The global demand for cooling is increasing with rising outdoor temperatures, higher requirements for thermal comfort and increased digitization with more heat-generating industries. To cover this increased cooling demand, significant amounts of electricity are currently used in air conditioners and electric fans, which increases emissions of greenhouse gases and puts pressure on electricity grids. It is currently estimated that electricity for cooling purposes accounts for 20% of the total electricity used in buildings. District cooling is a resource-efficient alternative to local conventional chiller systems, having the advantage of a flexible production with various cooling technologies. Cooling load variations in district cooling networks are both daily and seasonal. During the warmer season of the year, the electricity spot market prices correlate with peak cooling demand. To reduce the production costs, production can be shifted in relation to the demand by utilizing cold storages. When the demand and electricity spot prices are low, the cold storage can be charged and then discharged and used in the district cooling network when the demand and electricity spot prices increase. Furthermore, the most cost-effective cooling technologies can be used to charge the storage, which can minimize investments in production capacity. 

The aim of this thesis was to investigate how energy costs and greenhouse gas emissions change when implementing thermal energy storage in a district cooling network. This was performed by conducting a case study of Citynätet, which is one of five district cooling networks where Tekniska verken i Linköping AB distributes district cooling. Conducted literature reviews combined with collected data on hourly average cooling loads in the studied district cooling network constituted the required basis to dimension the cold storage. In this study, energy costs were defined as electricity spot market prices, energy tax and marginal heat costs related to the district cooling production. Greenhouse gas emissions were defined as indirect emissions of CO2-equivalents resulting from electricity and heat used in the district cooling production. Initially, two different storage scenarios were dimensioned with a cold-water accumulator tank as a reference case: capacity to cover daily and weekly cooling loads, respectively. In these cases, energy costs and greenhouse gas emissions were simulated for the year 2022, which were compared to the current system without access to any cold storages. 

Daily and weekly cold storage capacity volumes were dimensioned at 65 MWh and 402 MWh, corresponding to storage volumes of 5,589 m3 and 34,545 m3, respectively, if the storage medium is water. Annual financial savings when implementing a cold storage system amounted to 860 TSEK for daily storage and 1,145 TSEK for weekly storage, representing reductions of 13% and 18%, respectively. Furthermore, implementing cold storage was estimated to result in reduction of greenhouse gas emissions by 76 tonnes CO2-equivalents and 113 tonnes CO2- equivalents for daily and weekly storages, corresponding to reductions at 3% and 5%, respectively. In conducted sensitivity analyses for future scenarios with increased electricity prices, heat prices and cooling demand, greater annual economic savings were obtained compared to the base scenario. The largest economic saving amounted to 56% relative to the base scenario, which was achieved with a 30% increased cooling demand. If electricity prices from the year 2021 are used, the economic savings decrease by 41% and 35% for daily and weekly storage, respectively. The order of magnitude of estimated greenhouse gas emission reductions is highly influenced by the choice of applied environmental assessment perspective. In a specific case study perspective, the reduction of greenhouse gas emissions decreased by 47% and 44% for daily and weekly storage, respectively, compared to the base scenario where a marginal perspective was applied. For further investigations of the economic and environmental benefits of implementing thermal energy storage in district cooling networks, the possibilities for combined cooling-and-heating storages should be further explored. If technical limitations can be eliminated, significant amounts of economic and environmental savings are likely to be obtained in both district heating and district cooling networks.