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Pedestrian Comfort
A recent UN study reports more than 50% of the global population live in built up urban environments. In fact, with developed nations this proportion soars to over 75%, but as city growth and regeneration continues there is a corresponding aspiration for space. However, this can meet planning resistance as, rightly so, surrounding greenbelt is a protected resource. With our understanding of climate change and the importance of vegetation, there has been a subsequent push to vertical city growth through multi storey buildings instead.

With concrete jungle growth comes a greater demand for green space where people can congregate, relax and enjoy their surroundings. However, the presence of these green spaces within a myriad of high rise structures makes it tricky to ensure usability of the space throughout the year. It becomes necessary to understand the suitability of external comfort to ensure green spaces are optimally designed and located to maximise their function throughout the year, which includes alleviating the effects of flow around nearby high-rise buildings.

Take the case when the wind impinges on the face of a building. Bernoulli’s equation states the air will slow down and the building face pressure will increase significantly. The natural tendency then is the high pressure air will flow towards a lower pressure area which typically exists at the building’s base; an effect called downwash. These flows are regularly observed at the base of tall buildings, especially when surrounded by shorter buildings. Once the downwash reaches the ground level it spreads horizontally with pedestrians experiencing this as sudden gusts. These gusts occur even in conditions which are termed as a ‘light breeze’ by recorded weather data and can lead to micro climates.

A second example of air accelerating is when street layouts are funnelled from a wide to narrow path. This is a regular situation in existing city centre layouts, however this can be considered in new and regeneration schemes. It is also observed in cases where there are large openings at the base of the buildings used to create spaces like a reception concourse. Although visually impressive and imposing, its weakness is the potential for accelerating air.

Too often both situations come together with the effect multiplying, and at times generating hazardous conditions. There have been many cases where pedestrians have complained of difficulty opening doors and comfortably crossing open spaces due to pressure imbalance.

When buildings and sites are being planned, early stage conceptual modelling can measure the risk. Pedestrian comfort analysis is performed to study the conditions surrounding the site under a range of wind speeds and directions. Consider it as a virtual wind tunnel, where a 3D form of the site is massed and subjected to the test considerations. Air speed is measured at points of interest, and this data along with local weather data is used to obtain an annual perspective of the local air speed across the area of interest. Statistical analysis can then be performed to check compliance against various wind comfort criterion. Remember, the brilliance of the model is that the speed feedback can be introduced and the tests rerun to optimise the design.

Pedestrian Comfort

Now, turning to the popular metric currently in use, the Lawson criterion, which is divided into two parts. Firstly, it covers pedestrian comfort for regular activities like walking, standing and seating. This helps in determining the usability of a location or site against that particular activity. The criterion sets out threshold local air speeds based on the activity, which cannot be exceeded for more than 5% of the year. The other aspect is the safety criterion which stipulates the air speeds which cannot be exceeded even once a year. This ensures that pedestrians and cyclists are not in danger of physical harm from high air speeds.

The impact of urban developments is felt globally through carbon emissions, their internal conditions (as we live and work within them), but also in how we commute and enjoy the space between them. We can make the best of all three through modelling.

IES Consulting’s CFD experts use a combination of IESVE MicroFlo and the 3rd party CFD software package Engys® HELYX®. MicroFlo was developed to provide our customers with a relatively simple and accessible CFD package which can be used by engineers in conjunction with our ApacheSim tool. The Engys® HELYX® CFD package, derived from the OpenFOAM® libraries, allows us to use bespoke tools for performing complex analyses like data centres, external pollutant studies, pedestrian comfort and external flows with heat transfer, etc.

If you’d like to find out more about our CFD Consulting Services, please contact Harshad.Joshi@iesve.com.

Lindsey WELL BlogFor this blog Lindsey Malcolm of XCO2 discusses considerations of building services engineers and the potential role of simulation in catering for health and wellbeing in the building industry.

Health and Wellbeing. A phrase conventionally connoting to rhyming proverbs about the doctor-dodging power of a daily apple. Yet the proverbial days of the catchphrase are seemingly behind us, as ‘Health and Wellbeing’ is escalating into the latest buzzword within the building industry.

Our clients are demonstrating a growing demand for office spaces, retail areas and homes that enhance human health, productivity, and quality of environment. A business case for investment in health has driven interest in the commercial sector, and attention to this new industry buzzword in the retail and residential sector signifies this isn’t a short-term fad.

The vision of Health and Wellbeing is the long-term facilitation of productive and comfortable environments for the building occupant. Well-designed and operated environments should inspire conscious and subconscious positive lifestyle choices, resulting in healthier, more productive building users.

Considerations for design and beyond

Human health and wellbeing can obviously be impacted by an infinite number of factors; however, it is easier to consider if we chop this abstract concept into tangible and quantifiable chunks. Several core categories have been identified within the industry covering a broad spectrum of health and wellness drivers and indicators. These range from environmental (air quality, water quality, lighting) to behavioural (nourishment, fitness and lifestyle choices, working patterns and stress management).

As building designers, it is obviously outside our area of potential provision to shape to dietary and fitness of our building’s user. But implementing health and wellbeing into buildings is a holistic concept, and will have tangible effects on areas within our scope (see Figure 1).

The adjustment for engineers to consider is:

As building designers, it is obviously outside our area of potential provision to shape to dietary and fitness of our building’s user. But implementing health and wellbeing into buildings is a holistic concept, and will have tangible effects on areas within our scope (see Figure 1).

The adjustment for engineers to consider is: shifting our focus from the working of the building to the living of its user.

This shouldn’t be viewed as a trade-off against conventional design considerations such as energy efficiency or carbon emissions – our aim should be to adapt our existing solutions to improve our output for the people who will inhabit the building. This may involve throwing rules of thumb out of the window, or being guided by a forthcoming set of industry benchmarks – only time will tell. But for now, what we do know is that demand for healthier buildings is increasing, and we must respond accordingly to these requirements from our clients.

The Role of Simulation

Modelling and simulation support building design. Therefore, in order to improve our building design with occupants in mind, there is clearly opportunity to integrate cutting-edge areas of building simulation technologies.

Areas that could benefit from a simulation-based predictive approach could include:

  • Utilising CFD to assess indoor air quality;
  • Performing discretised zonal analysis of thermal comfort for individual occupants;
  • Performance and feasibility of different ventilation strategies;
  • Moisture and condensation management;
  • Reverberation and acoustic impacts;
  • Measuring and design ambient and circadian lighting.

An exciting assortment of modelling prospects; however, it is important for us to remember that modelling and simulation should support building design, rather than instructing. Particularly for health and wellbeing, where the benefits of a well-designed healthy building can be negated by poor operational use and user behaviours, the simulation of predictive conditions is less significant for design than other areas of the building industry.

And on a practical note, the feasibility of modelling so many different elements of building services is questionable – in terms of both metric limitations and issues on cost and resource effectiveness. Could an industry-wide interest in healthier buildings facilitate interest in the development of new metrics, as a way of regulating a better standard of living? Possibly so. Yet until that day comes, let us remember that simulation used for health and wellbeing should be taken with a pinch of salt – not too much salt, mind.

A healthy future for the industry

Simulation is a fantastic instrument to demonstrate the tangible benefits of health and wellbeing application. But let’s not forget the ultimate goal of the health and wellbeing – whether it be assessed through WELL or loosely ingrained concepts – is to facilitate a productive and comfortable built environment. Simulation can certainly be used to deliver this, but it cannot be considered a one-stop exercise. It must remain a tool to support operational-focused design and help to enforce the positive behavioural changes we are designing into our buildings.

As the health endemic continues to infect the building industry, a new ‘normal’ standard of building will emerge, requiring innovation and flexibility from all parties involved in the creative process to work with new concepts and metrics. As engineers and simulation specialists we can emphasise a greater focus on occupants, ensuring the holistic approach to health and wellbeing required to make a tangible difference to quality of life.

And as our building designs advance in the enablement of healthy living, our old proverb may just need a re-write. Forget the apples, dodge the doctor; it’s the engineers keeping illness at bay.


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