Abstract
Ground temperature at shallow depth (< 50 m) is not stable, nor in space, neither in time, and its behaviour is the result of superimposition of effects of heat pulses of different origin: solar, geothermal and anthropic. The correct assessment of ground temperature is a crucial point when designing a shallow geothermal energy system. In geothermal closed loop projects, more the borehole heat exchangers are short, more the contribution of the ground temperature variability on the heat exchange is prominent. Monitoring ground temperature can be very useful to correctly understand the behaviour of a shallow geothermal reservoir subjected to heat extraction and/or injection by a ground source heat pump system. The present work illustrates the practical aspects and main issues occurred in the installation, testing and working phases of a monitoring system realised to record ground temperature in a geothermal application. The case study is a field of eight coaxial borehole heat exchangers, 30 m long, connected to a novel prototype of dual source (air and ground) heat pump.
Highlights
A closed loop geothermal circuit is designed to exchange heat with the ground within a specified volume (Eskilson, 1987)
This paper shows the practical aspects and main issues arisen of a monitoring system of ground temperature installed on the first prototype of DSHP connected to Coaxial borehole heat exchangers (CBHE) of the GEOTeCH Project, whose results will be used for the validation of the coaxial borehole heat exchanger model
This paper presented the practical aspects related to the installation of a temperature monitoring system with the aim of understanding thermal behaviour of underground subjected to the work of a prototype of a dual source heat pump connected to a field of shallow coaxial borehole heat exchangers
Summary
A closed loop geothermal circuit is designed to exchange heat with the ground within a specified volume (Eskilson, 1987). Soils and groundwater are used to provide heat to the buildings, generally by ground source heat pumps (GSHP), or to receive and store their excess heat (Magraner et al, 2010). The standard depth of a vertical closed loop borehole heat exchanger lies between 50 and 150 m, allowing a high portion of heat exchange surface to be in contact with aquifers, soils and rocks at a stable temperature (Aresti et al, 2018). Drilling work down to 50 m depth and beyond is the major cost of the entire system and it negatively impacts the market of shallow geothermal components: geo-exchangers and GSHP (Tinti et al, 2016).
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