| Abstract |
As there is an increasing need, in Paris and its suburbs, for cooling, shallow ground water sources are targeted to provide sufficient flow rates in order to provide cool to offices, commercial and tertiary activity buildings. Water reinjection, abusive use of superficial ground water for cooling purposes, could lead to a short term increase of the aquifer temperature. Hence, sustainable use of the thermal energy stored in shallow seated aquifers requires to balance the amount of heat reinjected in the aquifer during the cooling season by injecting cooled water during the heating season. Inversion of fluid circulation in the geothermal loop (groundwater wells share seasonally both production and injection functions) results in seasonal heat and cold storage, thus upgrading heat pump performance. Two projects are presented. In the first one the well spacing is so short that theoretical thermal breakthrough and shtort circuiting for a single doublet occur in less than a month. Therefore, a quadruplet scheme, extracting heat and cold from two aquifers was contemplated in order to accommodate with the thermal breakthrough issue. The second one addresses the energy supply of two district heating and cooling grids from a highly productive shallow aquifer source. The need of continuous and simultaneous heat and cold suggests the use of high capacity, high efficiency heat pumps, able to produce hot water and chilled water at 80°C and 5°C respectively. Ground water is used, particularly during summer, when heat and cold requirements are not balanced and the peak load for space cooling may reach 22 MWth. Such ground water based designs should secure the development of large, environmentally compatible, district heating and cooling scheme, thus avoiding atmospheric cooling systems whose utilization is restricted in urban areas. |