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| METHODS OF INFORMATION ACQUISITION FOR PLANNING
(MEASUREMENTS, WIND TUNNELS, NUMERICAL MODELLING) |  |
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 4.2.1 Overview |
The requirements for the identification and illustration of environmental impacts in the field of urban land use planning have continuously increased, not least because of changes within the Federal Building Code (BauGB). For one thing, this might be due to people"s growing consciousness for environmental issues, for another it is the settlement becoming denser and denser in Germany , which forces conflictual uses closer together.
Increased requirements have sometimes led to costlier and more time-consuming examination methods, especially when material losses or damages are at stake. One of these methods is the use of a wind tunnel in the planning stage.
The following issues can principally be analysed and quantified in a wind tunnel: - a modification of the large-scale aeration within the planning area and its surrounding
- a modification of the small-scale dispersion of pollutants or smells due to buildings
- a modification of the wind comfort due to intended building projects
Wind tunnel experiments also help to illustrate flow and dispersion patterns in a more descriptive way for the use in committees or other decision-taking bodies.
Typical fields of application are:- the prevention of disturbing wind flows around tower blocks
- the effect of squares and roads on the aeration of urban areas
- the reduction of snowdrifts at roads or the migration from heaps
- the positioning of external air inlets for air conditioning systems
- the propagation of smells from commercial enterprises, landfills and factory farms
- the dispersion of emissions in the case of disturbances
The size of the area under investigation ranges from some metres (local wind comfort) to several kilometres (aeration of urban areas), depending on the topic.
Criteria for the assessment of wind comfort refer to either the average hourly value of the wind speed (Table 4/1) or the gust wind speed (Table 4/2). In the VDI is in progress - Directive 3787, Part 4 " methods to describe strong and weak winds in built-up areas and their evaluation " is an attempt to formulate a unified assessment methodology.
Wind velocity (m/s) |
Effect |
to approx. 1.5 |
calm, no noticeable air flow |
approx. 1.6 - approx. 3.3 |
in the face perceptible air flow |
approx. 3.4 - approx. 5.4 |
wind moves light flags |
approx. 5.5 - approx. 7.9 |
paper flies up, hair-style is destroyed |
approx. 8.0 - approx. 10.7 |
wind force at the body clearly noticeably |
approx. 10.8 - approx. 13.8 |
to use umbrellas with trouble |
approx. 13.9 - approx. 17.1 |
difficulties when going |
Table 4/1: Connection between wind velocity and wind effect upon humans (from STIEMER, 1977)
Gust wind velocity |
Excess frequency |
Evaluation criteria |
< 6 m/s
> 6 m/s |
-
max. 5% |
no wind comfort problems permissible in parks, waiting ranges, road cafes, on playgrounds |
> 6 m/s
> 15 m/s |
max. 20%
max. 0.05% |
permissible on surfaces for brief stay (less strict criterion), and/or which are fast exceeded |
> 8 m/s |
max. 1% |
permissible within waiting and seat ranges |
> 10 m/s |
max. 1% |
permissible on surfaces for brief residence time (strict criterion) |
> 13 m/s |
max. 1% |
permissible at corners of a building, permissible for problem-free running |
> 13 m/s |
> 1% |
unpleasantly, annoyingly, wind protection |
> 18 m/s |
> 1% |
danger |
Table 4/2: Criteria for evaluating the wind conditions for a specific object, Source: LOHMEYER et al., 1992
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