The purpose of the Cheong Soo trigeneration plant is to provide district heating and electricity to a suburban area covering approximately three square kilometres with about 6400 households and public buildings. The first phase of the project comprised two Wärtsilä 20V34SG natural gas-fuelled generating sets equipped with a heat recovery system for district heating purposes. Phase 1 was commissioned and handed over in February 2010. The second phase consists of an identical genset to the previous and was completed in 2015. The three gensets generate electricity in parallel with the electrical grid and supply district heating to the town network. During the warm summer periods the plant provides district cooling as well. Due to tariff policy in South Korea, selling only electrical power to the grid is not feasible. At night, the electrical load in the suburban area is so low that the amount of heat generated by the engines at this time is significantly reduced compared to daytime. Unfortunately, the amount of heat needed by households during this period of time in the 24-hour cycle is at its maximum. This is why installing a heat accumulator comes into question: it allows the Cheong Soo plant – operating essentially in island mode – to run continuously on high load and thus, at high levels of total efficiency (more than 85% in this case). The additional heat generated during daytime is partly stored in the accumulator for use during the following night.

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