Testing Water Penetration Resistance of Window Systems Exposed to Realistic Dynamic Air Pressures

Transcription

1 Testing Water Penetration Resistance of Window Systems Exposed to Realistic Dynamic Air Pressures R. A. Van Straaten 1, G. A. Kopp 2, J. F. Straube 3 1 Research Lab for Better Homes, University of Western Ontario, London, Canada. rvanstra@uwo.ca 2 Boundary Layer Wind Tunnel Lab, University of Western Ontario, London, Canada. gak@blwtl.ca 3 Building Engineering Group, University of Waterloo, Waterloo, Canada jfstraube@uwaterloo.ca ABSTRACT A method for testing a series of windows exposed to simulated real dynamic wind loads is proposed. Three vinyl framed residential windows installed in a full scale wood framed house were tested with the method. The windows were exposed to realistic fluctuating wind pressures on the surface of a building, obtained from wind tunnel experiments, and were replicated in full-scale using novel pressure loading actuators. In the series of tests reported herein, the incidence of water penetration was compared between static and dynamic pressure tests. It was found that the peak pressures at which the window s gasket systems could tolerate water exposure were much higher for realistic wind pressures than for those in the static pressure tests. The test methodology has the potential of providing greater insights of the performance of such systems exposed to actual severe wind storm conditions. 1. INTRODUCTION Water leakage, and particularly water leakage associated with window systems, has been identified as a significant contributor to moisture problems in buildings [1]. The recent North American Fenestration Standard/Specification for Windows, Doors, and skylights AAMA / WDMA / CSA 101 / I.S.2 / A [2] includes testing requirement for a window product s water infiltration performance under constant (i.e., static) pressure be reported as per test methodology ASTM E [3]. A methodology for water penetration testing under cyclical applications of air pressures is provided in ASTM E [4]. These cyclic pressures include application of a constant pressure for 5 minutes, reduced to no pressure for 1 minute, and repeated for at least 15 minutes. ASTM E [5] includes water penetration testing with rapid pulsed air pressure differences. These tests involve cycling pressure between 50% and 150% of a median air pressure. The frequency of the cycles is 0.5 Hz. The standard includes the detail The median test pressure used in this test method is defined as the specified test pressure supplied by the user and related to the maximum positive building design pressure. This detail will be discussed later in this paper. The standard also includes the commentary The pulsed pressure of this test method may act to pump water past dry seals and breather systems of units incorporating these features, thereby making the test method more severe than a static pressure

2 test method. On the other hand, the low pressure portions of the pressure cycles of this test method may allow weep systems and drainage dams to dissipate water from units incorporating these features, thereby making the test method less severe than a static pressure test method. From these comments it would seem sensible to apply realistic fluctuating pressures to such tests to address these concerns. Testing full scale building and building components under realistic wind pressures and driving rain conditions is undergoing or in development at several research institutions. Girma et al. [6] are using the International Hurricane Research Center s Wall of Wind, a wall consisting of large powerful fans, and water spray rack to expose building components to driving rain conditions. The advantage of introducing the water spray into a stream of air flowing past the specimen is that it allows the water droplets to follow more realistic paths. In ASTM testing the spray racks send a stream of water with impinging velocity and distribution irrespective of actual driving rain behaviour. Salzano et al. [7] have recently published testing on water penetration resistance of residential window installations using the University of Florida Hurricane Simulator. The system consists of water spray racks and eight large vaneaxial fans that produce stagnation pressures up to 1.67 kpa. The setup applies driving rain similarly to the Wall of Wind but they include rapidly varying cyclical pressures as high at 0.33 Hz. The Institute for Home and Business Safety [8] is developing a very large wind tunnel with capacity to test full scale houses. This facility will be able to replicate realistic fluctuating wind pressures (as opposed to sinusoidal pressures) and will also introduce wind driven rain into experiments. The Insurance Research Lab for Better Homes (IRLBH) at the University of Western Ontario has developed technology capable of imposing realistic static pressures following pressure traces derived from wind tunnel or field data. To date, use of this equipment in published research studies has been conducted the Cyclone Testing Station in Townsville Australia [9] to investigate structural performance of building components. IRLBH s equipment consist of relatively small pressure load actuators whose characteristic are described in greater detail by Kopp et. al. [10]. The equipment could be used for testing under realistic air pressure in small window test laboratories without the need for the electrical power and financial capital to construct large fan arrays. this paper reports on the most recent progress on the development of testing methodologies that utilize dynamic wind loads to investigate water penetration through window systems. 2. OBJECTIVE The objective of the work reported in this paper is to develop testing methodologies to investigate windows water penetration resistance performance under realistic fluctuating air pressures resulting from high wind conditions. 3. SCOPE The test method was applied to 89 cm x 153 cm windows installed in a house built to the Ontario Building Code in our laboratory. The house was used in a previous study which included application of high wind loads to the roof which may have affected the entire structure of the house. All windows were square and opened freely and did not appear to have significantly shifted or been effected structurally at the time of the testing. Some initial caulking failures on the exterior of the windows were evident prior to testing. Due to this consideration, the use of the results in this paper is limited to developing testing methodologies and not to make conclusion regarding window performance.

3 4. METHODOLOGY The facility utilized Pressure Load Actuators (PLAs) to provide the desired pressures. The units consist of a regenerative blower with high and low pressure side connected to a special valve. The valve position is changed by a high speed servo motor. The system is capable of following pressure traces with a frequency up of 7 Hz and pressures in a 1.2 m x 1.2 m enclosure air box up to 10 kpa when well air sealed. For this study a simple mobile air box was installed on the inside of the test house windows (Figure 1). Water was introduced with a spray rack system as prescribed in ASTM E and shown in Figure 2. Figure 2. Water Spray Rack. Figure 1.Air Box installed on inside of house. For this study, wind loads (air pressure traces) were drawn from positions on the building with high and moderate exposure and from a variety of wind velocities. The base wind pressures were derived from testing at the Boundary Layer Wind Tunnel Laboratory [11] and for higher wind velocities using previously developed techniques [12]. The pressures are spatially uniform, which is realistic for small windows away from corners. The windows were tested at constant pressures of 150 Pa, 360 Pa, 540 Pa, and 720 Pa with water exposure for 15 minutes as per ASTM E331. The windows were allowed to dry for at least 24 hrs between tests. These same windows were then tested when exposed to realistic air pressures traces derived from wind tunnel measurements of wall pressures at two points on a building at wind velocities of 20, 25 and 20 m/s. These traces had mean (peak) pressures of 113 (690) Pa, 169 (814) Pa, 180 (1078) Pa, 270 (1273) Pa, 261 (1552) Pa, and 394 (1832) Pa. Two of these traces are plotted in Figure 3. All pressure traces and exposures lasted for 15 minutes.

4 Pressure (kpa) m/s trace 20 m/s trace Time (s) Figure 3. Wind Pressure Trace with 20 m/s (690) Pa and 30 m/s (1552) Pa Mean (Peak) Pressure. In the test performed water leaked through the window gaskets well below rated performance of the window (B7 or 720 Pa static pressure as per CSA A440). We did not disassemble the window to investigate water leakage within the wall assembly between tests due to concerns about changing the nature of the window system between tests. Hence, water leakage may or may not have been occurring at the window to wall interface at the pressure reported in this paper or lower. A picture of a small water leak and a large water leak are shown in Figures 5 and 6. Water penetration on the indoor face of the specimen was recorded to identify failure. 5. RESULTS Measured pressure is plotted relative to the corresponding target pressure trace at peak pressure in Figure 4. Close agreement between targeted and achieved pressures are achieved in the test demonstrating the equipment s capabilities. Figure 5. Small (<5 g) Water Leak Air Pressure (kpa) m/s Trace Achieved 25 m/s Trace Achieved Figure 6. Large (>100 g) Water Leak Time (s) Figure 4. Trace (Targeted) and Achieved Air Pressure at 20 m/s (690) Pa and 25 m/s (1270) Pa Mean (Peak) Pressure Traces at Peak Pressure We did not attempt to measure the amount of water which leaked through the windows during the constant air pressure tests. However, it was generally a large amount which ran over the indoor window

5 sills, down the drywall, and onto the floor. These leaks are all indicated in Figure 7 as 100 g of water leakage even through they we not actually measured. Water Leakage (g) Window 1 Window 2 Window Static Pressure Test (Pa) Realistic Wind Test (Pa mean) Figure 7. Water Penetration Resistance Testing Results for Constant and Realistic Air Pressures. The results of the realistic pressure tests are also shown in Figure 7. Window 3 was the worst performer in both test methodologies. Windows 1 and 2 performed similarly. The windows failed at lower mean pressure conditions during the realistic fluctuating pressure testing than during the static pressure tests. Generally the water leakage in these tests appeared to be set off at peak gusts during the exposure period. During these tests we chose to measure the actual water leakage because in some cases only a small amount of water leaked through the gasket during a very brief and severe pressure fluctuation. The leakage was measured by weighing paper towels before and after being used to absorb as much of the leaked water as possible. 6. CONCLUSIONS The testing reported in this paper demonstrates the capability of pressure load actuator equipment to generate dynamic air pressures following real fluctuating wind data or wind tunnel data for water penetration resistance performance testing of building envelop components. Since only three samples were tested it is not possible to make broad conclusions relating the windows performance under static and dynamic pressure traces. However, the results suggest that testing windows at static pressures derived from mean wind induced surface pressures may optimistically predict performance during actual exposure. Providing a test methodology that more closely reflects real air pressure conditions could allow manufacturers to design to window to withstand more realistic wind conditions during exposure to exterior water. A review of wind conditions during rain events would assist selection of appropriate conditions for such tests under various climate conditions. A larger scale study of water penetration performance of windows utilizing realistic fluctuating wind traces would provide greater insights into to actual performance should be considered now that such capabilities are readily available. In future tests we would consider installing moisture detection systems within the assembly to investigate water penetration at the wall to window interface. Since reinstallation of the windows could affect performance, we are greatly interested in the potential for moisture detection devices to allow repeated testing on single installations with minimal time delay between tests. 7. ACKNOWLEDGEMENTS We would like to thank Juan Botero and Greg Hebb for there input and assistance in the lab. We would also like to thank Chris Schumacher at Building Science Corporation for his insights and lending equipment for this study.

6 8. REFERENCES [1] RDH Building Engineering Limited (2002) Water Penetration Resistance of Windows Study of Manufacturing, Building Design, Installation and Maintenance Factors, Report for CMHC, Canada. [2] AAMA/WDMA/CSA 101/I.S.2/A (2008) NAFS North American Fenestration Standard/Specification for windows, doors, and skylights. [3] ASTM E (2000) Standard Test Method for Water Penetration of Exterior Windows, Skylights, Doors, and Curtain Walls by Uniform Static Air Pressure Difference. [4] ASTM E (2000) Standard Test Method for Water Penetration of Exterior Windows, Skylights, Doors, and Curtain Walls by Cyclic Static Air Pressure Difference. [5] ASTM E (2004) Standard Test Method for Water Penetration of Exterior Windows, Skylights, and Doors by Rapid Pulsed Air Pressure Difference. [6] Girma B., Chowdhury A., and Sambare D. (2009) Application of a full-scale testing facility for assessing wind-driven-rain intrusion, Building and Environment, 44 pp [7] Salzano C., Masters F., and Katsaros J., (2010) Water penetration resistance of residential window installation options for hurricaneprone areas, submitted to Building and Environment. [8] Reinhold T. (2005) Testimony to the Subcommittee on Disaster Prevention and Prediction of the Committee on ommerce, Science, and Transportation of the United States Senate, June 29, [9] Henderson D., Ginger J., Morrison M., and Kopp G. (2009) Simulated tropical cyclonic winds for low cycle fatigue loading of steel roofing, Wind and Structures, 12(4) pp [10] Kopp G., Morrison M., Iizumi E., Henderson D., and Hong H. (2008) The Three Little Pigs Project: Hurricane Risk Mitigation by Integrated Wind Tunnel and Full-Scale Laboratory Tests, submitted to ASCE Natural Hazards Review. [11] Oh T., Surry D., Morrish D., and Kopp G. (2005) The UWO contribution to the NIST aerodynamic database for wind loads on low buildings: Part 1. Archiving format and basic aerodynamic data, Journal of Wind Engineering and Industrial Aerodynamics, 93 pp [12] St. Pierre L., Kopp G., Surry D., and Ho T. (2005) The UWO contribution to the NIST aerodynamic database for wind loads on low buildings: Part 2 Comparison of data with wind load provisions Journal of Wind Engineering and Industrial Aerodynamics, 93 pp