Wireless sensor network for measuring thermal properties of borehole heat exchangers

Ground coupled heat pumps are growing strongly due to its high energy performance, low power consumption and contribution to reduction in CO2 emissions. The ground heat exchanger sizing is a critical factor for the optimal system operation. Current methods for measure the thermal conductivity of soil, are expensive and do not allow to take advantage of the thermal behaviour of different geological layers, groundwater or dynamic features. In this work, we report the design of a new instrument for measure the inner thermal evolution of ground heat exchanger by autonomous wireless sensor, that traveling in the thermal fluid; the main characteristics of them: spatial and temperature resolution improve and new measurement methodology. The system consists of a device, which inserts and extracts sensors in the borehole, transmits the acquisition configuration of the sensors and carry out the data files of temperature along the heat exchanger; a variable number of autonomous wireless sensors, each in an 25 mm diameter sphere, containing a transceiver, a microcontroller, a temperature sensor and power supply; a mechanical subsystem, composed by a circulating pump and two valves, which allows thermal fluid circulation at the borehole and insert and extract sensors; a software for PC, which processes the received data and calculates the local conductivities along the borehole.