Performance of Variable Design Configurations for Wind Driven Rain (WDR) Shading Device in Tropical Climate

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1 Performance of Variable Design Configurations for Wind Driven Rain (WDR) Shading Device in Tropical Climate Selbin P.K., C.H. Lim, Seyedehzahra Mirrahimi, M. Alkhair, Elias Salleh, K. Sopian Solar Energy Research Institute (SERI) Universiti Kebangsaan Malaysia MALAYSIA Abstract: - Wind-driven rain (WDR) or driving rain is rain that is given a horizontal velocity component by the wind. Wind driven rain research is important in building science especially in the tropical regions due to heavy rain fall. WDR is the most important moisture source affecting the performance of building facades and building interior space. This paper explored and analyzed on various rain shading design configurations for WDR in tropical climate. Computational fluid dynamics (CFD) method was used to simulate the 6 different rain shading design configurations. Based on the CFD flow visualization analysis, it was found that the optimum rain shading device was the louvers type for the tropical climate. Key-Words: - Wind-driven rain, building façade, tropical area, CFD. 1 Introduction Wind driven rain or WDR is an important research subject in building science. Semi-enclosed spaces in café shops, restaurants and other shopping outlets can suffer from rainwater penetration during heavy rain coupled with strong wind. WDR is the most important moisture source affecting the hygrothermal performance and durability of building facades. Consequences of its destructive properties can take many forms. Moisture accumulation in porous materials can lead to water penetration, frost damage, moisture induced salt migration, discoloration by efflorescence, structural cracking due to thermal and moisture gradients, to mention just a few. WDR impact and runoff is also responsible for the appearance of surface soiling patterns on facades that have become characteristic for so many of our buildings [2]. Without the presence of wind, rain drops would have fall vertically on a roof with eaves and it would be all that was needed to protect windows and other sensitive building elements in the wall from getting wet [3]. Until today there are many buildings which still remain vulnerable to wind-driven rain especially in the tropical regions. In addition, the WDR can also cause critical building problem like moisture-induced salt migration which may cause structural issues. 2 Objective The 3 main objectives for this study are as follows: a. To explore various design configurations for WDR shading device in tropical climate; b. To analyse the flow distribution of the variable design configurations of the WDR; c. To identify the optimum WDR shading configuration in tropical climate. 3 Problem Solution Research on WDR for building can be predicted using 2 main methods namely the semi-empirical WDR method and the numerical simulations method based on Computational fluid dynamics (CFD). Both methods require standard wind and rain input data for the calculations such as wind speed, wind direction and horizontal rainfall intensity [4]. The study covered 6 different types of WDR shading design configurations namely the 0.5m length overhang, 1.0m length overhang, 1.5m length overhang, 2.0m length overhang, tilted overhang and louvers type overhang. A semienclosed model of a corridor space was modelled and used as base model for all the 6 different WDR shading configurations. It was also used as a ISBN:

2 base model for comparison and benchmarking. Each of the WDR shading design configurations were modelled and simulated using commercial CFD software called ANSYS Fluent version 14. The turbulence model used in the CFD simulation was the Euler Lagrangian model or also known as 2 phase flow model. The boundary conditions input parameters for the CFD simulations are as follows: 1. Mean outdoor air velocity = 2 m/s 2. Mean rainwater velocity = 4 m/s 3. Ambient air temperature during raining=25 deg C 4. Total cells = 4,322,748 cells 5. Turbulence model = 2 phase flow (Euler Lagrangian) 4 Result and Discussion Figure 1 shows the base model of a semi-enclosed corridor space. Fig. 1(a) revealed the CFD simulation result of the WDR penetration without any shading device. Based on the vector flow visualization, it was observed that a major portion of the semi-enclosed space was covered by the rain water. The blue coloured vector signified the wind whereas the pink coloured vector signified the rain water. Fig. 1(a) Fig. 2 shows the base model with 0.5m length WDR shading design. Fig.2(a) illustrates the CFD simulation result of the WDR penetration after installing the 0.5m length WDR shading device. Based on the vector flow visualization, it was observed that a major part of the building was still covered by the rainwater although the depth of WDR penetration was slightly reduced compared to the base model without overhang. Fig. 1 Fig. 1 Fig.2 (a) ISBN:

3 The CFD simulation was conducted on the 1m length WDR shading design. Fig. 3 shows the base model with 1m length WDR shading device. Figure 3a revealed the CFD simulation result of the WDR penetration for the 1.0m length horizontal rain water shading device. Based on the vector flow visualization, it was observed that the WDR penetration into the semi-enclosed space was further reduced compared to the 0.5m overhang. However, there was still rainwater accumulated along the openings of the space. Fig. 4 Fig. 2 Fig. 4 (a) Fig. 3 (a) Fig. 5 shows the base model with 2.0m length WDR shading device. Fig. 5(a) shows the vector flow and distribution of WDR. The vector flow and WDR distribution in Figure 5a revealed that most of the WDR was managed to be blocked and reduced by the 2.0m length WDR shading device before entering the semi-enclosed corridor space. It was revealed that the 2.0m length WDR shading device was effective in shading the WDR at external wind speed of 2 m/s. Fig. 4 shows the base model with 1.5m length WDR shading device. Based on the vector flow visualization in Figure 4a, the WDR penetration was reduced tremendously compared to the 0.5m length WDR shading device. Nevertheless, there was still some rainwater distributed along the edge of the opening of the semi-enclosed corridor space. Fig. 5 ISBN:

4 Fig. 5 (a) The final rainwater design configuration covered in this study was the louvers type as shown in Fig.7. Based on the CFD simulation result shown in Fig.7(a) revealed that the louvers type WDR shading device managed to block significant WDR penetration into the semi-enclosed space. The vector flow distribution showed that the louvers type was the most effective and optimum WDR shading device for the tropical climate. Furthermore, the louvers type rainwater shading device can be easily retrofitted into existing buildings as an architectural feature which were both functional and also aesthetically pleasing. Fig. 6 shows the base model with a tilted overhang WDR shading device. Based on the CFD simulation, Figure 6a revealed that the titled overhang was also effective in reducing the rainwater penetration into the semi-enclosed space although there was still some rainwater accumulated at the edge of the opening area. Based on the analysis, the tilted overhang can also be considered as an effective rainwater and wind barrier. Fig. 7 Fig. 6 Fig. 7(a) Fig. 6 (a) 5 Conclusion This paper has presented a study on the application of various WDR shading device configurations for tropical climate. There were total of 6 different types of WDR shading configurations covered in this study. Based on the CFD simulation results, the ISBN:

5 flow visualization analysis revealed that the optimum WDR shading design for tropical weather was the louvers type. The louvers type device also demonstrates both as an effective WDR shading device and also act as an aesthetically pleasing element for building design. References: [1] Bert Blocken, Jan carmeliet. A review of winddriven rain research in building science.wind Engineering and Industrial Aerodynamics, , [2] Bert Blocken, Jan carmeliet.high resolution wind driven rain measurements on a low rise building-experimental data for model development and model validation. Wind Engineering and Industrial Aerodynamics, 93(12), 2005, [3] GE Overton. An analysis of wind driven rain in New Zealand. Branz, Building Research Levy, and the Ministry of Business, Innovation and Employment, [4] Bert Blocken, Jan carmeliet. Guidelines for the required time resolution of meteorological input data for wind-driven rain calculations on buildings. Wind Engineering and Industrial Aerodynamics, 96(5), 2008, ISBN: