1、Sihyun Park is a Ph.D student and Minhee Kim is a master degree student at Department of Architectural Engineering, Ewha Womans University, Seoul, Korea. Jae-Han Lim and Seung-Yeong Song is a professor, Department of Architectural Engineering, Ewha Womans University, Seoul, Korea. Condensation Resis
2、tance Evaluation of a Double-Sliding Window System in Accordance with the Korean Design Standard for Preventing Condensation in Apartment Buildings Sihyun Park Minhee Kim Jae-Han Lim, PhD Seung-Yeong Song, PhD Member ASHRAE Member ASHRAE Member ASHRAE Member ASHRAE ABSTRACT In a cold climate, the co
3、ndensation risk for window systems during winter is high, and such condensation can lead to mold or mildew problems, thereby causing discomfort for building occupants. To eliminate condensation risks and secure the well-being of the occupants, the Korean Design Standard for Preventing Condensation i
4、n Apartment Buildings was announced in 2014. However, the current window systems on the market cannot fulfill the strengthened design standards. Therefore, a high-performance window system that satisfies the new enhanced standard is necessary. The most commonly used double-sliding window system with
5、 double glazing on a four-track PVC frame was examined as a reference model to evaluate the condensation resistance for apartment buildings. Several different window system models have been proposed as alternatives. The condensation resistance of the reference model was compared to that of the alter
6、natives using three-dimensional steady-state heat transfer simulations. The Temperature Difference Ratio (TDR) was calculated for each case using the lowest inside surface temperature determined by the simulation results, and these TDRs were then compared to suggest the most improved alternative. IN
7、TRODUCTION The occurrence of inside surface condensation depends on the inside air temperature, humidity and outside air temperature. Condensation can easily occur during a cold winter, when the difference between the outside and inside air temperatures is large. Condensation can damage interior sur
8、faces and cause serious problems involving mold or mildew, which can damage painted surfaces and lead to health problems, causing discomfort for building occupants. Recently built apartment buildings face increased condensation risk caused by airtight building designs that are implemented to reduce
9、building energy consumption. A growing desire for a better indoor built environment coincides with the steady domestic economic growth. In addition, there has been an increasing trend in the use of a slim window frame design with a large window area, which retains better prospect rights for the occu
10、pants. With respect to prevent condensation, the thermal performance of the slim frame and the glazings edge cannot reach the required thermal performance of window systems, and lead to weak edge-of-glazing performance. To eliminate condensation risks and secure the well-being and comfort of buildin
11、g occupants, the Korean government mandated the Korean Design Standard for Preventing Condensation in Apartment Buildings, such as for walls, windows and doors, in 2014. It is important to enhance the thermal performance of windows to achieve the implemented targets for the building envelopes conden
12、sation resistance level; because, characteristic Korean residential buildings are high-rise apartment buildings designed with a main living room and a bedroom with nearly floor-to-floor height windows, as shown in Figure 1. Figure 1 Typical Elevations of Korean Apartment Buildings In this study, the
13、 condensation resistance of a double-sliding window system with an aluminum spacer was used as a reference model, and possible alternatives were analyzed using a three-dimensional steady-state heat transfer simulation. The lowest interior surface temperature was determined from the simulation result
14、s and used to calculate the temperature difference ratio (TDR). OVERVIEW OF THE CURRENT WINDOW SYSTEMS IN KOREA: DOUBLE-SLIDING WINDOW The Korean Design Standard for Energy-Efficient Building defines the minimum building envelope design requirements, such as for walls, windows and doors. To meet the
15、 required U-value of a window system, most apartment buildings are designed with double glazing (5CL-12Air-5CL) on a polyvinyl chloride (PVC) four-track framed window system, although some use triple-glazing windows. Double-glazing can typically be assembled using different glass types for the inner
16、 and outer layers, and gas fill and applied low-emissivity (low-E) coatings decrease the radiative heat transfer through the glazing unit. An argon gas-filled double-glazing window with a 12-mm (0.04 in) cavity provides a measurable improvement in the thermal performance compared to an air-filled ve
17、rsion of the same window. PVC is the most popular frame material, with steel reinforcement inside of a large hollow chamber within the frame. Small extrusion details in the frame profiles are used to prevent the reinforcement steel surface from contacting the frame body; however, warped steel can ma
18、ke contact with the large frame area in practice. Creating smaller cells within the frame reduces this conduction. To ensure air-tightness, the glazing and frame are sealed with silicone sealing, and several weep holes are punched into the frame tracks to release accumulated condensed water. Typical
19、ly, in a Korean apartment building, the outer walls are designed as an entire window adjacent to the living area and bedrooms, as shown in Figure 1. Many cases of condensation occur on the edge-of-glazing area; in particular, lower surface temperatures are measured near the jamb and sill overlaps on
20、 the third and fourth tracks facing the building interior, as shown in Figure 3(a). CONDENSATION RESISTANCE INDEX The newly developed Korean Design Standard for Preventing Condensation in Apartment Buildings requires the allowed maximum TDR of building envelopes. Additionally, the standard requires
21、the inside surface temperature of evaluation locations to be calculated by a three-dimensional heat transfer simulation or measured by a mock-up test for quality assurance. This study conducted the condensation resistance evaluation using the simulation. The TDR is defined as the ratio of the differ
22、ence between the inside air temperature (Ti) and the inside surface temperature of the evaluation locations (Tsi) to the difference between the inside air temperature (Ti) and the outside air temperature (To). After obtaining the inside surface temperature of the evaluation locations, the TDR can be
23、 calculated using Eq. (1). This value is used to determine the level of condensation resistance and ranges from 0 to 1. To evaluate the simulation results, the required TDR evaluation locations were referenced from the standard; the locations are shown in Figure 2. (1) Figure 2 Evaluation Locations
24、of a Window System Table 2. Allowed Maximum Temperature Difference Ratio in Different Regions TDR Region IaRegion IIaRegion IIIaWindow directly facing the exterior Center-of-glazing 0.16 0.18 0.20 Edge-of-glazing 0.22 0.24 0.27 Frame 0.25 0.28 0.32 a Based on monthly average daily lowest air tempera
25、ture in January; the most extreme cold month in Korea, categorized regions by -20 C/-4 (Region I), -15 C/5 (Region II) and -10 C/14 (Region III). The Korean Design Standard divides the whole region into three climate regions; Region I (Extreme Cold), Region II (Cold) and Region III (Moderate). ANALY
26、SIS OF CONDENSATION RESISTANCE Overview of the Condensation Resistance Analysis To resolve the current window problems on the edge-of-glazing, this study analyzed the condensation resistance of a double-sliding window system consisting of double-glazing on four tracks with PVC frames; the reference
27、model was compared to alternatives with similar window U-values. This study selected the window U-value and TDR to meet the required values for Region II, where edge-of-glazing TDR value, 0.24 is hard to satisfy the requirement in the standard. The U-value of the window system was set to 1.5 W/m2K (
28、0.26 Btu/(hnullft2null) to meet the required window U-value for residential buildings in the Korean Design Standard for Energy-Efficient Building, and each alternative composition is presented in Tables 5 and 6. In this study, the window size is assumed to be 2 by 2 m (6.5 by 6.5 ft.), which is the
29、defined specimen size in the national standard for the window mock-up test, KS F 2295. A horizontal section; including all four jambs from the interior to the exterior; was chosen for the simulation, as shown in Figure 3 (a), and the simulated model size is shown in Figure 3 (b). The standard requir
30、ed evaluation locations are as shown in Figure 2; however, the edge-of-glazing that is 2 cm (0.78 in) from the jamb and sill frame end on the third track resulted in the lowest inside surface temperature from the previous two-dimensional simulation results, which could not meet the required target T
31、DR. Therefore, this study analyzed the two edge-of-glazing locations on the third (T1), and fourth tracks (T2), where three-dimensional heat transfer occurs and two center of frame locations (T3 and T4), were evaluated by the two-dimensional simulation tool. oisiiTTTTTDR=(a) (b) (c) Figure 3 (a) Sim
32、ulated Area of a Double-Sliding Window System, (b) Simulated Section and (c) Evaluation Locations Simulation Method The condensation resistance of a reference model and the alternatives were evaluated using a three-dimensional steady-state heat transfer simulation and used to derive the inside surfa
33、ce temperature at the edge-of-glazing and center-of-frame locations. All of the alternative cases were compared to the reference model to evaluate the increase in the inside surface temperature; as a result, better performing alternatives were suggested. Boundary conditions, such as the set-point te
34、mperature, the surface resistances for the internal and external surfaces of the building and the material properties, are presented in Table 3. The internal and external temperatures are referenced from the Korean Design Standard for Preventing Condensation in Apartment Buildings, and the surface r
35、esistances; the reciprocal of the convective and radiative heat transfer coefficients at the internal and external surfaces, are referenced from ISO 10077-2:2012, Annex B, Surface resistances. An internal surface convective part was treated in two different conditions, edges or junctions between two
36、 surfaces are treated as reduced surface resistance and treated as normal for the plane surface. The material properties are from ISO 10077-2:2012, Annex A. Thermal conductivity of selected materials, and calculation parameters are listed in Table 4. Figure 4 Simulated Internal Surface Resistance Tr
37、eatment at Edges According to ISO 10077-2:2012, Annex B Table 3. Boundary Conditions and Material Properties for the Heat Transfer Simulation Boundary Conditions Material Properties Temp (C)/() Surface Resistances (R) (m2K/W) /(Btu/(hnullft2null) Materials Thermal Conductivity Emissivity () W/mK Btu
38、/(hnullftnull) External -15.0/(5.0) 0.04/(4.40) Glazing Glass 1.00 0.577 0.84 Low-E Coating 1.00 0.577 0.04 Internal 25.0/(77.0) Normal 0.13/(1.35) Frame PVC 0.17 0.098 0.9 Reduced 0.20/(0.88) Glazing Beads 0.17 0.098 0.9 Steel 50.0 28.889 0.8 EPDM 0.25 0.144 0.9 Silicone Sealing 0.35 0.202 0.9 Moha
39、ir 0.14 0.080 0.9 Setting Block 0.20 0.115 0.9 Anchor Bolt 50.0 28.889 0.8 Spacer Aluminum 160.0 92.446 0.1 Sealant 0.35 0.202 0.9 Desiccant 0.13 0.075 0.9 Insulating Spacer Thermoplastic Spacer (TPS) 0.25 0.144 0.9 Table 4. Simulation Parameters Iterations Assigned Condition Maximum number of itera
40、tion cycles 5 Maximum number of iterations within each iteration cycle 10000 Maximum temperature difference within each iteration cycle 0.0001 C (32.00018) Maximum temperature difference between iteration cycles 0.001 C (32.0018) Maximum heat flow divergence for total object 0.001% Maximum heat flow
41、 divergence for any node 1% Radiation Linear Black radiation heat transfer coefficient (linear radiation) 5.1 W/m2K (0.898 Btu/(hnullft2null) Smallest accepted view factor 0.0001 Number of visibility rays between radiative surfaces 100 Default temperature difference across airspace 10 C (50) Figure
42、5 Simulation Model Mesh Grid on Each Axis (Max. 30 mm (1.18 in) EVALUATION RESULT OF CONDENSATION RESISTANCE The condensation resistance evaluation results of the simulated reference model and all of alternatives are listed in Tables 5 and 6. From the previous two-dimensional simulation results, the
43、 thermoplastic spacer (TPS) was the best thermally improved spacer among the many spacers on the market, thus, the TPS size optimization (Cases 1-3) was conducted first. Second, the best resulting case from the TPS size optimization with low-E coating in different glazing layers (Cases 4 and 5) were
44、 simulated. Finally, single and double argon gas fillings (Cases 6 and 7) with the best resulting model from the second step were simulated. Table 5. Models and Condensation Resistance Results - TPS Size Optimization Reference Model TPS Size Optimization Case 1 Case 2 Case 3 Model Temperature Distri
45、bution 25 C/77 -15 C/5 Glazing Spec. 5CL+12Air+5CL, 5CL+12Air+5CL, Aluminum Spacer 5CL+12Air+5CL, 5CL+12Air+5CL, TPS 12 mm (0.47 in) 5CL+12Air+5CL, 5CL+12Air+5CL, TPS 6 mm (0.23 in) 5CL+12Air+5CL, 5CL+12Air+5CL, TPS 3 mm (0.12 in) Temp (C/)aTDRbTemp TDR Temp TDR Temp TDR Edge-of-Glazing T1 13.0/55.4
46、 0.30 13.1/55.6 0.30 13.6/56.5 0.29 13.8/56.8 0.28 (0.0/0.0) (0.00) (+0.1/+0.2) (0.00) (+0.6/+1.1) (-0.02) (+0.8/+1.4) (-0.02) T2 16.0/60.8 0.23 16.5/61.7 0.21 16.9/62.4 0.20 17.0/62.6 0.20 (0.0/0.0) (0.00) (+0.5/+0.9) (-0.02) (+0.9/+1.6) (-0.02) (+1.0/+1.8) (-0.03) Center- of-Frame T3 15.1/59.2 0.2
47、5 15.1/59.2 0.25 15.1/59.2 0.25 15.1/59.2 0.25 (0.0/0.0) (0.00) (0.0/0.0) (0.00) (0.0/0.0) (0.00) (0.0/0.0) (0.00) T4 15.5/59.9 0.24 15.5/59.9 0.24 15.5/59.9 0.24 15.5/59.9 0.24 (0.0/0.0) (0.00) (0.0/0.0) (0.00) (0.0/0.0) (0.00) (0.0/0.0) (0.00) aVariation in the surface temperature compared to the
48、reference model: + performance improvement, - performance decline bVariations in the TDR compared to the reference model: - performance improvement, + performance decline Although the reference model and the alternatives were simulated with similar window U-values, simply substituting thermoplastic
49、spacer cases (Case 1-3) increased the temperature by 0.1-0.8C (0.2-1.4) on the third track edge-of-glazing and 0.5-1.0C (0.9-1.8) on the fourth track edge-of-glazing. This behavior occurs because TPS has a lower thermal conductivity of 0.25 W/mK (0.144 Btu/(hnullftnull) which thermally improved the edge of the glazing. Optimizing the thickness of TPS, the thinnest spacer resulted in a warmer surface temperature around the edge of the glazing. Characteristically, a spacer acts as a conductance p
