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The role of radiative-convective interaction in creating the microclimate of urban street canyons

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Abstract

An approximate sky view factor (SVF) has been developed, which is capable of estimating the mean rate of net longwave radiant energy loss from urban street canyons. Reduced scale models of typical canyon geometries were used in outdoor tests to verify the predictions of radiant fluxes obtained using the proposed SVF.

Air-surface temperature differences from the scale models are used together with hypothesized within-canyon airflow patterns to determine some quantitative characteristics of the wind field in canyons. Simple correlations are proposed for the relationship between mean in-canyon and pedestrian-level flow speeds on the one hand, and the ambient (above roof-level) wind speed on the other hand. As expected, the height/width ratio of a canyon controls the form and magnitude of the flow within.

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Abbreviations

a :

constant used in Equation (3) for Brunt number calculation

A :

area of the surface (m2)

b :

constant used in Equation (3) for Brunt number calculation

B :

longwave radiosity at the surface (W m−2)

Br:

Brunt number

F i-j :

view factor from surfacei to surfacej

FA :

area of the built-up portion of a neighbourhood (m2)

H :

average height of canyon walls (cm)

h c :

convective heat transfer coefficient at the surface (W m−2 K−1)

H i :

longwave irradiance at surfacei (W m−2)

L I :

incoming longwave radiative flux at the surface (W m−2)

L O :

outgoing longwave radiative flux at the surface (W m−2)

L * :

net rate of outgoing longwave radiation from the surface (W m−2)

N :

the number of surfaces forming an enclosure

Q :

overall net radiatn energy outflow from the canyon (W)

\(\bar q\) :

approximate mean rate of radiant energy loss to the atmosphere at the canyon facets (W m−2)

Q G :

conductive heat flux (W m−2)

Q H :

convective heat flux at the surface (W m−2)

canyon:

mean value over the canyon surfaces

e, w :

east wall, west wall

f :

canyon floor

t :

canyon top opening

w1, w2 :

wall 1, wall 2

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Author notes

  1. Hanna Swaid

    Present address: Department of Construction Management and Engineering, University of Reading, RG6 2BU, Reading, UK

Authors and Affiliations

  1. National Building Research Institute, Technion, Israel Institute of Technology, 32000, Technion City, Haifa, Israel

    Hanna Swaid

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Swaid, H. The role of radiative-convective interaction in creating the microclimate of urban street canyons. Boundary-Layer Meteorol 64, 231–259 (1993). https://doi.org/10.1007/BF00708965

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