"Open loop" groundwater-based heat pump systems extract energy directly from groundwater. This groundwater may be pumped from wells in gravel, sand or bedrock aquifers. This can be an elegant and efficient space-heating and -cooling solution, especially at larger scales.
Example of a groundwater-based “open loop” heat pump system. Groundwater at 6°C is pumped to the heat pump (“VP”), which extracts heat from the water. The chilled (3°C) return water is either recharged to the aquifer via a reinjection well or soakaway, or discharged to drainage or a surface water (e.g. river). (The chilled water could also, of course, be used to perform a cooling function).
Large quantities of heat energy can be extracted from groundwater from high-yielding wells. The energy potential is determined by the groundwater yield and the temperature of the water. Water quality can also be important for the operation of the plant, in order to avoid mineral scaling, biofouling and corrosion, and ought to be considered.
Click on the figure for enlarged version.The groundwater temperature is usually stable throughout the year and is commonly 1-2°C higher than the annual average air temperature at the location in question. Groundwater temperatures in the Nordic countries can be seen here.
Groundwater Abstraction Potential
In Norway, areas underlain by sand and gravel deposits are best-suited for groundwater abstraction for energy purposes. Such sand and gravel sediments can be found in glacial-, river- and, in some cases, moraine deposits. It is uncommon to achieve large groundwater yields from wells in Norwegian bedrock, but it does occasionally happen! For example, wells in rhomb-porphyry rocks (western side of Oslofjord) and the Brummundal sandstone can yield significant quantities of water. It is also possible to encounter large, water-bearing fractures when drilling in other types of bedrock, but they are, unfortunately, difficult to predict with any degree of certainty.
Groundwater resource potential in the Oslo area:
Published: 14. August 2009