| Title | Flexible Operation of a Dually Fed District Heating System in Iceland’s Capital Region: Improving Overall Resource Utilization |
|---|---|
| Authors | Baldur BRYNJARSSON, Arna PALSDOTTIR, Sigrun TOMASDOTTIR, Haukur Darri HAUKSSON, Gretar IVARSSON |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | district heating, reservoir management, geochemistry, scaling, hydrogeology, reservoir recharge |
| Abstract | Veitur Utilities operates a dually fed district heating system in the capital region of Iceland. About half of the district heating system is fed by low temperature wells in three geothermal fields in the capital region while the other half is fed by heated groundwater from ON Power’s two geothermal power plants in the Hengill area. Historically, the mixing of these two types of waters has been problematic due to scaling, resulting in Veitur Utilities operating two parallel district heating systems in the capital region with waters that cannot be mixed. In the summer of 2020, the neighborhoods in the capital region that normally receive low temperature geothermal water were switched to heated groundwater resulting in all of the capital region being temporarily fed by heated groundwater. The aim of this operation was to rest the low temperature fields in the capital region to be better prepared to meet the demand for hot water in the city over the wintertime. The duration each geothermal field was rested ranged from 8 to 17 weeks. During this rest, the response of the low temperature fields in the city was carefully monitored. Continuous logging of the water level, temperature and well head pressure was carried out in designated monitoring wells, weekly hand measurements of the water level were done in various other wells and the possible occurrence of surface manifestations was monitored with field visits. In addition, the district heating system was extensively monitored by chemical analysis of water samples, pH measurements and monitoring of oxygen and hydrogen sulfide levels. Chemical monitoring showed that the changes to the operation of the district heating system caused no significant scaling events or operational problems. However, a delayed recovery of magnesium and calcium ions was observed, which might indicate ion-exchange processes on pipe surfaces. A record seasonal water level increase in was observed in all three geothermal fields. In one of the fields, Laugarnes, the water level reached a record high since pumping from the field began more than half a century ago. The overall gain resulting from this operation will however not become apparent until the coming spring when the lowest yearly water levels are reached. |