Environmental Engineering Reference

In-Depth Information

Table 4.2
Measured energy delivered by the five vertical ground heat exchangers to the SIC building

in Freiburg, Germany

Hours

Hours

Cooling

Heating

COP

COP

cooling

cooling

Hours

Year

/ kWh

/ kWh

cool

heat

seminar

floor

heating

2005

2759

2846

20.1

12.8

233

2289

856

2006

4873

246

13.5

5.2

327

2911

289

Due to the significantly longer operating hours of both the ventilation system of

the seminar room and the floor cooling system in 2006, the cooling energy delivered

by the geothermal heat exchangers nearly doubled from 2.76 to 4.87 MWh. This

corresponds to 7-12 kWh per metre of heat exchanger and summer. The low COP

for heating in 2006 is due to the fact that the geothermal system was often operated

at a low temperature difference between the ambient air and ground heat exchanger.

Table 4.2 summarizes the measured results.

4.1.4 Modelling of Geothermal Heat Exchangers

Numerical heat transfer models for geothermal heat exchangers were developed and

implemented in the simulation environment INSEL. They are all based on the heat

conduction equation with explicit finite difference solutions. The simplest vertical

heat exchanger model uses a rectangular discretization geometry. Horizontally, nine

zones have been defined and, vertically, 30 elements are calculated for each time step

with only one-dimensional heat transfer considered (see Figure 4.23). To determine

Near soil

Filling material

Far soil

Brine inlet

Brine outlet

1

2

3

4

5

6

7

8

9

Undisturbed soil

Figure 4.23
Geometry of horizontal discretization of the two-dimensional model for a vertical earth

heat exchanger

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