The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) considers The Mean Radiant Temperature (Tmrt) to be a key metric for human energy balance and thermal comfort.
View at the Chinese University of Hong Kong. Image Credit: Chinese University of Hong Kong
Tmrt represents the uniform temperature of a hypothetical enclosure whereby radiant heat transfer from the human body is considered equal to radiant heat transfer in the actual non-uniform enclosure.
It is possible to combine measurements of short- and long-wave radiation fluxes from six different directions - up, down and the four cardinal points - to accurately determine outdoor Tmrt. This value can also be corrected to accommodate the view factor coefficients.
This is done in Hong Kong - one of the world’s most dense cities - by mounting three Kipp & Zonen CNR 4 net radiometers on a tripod. This approach provides a useful mobile meteorological station able to measure 3D radiant fluxes within outdoor urban environments.
The three Kipp & Zonen CNR4 net radiometers mounted on tripods. Image Credit: OTT HydroMet
Each CNR 4 is comprised of four sensors, meaning it is able to record short- and long-wave radiation from two sides.
In this particular setup, one CNR 4 is mounted horizontally to acquire measurements from the sky and ground, one is mounted vertically to acquire East and West measurements, and the third vertically-mounted CNR 4 measures North and South.
The CNR 4 mobile station is required to operate amidst a series of tall buildings with varying shapes, orientations, surface materials and other characteristics. This instrument helps study outdoor thermal comfort in the urban setting, evaluating this in terms of radiant fluxes and, therefore, Tmrt.
The overall aim of this work is to develop an outdoor thermal model of the Hong Kong urban environment based on the global Tmrt equation. This model will be used to help improve and optimize urban planning in high-density cities.
Produced from materials originally authored by Alan Lai from the School of Architecture, The Chinese University of Hong Kong.
This information has been sourced, reviewed and adapted from materials provided by OTT HydroMet - Meteorology. Kipp & Zonen is one of OTT HydroMet's brands for comprehensive environmental monitoring.
For more information on this source, please visit OTT HydroMet.