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2. Characteristics and Forms of the Urban Climate
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2.6       Bioclimate

Meteorological elements do not exert separately their effects on humans; as such, a combined assessment of these elements is necessary. The thermal complex is especially important, since it involves all of the climatic elements that directly influence the human heat budget. In this context, complex measurements such as sultriness, comfort, and perceived temperature are brought into play. An assessment of these quantities is subjective and depends upon the current temperament of the individual person.

It is above all the occasional overheating of the city that can exert a negative bioclimatic effect. The persistence of overheating during nights with calm winds can lead to negative sleep patterns. Overheating can be a problem during the day as well, often in connection with high air humidity and intensive sunshine. The thermal burden that is introduced leads further to reductions in human efficiency.

The assessment of the thermal complex is based upon the heat balance equation of the human body. Building upon this equation, the comfort equation according to FANGER (1972) is recommended as the standard application. Fanger created the PMV (Predicted Mean Vote) index as a measure of the degree of comfort or discomfort. The index shows the average subjective appraisal of a large group of persons, and several corresponding measurement devices have been developed to obtain measurements for determining the index.

A coupling of this basis with solar and terrestrial radiation flows has found wide acceptance as a planning tool under the name "Climate-Michel-Model" (JENDRITZKY et al., 1990), among other things because it makes possible planar representations.

Table 2/1 shows the feelings and comfort grades to be expected for each PMV value.

For more elaborate thermo-physiological observations the heat budget model "MEMI" (HOEPPE, 1984) is also available and is especially suited for cases in which medical concerns are of particular importance. From this model the PET (Physiological Equivalent Temperature) quantification was developed. Details of the bioclimatic assessment of the urban climate can be taken from the VDI guideline VDI 3787, Sheet 2 (1998), revised at the moment as well as the handbook "Bioclimate and Air Hygiene" (MORISKE and TUROWSKI, 1998).

PMV Thermal
perception		 Stage
of stress		 Physiological effect

-3,5
-2,5
-1,5
-0,5
-0,0
-0,5
-1,5
-2,5
-3,5

very cold
cold
cool
slightly cool
comfortable
slightly warm
warm
hot
very hot		 extreme
great
moderate
weak
none
weak
moderate
strong
extreme		  cold stress
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none
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heat stress

Table 2/1: Predicted Mean Vote (PMV), thermal perception and stage of stress
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Fig. 2/11d: "Klima-Michel-Modell"
with components of radiation balance

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Fig. 2/11e: Bioclimate map from Berlin,
felt temperature on one summer day, Source: DWD
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Fig. 2/11f: Bioclimate map from Dresden, number of days with heat emission per year, Source: DWD
 

Fig. 2/11g: Bioclimate map from Stuttgart, number of days with heat emission per year, Source: DWD
 
     

                                              

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