Bastian Stahra, Flow Simulation Specialist, ifes / TÜV Rheinland Image: TÜV
Opinion

Knowing where the wind blows

Would you visit a café where you knew that a constant cold draft would blow onto your neck, leaving you shivering as you quickly drank your coffee, unable to truly relax? Would you take time to go window-shopping if you knew that you would be constantly battered by turbulent wind?

BY BASTIAN STAHRA

By Bastian Stahra

Most people instinctively take detours around very windy streets and open spaces. When avoiding them is not possible, for example, because they are on the only route to and from work, people generally try to get out of these drafty areas as quickly as possible. We tend to do our after-work shopping or arrange to meet our friends after work in places with the best possible pedestrian wind comfort – the technical term for pleasant ventilation. Thus, stores in locations with generally high wind loads suffer from poor sales and find it difficult to attract customers – and not just on stormy days.

Local wind conditions are a major factor when choosing a location, a fact that becomes even more apparent when we consider just how sensitive many people are to wind flows and drafts. At anything above 18 km/h, which roughly corresponds to the average speed of a leisurely cyclist, wind speeds are deemed uncomfortable or even unsafe for pedestrians.

The primary aim for planners, investors, and building operators should, therefore, be to combine building cubature, orientation, and wind protection measures to minimize the likelihood of excessive wind speeds, taking into account the planned uses, local wind and microclimate conditions, and the interaction of the buildings with their surrounding environments. Contrary to common assumptions, local wind speeds do not depend entirely on weather conditions. The orientation, shape, and size of surrounding buildings and other elements also have significant influence on ground-level air flows and microclimate. With the help of wind flow simulations, these effects can be modelled during the early planning stages of any development, so costly planning mistakes can be avoided

From the very outset, pedestrian wind comfort should be incorporated into the development of retail properties and mixed-use buildings, playgrounds, parks, and marketplaces. The earlier wind speed and wind flow aspects are integrated into the planning, the better. After all, software-supported wind simulations can do far more than just identify spaces where wind speeds will be uncomfortable, or even dangerous, for pedestrians. In combination with early advice from wind flow specialists, it is possible to make small changes with great effect – without compromising the quality of a building’s design or breaking the budget.

But, what are your options if you have an existing building with wind-related problems? Even then, simulations are an indispensable planning aid in the development of solutions to alleviate flows in wind-plagued, public spaces, to minimize unpleasant gusts or – where the opposite is the case – to improve air circulation in stuffy areas. There are a number of measures to mitigate the negative consequences of imperfect planning. These include green islands with bushes and trees, wind barriers, canopies, and cleverly selected works of art. However, before effective countermeasures can be developed and deployed, it is important to first identify the precise cause of any wind-related problems.

For example, the reason(s) for low wind comfort in the foyer of a department store must first be determined in order to initiate cost-efficient and, above all, effective measures. The unique aerodynamics of a structure, and its interactions with surrounding structures, can create problematic local wind conditions that deviate from the assumed standard planning values, i.e., abnormal pressure and suction phenomena on and around the building. When the design of a building’s air curtains is based on simplified standard planning values, it is likely that they will not be as effective as intended.

All of which points to a wider range of applications for wind simulations, which could be used to model wind flows in the interiors of large buildings, such as multi-story department stores, but also in and around office, logistics and industrial buildings. Frequently, wind causes thermal effects and cross currents, which can result in unpleasant drafts throughout a building’s interior. Depending on the specific cause, a wide range of different countermeasures could potentially be implemented. In order to select the optimum countermeasure, it is essential to first initiate a thorough diagnosis.

Producing reliable forecasts of wind flows and speeds is complex, which means that it is usually impossible to rely on rules of thumb. Using an off-the-shelf air curtain system leads to discomfort and dissatisfaction among customers and employees as well as to substantial costs for the planning and installation of a new system. Exterior wind protection measures also require custom planning and testing if they are to be effective. For example, wind protection walls installed on a high-rise building’s roof terrace will most likely prove inadequate or ineffective due to the down winds they create. In the same situation, however, a well-positioned canopy roof could calm local wind conditions and create a pleasant level of wind comfort.

Ultimately, it doesn’t matter whether low wind comfort is caused by excessive wind speeds, air stagnation, or an annoying indoor draft – all of this negatively affects how people experience interior and exterior spaces. Any business that depends heavily on consumer foot traffic, such as restaurants, retailers, and property managers, should never underestimate the importance of wind comfort.

 


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