Wind-driven Rain Research Articles

Moisture dynamics in the masonry fabric of historic buildings subjected to wind-driven rain and flooding

Current climatic projections show clearly that increasingly more extreme weather events are to be expected in the future. Historic buildings are considered to be the most vulnerable to this adverse climatic impact, via moisture induced deterioration and resulting strength decay in their construction materials. Therefore, the identification of these climatic effects is important to be able to develop suitable tools to mitigate them, both for individual buildings and on a regional scale. This paper presents the analysis of a comprehensive environmental monitoring of two historic buildings in Tewkesbury, Gloucestershire, UK, to provide thorough insight on their performances under environmental loading on a comparative basis. Firstly, the effect of wind-driven rain (WDR) and flooding is assessed by correlation with relative humidity (RH) measurements. The WDR measurements are then compared against values calculated using well established semi-empirical models and reasons behind the limited correlation are discussed. The dynamic hygrothermal response of two different historic fabrics is studied in greater detail by monitoring in-wall temperature and RH. The conclusions drawn from the analysis of the monitoring outputs are then further elaborated on by using hygrothermal characterization obtained by dynamic vapour sorption (DVS) testing of material samples extracted from the fabric of these buildings. The study concludes that the current environmental conditions pose a threat on the building envelopes unless routine maintenance is provided, and that monitoring methodology devised is clearly successful in quantifying the exposure of the two historic buildings to environmental conditions, onsetting deterioration phenomena in the envelop materials.

Finite panel method for the simulation of wind-driven rain

In present numerical methods for the wind-driven rain (WDR) simulation, a large computational work for raindrop trajectories is required to obtain the distribution of the catch ratio because of the randomness of the initial conditions of the raindrops. A new method named Finite Panel Method (FPM) that is employed to acquire the catch ratio distribution is proposed to reduce the calculation amount and diminishes the randomness. In the FPM, raindrops ending in the corners of the panels which are divided on the surface are simulated, and then the distribution of catch ratio is acquired by a reconstruction method. As a demonstration, catch ratio results by FPM in typical flow fields are presented, including the case of the three-dimensional flow field of power-law velocity profile, and cases of the flow around two- and three-dimensional low-rise buildings. The FPM results are compared with these calculated by the classical method and literature. The results indicate that FPM can reduce the calculation amount of raindrop trajectories with equivalent accuracy compared to the classical method.

Computational fluid dynamics simulations of wind-driven rain on a mid-rise residential building with various types of facade details

Numerical studies of wind-driven rain (WDR), reporting detailed analysis of rain exposure on building facades, focus mainly on simplified building facades. However, small-scale facade details have a large impact on the rain exposure of a building, redistributing WDR locally. The present study reports results of computational fluid dynamics simulations with Eulerian multiphase (EM) model for WDR on a stand-alone mid-rise residential building. The influence of facade details, namely roof overhangs, balconies and window sills, is analysed. It is shown that even a very small surface detail, such as a window sill with a size of 0.10 m, can decrease catch ratio by up to 37% and droplet impact speed by up to 40%. Numerical simulations also show the practicality of the EM model for detailed analysis of WDR intensity on a complex building and its ability to be used as a design tool.

RETRACTED: Computational fluid dynamics, a building simulation tool for achieving sustainable buildings

Buildings use about 40% of the global energy, thus making them the prime consumers and therefore the center of attention. The analysis of most of the building related problems such as the thermal analysis, effects of wind loading, ventilation analysis and the environmental effects etc. were conducted by the wind tunnel tests, earlier. However, now days, all these test can be done effectively with the aid of a mathematical technique called computational fluid dynamics (CFD). This paper is a brief, non-exhaustive overview of the status of application of CFD in building performance simulation for the indoor and outdoor environment. The discussion is focused on the management of the thermal comfort based on the ventilation loss, thermal loss and some other topics like the effect of fire inside the building and the hospital environment along with the discussions on the movement of the pedestrians, effect of rain and wind or wind driven rain (WDR) and pollutants etc. on the buildings especially artifacts. It is seen that CFD technique offers many advantages over the wind tunnel testing and simplified empirical or semi-empirical equations. Deficiencies of steady RANS and LES modeling, the need for high-resolution grids and lastly, the requirement of a valid CFD model and its verification poses some limitations. Still efforts are being done and shall continue to focus on alleviating these limitations, but at least equally important is avoiding user errors.

Optimization of Wind Driven Rain Barrier for Tropical Natural Ventilated Building

Wind Driven Rain (WDR) is an inherent problem especially on open corridors and open areas like courtyard, balconies and terraces of naturally ventilated tropical buildings. The WDR can cause the building floor to be slippery and even flooding during heavy rain and strong wind. It can also eventually caused damages on building materials if exposed over a long period of time. Unfortunately, until to date there are not many researches conducted on WDR in tropical natural ventilated buildings. An experimental and CFD simulation analyses were taken into consideration to predict the percentage of water on a floor of case study building. Different types of rain barrier designs have been proposed to reduce the amount of wind driven rain entering the building. The CFD simulation results showed that the water percentage on the floor caused by the wind driven rain can be reduced from 78% of the floor area to about 42% using titled overhang rain barrier design.

Application of Data Sets Obtained from the Detached Experimental Weather Station in Conditions of Real Building

This article refers to the possibility and appropriate using of actual data sets for characterizing exterior conditions applied into the computer simulations or energetic analysis. The need of updated reference years is a consequence of the reason of global warming and climatic changes. There is shown the endeavour of creating the reference year concept as an innovative tool for chosen locality. Visions of following research would be the progressive addition of data sets of wind-driven rain falling to the vertical plane. Location of obtaining the weather data set is a significant factor for obtaining of correct results.

Measurements of Wind-driven Rain on Mid- and High-rise Buildings in three Canadian Regions

Wind-driven rain (WDR) is an important boundary condition for the study of the hygrothermal behaviour and durability of building envelopes. Understanding the WDR characteristics is important for establishing designs that minimize moisture related issues. Three buildings located in three Canadian cities (Fredericton, Montreal and Vancouver) have been instrumented with equipment to quantify the WDR loads on building façades. This paper presents the experimental setup, spatial distribution of WDR on façades in terms of wall factors, and the comparison between measurements and calculated WDR using the standard ISO 15927. The preliminary results show that the ISO model overestimates the WDR amount most of the time.

The Spell Definition in ISO-15927 and its Impact on the Rain Deposition on the Building Facade

Wind-driven rain (WDR) is one of the most important causes for water damage in buildings. Therefore, the first crucial step to assess the hygrothermal performance of the building envelope, is the appropriate estimation of the amount of rainwater striking the building's façade. ISO 15927 offers the annual average index –mainly to assess the moisture content of absorbent surfaces, and the spell index – more related to the likelihood of water penetration through joints. To calculate these indices, assumptions are made concerning the length of the period of ‘no rain’, called ‘spell definition’. Obviously, the choice of this spell definition will characterise the WDR-amount. In this paper, WDR measurements of a 3-storey building in Vancouver, Canada are used to investigate how this spell definition affects the rain load. Different filter criteria are used to exclude errors due to measurement equipment. By means of the catch ratio as a dimensionless parameter, the results of the analysis for different spell definitions are compared to hourly and 5-min data. It is concluded that longer spell definitions result in lower catch ratios and an underestimation of the WDR load. Hourly data turns out to be a more conservative approach for WDR-assessment of this case study, but is able to represent the spread on the catch ratio most closely to the original 5min-dataset.

The Design of a Modelling, Monitoring and Validation Method for a Solid Wall Structure.

Hygrothermal assessment is the combined analysis of heat, air and moisture transfer through the building fabric. The two approaches are covered by conventions known as the IS EN 5250:2011 (Glaser method) and IS EN 15026:2007 which differs from Glaser by solving the equations numerically using computer software. Results for hygrothermal analysis provide valuable information for surface and interstitial condensation risk assessment and the impact of energy upgrades. For traditional solid walled structures, conditions such as wind driven rain (WDR) and rising ground water can have a significant impact on the environmental behaviour and in particular the moisture behaviour of the building envelope. The convention IS EN 5250:2011 is still widely used to assess the moisture performance of buildings and their components, even though it is not a comprehensive assessment methodology as it fails to include the movement of liquid water and for solid wall structures in particular, it is imperative that all forms of moisture movement are assessed. This research sets out a design methodology, to establish the hygrothermal performance of rendered solid brick wall constructions to ultimately establish the optimum and most appropriate retrofit intervention. The methodology chosen establishes all material properties of a monitored wall. A weather station is used to establish all weather data for the site. The building, will be monitored initially for a 12 month period to determine its hygrothermal condition. The data logged monitoring will establish the temperature and RH profile through the wall. The data from this monitoring will be inputted to software which meets the IS EN15026:2007 convention-a dynamic model which assesses the movement of water both as a vapour and as a liquid.

Overhang Effect on Reducing Wind-driven Rain for a Mid-rise Building

Roof overhangs are a common feature that can be used to protect the building façade from wind-driven rain (WDR) as field measurements and CFD modelling have shown. However, the quantitative evaluation of the effectiveness of overhangs in protecting the building façade requires further investigation. A six-storey mid-rise building with a flat roof located in Vancouver, British Columbia, Canada has been selected for the experimental study. The study involves the analysis of the spatial distribution of WDR on the building façade before and after the installation of a temporary retractable roof overhang. This paper presents the experimental setup, preliminary result analysis including the spatial variation of catch ratios on the building façade, and the performance assessment of a 1.2 m overhang under two rain events.

Wind-driven rain on two parallel wide buildings: Field measurements and CFD simulations

Most studies of wind-driven rain (WDR) reported in the literature focus either on isolated buildings or on a particular building in geometrically complex environments. There is a need for experimental and numerical studies for more generic multi-building geometries. The present study reports detailed field measurements and numerical simulations of WDR that are conducted for an idealized geometry with two parallel wide buildings with different heights, located in Dübendorf, Switzerland. The datasets of rain events and WDR measurements with high spatial and temporal resolution are made available online to download and are intended for model development and validation. Numerical simulations are performed with computational fluid dynamics (CFD) based on the 3D steady Reynolds-averaged Navier–Stokes (RANS) equations and an Eulerian multiphase (EM) model for WDR, including the turbulent dispersion of raindrops. The numerical results are validated by comparing the calculated catch ratio values and cumulative WDR amounts with data from the field measurements. The CFD simulations accurately estimate the WDR intensities at the positions of 18 WDR gauges. The average discrepancies between the numerical and experimental results are found to be 6.9% for the rain event on February 20–21, 2014 and 4.9% for the rain event on August 2–3, 2014. In different building configurations, the influences of recirculation regions, sheltering, wind-blocking effect and acceleration of wind determine the WDR distribution on the downstream building. WDR can increase due to recirculation regions and acceleration of wind, while wind-blocking effect and sheltering decrease WDR.

Computational and Experimental Investigation for an Optimal Design of Industrial Windows to Allow Natural Ventilation during Wind-Driven Rain

With an increased awareness of sustainability issues, natural ventilation has become an elegant method for reducing the costs and environmental effects of the energy that is used to maintain comfortable indoor air quality rather than using mechanical ventilation. The windows in many industrial buildings are continuously open to exhaust pollutants and intake fresh air. Though windows are functional and efficient for natural ventilation, rainwater is able to penetrate through the windows during wind-driven rain. For industries in which the moisture content affects the quality of the product, the intrusion of a large amount of rainwater through windows must be prevented without compromising the effective ventilation. The aim of this research is to determine an innovative design for windows to accomplish the optimum of high ventilation and low rain penetration. For this purpose, windows are variously innovated and tested in full-scale measurements, reduced-scale wind-tunnel measurements and computational fluid dynamics (CFD). An artificial rain and wind velocity to mimic the average of the maximum values in Korea are created. The maximum reduction in rain penetration of over 98% compared to basic 90° open windows is attained with only a 4%–9% decrement of ventilation efficiency in the two recommended designs.

Future moisture loads for building facades in Sweden: Climate change and wind-driven rain

This work investigates the prospective impacts of climate change on wind-driven rain (WDR) and walls through simulating the hygrothermal performance of rain screen of common vertical wall constructions for the climatic conditions of Gothenburg in Sweden. While a substantial amount of work has been done on the impact of climate change on the thermal performance of buildings, this paper studies its impact – through changes in rain, wind and other climatic parameters – on the amount of water which penetrates the outmost layer of ventilated façades. Importance of three uncertainty factors of the climate data are investigated: uncertainties from global climate models, emissions scenarios and spatial resolutions. Consistency of the results is examined by modelling walls with different materials and sizes, as well as using two mathematical approaches for WDR modelling. Sensitivity of the wall simulations to the wind data is assessed by using synthetic climate with sole wind data. According to the results, higher amounts of moisture will accumulate in walls in the future; climate uncertainties can cause variations up to 13% in the calculated 30-year average of water content and 28% in its standard deviation. Using sole wind data can augment uncertainties with up to 10% in WDR calculations, however it is possible to neglect changes in future wind data.

External wood claddings – performance criteria, driving rain and large-scale water penetration methods

In Norway, wood is widely used as an external cladding material. The performance requirements of a facade cladding can be divided into technical and aesthetic performance, where the technical performance is more distinct than the aesthetic one. Performance models for technical performance of wooden facades and deckings are under development and there is also ongoing research on the parameters that affect aesthetic performance. Wooden facades are recommended to be designed as a two-step tightening with a ventilated air gap and drainage opening on the back. The technical performance is mainly related to the ability of the construction to withstand wind-driven rain and the drying out potential of the chosen material and solutions.This work presents the results from a large-scale laboratory trial on three different wooden cladding solutions. The objective was to investigate the rain tightness of the different types of cladding, to detect water that penetrates the cladding and monitor the uptake of moisture, and the subsequent drying out. The trial showed that even at large amounts of wind-driven rain, only little water penetrated through the investigated cladding types. From a technical performance point of view, it is important to focus on an accurate mounting routine.

Wind driven rain and moisture safety of tall timber houses – Evaluation of simulation methods

The research work presented here belongs to a transnational project which aims at the development of a moisture risk analysis method used for tall timber facades. The major interest covers heat, air and moisture simulation of wind-driven rain-(WDR) exposed multi-story timber-based building envelopes (over their entire cross-section). While available moisture-safety concepts are often rule based with limited performance-oriented parts and are limited to small-scale housing, further exploration involves exposure of tall facades. State-of-the-art research compiles WDR examinations and available field and laboratory data as well as monitoring and simulation results. That is followed by evaluations of simulation methods at a best practice wall cross-section with the aim of examining the sensitivity and uncertainty of different parameters in relation to outdoor climate. This approach is chosen to discern the complex relations between exposure and vulnerability and the number of different facade detailing. The findings hold a categorization model of facade cross-sections that is used for risk analysis to describe moisture impact and reaction of functional layer groups. Furthermore, all WDR models and measured data show a high level of uncertainty and simulation results are strongly dependent on that input. An additional consideration of deficiencies and WDR penetration into the core layer of the facade shows only vague results of moisture accumulation. Under these circumstances failure modes of structural members are hard to determine. Therefore, this research is ongoing with a focus on more suitable exposure parameters and calibration of simulation methods for tall timber facades.

Influence of time resolution and averaging techniques of meteorological data on the estimation of wind-driven rain load on building facades for Canadian climates

This paper investigates the influence of time resolution of meteorological data and the averaging techniques on the quantification of wind-driven rain amount on building facades for Canadian climates using three WDR models, i.e. the ISO and ASHRAE 160P semi-empirical models, and the CFD-based catch ratio method. A cubic low-rise building is used as a case study. Meteorological data i.e. wind speed, wind direction and rainfall intensity are collected at 5-min intervals at three building sites in Vancouver, Montreal and Fredericton. The 5-min data is used as the reference. The analyses show that when semi-empirical WDR models are used, the arithmetic averaging gives a better estimation while the weighted averaging tends to overestimate the WDR amount. When the detailed CFD-based catch ratio method is used, the weighted averaging technique provides a better estimation, however, the difference between the arithmetic and weighted averaging is within 3–7% for the three Canadian cities investigated. Therefore, the choice of averaging techniques depends on the WDR models to be employed and the climates.

Impact of eaves on cross-ventilation of a generic isolated leeward sawtooth roof building: Windward eaves, leeward eaves and eaves inclination

An eaves is a roof extension that can protect the indoor environment from direct solar radiation, the exterior facade from wetting of by wind-driven rain and can be useful to enhance cross-ventilation. This paper evaluates the impact of eaves configuration on wind-driven cross-ventilation of a generic leeward sawtooth roof building. Both the type of eaves (windward versus leeward) and the eaves inclination angles are investigated. Isothermal Computational Fluid Dynamics (CFD) simulations are performed using the 3D steady Reynolds-Averaged Navier–Stokes (RANS) approach. A grid-sensitivity analysis is performed and validation of the CFD results is conducted based on wind-tunnel measurements with Particle Image Velocimetry from literature. The ventilation evaluation is based on the volume flow rates and the indoor mean velocities. The eaves length is 1/4 of the building depth and the inclination is varied between 90° and −45° for both the windward and leeward eaves. The results show that windward eaves with an inclination of 27° (equal to roof inclination) result in the highest increase of the volume flow rate (15%) compared to the building without eaves. Furthermore, the flow through the occupied zone is more horizontally directed. Leeward eaves have a smaller influence on the ventilation volume flow rate than windward eaves; the maximum increase in volume flow rate is only 6% when a 90° inclination is employed. Application of both (windward and leeward eaves) results in an increase of the volume flow rate of 24%, which is 3% more than the sum of the increases by the two eaves separately.

Experimental investigation of the wetting and drying potentials of wood frame walls subjected to vapor diffusion and wind-driven rain loads

This paper aims to study the effects of wind-driven rain load and vapor diffusion on the hygrothermal performance of wall systems in a wet and mild climate through a field experimental study. In the study, four test panels with a combination of vapor barrier and capillary break are manufactured, instrumented and installed in a field experimental facility. The wetting and drying potentials of the test panels in response to a predominately vapor diffusion and a wind-driven rain load are discussed based on the analysis of 15 months of measurement data. The experimental result shows that, in a yearly basis, the wetting and drying rates of a wall without a capillary break are about two times higher than that of the wall with a capillary break. While the wetting and drying rates are comparable in a wall system with a vapor barrier, the drying rate is 38% higher than the wetting rate in a wall with no vapor barrier. In general, a wall with no vapor barrier wets and also dries faster than a wall with a vapor barrier. For the wall types and climate considered in this paper, the wetting rates of walls with a predominately wetting mechanism of vapor diffusion and wind-drive rain load are comparable. In general, the experimental data suggest that even in a mild climate, vapor diffusion is a critical moisture load with comparable effect that wind-driven load induces.

Evaluation of Surface Humidification of Exterior Insulation and Finish Systems

AbstractExterior insulation and finish systems (EIFSs) are common in Europe nowadays. These systems bring thermal benefits, in addition to being cheap and easy to apply, but there are often serious problems with biological growth, causing cladding defacement. The physical phenomenon causing EIFS defacement is known, and mathematical models simulating its performance have been developed. However, no simple process exists to evaluate the risk of EIFS surface humidification (which contributes to surface defacement) that might be used by designers and by the building industry. This paper presents a methodology to assess EIFS surface humidification based on the definition of indices that combine the effect of surface condensation, wind-driven rain, and the drying process, three of the most prevalent parameters influencing surface moisture content. The proposed indices were calculated using data collected during a 1-year in situ test campaign, which provided information about the exterior climate conditions and...

Numerical simulations of wind-driven rain on building facades under various oblique winds based on Eulerian multiphase model

Wind-driven rain (WDR) is an important factor affecting the hygric behavior and durability of building facades. In recent years, CFD simulations of WDR impinging on building facades almost have been focusing on isolated buildings for wind directions perpendicular to the facades. Very few efforts have been made towards study of complicated WDR on buildings considering group effect and the effect of varying wind direction. By virtue of the WDR simulation approach based on the Eulerian multiphase model, this paper presented a validation study of CFD simulations of WDR for an array of low-rise building models provided by recently field measurements. The simulation results suggested that CFD simulations can provide fairly accurate estimates of WDR for complex situations by the present method. And simulations of WDR are performed for a single building and building complex, analyzing the characteristics of catch-ratio distribution with various wind directions and focusing on the impact of group effect and varying wind direction on WDR. The differences of WDR distribution on the building facades are presented and discussed by comparing the results of the single with those of the complex. The conclusions in this paper can provide references for further research of WDR and design of engineering.