environmental temperatures, respectively, ρ [kg/m ] from inside the building. The qualitative evaluation is is the air density, C [J/(kg K)] is the specific heat Journal of Asian Architecture and Building Engineering/November 20XX/111 1 JAABE vol.14 no.1 January 2015 Aya Yaegashi 215 Journal of Asian Architecture and Building Engineering/November 20XX/111 1 o capacity of air, and θ and θ [ C] are the exhaust and environmental temperature was taken from the SAT for ea out outdoor air temperatures, respectively. a horizontal surface at the site. The heat loss from the building envelope was obtained by subtracting the sum of the ventilation load and kinetic energy of the ventilation from the rate of internal heat generation and dividing this value by the environmental temperature difference between the indoors and outdoors. The rate of internal heat generation is given by adding the measured energy consumption to the assumed energy consumption from the fluorescent light (35 W) and sirocco fan (5 W). In this experiment, the indoor environmental temperature was provided by the global temperature located at the center of the room, and the outdoor environmental temperature was provided by the sol-air temperature (SAT) for a horizontal surface at the site (Hattori, 2008). Fig.6. shows the variation in heat loss during the experiment. Fig.7. shows the measured heat loss for each weather condition. The hourly averaged data from 17:00 to 6:00 was used to exclude the influence of solar radiation. Fig.7. shows that the heat loss in the case with DI was reduced compared to the case without DI under the identical weather conditions of cloudy and rainy. A statistically significant difference was recognized in the heat loss of each case (p < 0.05). This suggests that the thermal performance improved by using the DI technology. Although the data were only obtained for the case with DI, the rate of heat loss decreased in clear weather, which implies a dependence on the weather. The reference outdoor environmental temperature was lower than the actual temperature in clear weather because the outdoor Fig.5. Thermal Image and Picture of the Experimental Building Fig.6. Variation in Heat Loss during the Experiment 216 JAABE vol.14 no.1 January 2015 Aya Yaegashi The Q value was used to evaluate the effect of applying DI technology. Table 5. shows the Q value and details of the heat loss from each element. The Q value of the experimental building was calculated to be 2.30 W/m K based on the specifications. The actual Q value was calculated to be 2.26 W/m K based on the measured heat loss from the entire building envelope in the case without DI. Assuming that the difference between the theoretical and actual Q values was because of a construction error, the difference was distributed at the area ratio to the heat loss from the walls. To account for the heat loss from the DI-applied area, the heat loss difference between the cases with and without DI was assumed to be because of the effect of the DI technology. The heat loss per unit temperature at the DI-applied area was 3.19 W/K without DI and 1.83 W/K with DI. This indicates that applying DI Fig.7. Heat Loss for Each Weather Condition technology reduced the heat loss by 42.6%. Table 5. Q Values and Details of the Heat Loss Case 4. Conclusion Theoretical Without With Value The authors applied DI technology to the walls and DI DI ceiling of a timber framework house and evaluated the Q Value [W/m K] 2.30 2.26 1.99 thermal performance through actual measurements. Ventilation 9.06 9.06 8.79 The heat loss through the building envelope was Heat Loss Total Envelope 9.53 9.31 7.95 from Each significantly reduced with DI technology. The heat loss Opening 3.41 3.41 3.41 Element was reduced by 42.6% for the DI-applied wall. Normal Wall 2.80 2.70 2.70 [W/K] This study mainly focused on the thermal DI Wall 3.31 3.19 1.83 performance. The application of DI technology, however, has a risk of decreasing the thermal comfort References 1) Chung, M.H. and Rhee E.K. (2013) Development of System- because of the decrease in the inner wall surface Integrated Design Prototypes for Zero Emission Buildings. Journal temperature. Conversely, the application can also of Asian Architecture and Building Engineering, 12 (1), pp.133- contribute to an increase in thermal comfort because of a rise in temperature resulting from outdoor air intake. 2) Baily, N.R. (1987) Dynamic insulation systems and energy These phenomena have been analyzed in continuous conservation in buildings. ASHRAE Transactions, 93 (1), pp.447- studies (Yaegashi, 2014). 3) Qiu, K. (2007) Modeling the combined conduction-air infiltration through diffusive building envelop. Energy and Buildings, 39, Note pp.1140-1150. Whereas the air-conditioning system is on in the summer, the air 4) Gan G. (2000) Numerical evaluation of thermal comfort in rooms flow should be reversed to prevent condensation in the wall by with dynamic insulation. Building and Environment, 35 (5), introducing cooled and dried indoor air into the wall. The indoor pp.445-453. wall surface temperature approaches the indoor air temperature 5) Imbabi, M.S. (2013) A passive-active dynamic insulation system and the heat flow from indoors to the indoor wall surface for all climates. International Journal of Sustainable Built decreases. Concurrently, the outdoor wall surface temperature Environment. approaches the indoor air temperature resulting in the increase in 6) Hattori, T. (2008) Developments and examples related to practical the heat flow from the outdoor wall surface to the outdoors. The field measurements of the heat loss coefficients of detached increased heat flow, however, can be replaced by the heat flow houses. Architectural Institute of Japan, 14 (28), pp.491-496. between the exhaust air and outdoor environment. Thus, this flow 7) Yaegashi, A. et al. (2014) Experimental Evaluation of Dynamic does not result in an increase in the heat loss through the wall Insulation Applied to Timber Framework House in Real when the heat loss is discussed for the entire building system. In Environment. Summaries of technical papers of annual meeting winter, the heat loss because of exhaust air can be recovered by 2014, Environmental Engineering II, pp.123-124. heat pump systems, whereas the recovery is difficult in summer. In this sense, the application of the DI system has an advantage in Symbols winter. C : specific heat capacity of air [J/(kg K)] H: internal heat generation [W] Acknowledgment L: heat load because of ventilation [W] This study was performed with financial support P: kinetic pressure in the exhaust air [Pa] from the Ministry of the Environment, Japan. Q′: heat loss from the building envelope divided by the environmental temperature difference [W] We appreciate Mr. X. Cheng's assistance with the V: air flow rate [m /s] experiment. V': air flow rate [m /h] Δp: pressure difference [Pa] JAABE vol.14 no.1 January 2015 Aya Yaegashi 217 o θ : indoor environmental temperature [ C] θ : outdoor environmental temperatures [ C] θ : exhaust air temperatures [ C] ea θ : outdoor air temperatures [ C] out ρ: air density [kg/m ] 218 JAABE vol.14 no.1 January 2015 Aya Yaegashi
Journal of Asian Architecture and Building Engineering – Taylor & Francis
Published: Jan 1, 2015
Keywords: Dynamic Insulation; Thermal Performance
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