**9. Conclusion**

142 Modeling and Optimization of Renewable Energy Systems

In the past ten years a number of GHE models have been developed for use with various building simulation programs. In view of this, one of the authors together with other researchers conducted a comparison of GHE models developed for use with programs, including GeoStar, TRNSYS, HVACSIM+, GEOEASEⅡ and eQuest (Spitler et al., 2009). The experimental validation was also carried out between the models and the experimental results. One of the research results is described in Fig. 19, which illustrated the predicted monthly average borehole ExFT and the measured data, when the hourly heat transfer rate was specified. It can be seen that all of the models (including GeoStar) predicted the ExFT within 1°C, except HVACSIM+ which overpredicted a maximum of 2°C, for the summer cooling months during the first year. For the shoulder seasons and heating months, the

> Experimental Geostar TRNSYS HVACSIM+ GEOEASE II eQUEST

0 2 4 6 8 10 12 14 16 18 20 **Month**

Fig. 19. Comparisons of experimental and predicted monthly average borehole ExFTs

Fig. 18. Wizard user interface

errors decreased slightly.

**ExFT (C)**

This chapter presents a comprehensive review of the study on heat transfer modeling of the ground heat exchangers in ground-coupled heat pump systems by means of superposition principle and analytical solutions. An entire set of techniques are provided to develop computer software for thermal analysis and design of GHEs in practical engineering.

Contributions of our research group to improvement of the GHE heat transfer modeling are expounded in particular, which include mainly


The entire modeling uses the techniques of spatial superimposition for multiple boreholes and sequential temporal superimposition for arbitrary heating/cooling loads of the systems. The heat transfer models for the borehole GHE have been incorporated into a computer program, developed by our research group for providing a reliable and useful tool to design and simulate the GHE of GCHP systems. These studies on GHE heat transfer modeling in this chapter is expected to provide supports for developing the technique and promoting applications of the GCHP systems.
