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

Can productivity be modelled?

Posted : October 11, 2016 by Naghman Khan

Health, Wellbeing and…. Productivity! Time has come where we can take a closer, empirical and quantifiable look at productivity. Our recent blog and event on Health & Wellbeing (How to do WELL with IES) has generated significant interest and participation from a wide range of stakeholders. Similarly, the Health and Wellbeing movement, including the WELL […]

For 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 […]

+3.8°C in Brussels by 2080!

Posted : September 15, 2016 by Johan Haeberle

This morning, a client called me and asked for some help. He needed to generate future weather files for a BREEAM certified project in Brussels (necessary for HEA04 – Thermal Comfort credit). I was happy to lend a hand! The methodology is to use the climate change world weather file generator named CCWorldWeatherGen. It uses […]

What do you get when you challenge nine interdisciplinary teams to design a net zero (or below) 50,000 ft2, 3-story Outpatient Health Care facility in Omaha, Nebraska? You get ASHRAE’s Lowdown Showdown, an energy modeling competition that showcases the talent and innovation of those in our industry using building performance analysis software. Last year, Team […]

IES shows off the best of British

Posted : September 2, 2016 by Suzanne

Russia’s largest retailer approached IES recently to ask for help in designing significantly better performing buildings – the result a UK 4-day study tour led by our Business Development Consultant for CEE, Guy Eames. “Britain is one of the leading countries when it comes to high performance or “green” buildings”, boasts Guy, “IES’ technology highlights […]

All Good Things Come in Threes…

Posted : August 15, 2016 by Karen Duffin

They say all good things come in threes and that certainly seems to be the case for us here at IES right now as we recently found out that we have been shortlisted for – not just one – but three awards! We are delighted to announce our place as finalists in the following award […]

In our last article on project management, we called upon the famous words of Mike Tyson to discuss design team management and achieving your desired certification. This time we’ll put our boxing analogies aside and instead focus on the insight and knowledge of the team behind IES TaP, our online project management system. They’ve come […]

What next for building design? WELL?

Posted : July 25, 2016 by Suzanne

Health & Wellbeing is the new frontier for making our buildings even better. A rich body of academic research and business case studies have arisen over the last five years, showing the physical, physiological, cognitive, health and wellness benefits of positive interactions between Humans and the built environment. The WELL standard is a specific example […]

1 2 3 35

Featured Video