Efficiency of closed loop geothermal heat pumps: A sensitivity analysis

Geothermal heat pumps are becoming more and more popular as the price of fossil fuels is increasing and a strong reduction of anthropogenic CO2 emissions is needed. The energy performances of these plants are closely related to the thermal and hydrogeological properties of the soil, but a proper design and installation also plays a crucial role. A set of flow and heat transport simulations has been run to evaluate the impact of different parameters on the operation of a GHSP. It is demonstrated that the BHE length is the most influential factor, that the heat carrier fluid also plays a fundamental role, and that further improvements can be obtained by using pipe spacers and highly conductive grouts. On the other hand, if the physical properties of the soil are not surveyed properly, they represent a strong factor of uncertainty when modelling the operation of these plants. The thermal conductivity of the soil has a prevailing importance and should be determined with in-situ tests (TRT), rather than assigning values from literature. When groundwater flow is present, the advection should also be considered, due to its positive effect on the performances of BHEs; by contrast, as little is currently known about thermal dispersion, relying on this transport mechanism can lead to an excessively optimistic desig

Biogas upgrading using algal-bacterial processes

Photosynthetic biogas upgrading constitutes, to the best of our knowledge, the only biotechnology capable of simultaneously removing CO2 and H2S from raw biogas. Recent studies at the pilot scale confirmed the potential of algal-bacterial processes to obtain a biomethane with sufficient quality to be injected into natural gas networks. The main limitation identified in this novel biotechnology is the large land requirement for microalgae to fix all CO2 removed from biogas, which would eventually limit its applicability to biogas design flow rates < 500 Nm³ h− 1. Algal-bacterial photobioreactors also exhibit a high-water footprint, which can compromise the environmental sustainability of the process. The latter limitation can be overcome by coupling biogas upgrading to wastewater/digestate treatment, which would allow reducing the eutrophication impact of these wastewaters while producing a valuable algal biomass. The valorization of the algal biomass using a biorefinery approach would also contribute to the sustainability and economic viability of this technology