Chinese University of Hong Kong Studies Outdoor 3D Radiant Fluxes

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The Mean Radiant Temperature (Tmrt) is one of the important indices governing human energy balance and thermal comfort of man as defined by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE).

This is the uniform temperature of an imaginary enclosure in which radiant heat transfer from the human body equals the radiant heat transfer in the actual non-uniform enclosure.

Measurement of Short and Long Wave Radiation Fluxes

Measurements of the short and long wave radiation fluxes from six directions: up, down, and the four cardinal points - can be combined to give the most accurate outdoor Tmrt with appropriate corrections for the view factor coefficients.

Hong Kong, One of the Highest Density Cities on Earth

By mounting three CNR 4 net radiometers on a tripod, a mobile meteorological station for 3-dimensional radiant fluxes is set up within the outdoor urban environment in Hong Kong, one of the highest density cities on Earth.

Each CNR 4 consists of four sensors, recording both short and long wave radiation from two sides.

Setup for the Three CNR 4 Net Radiometers:

• One CNR 4 is mounted horizontally looking at the sky and ground
• Another is mounted vertically looking East and West
• The third looks North and South

The CNR 4 mobile station will be surrounded by different combinations of tall buildings of different orientations, shapes, surface materials, and so on. The outdoor thermal comfort in the urban setting is being studied in terms of radiant fluxes and hence Tmrt.

An outdoor thermal model of the Hong Kong urban environment will be developed based on the global Tmrt equation in order to seek improvements in urban planning in high density cities.

Article by Mr. Alan Lai of the School of Architecture, The Chinese University of Hong Kong