Bjarne Olesen, Philo Bluyssen and Claude-Alain Roulet
ms–1
ms–1
ms–1
0.4
0.4
Tu
0.3
0.2
Tu
0% =1 % 0 2 % 40
60 %
0.1 0
va, l
va, l
0.3
A: DR = 10 %
18 20 22 24 26 °C t a, l
=
10
%
20
%
% 40 % 60
0.2
0.4
0.1
0.3 va, l
90
Tu
=
10
% 20
%
% 40 % 60
0.2 0.1
B: DR = 20 %
0
18 20 22 24 26 °C t a, l
0
C: DR = 30 % 18 20 22 24 26 °C t a, l
Figure 2.3 Mean air velocity as a function of local air temperature and turbulence intensity for the three categories of the thermal environment.
The turbulence intensity may vary between 30 and 60 per cent in spaces with mixing flow air distribution. In spaces with displacement ventilation or without mechanical ventilation, the turbulence intensity may be lower. Based on the above equations, the diagrams in Figure 2.3 were made. Increased air velocity Standards 55-2004 and ISO7730-2005 include a diagram to estimate the air speed required to offset an increase in temperature (Figure 2.4). This shows that the requirement for personal control to increase the air speed is essential for accepting the higher speed. Therefore, it may not be appropriate to offset a temperature increase by increasing the air speed within a centrally controlled air system. Vertical air temperature difference A high vertical air temperature difference between head and ankles may cause discomfort. The recommended criteria in Table 2.9 for the vertical air temperature difference are valid only for people with low activity level like sedentary and standing. For higher activities, as is often found in industry, people are less sensitive to this temperature difference. Warm or cool floors If the floor is too warm or too cool, the occupants may feel uncomfortable because of warm or cool feet. For people wearing light indoor shoes, the recommended floor temperatures are summarized in Table 2.10a. It is