Assessing Microclimate in Urban Environments

“People, life and vitality are the biggest attractions in a city. We see it in the choice of peoples seating, where the most populated benches are located, how people choose to sit on sidewalk cafes facing the people walking by rather than the buildings behind them.

The biggest quality of a sidewalk café is simply the interaction with other people. Do you have a choice between walking through a deserted, empty street and a street with other people walking, people will choose the liveliest street that provides them with more experiences, visual variety and a feeling of safety.” Jan Gehl 2002

This quotation from Jan Gehl, and many others like it, have brought home to the design professions how much we had moved away from a human-centric design philosophy to a building-centric and car-centric design philosophy for much of the 20th Century. Even now we are still living with many of the mistakes made in those decades, a car dominated lifestyle, buildings that don’t address the street, housing with high level access walkways, large highways that unsympathetically cut through historic urban fabric, the list is a long one.

Considering the human impact of buildings and the quality of spaces between them means that we should spend much more time considering, drawing and analysing these spaces than we previously did. The tools are now more available to analyse these spaces than ever before, now we just need to use them more often. Here are some examples of the tools available and where to use them.

1. One can use tools like IES to assess the Wind Microclimate between buildings. The tool uses historic weather data to predict the wind conditions between buildings by calculating how the shape of the buildings that are there already and that are in our proposals will affect the wind speeds throughout the year. This calculation is usually carried out at pedestrian level because that is where the pedestrians are, as well as at higher levels where people might sit on balconies or on roof terraces. The results are compared against the Lawson criteria for pedestrian comfort, a scale that compares the type of activity with the prevailing wind speed. Activities such as sitting outside cafes and window shopping are suggested to be best places where the Beaufort Level 3 ‘Gentle Breeze’ is not exceeded for more than 1% of the time in a simulation. It is a notable failing in the Lawson Criteria that it doesn’t adequately deal with cycling and ‘windiness’. Cycling and wind are are particular problem as this combination presents a risk to life where cyclists can be blown into traffic by sudden gusts of wind, a problem not normally faced by pedestrians. Any suggestions by readers as to what an appropriate criterion would be are welcome.

2. IES can also be used to assess the solar irradiation on roofs to highlight locations for renewable energy systems, helpful in determining whether some buildings overshade others or whether some roofs will get ehough solar insolaton to make it worthwhile putting renewable systems there art all.

3. One can use ENVI-met to carry out a similar assessment, but with the additional sophistication of assessing the impact of planting and street trees on the local environment.

4. We can use ECOTECT to evaluate the solar incidence on the facades of buildings to tell us whether the cafe will be in sunshine for long periods of the year and whether people will get too hot sitting there and whether we should provide an awning. Ecotect is useful for many other type of analysis as well, but its imagery for this type of use is particularly helpful.

5. We can use simple tools like SketchUp to look at shadows cast by our designs at a early stage to assess the impact of one design versus another by comparing the impact at the equinoxes and solstices. This is paricularly helpful as it can be done easily and quickly by the designer in the tool that they are woring on (assuming that they are using SketchUp for early stage designs) and gives them immedate feedback. The other tools used here are for more specialist use and are typically used by consultants who specialise in this type of analysis.

6. There is a substantial piece of work being carried out at MIT to develop a suite of tools for urban design analysis based on the Rhino modelling software. This suite is intended to include tools for early daylight, energy and embodied energy analysis. It is still a work in progress but highlights the level of ambition made possible by readily available computing power. An example of the progress to date is the DAYSIM engine used for modelling daylight in and around buildings.

These are just some examples of the tools available to investigate whether the spaces we are creating between and around our buildings are going to be fit for purpose and enjoyable to use. Here is an example from the Kings Cross masterplan of a very successful intervention, a set of sout-facing steps connecting to the canal. It was popular before the astroturf was added, being a sheltered and sunny place to sit and chat, drink a coffee or eat lunch, now it is both sunny, and more comfortable to sit on.

Rory Bergin – Sustainability Consultant