Efficient use of heat from CHP distributed by district heating system in district cooling networks

Abstract

District cooling (DC) can play an important role in smart energy systems. With the global trend of reducing heat loss in buildings, cooling demand will continue to increase. Considering the potential for free cooling and waste heat utilisation in DC systems, a practical approach is needed to develop new DC networks. Tallinn has over 60 years of experience in developing district heating (DH) networks. The city has installed large capacities of biomass-based combined heat and power plants (CHPs). National support mechanisms allow the DH operator to generate power from CHPs and reject heat during warmer months when the heat load is insufficient. This heat can be used for DC. This study investigates an applied approach to DC development in Tallinn’s Ülemiste City. Ülemiste City is a business park with an existing developed area of 160 000 m 2 . The main source of cooling for the DC network is an absorption chiller that uses rejected heat from a CHP 7 kilometres away from the DC plant. The current DH supply temperature in Tallinn during the non-heating season is 70 °C. To determine the optimal technical solution for an effective energy efficiency ratio of the absorption chiller and heat transmission in the DH network, various scenarios were evaluated where the DH supply temperature was 70 °C, 80 °C, and 90 °C. An assessment of the technical parameters is provided for these scenarios. The paper presents an overview of the efficient use of rejected heat from CHPs in DC.