Monitoring a Borehole Heat Exchanger Field of a Multifunctional Office Building

Abstract

Heating and cooling account for large energy consumption in office buildings. Here, use of renewables may reduce CO2 emissions msignificantly. We present the E.ON Energy Research Center, a multifunctional building in Aachen and its new energy concept. It’s energy derives from a geothermal borehole heat exchanger (BHE) field, a gas-fired combined heat and power (CHP) unit, and photovoltaics. The field comprises 40 double U-tube BHEs, each 100 meters deep. The working fluid is a 35 % glycol-water solution. The project aim is to ensure a sustainable and long-term operation responding to the heating and cooling load from different types of space, such as offices, conference or server-rooms. We present different tools, such as Distributed Temperature Sensing (DTS) for monitoring temperature within the BHEs, Enhanced Geothermal Response Test for measuring the apparent thermal conductivity, and SHEMAT, a simulator for heat and mass transport for numerical simulation. Specific groundwater flow is an important process which affects strongly the long-term efficiency of a BHE field. For estimating specific discharge rate and direction of groundwater flow, temperature sensor-rings are placed within one of the BHEs providing information on the temperature distribution outside the BHE. Forward simulations are performed for different discharge rates, inlet and outlet temperatures. Assimilation of this data is used for estimating groundwater discharge rate and direction, thus helping to optimize and calibrate the numerical sub-surface model of the BHE field. We present long-term numerical simulations and different scenarios for optimized operation of this BHE field.