Change capacity location bauer

Hi, I notice some problems with the dynamics of the current Borehole model.

According to me, this is due to the capacity location in the element HexInternalElement. The capacities of the grout (filling material) are at the pipes and not "in the area center" of the grout, as advised by Bauer et al. [1]. 

To be able to place them differently, the resistances network needed to be adapted. I followed the procedure of Bauer et al. but I improved it by implementing the full expression of the multipole technic of Claesson and Hellstroem [2] to calculate Rb and Ra (the fluid to wall resistance, resp. the grout to grout resistance). According to the review paper of Lamarche et al. [3], the technic is the most accurate.

I compared the results (see figure) of the adapted model (Buildings adapted) with the previous model of Buildings (Buildings) for the Sandbox experiment ([4]) (Sandbox). The result are also compared with the DST model of TRNSYS and with the multiple boreholes model that I implemented (HSRM) (Picard and Helsen [4]). Notice that the models in the sandbox experiment, the grout is casted into an aluminium pipe which causes a fin effect, and so decreases the borehole resistance. All the models should therefore show a higher fluid temperature as the experiment.

![image](https://f.cloud.github.com/assets/2987659/1983730/5b3c02dc-841b-11e3-8d8f-26147a5e094a.png)

Kind regards,
Damien Picard

[1] D. Bauer, W. Heidemann, H. Müller-Steinhagen, and H.-J. G. Diersch. Thermal resistance and capacity models for borehole heat exchangers. internal journal of energy research, 35:312–320, 2010.
[2] G. Hellström. Ground heat storage: thermal analyses of duct storage systems (Theory). Dep. of Mathematical Physics, University of Lund, Sweden, 1991.
[3] L. Lamarche, S. Kajl, and B. Beauchamp. A review of methods to evaluate borehole thermal resistance in geothermal  heat-pump systems. Geothermics, 39:187–200, 2010.
[4] D. Picard and L. Helsen. Advanced hybrid model for borefield heat exchanger performance evaluation, an implementation in Modelica. In 10th International Modelica Conference, 2014.