**Desiccant-Assisted Air Conditioning System Relying on Solar and Geothermal Energy during Summer and Winter** †

#### **Peter Niemann \*, Finn Richter, Arne Speerforck and Gerhard Schmitz**

Institute of Engineering Thermodynamics, Hamburg University of Technology, 21073 Hamburg, Germany **\*** Correspondence:peter.niemann@tuhh.de;Tel.: +49-(0)40-42878-3273

† This paper is an extended version of our paper published in the 2018 International Sustainable Energy Conference (ISEC), Congress Graz, Austria, 3–5 October 2018.

Received: 19 July 2019; Accepted: 15 August 2019; Published: 19 August 2019

**Abstract:** At Hamburg University of Technology the combination of an open cycle desiccant-assisted air conditioning system and a geothermal system is investigated in the framework of di fferent research projects for several years. The objective of this study is to investigate the energy e fficiency of the overall system and to evaluate the geothermal system during summer and winter mode, based on data measured for a temperate climate region. Monitoring results of the performance for dehumidification and remoistening of supply air are presented. Furthermore, the investigated system is compared to reference air conditioning processes. During summer mode, an average dehumidification e fficiency of 1.15 is achieved. The electrical energy savings compared to a conventional reference system sum up to 50% for the investigated cooling period. System operation during winter shows an average moisture recovery e fficiency of 0.75. The electrical energy demand for air humidification is reduced by 50% compared to a system with electric isothermal air humidification. The geothermal system is operated e fficiently throughout the year for cooling and heating application. Besides the energetic system evaluation, measured data regarding the soil temperature and thermal comfort are presented.

**Keywords:** air conditioning; borehole heat exchanger; desiccant dehumidification; enthalpy recovery; heat pump; system evaluation; experimental
