Building Services Engineering 5th Edition Handbook

Built environment 13
1.3 Thermal comfort data logger (reproduced by courtesy of Mobile Architecture and Built Environment
Laboratory, Deakin University, Geelong).
External environments
Extremes of external climate are mainly of concern to construction workers in severe
environments. There are two main indices: wind chill index (WCI) and heat stress index (HSI).
Wind chill index measures the cooling effect on the body of a moving air stream, given by:
WCI = (10.45 + 10 √ v − v)(33 − t a )
Wind speed v is in metres per second; the equation can be used for values of up to 22.0 m/s
(79 km/h (kilometres per hour)). Frostbite should be avoided if the wind chill index is less than
1400 at an air temperature of −10.0 ◦ C d.b. during a maximum exposure of 30 min. A convenient
use of the wind chill index is to calculate the equivalent wind chill temperature (EWCT), which is
the air temperature, calculated from measured data, that would provide the same chilling effect
but at an air velocity of 1.78 m/s (6.4 km/h):
EWCT = (−0.045WCI + 33) ◦ C
EXAMPLE 1.5
A winter day in northern England has an outdoor air velocity measured as 25.2 km/h (7 m/s)
and the sling psychrometer air temperature showed −2.5 ◦ C d.b. Find the wind chill index
and the equivalent wind chill temperature.