Environmental Engineering Reference
In-Depth Information
Internal Loads
Under moderate climatic conditions, demand for air-conditioning exists only in
administrative buildings with high internal loads, provided of course that external
loads transmitted via windows are reduced effectively by sun protection devices. About
50% of internal loads are caused by office equipment such as PCs (typically 150 W
including the monitor), printers (190 W for laser printers, 20 W for inkjets), pho-
tocopiers (1100 W), etc., which leads to an area-related load of about 10-15 W m 2 .
Modern office lighting has a typical connected load of 10-20 W m 2 at an illuminance
of 300-500 lx. The heat given off by people, around 5 W m 2 in an enclosed office or
7Wm 2 in an open-plan one, is also not negligible. Typical mid-range internal loads
are around 30 W m 2 or a daily cooling energy of 200 Wh m 2 d 1 , and in the high
range between 40-50 and 300 Wh m 2 d 1 (Zimmermann, 2003).
Detailed three-year measurements in an energy-efficient office building varied be-
tween 30-35 W m 2 for a southern office with two persons and one computer work-
station and around 50 W m 2 for a northern office occupied by two persons with two
computer workstations. This resulted in daily internal loads in the south-facing office
of around 200-300 Wh m 2 d 1 and 400-500 Wh m 2 d 1 for the heavier equipped
northern office. Detailed monitoring results from four other office buildings in
Germany showed that appliances always dominate the internal loads, which were
between 92 and 188 Wh m 2 d 1 (Voss et al ., 2007, see Figure 1.16).
External Loads
External loads depend greatly on the surface proportion of the glazing as well as the
sun-protection concept. On a south-facing fa¸ade, a maximum irradance of 600 W m 2
can occur on a sunny summer's day. The best external sun-protection can reduce this
Figure 1.16 Measured internal gains in new office buildings in Germany
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