2. Climate and air as planning factors
Air temperature


The climatic element air temperature generally refers to a measuring altitude of 2 m above ground. Radiation influences are mostly eliminated by the use of a measuring cabin.

Besides the average temperature of a place, the average annual amount of days is given when particular threshold values are exceeded or fallen short of.

Ice days (daily maximum < 32 °F/0 °C) Frost days (daily minimum < 32 °F/0 °C) Summer days (daily maximum ≥ 77 °F/25 °C) Hot days (daily maximum ≥ 86 °F/30 °C)

The definition of heating days refers to the heating activity (average daily temperature < 59 °F/15 °C) and what can be deduced is the degree-day figure (Gt, Gradtagzahl) as a measure for the heating requirements during a heating period (DIN 4701, VDI 2067).

Gt = Z (ti - tz)

Z = number of heating days during the reference period

ti = 68 °F/20 °C (room temperature)

tz = average temperature from the average daily air temperature values of all heating days during the reference period

Knowing the degree-day figure of an area helps you to calculate the pollutant emissions from the heating activity of an existing or planned building area if you calculate its heating requirements and know or assume the heating structure.

What is typical of cities is the heat island effect (VDI COMMISSION, 1988), i.e. a higher temperature compared with their surroundings. This effect has been known for long and is not restricted to big cities. The biggest differences compared to the surrounding region appear as for the minimum temperatures during the night. These temperature differences can add up to 12 K in cities with more than one million inhabitants.

The heat island effect is judged negatively in summer and especially during the night due to the higher heat stress for people. In wintertime, however, it helps to save heating energy and reduce emissions. As the heat island effect leads to a higher frequency of elevated inversions in cities, there is more room for the mixing of the air. On the other hand, as a result of the lifting of the lowest border of the inversion, exhaust gases in higher layers are also mixed and this leads to a poorer air quality.

© City of Stuttgart, Office for Environmental Protection, Section of Urban Climatology

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