Passive Cooling Strategies - Low Energy Cooling for Sustainable Buildings - page 66

80

North office
South office

70

60

50

40

30

20

10

0

0 4000 8000 12 000 16 000 20 000 24 000

Hours from 1January 2001

Figure 3.5 Hourly internal loads of the northern and southern offices

workstation and on the north-east side a similar office has two persons with two CAD
workstations. The hourly internal loads were monitored for three years and are about
30 35Wm − 2 for the southern office and around 50Wm − 2 − for the northern office

(Figure 3.5).
The main part of the load is due to the computer equipment. Measurements have
been taken to separate lighting energy consumption, the plug electricity consumption
for all other equipment and the heat contribution of the persons using presence sensors.
The lighting energy consumption in winter is about 100Wh m − 2 d − 1 , slightly higher
in the northern office than in the south-facing office. In summer, lighting energy
consumption ismostly zero, but about once aweek, 50Wh m − 2 d − 1 is used for lighting.
The people contribute between 50 and 100Wh m − 2 d − 1 , depending on presence, and
the main consumption is due to other electrical equipment, mainly computers. If both
persons are present and use their electrical equipment, the daily load from electricity
consumption alone is about 300Wh m − 2 d − 1 (Figure 3.6).
During summer the daily internal loads in the south-facing office are around
200-300Wh m − 2 d − 1 and 400-500Wh m − 2 d − 1 for the heavier equipped north
office. The external loads from solar irradiance and wall transmission cannot be
easily measured and have been evaluated using building simulation as described
below. Typical external loads per square metre of floor space on a sunny day with
partly shaded southern windows are 30Wh m − 2 d − 1 from short-wave transmission
and 15Wh m − 2 d − 1 from secondary heat flux. Transmission through the glazed fa¸ade
is usually negative, as internal temperatures are higher than external temperatures dur-
ing the night and morning hours and amount to about

40Wh m − 2 d − 1 . In total the

−

external loads are therefore not very significant.
Under typical German climatic conditions such as the summers of 2001 and 2002,
the night ventilation concept is highly efficient with only 1.9 to 2.4% of all office hour
room temperatures above 26 ◦ C. This corresponds to only 50-60 hours above 26 ◦ C