Passive Cooling Strategies - Low Energy Cooling for Sustainable Buildings - page 70

Table 3.1 Air and surface temperature profiles during a warm summer's night (8 to 9 August 2003).
The ceiling temperatures were measured near the windows, at the centre of the room and between the
centre and the windows
Time Ambient Room Floor Ceiling Ceiling Ceiling

air air to corridor centre between at windows

/ ◦ C / ◦ C / ◦ C / ◦ C / ◦ C / ◦ C

20:00 29.3 28.8 26.7 29.1 28.4 28.0

22:00 25.3 28.7 26.7 29.0 28.3 27.8

00:10 23.5 28.5 26.6 28.9 28.1 27.2

00:50 23.1 27.5 26.5 28.8 28.0 26.7

03:00 21.2 26.2 26.1 28.4 27.8 26.2

05:00 19.8 26.3 25.6 28.0 27.5 25.8

07:10 19.7 26.1 25.2 27.7 27.2 25.4

09:30 22.6 26.7 25.3 27.9 27.3 26.5

In the early morning hours with a more useful 5 to 6 K temperature difference between
room and ambient air, the air changes were down to 6 to 8 h − 1 .
Simply multiplying the measured air volume flow by the measured temperature
difference between the inside and outside from 21:30 to 08:00 gives a cooling energy
of 9 . 3 kWh. Equally distributed over the room surface areas of 94m 2 this gives an
average nightly removed heat flux of 100Wh perm 2 and night. Heat fluxmeasurements
taken at several points of the ceiling, however, gave only low integrated values of 15-
20Wh per m 2 and night. During the day, about 45-50Wh m − 2 d − 1 is taken up by the
ceiling. Rather than just the ceiling, the floor and the internal walls also contribute to the
night discharging of the room. There is also the effect that air flow is not unidirectional
from the outside to inside; that is, it is not only ambient air entering the room, but
also partly air flowing from the warm corridors. The simulation studies showed that
for air change rates of 8 to 10 h − 1 , there should be a more significant drop in room

Figure 3.10 Development of room and ambient air temperature as a function of air change and wind
speed