Environmental Engineering Reference
In-Depth Information
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Measured air temperature
Simulated air temperature
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Figure 4.8 Cumulative frequency distribution of measured and simulated exit air temperatures in 2001
4.1.2 Performance of Horizontal Earth Brine to Air Heat Exchanger
in the eb ok Building
An alternative to the direct-air-based ground heat exchange is the indirect cooling of
air by circulating a brine solution through the ground and then using an air to brine
heat exchanger. This system has the advantage of avoiding any hygienic problems,
which might occur in air-based systems if condensation water is not reliably removed.
Furthermore, pressure drops are usually lower in such liquid-based systems. A simple
horizontal absorber placed around the perimeter of a rehabilitated office building was
experimentally analysed in 2005.
For air preheating and cooling of the ebok building in Tubingen, Germany, five
horizontal earth to brine heat exchangers with a length of 100 m each were installed
shallowly under the soil surface (about 1 . 2 m depth). During summer they are used to
cool the supply air (see Figure 4.9). The volume flow of air during daytime is about
1750 m 3 h 1 .
The earth temperature levels were measured for 2 years directly in between the
tubes at 1 . 2 m depth and a distance of 0 . 5m from the building and compared with the
undisturbed soil temperatures at 1.2 and 2 . 0 m depth. The sensors for the undisturbed
temperature measurements were placed 3 . 5m away from the northern part of the
building and 12 m from the next neighbouring building. The time phase shift between
the ambient air maximum temperature and soil temperature is about 1.5 months at
2 m depth. When the earth heat exchanger is operating, for example for two months
during summer 2006, the daily mean earth temperature increases by about 2-3 K (see
Figure 4.10). The regeneration of the soil temperature is very fast in both summer and
winter.
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