1 Geothermal energy use for heating and cooling of a low energy building Ursula Eicker, Ruben Pesch, Felix Thumm, Antoine Dalibard University of Applied Sciences Stuttgart, zafh.net, Germany Schellingstrasse 24, 70174 Stuttgart, Germany ursula.eicker@hft-stuttgart.de Abstract Vertical geothermal heat exchangers can be used for heating and cooling of buildings and entire neighbourhoods. In winter operation, they provide heat at temperature levels close to the mean annual ambient temperatures to heat pumps and thus improve the heat pump seasonal performance factor. In summer they can be used for direct cooling of buildings, if surface cooling provides large areas for cold distribution. Furthermore, heat rejection of chillers at temperature levels well below ambient is an interesting option for low depth geothermal energy use. Geothermal energy use is possible for decentral building installations, but also on a district level, where either a district heating network can be supplied with a geothermal heat pump or cold distribution with decentral heat pumps takes place. The paper presents monitoring and simulation results from a low energy building using a heat pump with vertical ground heat exchangers. Introduction Water or brine filled ground heat exchangers are either designed in a horizontal configuration with a shallow depth of about 2 m or installed as vertical loops. Vertical ground heat exchangers are usually constructed by inserting one or two high density polyethylene U-tubes in vertical boreholes of 75 to 220 mm diameter. Vertical loops are usually connected in parallel to reduce pressure drop. In Europe, double U-tubes are common, whereas in the United States single tubes prevail. Zeng et al. [9] show that double U-tubes reduce the borehole resistance by 30 - 90% and thus improve heat transfer. Vertical pipes up to a depth of 100 meters are mainly used for heat pump applications, but also increasingly for closed - loop direct cooling of buildings, with water as the heat transfer fluid. The high heat capacity of water is advantageous, as the electrical energy needed for circulating the fluid through the earth heat exchanger is considerably lower than if air is used. The water cooled through contact with the earth is then distributed in the building using either activated concrete slabs with buried pipes or an air - based ventilation system, in which the air is cooled by the water in an additional heat exchanger. If the ground temperature level is too close to the desired room temperature, the cooling power of such a system is too low to be cost effective. This problem may be overcome by one of two methods: Published in: Proceedings of the IXth International scientific and technical conference on New building technologies and design problems, 20.-21. October 2011, Krakow.