**4. Conclusions**

In this study experimental investigations of an air conditioning system during summer and winter mode relying on desiccant assisted dehumidification and enthalpy recovery and a geothermal system used for cooling and heating are presented. The investigated system is able to fulfill the requirements regarding comfortable indoor air conditions during the investigated periods. A desiccant wheel based on LiCl is used for air dehumidification and remoistening, achieving an average dehumidification efficiency of 1.15 and a moisture recovery e fficiency of 0.75. Compared to reference processes the investigated system is beneficial during summer mode. Savings in electrical energy demand of up to 50% are achieved compared to a conventional air conditioning process. In contrast, a reference system relying on adiabatic air humidification shows slight benefits for the investigated heating period. Nevertheless, desiccant assisted humidification is advantageous compared to other humidification processes regarding hygienic aspects. If full year operation of an air conditioning system requires air dehumidification during summer it is essential to make use of the pre-existing desiccant material for remoistening of process air during winter. Additionally, the amount of mode specific equipment is reduced for desiccant assisted air conditioning with respect to full year operation. Required temperature levels of the working fluids enable the energetic use of a geothermal system for cooling and heating applications. The thermal energy balance of the soil is equalized throughout full year operation, enabling the soil to be used as heat source and heat sink for long-term periods. Thus, the amount of renewable energy sources is increased significantly to ensure environmental friendly air conditioning.

The research project includes detailed investigation of thermal comfort and economic assessment that are not presented in this study. For future research work, the most beneficial system configuration has to be found with respect to full year operation including transition periods as well. Additionally, other desiccant materials will be investigated. Furthermore, a system simulation model is created in order to carry out dynamic system simulations to analyze applicability of the investigated system for di fferent locations during full year operation as well as di fferent system setups.

**Author Contributions:** Conceptualization, P.N., F.R. and A.S.; methodology, P.N. and A.S.; software, P.N. and A.S.; validation, P.N., F.R. and A.S.; formal analysis, P.N., F.R. and A.S.; investigation, P.N. and A.S.; writing—original draft preparation, P.N.; writing—review and editing, P.N.; visualization, P.N.; supervision, P.N., F.R. and A.S.; project administration, F.R.; G.S.; funding acquisition, G.S. All authors have read and approved the final manuscript.

**Funding:** This work is being conducted in the frame of a project funded by the Federal Ministry for Economic A ffairs and Energy (www.bmwi.de), cf. project funding reference number 03ET1421A.

**Conflicts of Interest:** The authors declare no conflict of interest.
